University of Southern California Dissertations and Theses

A systematic review of Enantiornithes (Aves: Ornithothoraces)

(USC Thesis Other)

A systematic review of Enantiornithes (Aves: Ornithothoraces)

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content A SYSTEMATIC REVIEW OF ENANTIORNITHES (AVES: ORNITHOTHORACES)

by

Jingmai Kathleen O’Connor

A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(GEOLOGICAL SCIENCES)

December 2009

Copyright 2009 Jingmai Kathleen O’Connor
ii 
DEDICATION
To my loving family.
iii 
ACKNOWLEDGEMENTS
I would like to thank my committee for their excellent academic support,
comments, questions, and criticism throughout research, which have greatly benefited
this project as well as my scientific development. I would also like to thank my peers,
especially the Vertebrate Paleontology department of the LACM, whom I learned a great
deal through interactions and shared many a laugh. Special thanks to Jonah Choiniere,
Dr. Gareth Dyke, and Zhijie ‘Jack’ Tseng for the many fun and enlightening academic
discussions as well as very helpful comments and suggestions on this project.
Even with the support of colleagues, this project would not have been possible
without the constant loving support of my family and friends. I could not have made it
through the stressful times without their constant source of encouragement and support.
Thank you so much for your patience when things got rough and all the great memories
that will I cherish in my heart always. I love you all very much.
Finally, I would like to thank my undergraduate advisor, Dr. Donald Prothero.
Without his enthusiasm, encouragement, education and guidance, I likely would not be a
paleontologist today. Beyond captivating my imagination with energetic lectures on the
evolution of life (and swaying my interests from volcanology to paleontology), as an
advisor, Dr. Prothero went above and beyond what was required to facilitate the
education of his students. Thanks to no small effort on his part, I received a strong
foundation in vertebrate paleontology and independent research that greatly helped me
through the early years of graduate school. A stark contrast to his peers, I have never had
iv 
such a genuinely enthusiastic teacher and will always appreciate the opportunities that
were opened for me through his invested efforts, thank you!
Thank you everyone who has been there for me throughout this process.

v 
TABLE OF CONTENTS

Dedication ii
Acknowledgements iii
List of Tables vii
List of Figures viii
Abstract xiv
Chapter 1: INTRODUCTION, MATERIAL, AND PREVIOUS RESEARCH 1
Chapter 2: THE SYSTEMATIC POSITION OF AVES AND CLADISTIC THEORY 27
Chapter 3: TAXONOMIC REVIEW 66
Chapter 4: SKULL MORPHOLOGY 122
Chapter 5: POST-CRANIAL MORPHOLOGY 164
Chapter 6: THE MORPHOLOGY OF DNHM D2950/1, A WELL PRESERVED
SPECIMEN FROM THE QIAOTOU FORMATION OF NORTHEASTERN CHINA 197
Chapter 7: MORPHOLOGICAL DESCRIPTION OF SHANWEINIAO COOPERORUM,
A NEW LONGIPTERYGID ENANTIORNITHINE FROM NORTHERN CHINA 216
Chapter 8: A REDESCRIPTION OF THE HOLOTYPE OF RAPAXAVIS PANI (AVES:
ENANTIORNITHES) AFTER PREPARATION 237
Chapter 9: ENANTIORNITHINE LIFE HISTORY 261
Chapter 10: INTEGUMENT 297
Chapter 11: PREVIOUS ENANTIORNITHINE SYSTEMATIC HYPOTHESES 336
Chapter 12: ENANTIORNITHINE PHYLOGENY 366
Chapter 13: DISCUSSION AND CONCLUSIONS 412
References 433

vi 
Appendices
Appendix A: LIST OF OUTGROUP AND INGROUP TAXA 467
Appendix B: LIST OF CHARACTERS AND CHARACTER STATES 477
Appendix C: CHARACTER MATRIX 499

vii 
LIST OF TABLES

Table 1.1. List of published enantiornithine material. The collection
number refers to the holotype specimen. A bullet denotes taxa that
have been suggested to be invalid in the literature; a diamond
denotes a taxon that is accepted as invalid. 4
Table 1.2. List of all unpublished material included in this study. 8
Table 3.1. Fragmentary taxa and their revised assignment based on this
study. 84
Table 3.2. All Chinese enantiornithines currently considered invalid. 91
Table 4.1. Current published enantiornithine material separated into Early
and Late Cretaceous collections. 126
Table 10.1. List of enantiornithine material with feathers incorporated in
this review; includes current published material as well as four
unpublished specimens from the DNHM and two from CAGS. 299
Table 10.2. Enantiornithine specimens preserving wing integument. Basal
birds for comparison. Measurements in mm. 301
Table 10.3. Enantiornithine specimens preserving elongate rectrices with
Confuciusornis and ornithuromorphs for comparison
(measurements in mm). 310
Table 12.1. A list of all enantiornithine OTU's scored for phylogenetic
assessment. OTU’s highlighted in grey were not included in the
final analysis. The material column lists what is known for each
OTU and the method column, if empty, indicates first hand study
of the material. The fraction on the right is the degree of
incompleteness in terms of how much missing data is scored for a
given OTU. 369
Table 13.1. List of published enantiornithine species and their current
taxonomic status as of this study. 414

viii 
LIST OF FIGURES

Figure 1.1. A, Early Cretaceous enantiornithine localities; B, Late
Cretaceous enantiornithine localities. 13
Figure 1.2. Time scale (modified from Geological Society of America,
1999) showing temporal distributions of major enantiornithine
localities broken down according to continent. Abbreviations: N,
North America; S, South America; As, Asia; E, Europe; Au,
Australia; Af, Africa. 15
Figure 1.3. Size range of Cretaceous enantiornithines: A, B, Gurilynia
nessovi (from Kurochkin, 1999); C, Iberomesornis romerali (from
Sereno, 2000). Scale bar equals two cm. 20
Figure 2.1. Diagram showing the relationships of Ornithodira (from
Gauthier, 1986). 37
Figure 2.2. Possible originations of Aves (modified from James and
Pourtless IV, 2009). 40
Figure 2.3. Relationships of clade Maniraptora (from Senter, 2007). 45
Figure 3.1. A, IVPP V9769, holotype of Cathayornis yandica; B, BNHM
BPV538, holotype of Sinornis santensis (from Sereno and Rao,
1992). 73
Figure 3.2. A, carpometacarpus of Cathayornis yandica; B, hand of
Sinornis santensis; C, postacetabular ilium of C. yandica; D,
postacetabular ilium of S. santensis. 75
Figure 3.3. Uzbekistan coracoid fragments (from Panteyelev, 1998): A,
PO 4819 (Explorornis nessovi); B, PO 4818 (Explorornis sp.); C,
PO 4825 (Enantiornis walkeri); D, PO 4606 (Catenoleimus
anachoretus); E, PO 4604 (Incolornis silvae); F, PO 4609 (I.
martini); G, TGNIGRM NTS 56/11915 (Abavornis bonaparti); H,
PO 4605 (Abavornis sp.); I, PO 4821 (Alexornithiformes indet.). 82
Figure 3.4. A referred specimen of Alethoalaornis agitornis (LPM
B00017, formerly LPM 00040); scale bar equals one cm. 93
Figure 3.5. The holotype of Dapingfangornis sentisorhinus LPM-B00027
(formerly LPM 00039; Li et al., 2006). 97
ix 
Figure 3.6. A, holotype of Boluochia zhengi (IVPP V9770); B, camera
lucida drawing of boxed region. 110
Figure 4.1. Camera lucida drawings of select enantiornithine skulls with
cranial elements color-coded to highlight morphological disparity.
A, Pengornis houi IVPP V15336; B, Cathayornis yandica IVPP
V9769; C, Eoenantiornis buhleri IVPP V11537; D, Rapaxavis
pani DNHM D2522; E, DNHM D2950/1; F, Longipteryx
chaoyangensis IVPP V12552; and G, Gobipteryx minuta IGM
100-1011. All scale bars equal one cm. 129
Figure 4.2. Enantiornithine basicrania, photographs and camera lucida
drawings. A,B, DNHM D2950/1; C,D, Neuquenornis volans
MUCPv 142; E,F, Hebeiornis fengningensis NIGPCAS 130722. 140
Figure 4.3. Ternary diagram depicting the range of skull proportions
within Archosauria. The most reliable enantiornithine
measurements have been added to the dataset (yellow) for
comparison. Enantiornithines cluster approximately within the
center of neornithine morphospace. B, braincase; O, orbit; R,
rostrum (modified from Marugan-Lobon and Buscalioni, 2003). 153
Figure 4.4. Size and morphological variation within enantiornithine
dentition. 159
Figure 5.1. Enantiornithine pygostyles: A, Hebeiornis in ventral view; B,
Iberomesornis in lateral view. C-F, the typical modified
enantiornithine morphology: C, Dapingfangornis in lateral view;
D, Rapaxavis in ventral view; and E, Halimornis in dorsal view. 168
Figure 5.2. Enantiornithine coracoids (not scaled); A-C in ventral view, D-
F in dorsal view. A, Concornis; B, DNHM D2950/1; C,
Rapaxavis; D, PVL 4034; E, M 192; F, Enantiornis PVL 4035. 170
Figure 5.3. Medial processes and procoracoid processes (indicated by
arrows) in Ornithothoraces. A, Protopteryx (from Zhang and Zhou,
2004); B, Protopteryx as constructed here; C, Elsornis; D, Gansus;
E, Aquila. 172
Figure 5.4. Furcular variation across enantiornithines; all in ventral view
except D and E. A, Eoalulavis; B, Longipteryx; C, Shanweiniao;
D, DNHM D2567/8; E, Noguerornis; F, DNHM D2950/1. 175

x 
Figure 5.5. Sternal variation among enantiornithines; all in ventral view
(except E). A, Longipteryx; B, Concornis; C, Eoalulavis; D,
Longirostravis; E, DNHM D2567/8; F, Eoenantiornis; G,
Rapaxavis; H, Elsornis. 177
Figure 5.6. Humeral variation within Enantiornithes. A, Pengornis (caudal
view); B, Cathayornis (cranial); C, Eocathayornis (caudal); D,
Concornis (cranioventral); E, F, Elsornis in caudal and cranial
view; G, H, Martinavis in cranial and caudal view; I, J,
Enantiornis in caudal and cranial view. 179
Figure 5.7. Enantiornithine tibiotarsi. A, Nanantius in medial and cranial
view (from Molnar, 1986); B, CAGS-04-CM-006 in medial and
cranial view; C, D Soroavisaurus PVL 4030 and PVL 4033 in
cranial view (from Chiappe and Walker, 2002); E, Lectavis in
cranial and medial view (from Chiappe, 1993). 186
Figure 5.8. Enantiornithine tarsometatarsi: A, Boluochia; B,
Yungavolucris (from Chiappe, 1993); C, CAGS-04-CM-007; D,
Avisaurus archibaldi (from Chiappe, 1993). 188
Figure 5.9. Select enantiornithine metatarsal I: A, Rapaxavis in
craniomedial view; B, DNHM D2950/1 in medioplantar view; C,
Neuquenornis in medial view (from Chiappe, 1993); D,
Soroavisaurus in medial view (from Chiappe, 1993). 191
Figure 6.1. Photograph of A, DNHM D2950; B, DNHM D2951. 199
Figure 6.2. Camera lucida drawings of A, DNHM D2950; B, DNHM
D2951. 204
Figure 6.3. Detail photographs of DNHM D2950/1. All scale bars
represent one cm: A, skull in right lateral view; B, upper dentition;
C, lower dentition; D, left manus; E, thoracic girdle, slab 0; F,
thoracic vertebrae; G, cervical vertebrae; H, thoracic girdle, slab 1;
I, pelvic girdle. 208
Figure 7.1. Holotype (DNHM D1878/1) of Shanweiniao cooperorum. A,
photo; B, camera lucida drawing. 218
Figure 7.2. Holotype (DNHM D1878/2) of Shanweiniao cooperorum. A,
photo; B, camera lucida drawing. 219
Figure 7.3. Skull of Shanweiniao cooperorum in left lateral view. A,
photo; B, camera lucida drawing. 223
xi 
Figure 7.4. Reconstruction of ‘longipterygid’ sterni. A, Shanweiniao
cooperorum; B, Longirostravis hani; C, Longipteryx
chaoyangensis. 226
Figure 7.5. Left tarsometatarsus of Shanweiniao cooperorum in dorsal
view. A, photo; B, camera lucida drawing. 231
Figure 8.1. Photograph of DNHM 2522 before preparation. 240
Figure 8.2. Photograph of DNHM 2522 after preparation. 241
Figure 8.3. A, detail photograph of the skull of DNHM 2522 before
preparation, B, after preparation, and C, camera lucida drawing. 243
Figure 8.4. Select camera lucida drawings of DNHM D2522 exposed in
ventral view: A, synsacrum; B, distal caudals and pygostyle. 246
Figure 8.5. A, B, close up of thoracic girdle before and after preparation;
C, D, close up of sternum left outer trabecula before and after
preparation; E, F, close up of left tarsometatarsus before and after
preparation. 249
Figure 8.6. A, close up of pectoral region of DNHM D2522; B, close up of
pectoral region of Concornis lacustris LH-2814. 252
Figure 9.1. A, a reconstruction of the egg size of the Rio Colorado
Formation eggs (Schweitzer et al., 2002), and the preserved
elements that suggest these eggs are enantiornithine. 265
Figure 9.2. Early Cretaceous subadult birds from Liaoning, China. A,
GMV 2159; B, GMV 2158; C, embryo IVPP V14238; D,
‘Liaoxiornis delicatus’ GMV-2156. All arrows indicate remiges
and rectrices (in A). 271
Figure 9.3. Cross-sections of enantiornithine femora: A, ‘Gobipteryx’
ZPAL-MgR-/90; B, Concornis LH-2814; C, MACN-S-01; D,
PVL-4273. Hypothetical enantiornithine growth strategies: E, rapid
embryological growth followed by prolonged, slow, interrupted
growth, as inferred from ‘Gobipteryx’ embryo ZPAL-MgR-/90 and
Lecho femora MACN-S-01 and PVL-4273; F, rapid growth until
adult or near adult-size followed by slow, interrupted growth as
inferred from LH-2814; G, intermediate rapid growth phase
(followed by slow, interrupted growth) as interpreted from
histological analyses and the known distribution of sampled
fossils. 278
xii 
Figure 10.1. Slab one of DNHM D2884 ½ with feather impressions; scale
bar = 1 cm. 304
Figure 10.2. Manus of Protopteryx IVPP V11665; A, photograph; B,
camera lucida drawing. 307
Figure 10.3. Enantiornithine alula, photograph with line drawing: A,
Eoenantiornis; B, Eoalulavis. 310
Figure 10.4. Typical enantiornithine caudal integument (elongate rectrices
absent): A, Longipteryx IVPP V12352; B, IVPP V13939; C,
Eoenantiornis IVPP V11537. 312
Figure 10.5. Close-up of the right rectrice of Dapingfangornis LPM 00027
(formerly LPM 00039): A, photograph; B, camera lucida drawing. 314
Figure 10.6. Close up of the pygostyle and proximal rectrices of DNHM
D2884 ½ clearly showing the elongate tail feathers emerging from
the caudal coverts: A, photograph; B, camera lucida drawing. 317
Figure 10.7. The tail feathers of Shanweiniao DNHM D1878 ½ : A,
photograph of slab one; B, close up of photograph of boxed area
preserving rectrices; C, camera lucida drawing of rectrices. 323
Figure 10.8. Close up of isolated body covert of Protopteryx IVPP
V11665 showing absence of vane. 324
Figure 10.9. Hind limb feathers of maniraptorans: A, Microraptor gui
IVPP V3352; B, Berlin Archaeopteryx (from Longrich, 2006); C,
Golden Eagle Aquila chrysaetos; D, Longipteryx IVPP V12325; E,
DNHM D2884 ½; F, G, IVPP V139139. 329
Figure 11.1. Cladogram depicting the general placement of Mesozoic
birds as resolved by a majority of recent cladistic analyses
(simplified from O’Connor et al., 2009). 338
Figure 11.2. Alternative hypotheses regarding the placement of
Enantiornithes; relationships not derived by the cladistic method.
A, Kurochkin’s (2006) Sauriurae with a paraphyletic Aves (from
Kurochkin, 2006). B, Martin’s (1987) Sauriurae with a
monophyletic Aves (modified from Chiappe and Walker, 2002). 341
Figure 11.3. The results of two recent cladistic analyses (A, modified from
O’Connor et al., 2009; B, modified from Zhou et al., 2009), which
highlight the current plasticity of certain basal bird relationships. 345
xiii 
Figure 11.4. A-F, Previous cladistic phylogenetic hypotheses regarding
enantiornithines: A, Chiappe, 1993 (modified from Chiappe and
Walker, 2002); B, Sanz et al., 1995 (modified from Chiappe and
Walker, 2002); C, from Chiappe, 2002; D, from Chiappe and
Walker, 2002; E, from Chiappe et al., 2006; F, from Cau and
Arduini, 2008. G, hypothetical enantiornithine phylogenetic
relationships from Kurochkin, 1996. 348
Figure 11.5. Differential preservation within the enantiornithines: A,
crushed coracoid from the complete slab and counterslab specimen
DNHM D2567/8; B, isolated three dimensionally preserved
coracoid (PVL 4035) from El Brete collection assigned to
Enantiornis leali. 361
Figure 12.1. Strict consensus tree (length 902 steps) from 15,268 MPTs. 373
Figure 12.2. Enantiornithine clade in reduced strict consensus tree (with
Gurilynia, Nanantius, and Otogornis removed). 375
Figure 12.3. Reduced strict consensus tree of hypothetical enantiornithine
relationships indicating temporal placement of taxa within the
Cretaceous. 395
Figure 12.4. Reduced strict consensus tree of hypothetical enantiornithine
relationships with locality information illustrating the diversity
present from each geologic unit. Mono-specific localities are
unlabelled. 396
Figure 12.5. Reduced strict consensus tree of hypothetical enantiornithine
relationships showing size distributions. Note the fairly large size
of basal taxon Pengornis houi, but that the largest specimens are
found in the most derived clade. 403
Figure 12.6. Reduced strict consensus tree of hypothetical avian
relationships mapped with integumentary structures. Grey taxa
preserve no integument; black taxa with no information preserve
no integumentary structures. Grey symbols indicate ambiguous
data (i.e. crural feathers in Archaeopteryx). 406
xiv 
ABSTRACT
Enantiornithes is a diverse group of Mesozoic birds, however little is understood
about their interrelationships, and even their monophyly has been questioned. Repeated
attempts to yield phylogenetic hypotheses at the species level have resulted in trees with
low support that are largely inconsistent between matrices. These hypotheses consistently
place Enantiornithes as sister group to Ornithuromorpha, together comprising the clade
Ornithothoraces, which includes Neornithes. Because of their phylogenetic position,
intermediate between Archaeopteryx and modern birds, as well as their success during
the Cretaceous, enantiornithines are important for better understanding early avian
evolution and the evolution of the anatomically modern bird. This large-scale study of
enantiornithines has three main aspects; a taxonomic review in order to determine the
validity of the over fifty named taxa, a morphological review, and a systematic study
through a species level cladistic analysis of the group. Twenty-one species are here
considered invalid, leaving 37 valid species in the literature. A cladistic analysis of 237
characters, including 42 novel enantiornithine characters, for 56 OTU's, 40 of which are
enantiornithine, reveals 15,268 trees of 902 steps. The reduced strict consensus tree with
three taxa removed is fairly resolved, although derived taxa still form a polytomy.
Pengornis is resolved as the basal most known taxon, suggesting that size reduction in
Mesozoic birds only occurred within the ornithothoracine clades. Interpretations of the
current phylogenetic hypothesis suggest a Eurasian origin for Enantiornithes, a mid-
Cretaceous global dispersal for Euenantiornithes, and suggest certain features such as the
fan-shaped tail evolved independently within both ornithothoracine clades.
1 
CHAPTER 1: INTRODUCTION, MATERIAL, AND PREVIOUS RESEARCH

i. Introduction
Enantiornithines are an important group of Mesozoic birds with a relatively short
scientific history. Since the group was formally recognized in the 1980’s (Walker 1981),
approximately 60 species have been named (Table 1.1), and specimens have been
collected from every continent with the exception of Antarctica (Fig. 1.1; Chiappe and
Walker 2002). These primitive birds comprised a major component of Cretaceous
avifaunas, coexisting with other groups of birds, both more primitive and advanced.
Despite the fact Enantiornithes was unrecognized as a group until less than three decades
ago, enantiornithines are more taxonomically diverse than any other group of birds in the
Mesozoic. Their range, from the Early Cretaceous until the very end (131 – 65.5 Ma; Fig.
1.2) is the longest of any group of Mesozoic birds; the incredible diversity and temporal
span of the clade has led to the interpretation that Enantiornithes represent the first group
of birds to undergo a large-scale radiation (Chiappe, 2007). Enantiornithines represent
the dominant avian component in most Cretaceous faunas making their subsequent
extinction at the end of the Cretaceous perplexing. Their intermediate phylogenetic
position between Archaeopteryx and modern birds makes understanding the
enantiornithines crucial for understanding early avian evolution as a whole. Inferences
about avian evolution should be placed in a phylogenetic context; this requires a strong
foundation of morphology and taxonomy from which to create the character matrix. This
research consists primarily of a taxonomic revision of the clade and a morphological
2 
review that includes much new information. Much of the information gathered during the
process of reviewing the clade was then translated into the most comprehensive
phylogenetic analysis conducted on the clade to date. This chapter provides an overview
of our knowledge of the enantiornithines prior to the completion of this research. Most
enantiornithine taxa are known from a single specimen (with the exception of
Longipteryx and Alethoalaornis, see Chapter 3) and or species (exceptions including
Martinavis vincei and M. cruzyensis). For monospecific genera, unless specified,
throughout this text where the generic name is used, it is referring to the holotype
specimen.

ii. Institutional Abbreviations
ACAP, Musee de Cruzy, Cruzy (l’Association Culturelle, Arch́eologique et
Paĺeontologique de l’Ouest Biter rois), Cruzy, France; AM, Australian Museum, Sydney,
Australia; BNHM(C), Beijing Natural History Museum (Collections), Beijing, China;
CAGS, Chinese Academy of Geological Sciences, Beijing, China; DNHM, Dalian
Natural History Museum, Dalian, China; GMV, National Geological Museum of China,
Beijing, China; IGM, Geological Institute, Mongolian Academy of Sciences, Ulaan
Bataar, Mongolia; IVPP, Institute of Vertebrate Paleontology and Paleoanthroplogy,
Beijing, China; KU-NM, University of Kansas, Natural History Museum, Lawrence,
USA; LACM, Natural History Museum of Los Angeles County, Los Angeles, USA; LP,
Institut d'Estudis Ilerdencs, Lleida, Spain; LPM, Liaoning Provincial Museum,
Shenyang, Liaoning, China; MPD, Mongolian Palaeontological Centre, Ulaanbaatar,
3 
Mongolia; MSNM, Museo di Storia Naturale di Milano, Milan, Italy; MUCPv, Museo de
Ciencias Naturales, Universidad Nactional del Comahue; NIGP-CAS, Nanjing Institute
of Geology and Paleontology, Chinese Academy of Sciences, Nanjing, Jiangsu, China;
PIN, Paleontological Institute, Moscow, Russia; PVL, Paleontologia de Vertebrados
Lillo, Universidad Nacional de Tucúman (National University of Tucúman), Tucúman,
Argentina; QMF, Queensland Museum, Brisbane, Australia; TsNIGRI, Chernyshev’s
Central Museum of Geological Exploration, Central Geological Research Institute
Museum, Saint Petersburg, Russia; UAMNH, University of Alabama Museum of Natural
History, Tuscaloosa, USA; UCMP, University of California Museum of Paleontology,
Berkeley, USA; ZPAL, Zoological Institute of Paleobiology, Polish Academy of
Sciences, Warsaw, Poland.

iii. Material
The initial goal for this project was to see the enantiornithine record in its entirety,
including all published as well as unnamed or possibility misidentified material; this was
not feasible due to time and funding constraints. Most specimens including nearly all the
most important and complete specimens were studied “first hand” – including material
from Europe, South America, North America, Australia, and Asia. Several unpublished
specimens were also included (Table 1.2). The material is broken down by continent:
4 
Table 1.1. List of published enantiornithine material. The collection number refers to the
holotype specimen. A bullet denotes taxa that have been suggested to be invalid in the
literature; a diamond denotes a taxon that is accepted as invalid.
5 
Table 1.1, Continued.
6 
Asia
A majority of the published Chinese enantiornithines from both the Jehol Group
and Xiagou Formation (Cathayornis yandica - Zhou et al., 1992; Otogornis genghisi -
Dong, 1993; Boluochia zhengi - Zhou, 1995; Longchengornis sanyanensis and
Cuspirostrisornis houi - Hou, 1997a; Eoenantiornis buhleri - Hou et al., 1999;
Protopteryx fengningensis IVPP V11665 - Zhang and Zhou, 2000; Longipteryx
chaoyangensis IVPP V12325 and IVPP V12522 - Zhang et al., 2000; Longirostravis hani
- Hou et al., 2003; CAGS-02-0901 - You et al., 2005; Dapingfangornis sentisorhinus - Li
et al., 2006; CAGS−IG−04−CM−007 - Lamanna et al., 2007; Alethoalaornis agitornis -
Li et al., 2007; Pengornis houi - Zhou et al., 2008a; Shanweiniao cooperorum -
O’Connor et al., 2009; and Rapaxavis pani DNHM D2522 - Morschhauser et al., 2009)
were studied first hand. CAGS-IG-04-CM-023 (Harris et al., 2006), Paraprotopteryx
gracilis (Zheng et al., 2007), Jibeinia luanhera, Cathayornis caudatus, Largirostrornis
sexdentornis (Hou, 1997a), Cathayornis aberransis (Hou et al., 2002), and Cathayornis
chabuensis (Li et al., 2008) were not studied first hand. Dalingheornis (Zhang Z-H. et al.,
2006) belongs to a private collection and thus is here considered a nomen dubium (see
Chapter 3). Aberratiodontus wui, described as an enantiornithine (Gong et al., 2004) is
here considered a probable junior synonym of Yanornis martini (Cau and Arduini, 2008;
Zhou et al., 2008a) and not included in this review. A positive cast of Sinornis santensis
(Sereno and Rao, 1992) and a peel of Hebeiornis fengningensis (Xu et al., 1999;
Vescornis hebeiensis, Zhang et al., 2004; see Chapter 3) were studied since these
specimens are preserved as voids. Several unpublished Jehol specimens, including two
7 
unpublished Longipteryx, several ‘cathayornithiforms,’ and a new species (DNHM
D2950/1) from the Dalian Natural History Museum, and a new species currently under
study at the Chinese Academy of Geological Sciences (CAGS-IG-05-CM-006 and
CAGS-IG-04-CM-006) were also included in this study (see Table 1.2 for a full list of
unpublished specimens included in this study).
Most of the central Asian material was not studied in the first hand, including the
collections from the Gobi desert: Elsornis keni (Chiappe et al., 2007), Gobipteryx minuta
(Elzanowski, 1977; Elzanowski, 1981; Kurochkin, 1996; Chiappe et al., 2001) and
Gurilynia nessovi (Kurochkin, 1999); casts of Elsornis were available at the LACM. A
collection of bone fragments from Uzbekistan (Kizylkumavis cretacea, Zhyraornis
logunovi and Zhyraornis kashkarovi - Nessov, 1984; Sazavis prisca - Nessov and Jarkov
89; Enantiornis martini and E. walkeri - Nessov and Panteleyev, 1993; Lenesornis
maltshevskyi – Kurochkin, 1996; Abavornis bonaparti, Catenoleimus anachoretus,
Incolornis silvae, and Incolornis martini - Panteleyev, 1998) could not be accessed,
although these are extremely fragmentary and thus, provide very limited information. The
Lebanon enantiornithine (MSNM V 2882a) recently described as Enantiophoenix
electrophyla (Dalla-Veccia and Chiappe, 2002; Cau and Arduini, 2008), was studied
from publication only. Isolated fragments reported from Japan were not included
(Matsuoka et al. 2002).

8 

Table 1.2. List of all unpublished material included in this study.
9 
South America
The entire El Brete collection (Enantiornis leali - Walker, 1981; Lectavis
bretincola, Soroavisaurus australis, and Yungavolucris brevipedalis - Chiappe, 1993;
Chiappe and Walker, 2002; Martinavis vincei - Walker et al., 2007) was included in this
review. The only other South American enantiornithine, Neuquenornis volans (Chiappe
and Calvo, 1994), was only studied from a cast. Birds have been reported from Brasil
(Alvarenga and Nava, 2005) but so far the only described specimen is an unnamed
specimen in private hands (Naish et al., 2007), and not incorporated into this study.

Europe
The largest European collection, the Las Hoyas birds from Spain (Iberomesornis
romerali - Sanz and Bonaparte, 1992; Concornis lacustris - Sanz and Buscalioni, 1992;
Eoalulavis hoyasi - Sanz et al., 1996), were all studied with the exception of a cluster of
juvenile specimens interpreted as a pellet (LH 11386; Sanz et al., 2001). The Spanish
Montsec specimens, Noguerornis gonzalezi (Lacasa-Ruiz, 1986) and the nestling (LP
4450; Sanz et al., 1998) were not studied first hand though a cast was available of
Noguerornis. None of the isolated and fragmentary European material (M 192 and M 193
- Buffetaut, 1998; M n 606 - Buffetaut et al., 2002; Martinavis cruzyensis - Walker et al.,
2007; Osi, 2008) was studied first hand.

10 
North America
Most of the North American avisaurid collection, unfortunately not including the
yet undescribed Kaiparowits enantiornithine (Hutchison, 1993), was studied first hand
(Avisaurus archibaldi - Brett-Surman and Paul, 1985; Avisaurus gloriae - Varricchio and
Chiappe, 1995). Casts of both Halimornis thompsoni (Chiappe et al., 2002a) and
Alexornis antecedens (Brodkorb, 1976) were studied. Isolated and extremely fragmentary
material from Canada and the USA (Marsh, 1892; Chiappe and Walker, 2002; Chiappe et
al., 2002a; Morrison et al., 2005; Martinavis sp. KU-NM-37 - Walker et al., 2007) was
not included.

Australia
The holotype and referred material of Nanantius eos (Molnar, 1986) has been lost
(pers. obs.) however a partial cast was studied for this review. The Lightning Ridge
material (Molnar, 1999; Close et al., 2009) was studied from casts.

Africa
Isolated material from Madagascar (Forster et al., 1998) has been reported but not
published at the time of this study and thus could not be included here.

iv. Research Bias
Despite the relative richness of the enantiornithine fossil record relative to some
other groups of Mesozoic birds, avian fossils are generally rare and in the case of the
11 
enantiornithines, a majority of the richness is from a single geologic unit, the Jehol
Group. Limited in size by the constraints of flight, birds tend to be small and their bones
are often pneumatic, and thus hollow with thin walls. This makes avian bones particularly
susceptible to destructive diagenetic processes such as crushing. Due to their delicate
nature, avian remains are rarely preserved outside the taphonomic window provided by
lacustrine deposits (Davis and Briggs, 1998). Lakes are ideal preservational settings for
bird remains and other small vertebrates; their anoxic bottom waters prevent the carcass
from being disturbed and the slow continual deposition of fine sediment ensures that it
will be buried. Three of the richest enantiornithine localities represent primarily
lacustrine deposits (Las Hoyas-Montsec, Liaoning-Hebei, Changma). Enantiornithine
fossils are also collected from other lithologies (see below), although specimens from
higher energy deposits (i.e. fluvial) are typically more incomplete.
A majority of enantiornithines are known from localities in Liaoning-Hebei, and
thus most of the data on enantiornithine feather patterns and morphology, skull
morphology and trophic adaptations, proportions and diversity come from the three
formations sampled in this region (Dabeigou, Yixian, and Jiufotang Formations),
preserving approximately 11 My of enantiornithine evolution, and the earliest known
record (Zhou, 2006). The nature of the rapidly expanding record of Jehol fossils has
unfortunately resulted in poor locality information for many specimens. For this reason,
not many detailed inferences into the evolutionary history of the Jehol biota can be made
based on locality or stratigraphic data.
12 
Such biases in the fossil record cannot be avoided, and researchers must conduct
their work within the realm of what is currently known. However, when reviewing
enantiornithine skull morphology, for example, the study is largely based on the variation
and diversity within a restricted geographic region and specific temporal range. Nearly
all feather information is restricted to this unit as well, and discussions of their
morphology and diversity are limited to the early diversification of the clade, with little to
know information on the integument of the last members of the clade.

v. Enantiornithes (Aves: Ornithothoraces) Background Information
Age
The known range of enantiornithines is currently limited to the Cretaceous (Fig.
1.2). The earliest record is that of Protopteryx from the lowest unit of the Jehol Group,
the Dabeigou Formation (131 Ma; He et al., 2006), at the Senjitu locality near Fengning,
Hebei Province (Zhang and Zhou, 2000). This locality was originally thought to represent
rocks from the middle Jehol member, the Yixian Formation, which has yielded numerous
enantiornithines from localities in Liaoning Province with already an impressive range of
morphologies (ex, the tail morphologies of Eoenantiornis and Shanweiniao) and
specializations (Longirostravis). Recent Ar/Ar analyses, however, estimate that the
deposits at the Protopteryx locality are Late Hauterivian in age, approximately 131 Ma
(He et al., 2006), and thus older than the Yixian Formation (125 Ma; Swisher et al., 1999,
2002), representing the earliest stage in the evolution of the Jehol fauna, the Dabeigou
Formation (Zhou, 2006). The status of several enantiornithines described from “Yixian”
13 
Figure. 1.1. A, Early Cretaceous enantiornithine localities; B, Late Cretaceous
enantiornithine localities.

14 
deposits near Fengning, Hebei Province (Hebeiornis, Paraprotopteryx, Jibeinia) and
whether they too are from the older Dabeigou Formation is currently unknown and
complicated by the paucity of locality information for some specimens (Jibeinia,
Paraprotopteryx).
Protopteryx is not only the earliest record of enantiornithines, but also suggested
to be a very primitive taxon (Zhang and Zhou, 2000), an inference supported by recent
cladistic analyses (Cau and Arduini, 2008; Zhou et al., 2008a). However, the incredible
diversity already unearthed from the overlying Yixian Formation (125-120 Ma; Swisher
et al., 1999, 2002) suggests that the origin of Enantiornithes is likely rooted in the
Jurassic. Indeed, early interpretations of the lower Jehol Group attempted to assign a
Late Jurassic age (Chen, 1988; Hou et al., 1995; Lo et al., 1999), however there is now
strong support that these rocks were deposited during the Early Cretaceous (Swisher et
al., 1999, 2002; He et al., 2006). Recently, a new enantiornithine (DNHM 2950/1) was
described from the Senjitu locality, but from the Qiaotou Formation. The age of this
formation is currently under study, but has been interpreted as Late Jurassic – Early
Cretaceous based on the fauna (Ji et al., 2005; Wang et al., in press). It is possible that
this may represent an even earlier first appearance datum, but it is likely that upon
analysis, this formation may also prove to be Early Cretaceous.
The latest record of the enantiornithines comes from the uppermost Cretaceous
Hell Creek Formation of North America. This formation records strata from the latest
Cretaceous, through the K-Pg event itself as evidenced from a discontinuous but present
iridium layer found towards the upper boundary of the formation, and into the lower-most
15 

Figure 1.2. Time scale (modified from Geological Society of America, 1999) showing
temporal distributions of major enantiornithine localities broken down according to
continent. Abbreviations: N, North America; S, South America; As, Asia; E, Europe; Au,
Australia; Af, Africa.
16 
Paleogene (Hicks et al., 2002). Enantiornithines from this formation include the holotype
of Avisaurus archibaldi and isolated bone fragments (Brett-Surman and Paul, 1985). The
duration of the formation is estimated to be 1.36 Ma (Hicks et al., 2002). No
enantiornithine remains have ever been collected from Tertiary deposits and it is believed
that the clade went extinct with other non-avian dinosaurs. Therefore, the youngest
enantiornithine record is in the upper-most Cretaceous, 66.87 - 65.51 ± 0.1 Ma (Hicks et
al., 2002).

Environment and Ecology
Enantiornithines occupied a range of environments and at least some ecological
specialization is evident. The original El Brete enantiornithine material comes from fine-
grained continental sandstone deposits (Walker, 1981; Chiappe, 1993), interpreted as
deposited in a fluvial-lacustrine setting (Bonaparte et al., 1977). Several other specimens
have been recovered from fluvial deposits (A. archibaldi - Brett-Surman and Paul, 1985;
Avisaurus sp. – Hutchison, 1993; Forster et al., 1996; Buffetaut, 1998; Martinavis sp. –
Walker et al., 2007) suggesting that this is a primary environment of these birds. Still,
specimens have been collected from a wide range of environments including continental
sand dunes (Gobipteryx - Elzanowski, 1977; Gurilynia - Kurochkin, 1999; Elsornis –
Chiappe et al., 2007), and near shore marine (Halimornis - Chiappe et al., 2002a;
Enantiophoenix – Dalla Vecchia and Chiappe, 2002) and coastal deposits (Alexornis –
Brodkorb, 1976).
17 
The majority of enantiornithines however, are known from lacustrine deposits
including the enormous diversity of taxa from China and the exceptional specimens from
Spain. Lakes are known to represent a taphonomic window for the preservation of small
and delicate vertebrates including birds (Davis and Briggs, 1998). The two main bird
fossil producing geologic units in China, all members of the Jehol Group (Liaoning,
Hebei, and Inner Mongolia Provinces) and the Xiagou Formation of the Xinminpu Group
(Gansu Province) are both lacustrine deposits but differ in their environment. The Jehol
deposits represent a forested coastal lake system while the Xiagou lakes were located
much farther inland. The enantiornithines from these localities, however, do not possess
obvious or well-supported aquatic locomotor specializations, unlike many
ornithuromorphs from the same localities (hongshanornthids, Gansus) which show
features such as elongate hindlimbs, proximally projecting cnemial crests on the
tibiotarsus, or a dorsal supracondylar process on the humerus, associated with aquatic
specialization in extant taxa (You et al., 2006; O’Connor et al., in press). Instead, the
small enantiornithines that dominate the Jiufotang Formation are argued to be arboreal
(Zhou and Zhang, 2006a; Li et al., 2008), based primarily on hindlimb proportions (short
tarsometatarsus) and pedal morphology (highly recurved pedal claws, a long and low
reversed hallux). The Spanish Montsec and Las Hoyas lake deposits are interpreted as a
near shore seasonally dry lake system that may have had some marine influence (Sanz et
al., 2002; Chiappe and Lacasa-Ruiz, 2002).
Though not developing the locomotor adaptations for aquatic environments
observed in more advanced birds, enantiornithines from the Jehol Group show a range of
18 
trophic specializations associated with such a niche (Zhang et al., 2001; Hou et al., 2003;
O’Connor et al., 2009). The longipterygid enantiornithines possess elongate rostra but in
two different morphologies so that the smaller Longirostravis hani and Shanweiniao
cooperorum have been interpreted as mud-probers (Hou et al., 2003; O’Connor et al.,
2009), while the larger and more robust Longipteryx chaoyangensis is interpreted as a
piscivore perhaps similar to modern Kingfishers (Zhang et al., 2000).
While enantiornithines are considered to be capable fliers, having evolved
associated aerodynamic specializations such as an alula (Sanz et al., 1996), fan-shaped
tail (O’Connor et al., 2009) and modern wing proportions (Dyke and Nudds, 2009), a
single taxon, the Late Cretaceous Elsornis keni, is interpreted as having limited flying
capabilities (near flightless) based on forelimb proportions and morphology (Chiappe et
al., 2007).

Size
Enantiornithines occupy a large size range. The purported smallest Mesozoic bird
Liaoxiornis delicatus (Hou and Chen, 1999), from the Jehol Biota of northeastern China,
is largely suspected to be a juvenile specimen (and a nomen nudum; see Chiappe et al.,
2007) and thus its small size only reflects an early ontogenetic state. Still, other
enantiornithines from the Jehol Biota are also quite small, despite the interpretation that
their development was largely complete at time of death (Longirostravis). The smallest
adult enantiornithine taxon, Iberomesornis romerali from the Early Cretaceous of Spain
(Sanz et al., 2002), is approximately one-tenth the size of the largest enantiornithine (Fig.
19 
1.3), Gurilynia nessovi from the Late Cretaceous of Mongolia (Kurochkin, 1999).
Iberomesornis has been considered a juvenile (Martin, 1995; Feduccia, 1996) but Sanz et
al. (2002) strongly argue for an adult or near-adult ontogenetic status for the holotype
specimen based on fusion between the ischium and pubis and the fully ossified periosteal
surface. The true range of size within the clade is obscured by uncertain growth
trajectories for enantiornithines and the isolated nature of most specimens.

vi. The Validity of Enantiornithes
In the past three decades, what has been known of enantiornithines has undergone
a flurry of change. Walker’s original description of the group was based on material from
the Lecho Formation, El Brete, northwestern Argentina (Walker, 1981). Previous
enantiornithine material had been discovered and published (Alexornis; Brodkorb, 1976)
but the identification of these specimens as part of a unique class did not occur until
Walker’s description of the El Brete material. The El Brete material consisted of
approximately 60 disassociated individual bones preserved in 3D. Five genera have since
been named based on the material: Enantiornis leali, Yungavolucris brevipedalis,
Lectavis bretincola, Soroavisaurus australis and Martinavis vincei (Walker, 1981;
Chiappe, 1993; Chiappe, 1996; Walker et al., 2007). The disassociated nature of the El
Brete material raised concerns that the elements did not necessarily come from a single
group of closely related individuals, but rather from a diverse group of distantly related
birds (Steadman,1983).
20 
Figure 1.3. Size range of Cretaceous enantiornithines: A, B, Gurilynia nessovi (from
Kurochkin, 1999); C, Iberomesornis romerali (from Sereno, 2000). Scale bar equals two
cm.
21 
The discovery of Neuquenornis volans, an articulated partial skeleton from the
Rio Colorado Formation also in Argentina, definitively showed the same co-occurrence
of the primitive and derived characters observed in the different elements collected from
El Brete but within a single specimen. Chiappe’s (1991) description of the “Neuquén
bird” and the detailed follow-up description of Neuquenornis corrected several
inaccuracies from Walker’s original description of the group, such as the absence of the
so-called ‘reversed articulation’ between the scapula and coracoid that earned the
enantiornithines the colloquial name “opposite birds” (Chiappe and Calvo, 1994).
The following are a number of the characters that have been regarded as
synapomorphies of Enantiornithes: triangular fossa on dorsal surface of coracoid; a
prominent and proximally extending posterior trochanter; Y-shaped furcula; poorly
developed distal condyles of the humerus; minor metacarpal extending distally farther or
as far as the major metacarpal; reduced intermetacarpal space; and laterally excavated
thoracic vertebrae (Sanz et al., 2002; Chiappe, 2002). The level at which these characters
are synapomorphic of the entire clade is not certain. Characters originally thought to be
synapomorphies of Enantiornithes are now known to be diagnostic of more exclusive
groups (ex: the presence of a longitudinal groove on the ventral surface of the radius,
Euenantiornithes) (Chiappe and Walker, 2002). As the number of enantiornithine species
increases, it becomes increasingly difficult to identify characters that not only diagnosis
the group as a whole, but can also be indentified in a majority of specimens.
Currently, to be assigned to Enantiornithes a taxon must only be phylogenetically
closer to Sinornis than to Neornithes (Sereno, 1998), a stem-based definition. The
22 
controversy in defining enantiornithines has led some researchers to question the
monophyly of the group itself (Norell and Clarke, 2001). The inaccurate assignment of
specimens to enantiornithines, the creation of numerous taxa based on extremely
fragmentary material, and the poor morphological description of some new taxa has
created further confusion to the issue of diagnosing the Enantiornithes, thus creating what
some would interpret as an apparent paraphyly.
Despite these reservations some researchers have regarding the clade, nearly all
Mesozoic bird cladistic analyses have produced hypotheses with a monophyletic
Enantiornithes (Norell and Clarke, 2001; Chiappe, 2002; Zhou and Zhang, 2006a; Gao et
al., 2008; Zhou et al., 2008a).

vii. Enantiornithine Inter-relationships
The interrelationships of enantiornithines are poorly understood and shift
considerably between different analyses (Chiappe et al., 2007; Cau and Arduini, 2008;
Zhou et al., 2008a; O’Connor et al., 2009). Recent cladistic analyses at the Mesozoic bird
level strongly support enantiornithine monophyly (Gao et al., 2008; Zhou et al., 2008a).
Unfortunately, these analyses are either unable to resolve the interrelationships of the
clade (Chiappe 2002; Clarke and Norell, 2002) or relationships are only weakly
supported (Cau and Arduini, 2008; Zhou et al., 2008a).
Despite this, there are small aspects of existing phylogenetic hypotheses that are
consistent between analyses. For example, Longipteryx and Longirostravis consistently
group together to form a more exclusive clade of “longirostrine” enantiornithines
23 
(Chiappe et al., 2007; Cau and Arduini, 2008; O’Connor et al., 2009). Protopteryx is also
fairly consistently placed basal in the tree, as suggested in the original publication
(Chiappe et al., 2007; Zhou et al., 2008a; Cau and Arduini, 2008). Iberomesornis also
consistently falls at the base of the tree (Chiappe, 2002; Cau and Arduini, 2008).
Difficulties arise when comparing phylogenetic hypotheses typically as a result of
differential taxonomic sampling.
Within Enantiornithes there are several issues that hinder attempts to resolve their
phylogeny. These include not only the few specimens that require taxonomic revision,
but also the brevity of a majority of recent publications making it difficult to score
morphological characters. This results in large amounts of missing data even for
complete taxa and differential scorings between researchers due to the lack of clear
photos and illustrations for many specimens. The results are disparate or weakly
supported trees between researchers with variable specimen access. These issues are
discussed further in Chapter 11 and in Chapter 12, where enantiornithine relationships are
explored through a new phylogenetic analysis of all taxa post taxonomic review, which
supports the monophyly of enantiornithines.

viii. Current Taxonomy
Enantiornithes, as a clade, is riddled with taxonomic issues. While the clade has
only been formally recognized for less than three decades (Walker, 1981), species existed
in the literature dating back to the late 1800’s (Marsh, 1892; Elzanowski, 1974). The past
two decades has witnessed a deluge of material discovered in China, where hundreds if
24 
not thousands of specimens remain undescribed. To date, sixty species have been named
and at least 18 unnamed occurrences, some of which may represent distinct taxa, have
been reported (Table 1.1). Nearly a third of named species are based upon extremely
fragmentary and non-overlapping material from Uzbekistan (Nessov, 1984; Panteyelev,
1998; Kurochkin, 1999). These specimens, while their presence in a given locality is
worth publication, are difficult to compare to other taxa and thus contribute to an overall
lack of clarity within enantiornithine taxonomy.
The rapid succession of discoveries in China resulted in numerous publications
appearing nearly simultaneously. In just over fifteen years, more than twenty-five
species were named from China alone (including taxa in review or in press by the
author). Often new taxa appeared similar to those appearing in contemporaneous
publications and, with comparisons, clear images or lengthy descriptions absent,
diagnostic distinctions between species are often unclear. While the rate of discovery for
several Early Cretaceous clades in China has been rapid, the situation within
Enantiornithes is exacerbated due to the small size and morphological similarity typical
between taxa, comparable to the modern Passeriformes.
Despite the focus on new material, small corrections have been made to rectify
enantiornithine taxonomy (Chiappe et al., 1999; Sereno et al., 2002; Zhou et al., 2008a;
Zhou et al., 2008b). Most of these corrections, however, are either not strongly
substantiated so that there is no consistency in taxonomic use between researchers (C.
yandica and Sinornis), or not largely available to the public (Sereno et al., 2002; Zhou
and Hou, 2002; Zhou et al., 2008b). There are exceptions; ‘Nanantius valifanovi’ is
25 
considered a junior synonym of Gobipteryx after a reinterpretation of the skull material in
the N. valifanovi holotype (Chiappe et al., 1999); and Aberratiodontus (Gong et al., 2004)
is tentatively reassigned to Yanornis (Ornithothoraces: Ornithuromorpha) based on
morphology (Zhou et al., 2008a; pers. obs.) and supported by cladistic analysis (Cau and
Arduini, 2008). Lingyuanornis (Ji and Ji, 1999) is junior synonym to Liaoxiornis (Hou
and Chen, 1999), which at the same time has been considered to be a nomen dubium
(Chiappe et al., 2007). The validity of Liaoxiornis, however, is still controversial and will
be further discussed in Chapter 3. Thus, at the beginning of this project only two of the
60 taxa that have been named are invalid. The results of this project will make a number
of recommendations regarding the validity of these remaining 58 named taxa.

ix. Conclusions
The enantiornithines are a fascinating group of birds that have the potential to
reveal an enormous amount of information about Mesozoic birds and the evolution of
crown group Aves. However, before inferences can be made regarding the evolution of
the clade, a strong phylogeny must be available on which to base evolutionary
hypotheses. Given the size of the clade, the gross amounts of missing data in the
literature, and lack of resolution in previous enantiornithine phylogenies with insufficient
data, considerable review is necessary prior to any further attempt. If the taxonomy is
riddled with erroneous identifications and morphological data is unavailable for a large
number of specimens, then creating a phylogenetic hypothesis that is going to accurately
reflect the entire diversity of the group is impossible. In order to facilitate future research
26 
on the enantiornithines, a large-scale taxonomic and morphological review is conducted.
This study also attempts to utilize this information to create a phylogenetic hypothesis for
which to better understand enantiornithine and early avian evolution.
27 
CHAPTER 2: THE SYSTEMATIC POSITION OF AVES AND CLADISTIC THEORY

i. Introduction to the Issues
Although this project seeks to understand genealogical relationships within the
enantiornithine clade, and thus is rooted in Aves and unaffected by hypotheses
concerning avian origins, throughout the text morphological comparisons and hypotheses
regarding enantiornithine and Mesozoic bird systematics are rooted in the ‘birds are
maniraptoran theropod dinosaurs’ (BAMTD) hypothesis. This argument needs to be
justified in light of existing competing hypotheses and recent criticism (e.g., Dodson,
2000; Kurochkin, 2006; James and Pourtless IV, 2009). Though many researchers
consider the debate closed, opponents of the BAMTD theory have garnered additional
support in light of the discovery of new fossils (i.e. Microraptor) that break down old
dogmas such as the cursoriality of all theropods (Xu et al., 2003). However, the basis of
this project is that a theropod origin for Aves currently receives the strongest support
from phylogenetic systematics, as applied by cladistics, the methodology employed here
for investigating phylogenetic relationships. Together with support from several other
lines of evidence (Chiappe and Dyke, 2006; Chiappe, 2009), birds are considered
maniraptoran theropod dinosaurs, pending further investigation beyond the scope of this
study of enantiornithine relationships. Cladistics as a method, though widely practiced
among systematists, has its opponents (Dodson, 2000; Kurochkin, 2006). Thus, a succinct
historical overview of the phylogenetic systematic method is followed here by a
discussion of some observed pros and cons of the method, as applied to paleontology.
28 
Competing hypotheses regarding the origin of birds are discussed followed by a brief
background to dinosaur phylogeny, in particular the branch of theropods hypothesized to
include Aves; since several groups of dinosaurs have been variously considered as
closely related to birds (i.e. Troodontidae, Dromaeosauridae) and Mesozoic avians are
commonly discussed, the morphology of each group is briefly discussed. Enantiornithine
phylogeny is discussed in detail in Chapters 11 and 12.

ii. The Phylogenetic Systematic Method: Pros and Cons
Prior to the 20
th
Century, genealogical relationships between taxa were entirely
based on an author’s interpretation of observations from the fossil record, with no
methodology other than inferred similarity and personal interpretation of observed
evidence. As a result, authors often created summaries of relationships to support their
existing hypotheses based on preconceived views of the trajectories of character
evolution between fossil taxa. With no way to test relationships formed this way, support
for and the accuracy of such hypotheses cannot truly be assessed. Despite this, many
early inferred relationships still hold true today (Goloboff et al., 2009); for example, a
close relationship between dinosaurs and birds based on morphological inferences was
popularized in the nineteenth Century by Thomas Huxley, ‘Darwin’s bulldog’ (Huxley,
1868).
During the mid 20
th
Century, methods based on stricter methodology began to
appear, such as phenetics (also known as numerical taxonomy; Sneath and Sokal, 1963).
This set of approaches is often referred to as the predecessor to cladistics, although this is
29 
not very accurate because phenetics identifies similarity, not phylogeny (Mayr, 1982).
Since hypotheses of relationship are built purely on morphological similarity, not
accounting for shared primitive conditions (plesiomorphies) or derived similarities
(apomorphies), phenetics is not as useful to paleontologists who seek genealogical
relationships rather than overall shared similarity (Dupuis, 1984). This method is widely
applied nevertheless (Legendre and Legendre, 1998).
During the early 1960’s a new method aimed at discerning phylogenetic
relationships was published (in English) by German scientist Willi Hennig (1966).
Hennig’s cladistic method assumes that some shared morphologies between organisms
are strongly indicative of relationships (homologies) while others are not (homoplasies);
to distinguish these competing character types, a cladistic analysis must be rooted by one
or more outgroups, considered to possess plesiomorphic morphologies with respect to the
clade in question. For example, analyses aimed at Mesozoic bird relationships are
typically rooted with one or both of the deinonychosaurian clades, which in general
represent the plesiomorphic condition, and in Neornithes, which represent the derived
condition (Kitching and Forey, 1992). Cladistic methods can utilize morphological
characters, in the case of paleontology (Cobbett et al., 2007), and sophisticated
mathematical algorithms to find the most parsimonious relationships (i.e., shortest
resolution of character state changes in the form of a tree) between a given sampling of
taxa with a given set of morphologies (Nixon, 1999; Goloboff, 2003; Farris, 2008). For
this reason, cladistics—practiced as numerical analyses—was not widely utilized until
30 
the 90’s when fast personal computers, capable of searching large numbers of trees in a
reasonable amount of time, became economically available.
Thus the raw materials for this set of analyses are characters. Usually
morphological variation is expressed numerically through character states that describe
different possible shapes for an indicated structure (Hennig, 1966; Kitching and Forey,
1992), and these can be either binary or multi-state (continuous). One example of a
continuous character describes the morphological condition of the tail in theropods. A
“0” could be scored for a tail with more than 35 caudal vertebrae, while a “1” might
indicate all taxa with 35 to 26 caudals, a “2” indicating taxa with 25 to 20 caudals, a “3”
indicating taxa with 19-9 caudals, and a “4” indicative of taxa with eight or fewer
caudals. As new states are revealed by new taxa, existing characters are expanded and
new characters are created. For example, prior to the discovery of Zhongornis haoae
(Gao et al., 2008), this character for caudal vertebra had only four states (Chiappe, 2002);
the state for taxa with 19 to nine vertebrae had to be added to distinguish the unique tail
morphology of this taxon from other longer and shorter-tailed relatives. This is an
example of an ordered multi-state character, in which two adjacent character states are
inferred to have greater shared homology, representing a morphocline (Lipscomb, 1992).
Binary characters cannot be ordered because they consist only of two states (Kitching and
Forey, 1992). There has been a great deal of controversy over the usefulness of different
types of characters and the use of assumptions regarding whether a character should be
ordered or not (Hauser and Presch 1991; Lipscomb, 1992; Wilkinson, 1992; Slowinski,
1993; Pleijel, 1995), however, fundamentally all characters have been shown to be useful
31 
in phylogenetic systematics (Lipscomb, 1992; Slowinski, 1993) and some are typically
treated as ordered (or additive) if they contain states that represent intermediates between
the two ends of a morphological transformation (Lipscomb, 1992).
The process of expanding and refining the character list should be a continual
challenge to its authors and those who utilize it, in order to generate hypotheses with
increasing accuracy and resolution (Jenner, 2004). This method of increasing not only
taxonomic sampling but also morphological sampling theoretically will increase the
chances the phylogenetic hypotheses proposed will accurately reflect current information
(Hills, 1998; Jenner, 2004). Thus the resultant phylogenetic hypothesis from a given
matrix should be considered as subject to change with the discovery of new data. For this
reason, character lists and matrices used to support published hypotheses must become
publicly accessible so that the morphological observations used to infer relationships by
one author can be reviewed by another. The testability of hypotheses derived by the
cladistic method is also its major strength. However, there are numerous cons associated
with the practice of cladistic analyses and too often these are disregarded and the
outcomes of cladistic analyses are regarded as fact, rather than, as in many cases, a
weakly supported hypothesis.
There are several problems associated with the cladistic method, despite its
positive attributes. Fundamentally, there are also those who oppose the optimization
methods utilized by cladistics programs, arguing that parsimony is an assumption about
nature that is contradicted by our knowledge of back mutations and homoplasy (Dodson,
2000) or that the statistical basis of the maximum-likelihood method cannot be used to
32 
describe an evolutionary event that occurred only once. While there are several
optimization criteria from which to choose in cladistics, parsimony has been shown to be
an excellent optimization criterion (Goloboff, 2003; Farris, 2008) and is widely utilized
throughout paleontology, as it here (Chapter 12). Cladistic analysis produces
phylogenetic hypotheses, not true relationships and for the most part, the results of
maximum likelihood, parsimony and morphology/size analyses often produce similar
results (Dodson, 2000; Morrison, 2007).
Another argument is that the cladistic method ignores important evidence such as
ecological, temporal and geographical information (Dodson, 2000; Kurochkin, 2006);
this information, however, isn’t necessary for determining relationships that are neither
controlled by age nor ecology. It is important to root phylogenetic hypotheses within a
temporal reality (and thus create hypotheses regarding the timing of origination and
speciation events), however arguing for a strict following of the law of superposition is
also incorrect, especially with poorly-sampled taxa such as Early Cretaceous birds,
mostly known from a single specimen or formation (Dyke and Nudds, 2009). Most taxa
represent a single point in time but originated prior to that point and went extinct after
(and thus the first appearance of a species in the fossil record is called a ‘first appearance
datum’ (FAD), and not the exact time it evolved). It is also recognized that there are
unknown forms that spanned between two taxa purportedly related in a phylogenetic
hypothesis but distantly separated in time. Yes, Velociraptor is not a direct ancestor of
Archaeopteryx as it is younger and morphologically disparate; however, cladistics, upon
analyzing the vast amount of morphological data concludes that the large number of
33 
shared characters suggests that these taxa are related (and given their ranges, distantly
separated by yet unknown related taxa). Nevertheless the highly fragmentary nature of
the fossil record is often unemphasized (e.g., only putative Jurassic maniraptorans more
basal to Archaeopteryx are known) within paleontology (Foote and Sepkoski, 1999;
Fountaine et al., 2005); with this in mind those who oppose cladistics and those who
utilize it might not be greatly at odds. Furthermore, those who oppose cladistics do not so
much find fault with the methodology, but with its orthodoxy (Dodson, 2000), and it is
true that often proponents of this methodology defend themselves vehemently (Farris,
2008). However, in the case of birds and dinosaurs (see below), as it should be the case
with all hypothetical relationships, supporting data comes from a variety of sources not
related to skeletal morphology (i.e. tissue structure, egg shell morphology, behavior).
Thus, if one opposes the BAMTD hypothesis, an attack on cladistics still does not
invalidate the vast lines of evidence from other sources (Xu and Norell, 2004; Schweitzer
et al., 2005; Grellet-Tinner et al., 2006).
Beyond the exclusion of important data, arguments against parsimony, and the
conclusion that a hypothesis with a tree of 200 steps is stronger than a hypothesis
requiring 201 steps (which is admittedly weak but far more likely than a tree of 400
steps!), cladistic analyses are based on anatomical observations, despite the sophisticated
algorithms that seek through hundreds of thousands of trees for the most parsimonious
possibility (Goloboff, 1993; Goloboff et al., 2008), are still limited by the morphological
variation encapsulated by the character list (approximating, but not the same as, true
morphological variation) (Jenner, 2004; Assis, 2009) and thus there are numerous cons
34 
associated with the practice of cladistics. When a character list is created, it essentially
expresses the variation observed by the creator; if a difference between two taxa is
observed a character is created to express this variation. In the end, a character list is all
the morphological variation that a given researcher can discern (or chooses to discern),
which is more likely to support the conclusions and relationships held in mind by the
creator, consciously or not, when the research was conducted. Furthermore, as lists are
compiled, characters and taxa can be cherry picked to create widely different results;
obviously it is preferable that analyses incorporate as much information as possible to
avoid a biased interpretation (Jenner, 2004).
Of course there will always be interpretational differences between researchers
that will result in differential scorings within a taxon. This problem is exacerbated by the
extremely loose and non-specific way characters are often constructed (Assis, 2009). For
example, take the character ‘well-developed tarsometatarsal intercondylar eminence:
absent (0); present (1)’ as first formulated by Chiappe (1995). What one researcher
regards as ‘well-developed’ or ‘prominent’, ‘rudimentary’, ‘poorly-developed’,
‘hypertrophied’ etc., depends on interpretation itself largely influenced by the range of
fossil material studied. When a character list is utilized by someone without a
comprehensive understanding of variation across the clade in question, differences in
interpretation are likely to be even greater (Jenner, 2004). While this cannot be
completely avoided, characters should be constructed in such a way to avoid
misinterpretation or different interpretations between researchers. This is a challenging
task for many morphologies that are difficult to fully encapsulate within discrete
35 
character states. For example, one cannot replace ‘prominent’ with a ratio reflecting the
minimum height of the intercondylar eminence relative to overall tarsometatarsal length
necessary to be considered prominent because the length of the tarsometatarsus varies
widely with ecological specializations (Zeffer et al., 2003). A recently published version
of this character, ‘intercotylar eminence: absent (0); well developed, “globose”’ (Clarke,
2004; Clarke et al., 2006) is also confusing; if the eminence is ‘present’ but not ‘globose’
is it scored as ‘absent’? The updated version of this character utilized here distinguishes
three discrete states: ‘absent (0)’, ‘present, low and rounded (1)’, and ‘present, high and
peaked (2)’; this is admittedly less than perfect and this character may have to be revised
again with the discovery of new material (i.e. an intercotylar eminence that is ‘low and
square’). Descriptive terminology such as ‘well-developed’ are useful in morphological
manuscripts where adjectives can be used in combination with comparisons to other taxa
in order to specify how the word is being used (for example, the intercondylar eminence
is well-developed relative to another taxon). For cladistic analyses, accurate reflection of
fossilized evidence is of the upmost importance for congruence, and therefore characters
should be as non-abstract as possible. Given the example above, this is difficult;
therefore, abstract characters have been annotated and figured (see Appendix 2).
Cladistics is not a perfect methodology by any means, but it facilitates the continual
refinement of phylogenetic hypotheses as the fossil record grows, as well as cooperative
research (through the utilization of a character list by multiple researchers), and therefore
is a useful methodology for investigating phylogenetic relationships to be used in concert
with other lines of evidence.
36 

iii. Review of Dinosaur Systematics and Background to the Origin of Birds
As introduced above hypotheses regarding avian relationships are rooted here in
the hypothesis that birds are members of clade Dinosauria (e.g., Gauthier, 1986; Witmer,
1991; Sereno, 1999; Mayr et al., 2005; Senter, 2007). This project deals entirely with
relationships within Aves, and more specifically within Enantiornithes, and therefore the
evolutionary origin of the entire lineage is not questioned; Archaeopteryx is utilized as
the outgroup and thus discussions of the avian outgroup are avoided. However, a brief
overview of the hypothesized higher-level relationships of Aves and the position of the
clade in a wider context is warranted.
Dinosaurs are archosaurs, a group of diapsid reptiles, most closely related to
pterosaurs, the great flying reptiles of the Mesozoic; Dinosauria and Pterosauria together
form the clade Ornithodira (Fig. 2.1; Gauthier, 1986). The only living archosaurs are
crocodiles and birds, yet these are separated by a great diversity of extinct animals and
millions of years of independent evolution (Benton, 2004).
Dinosauria is divided into two major clades, Saurischia and Ornithischia (Sereno,
1999). The ornithiscian or ‘bird hipped’ dinosaurs (referring to the retroverted position of
the pubis as in modern birds) include the armored thyreophorans such as Stegosaurus and
Ankylosaurus, the duck-billed ornithopods such as Hadrosaurus, and the
marginocephalians including Triceratops (Benton, 2004). Saurischia, meaning ‘lizard-
hipped’ referring to the cranially directed pubis present in all but the most derived
members of the theropod lineage, is broken into two major clades: Theropoda and
37 

Fig. 2.1. Diagram showing the relationships of Ornithodira (from Gauthier, 1986).
38 
Sauropodomorpha (Gauthier, 1986). Theropoda, a group of mostly carnivorous bipedal
saurischians, includes the infamous Tyrannosaurus and Aves, supported by phylogenetic
hypotheses (e.g., Sereno, 1997; Senter, 2007) and a myriad of physical evidence
(Chiappe, 2004; Chiappe, 2009). Sauropodomorpha includes the large diversity of
herbivorous and enormous long-necked dinosaurs such as Brachiosaurus, although early
members were smaller with short necks (Upchurch et al., 2004; Martinez and Alcobar,
2009).
Theropoda, which includes birds, is a speciesous clade. The earliest theropod is
currently known from the Late Triassic Ischigualasto Formation of Argentina (Reig,
1963) and an incredible diversity is known from the Cretaceous (e.g., Clark et al., 2001;
Chiappe et al., 2002b; Xu and Norell, 2006). As alluded to above, the overall
morphological similarity between the skeletal morphology of Archaeopteryx and small
bipedal theropods led Huxley (1868) to suggest in the 19
th
Century that Aves and
dinosaurs are related. This hypothesis lay dormant for most of the 20
th
Century and birds
were largely considered to have evolved from a basal archosauromorph or “thecodont”
form (Heilmann, 1926). Ostrom (1973) resurrected the dinosaurian hypothesis and
specifically argued strongly for a theropod origin for birds, based on his study of the bird-
like Deinonychus antirrhopus in the Cretaceous of Montana (Ostrom, 1969). Today, the
BAMTD hypothesis is widely accepted and supported by diverse lines of evidence
including similarities in the skeletal morphology, egg structure, behavioral patterns,
integumentary anatomy, bone histology, and genome architecture (Ostrom, 1973;
Gauthier, 1986; Chiappe, 2001, 2007; Holtz, 2001; Norell et al., 2001; Padian et al.,
39 
2001; Chiappe and Dyke, 2002; Clark et al., 2002; Erickson, 2005; Xu, 2006; Organ et
al., 2007). Opponents of the theropod hypothesis who argue cladistics does not seek
actual phylogenetic relationships but rather theoretical morphological gradients
(Kurochkin, 2006) must still acknowledge the vast amount of evidence available from
other lines of investigation. Based on the wealth of multidisciplinary evidence currently
available, strong cladistic support (Sereno, 1997; Senter, 2007; Turner et al., 2007a), and
wide acceptance of this hypothesis, birds are evaluated in the pretext that they are living
theropod dinosaurs.
While there are alternative hypotheses that place the origin of Aves within an
unknown group of basal archosauromorphs (Walker, 1972; Martin and Steward, 1999;
Martin, 2004; Kurochkin, 2006) or in crocodylomorphs (Welman, 1995), until recently
no alternative hypothesis has ever received cladistic support (James and Pourtless IV,
2009). Alternative hypotheses typically find fault in one character suite supporting the
theropod hypothesis, namely the inferred metacarpals forming the hand of birds and
theropods (2-3-4-x-x and 1-2-3-x-x respectively; Sereno, 1993; Burke and Feduccia,
1997; Feduccia and Nowicki, 2002; Galis et al., 2003), which is admittedly an over
assumption in homology given conflicting evidence, and propose alternative originations
but do not provide support beyond a few morphological similarities that are often
inaccurate or unparsimonious given the morphology of some Mesozoic birds (Feduccia,
1996; Witmer, 2001; Martin, 2004; ). In light of the large amount of evidence aligning
birds and dinosaurs, arguments have been made for a dinosaurian origin for Aves, but
nested deep within the tree (i.e., a basal coelurosaur), and thus all similarities with
40 
maniraptorans (see below) are convergence or alternatively, some or all maniraptorans
are interpreted as flightless birds (Chiappe et al., 1998; Paul, 2002; Maryanska et al.,
2002; Xu et al., 2002), in some cases removing Maniraptora from Dinosauria (Martin,
2004; Feduccia et al., 2005). The ‘basal coelurosaur’ hypothesis is largely supported by
those who oppose the cladistic method (Dodson, 2000; Kurochkin, 2006). This
hypothesis is plausible but requires fossil evidence that is currently unknown and when
found, will be incorporated into current character matrices, subsequently changing the
resulting hypotheses.
A recent study tested the BAMTD hypothesis with a cladistic analysis of 79
operational taxonomic units (OTU's) that span Archosauria, including the basal archosaur
Longisquama (Sharov, 1970), crurotarsans (Sereno and Arcucci, 1990), theropod
dinosaurs and birds (James and Pourtless IV, 2009). The results weakly support placing
Aves within Maniraptora, however statistical analysis revealed equal support for all four
major hypotheses regarding avian origins (i.e., birds are maniraptoran, maniraptorans are
flightless birds, birds are crocodylomorphs and birds are ‘early archosaurs’ or
archosauromorphs; Fig. 2.2). Although the matrix of 242 characters is relatively small
considering the diversity it seeks to encapsulate (across Archosauria), this study
nevertheless seeks to highlight weaknesses of the theropod hypothesis, the often over-
zealous nature in which it is championed, and emphasizes the need for further
investigation. The conclusions of James and Pourtless IV (2009) are consistent with the
hypothesis that cladistics will continue to generate new and potentially alternative
hypotheses as new fossils are uncovered. However, these conclusions are also an
41 

Fig. 2.2. Possible originations of Aves (modified from James and Pourtless IV, 2009).
42 
example of how incomplete sampling, whether it is taxonomic or morphological, will
produce variable parsimonious solutions reflecting the encapsulated morphological
variation.
The James and Pourtless IV (2009) study argues against certain ‘assumed’
homologies between birds and theropods (i.e. semilunate carpal, metacarpals) and thus
removed many characters that suggest a strong relationship between the two clades
(Clark et al., 2002). Hypotheses regarding homology are rooted in phylogenetic
hypotheses (McKitrick, 1994) and thus ignoring supported homologies in also incorrect
(Clark et al., 2002; Senter, 2007). However, the assumed homology between the hand of
maniraptorans and birds has been admittedly weak in light of conflicting interpretations
(Hinchliffe, 1985; Burke and Feduccia, 1997; Larsson and Wagner, 2002). As the fossil
record grows, so does our knowledge and thus interpretation of it, and the incongruency
between the manual phalangeal formulas of birds and derived theropods may no longer
impede the BAMTD hypothesis, thanks to the recent discovery of the basal ceratosaur
Limusaurus inextricabilis from the early-Middle Jurassic Shishugou Formation of China
(Xu et al., 2009a). Despite the systematic placement of this taxon outside Tetanurae,
Limusaurus still has an ossified sternum and a robust furcula. However, its most
interesting feature is a manus in which metatarsals I and IV are reduced (i.e., V is absent
as in other ceratosaurs), the former with no phalanges and the latter with an indeterminate
number (Xu et al., 2009a). In contrast, the early theropods Herrerasaurus and Eoraptor
retain five digits but display reduction in the outer two digits IV and V, leading to the
interpretation that all theropods retain digits I-II-III (Sereno, 1993). This new basal
43 
ceratosaur shares derived features with tetanurans suggesting a close relationship between
the two groups, and reinterpretation of the tetanuran manus as II-III-IV also reveals
several new plesiomorphies (Xu et al., 2009a). The disparity in the manual morphology
between birds and non-avian dinosaurs has long been pitched by opponents as a major
thorn in the BAMTD hypothesis (Feduccia, 1996; Feduccia, 2001; Kurochkin, 2006),
which proponents have tried to explain away with hypotheses regarding lateral gene
shifts (Wagner and Gauthier, 1999). While this debate cannot be considered closed based
on the reduction of digit I in one taxon, it is worth remembering that the Triassic and
Jurassic theropod fossil record is highly fragmentary, and could easily have been
misinterpreted, as demonstrated by Limusaurus. For this reason, the digits of the avian
hand are referred to as the alular (I or II), major (II or III) and minor (III or IV),
respectively in this project.
Within the BAMTD hypothesis the closest-sister group to Aves within Theropoda
is also controversial due to the scarcity of theropod fossils in the Jurassic compared to the
well-sampled Cretaceous (resulting in what has been referred to as a ‘temporal paradox’
between the age of Archaeopteryx [Jurassic] and it’s presumed theropod sister-taxa
[Cretaceous]; e.g., Feduccia, 1996; Martin, 2004). Still, most researchers agree that the
common avian ancestor belonged within the clade Maniraptora, a group of small, derived
coelurosaur theropods known primarily from the Cretaceous (e.g., Sereno, 1999; Turner
et al., 2007a). The actual relationships, clade names and definitions shift between
analyses (Gauthier, 1986; Holtz, 1994; Forster et al., 1998; Makovicky and Sues, 1998;
44 
Huang et al., 2002; Mayr et al., 2005) and the point is not to explore the relationships
between birds and other maniraptorans, but rather to put Aves in a phylogenetic context.
Most recent cladistic analyses place Aves as most closely related to either
Dromaeosauridae (Holtz, 1994; Norell et al., 2001) or Troodontidae (Forster et al., 1998).
Together, these two clades are commonly grouped in a larger clade, Deinonychosauria,
which forms a sister-group relationship with birds (Gauthier, 1986; Sereno, 1997; Huang
et al., 2002; Makovicky et al., 2005; Novas and Pol, 2005; Gölich and Chiappe, 2006;
Turner et al., 2007a), together referred to as clade Paraves (Fig. 2.3). Some other
maniraptoran theropod groups such as the oviraptorosaurs possess some avian-like
features (i.e., edentulous beak, uncinate processes, a pygostyle in at least on taxon) and
thus have also been suggested to be closely related to birds (Maryanska et al., 2002);
most recent analyses however, consistently place oviraptorosaurs more basal in the
maniraptoran clade, together with Therizinosauridae forming the sister group to Paraves
(Huang et al., 2002; Makovicky et al. 2005; Norell et al., 2006). The basic morphologies
and avian characteristics of deinonychosaurians are briefly discussed below.
Recently the small, largely complete yet bizarre maniraptorans Epidexipteryx hui
and Anchiornis huxleyi have been uncovered in China (Zhang et al., 2008a; Xu et al.,
2009b). These taxa form the outgroup to Archaeopteryx (together forming a clade
referred to as ‘Avialae’ but differing in the normal usage of this term, as synonymous
with Aves, when Aves is used for what is here referred to as Neornithes, see Chapter 3
xiii; Gauthier, 1986; Chiappe and Padian, 1998; Zhang et al., 2008a; Xu et al., 2009b) yet
the morphological disparity between these taxa and Archaeopteryx questions this
45 

Fig. 2.3. Relationships of clade Maniraptora (from Senter, 2007).

46 
placement (i.e. ischium lacking processes and longer than pubis in Epidexipteryx). A
better understanding of these fossil taxa is required to determine their relationships
relative to other maniraptorans and birds, and so each relevant grouping of specimens is
briefly discussed.

Dromaeosauridae
This clade, which includes Deinonychus and the ‘tetrapteryx’ Microraptor gui,
consists of small to medium bipedal, primarily cursorial, carnivorous dinosaurs known
mostly from Cretaceous deposits in Asia and North America but have been recorded on
every continent including Antarctica (Norell and Makovicky, 2004; Case et al., 2007).
Teeth of these dinosaurs have been described from Middle Jurassic sediments (Metcalf et
al., 1992) and the diversity present in the Cretaceous clearly suggests an earlier origin for
the clade. Dromaeosaurs possess a furcula lacking a hypocleidium, unfused paired sternal
plates, a semi-lunate carpal in the wrist and a partially retroverted pubis with an expanded
distal boot (Norell and Makovicky, 2004). Feathers are known throughout the clade in a
variety of morphologies (Ji et al., 2001; Xu et al., 2003); feathers differentiated into tracts
with fully pennaceous, asymmetrical feathers interpreted as aerodynamic are known in at
least one taxon, Microraptor (Xu et al., 2003). Dromaeosaurs are also characterized by a
hyper-extendible second pedal digit, a predatorial adaptation also present in the Late
Cretaceous Rahonavis, which may or may not be a bird (Forster et al., 1998; Ji et al.,
2005; Gölich and Chiappe, 2006; Turner et al., 2007a).

47 
Troodontidae
Troodontidae comprises small bipedal dinosaurs known only from a handful of
taxa from North America and Asia (Makovicky and Norell, 2004). Historically this group
was known only from a few fragmentary specimens (Leidy, 1856), however, recent
discoveries of articulated and nearly complete fossils from the Early Cretaceous of China
(Xu et al., 2002; Xu and Wang, 2004; Ji et al., 2005) indicate that basal troodontids share
several characters with Archaeopteryx, including an enlarged braincase and orbit, a
laterally projected glenoid facet of the scapulocoracoid, a small ischium with a distally
positioned obturator process, incipient development of the medial cnemial crest on the
tibia and pennaceous feathers (Makovicky and Norell, 2004; Ji et al., 2005; Turner et al.,
2007a). A furcula is preserved in at least one taxon (Mei long), where it possesses a short
hypocleidium (Xu and Norell, 2004) reminiscent of the basal bird Sapeornis (Zhou and
Zhang, 2003; pers. obs.). Members of this clade typically have numerous small teeth,
some of which possess denticles (Currie and Dong, 2001), their hindlimbs are fairly long
relative to the forelimbs and the foot possesses a modified second digit, although the
ungual is not as recurved or enlarged as in dromaeosaurids. The holotype of Mei long
(IVPP V12733; Xu and Norell, 2004), from Early Cretaceous of China, is preserved
sleeping like a modern duck, with its head tucked under its wing, behavioral evidence
that also aligns the group with birds.

48 
Anchiornis (Xu et al., 2009b)
The single published specimen of Anchiornis is incomplete and unfortunately
lacks both age and locality information beyond that it was collected in western Liaoning
Province, China. The specimen (IVPP V14378) is interpreted as a juvenile, which
indicates many features may not have developed. Incipient heterocoely was described as
characterizing the caudal cervicals (Xu et al., 2009b), a morphology more derived than
Archaeopteryx (Elzanowski, 2002); however these elements appear very poorly preserved
in the Anchiornis holotype. The taxon also possesses a long bony tail, with truncated
proximal caudals as in deinonychosaurs (Xu et al., 2009b). No sternum is preserved and
the interclavicular angle is much wider than in basal birds such as Archaeopteryx and
Confuciusornis (Chiappe et al, 1999; Elzanowski, 2002). The forelimb is shorter and less
robust than the hindlimb (intermembral index, measured as the combined lengths of the
humerus and ulna over those of the femur and tibiotarsus, of 0.7 vs. 1.05 – 1.09 in
Archaeopteryx). The semilunate carpal appears fused to the major and minor metacarpals,
a greater degree of fusion than present in Archaeopteryx (and at odds with the suggestion
that the Anchiornis holotype is a juvenile), and the alular metacarpal is much longer than
in avians. The pelvic girdle is very similar to the Archaeopteryx and troodontids (i.e.
Sinovenator changii from the Early Cretaceous Yixian Formation; Xu et al., 2002) with a
triangular tapering post-acetabular wing and a proportionately short ischium. The femur
is distally more robust, as in Rahonavis; the tarsometatarsus is unfused and metatarsal III
is laterally compressed as in basal troodontids (Currie and Dong, 2001). The hallux
49 
projects medially (as in Archaeopteryx) and an enlarged ungual phalanx is present on the
second digit (as in non-avian deinonychosaurs and Rahonavis).
Given the fragmentary and subadult nature of the only known specimen of
Anchiornis, as well as the presence of morphologies unknown in other birds but present
in other groups of non-avian maniraptorans, this taxon cannot yet considered avian
pending additional information. Anchiornis is here regarded as a maniraptoran of
uncertain phylogenetic placement; new information will be needed to confirm the sister
relationship of this taxon with Aves (Xu et al., 2009b).

Scansoriopterygidae (Czerkas and Yuan, 2002)
The newly discovered Epidexipteryx (Zhang et al., 2008a) is assigned to this
clade, which now consists of three genera, including Epidendrosaurus and
Scansoriopteryx. Recent phylogenetic analyses have placed Epidendrosaurus as sister
taxon to the avian clade (Senter, 2007); the recent study describing Epidexipteryx
supports hypotheses that these taxa are closely-related and maintains their placement
relative to Aves (Zhang et al., 2008a). The only published specimen of Epidexipteryx
(IVPP V15471) is nearly complete with feather impressions and comes from Middle to
Late Jurassic deposits in Inner Mongolia, China; the specimen is pigeon-sized but may be
subadult given the incomplete epiphysial ossification of some bones (Zhang et al.,
2008a). Epidexipteryx has a short and high skull with massive and procumbent rostral
teeth that taper caudally, as in basal maniraptorans (i.e. oviraptorosaurs and
therizinosaurs; Zhang et al., 2008a) and its dentary is perforated by a large mandibular
50 
fenestra. The tail, composed of sixteen vertebrae, possesses a tapering pygostyle-like
structure composed of the caudal-most ten vertebrae, which remain unfused (Zhang et al.,
2008a); this differentiates Epidexipteryx from other scansoriopterygids, which have long
bony tails (more than 40 caudal vertebrae in Epidendrosaurus with no incipient
pygostyle; Zhang et al., 2008a). A ‘proto-pygostyle’ structure is also known in a Late
Cretaceous oviraptorosaur (GIN 940824), which has 24 caudals, the last four of which
are co-ossified in to a tapering structure (Barsbold et al., 2000). Two small sternal plates
are incompletely fused into a sternum (Zhang et al., 2008a), a more derived condition
than Archaeopteryx, and the coracoid is short while the scapula appears to be expanded
caudally, unknown in other avians. The ilium of Epidexipteryx has a long preacetabular
wing, as in basal birds, but its pubis is un-retroverted and shorter than the ischium, which
lacks dorsal and obturator processes. Indeed, the proportions of the ischium and pubis are
unusual for theropods and differ from Archaeopteryx in which the ischium is less than
half the length of the pubis, and other basal birds in which the pubis exceeds the ilium in
length (Zhang et al., 2008a; Chiappe et al., 1999; Chiappe and Walker, 2002; Zhou and
Zhang, 2003). The tail of Epidexipteryx has four elongate feathers (a morphology also
know in the enantiornithine Paraprotopteryx; Zheng et al., 2007), and short coverts are
preserved around the thoracic and sacral region; no pennaceous feathers appear
associated with the forelimb.
Given the preserved morphology of this specimen (i.e. skull, pelvis), the
placement of Epidexipteryx within ‘Avialae’ remains dubious. The published information
is fairly succinct; pending new information, this taxon and the other poorly known
51 
scansoriopterygids, are not here considered birds but left as maniraptorans of uncertain
phylogenetic affinities. Addressing the relationships of these taxa is beyond the scope of
this project; however, scansoriopterygids are nevertheless very interesting given their
morphology and age. There is no doubt that the new information afforded by these fossils
will help to clarify early maniraptoran evolution and diversification.

Homoplasy of ‘Avian Morphologies’
Maniraptoran clades display morphologies traditionally associated with birds (i.e.
beak, pygostyle, furcula) but in varying combinations presenting no clear trend in
character acquisition (Chiappe, 2007). The presence of more derived ‘avian’ characters in
non-avian theropods and their absence in Archaeopteryx further indicates that a large
amount of the morphological similarity could be the result of convergent evolution. For
example, the recent coelurosaur phylogeny by Senter (2007) suggests that the retroverted
pubis and elongate forelimbs of some dromaeosaurs and derived birds represents
convergence, as inferred by their vertical position in Archaeopteryx and Epidendrosaurus
(which is recovered as an avian). Inferences regarding homoplasy, however, must be
rooted in phylogenetic hypotheses (McKitrick, 1994). The discovery of very new taxa
such as Epidexipteryx and Anchiornis (Zhang et al., 2008a; Xu et al., 2009b) highlights
the extreme diversity and evolutionary experimentation within Theropoda at the time.
New information on early maniraptorans will help to resolve issues within the ‘birds are
maniraptoran theropod dinosaurs’ hypothesis, however the search for the origin of this
clade should not be limited to Maniraptora, as evidenced by long standing alternative
52 
hypotheses (Heilmann, 1926; Walker, 1972; Welman, 1995; Martin and Stewart, 1999;
Dodson, 2000; Martin, 2004; Feduccia et al., 2005; Kurochkin, 2006; James and
Pourtless IV, 2009).
While the fossil record does not present a clear picture of character acquisition
through the maniraptoran clade, a majority of cladistic analyses support the placement of
Aves in Maniraptora and therefore for the sake of this study, which deals with more
specific avian inter-relationships, this hypothesis is followed here and birds are
considered living maniraptoran dinosaurs.

iv. The Mesozoic Aviary
Until recently, the fossil record of Mesozoic birds was greatly limited. Prior to
the later half of the last century, the entire known record comprised just the Late Jurassic
Archaeopteryx and the Late Cretaceous ornithurine birds of North America (Hesperornis
and Ichthyornis; Marsh, 1880). The anatomical and temporal disparity between the two
groups clearly attested to an enormous gap in their evolutionary histories, making it
difficult to understand the origin and evolutionary trajectories of and within the avian
clade. The late 20th Century witnessed rapid growth of the fossil record, particularly
from the Early Cretaceous of China, where thousands of specimens of birds have been
uncovered during the past twenty years alone and discoveries continue at an
unprecedented rate (Zhou and Zhang, 2006a). These discoveries, and other important
finds from Spain, Argentina and Madagascar, have revealed new clades (i.e.
Confuciusornithidae, Enantiornithes, Sapeornithidae), and filled much of the anatomical
53 
and temporal gaps that existed previously (Walker, 1981; Sanz et al., 1988; Zhou et al.,
1992; Hou et al., 1995; Forster et al., 1998). Discussions regarding the phylogenetic
placement of Enantiornithes have thus to be placed in context of other groups of birds
and discussions of morphology refer to other groups with comparable or disparate
morphological states. For these reasons, a basic understanding of other Mesozoic birds is
required. The currently known clades of Mesozoic birds are briefly discussed below.

Archaeopterygidae
Archaeopteryx is the oldest and most primitive definitive bird in the fossil record,
known only from the 150 million-year-old Solnhofen limestones of central Bavaria,
Germany (Wellnhofer, 2008). The taxonomy of the ten known skeletal specimens varies
between researchers; at one extreme all are regarded as a single taxon (Archaeopteryx
lithographica) with all differences treated as ontogenetic (Senter and Robins, 2003;
Chiappe, 2007), while other workers separate the specimens into two genera and multiple
species based primarily on their size range (because the smallest specimen is half the size
of the largest) (Houck et al., 1990; Elzanowski, 2002; Mayr et al., 2005).
The anatomy of Archaeopteryx represents the most primitive condition known in
Aves although the presence of less derived features in more advanced birds suggest that
this taxon is not the ancestor of all birds although it is regarded as the most basal known
member of Aves. The toothed skull of Archaeopteryx has a small premaxilla, retains a
postorbital bar and is generally highly unfused, while at the same time shows an increase
in orbit and brain size compared to non-avian theropods (Elzanowski, 2002). The
54 
postcranial skeleton on the other hand lacks many avian modifications for flight; a
synsacrum is absent, the scapula and coracoid are fused, the sternum is unossified, the
pubis is only partially retroverted (ending in an elongate symphysis), and the long tail is
composed of 21-22 free vertebrae all with elongate prezygapophyses (Elzanowski, 2002;
Mayr et al., 2007). In contrast the forelimb of Archaeopteryx is extremely similar in
morphology—albeit proportionally longer—to those of its immediate non-avian
predecessors; the humerus is longer than the ulna and the manus is unreduced and
unfused. The feathered wing is composed of 11-12 primaries and 12-14 secondaries
(Elzanowski 2002; Wellnhofer, 2008), comparable to those of living birds.

Rahonavis ostromi
This taxon is known only from 75 million-year-old deposits in Madagascar
possibly representing a relic taxon (Forster et al., 1998). The scapula and coracoid in this
taxon are unfused and the presence of quill knobs on the ulna (unknown in other
Mesozoic birds but present in Velociraptor; Turner et al., 2007b), indicate that at least ten
flight feathers were attached (no integument preserved). Like Archaeopteryx, the
compound bones of the hindlimb remain unfused and the tibia bears an incipient cnemial
crest. The number of sacral vertebrae is greater than Archaeopteryx (six compared to five
in Archaeopteryx) and they are fully fused into a synsacrum; the long bony tail is
incomplete (thirteen preserved) and the total number of caudals is unknown. Rahonavis
also possesses an enlarged, sickle-shaped claw on the second digit, a predatorial
adaptation present in dromaeosaurid and troodontid theropods (Forster et al., 1998). Most
55 
cladistic analyses resolve Rahonavis as more derived than Archaeopteryx (Holtz 1998;
Chiappe 2002; Zhou and Zhang 2002a; Norell et al., 2006), however other analyses
suggest the taxon is outside Aves (Ji et al., 2005; Senter, 2007; Turner et al., 2007a,c).

Chinese “Long-tailed” Birds
Several long-tailed birds are known from the Early Cretaceous Jehol deposits of
northeastern China (Zhang et al., 2003); Jeholornis prima (Zhou and Zhang, 2002a) from
the Jiufotang Formation (120 Ma) is known from multiple specimens, which display a
myriad of basal and derived features. This taxon has reduced dentition including
edentulous mandibles and a curved and tapered scapula that is unfused to the strut-like
coracoid, however the pubis is vertically oriented, compound bones remain unfused (e.g.,
tibiotarsus, tarsometatarsus), a splint-like fifth metatarsal is present and the long tail is
composed of 27 vertebrae (several more than Archaeopteryx). The long tail bears
chevrons of similar morphology to dromaeosaurs and a fan-shaped tuft of terminal
feathers as in dromaeosaurs (Xu et al., 2003; Norell and Xu, 2005) and troodontids (Ji et
al., 2005).
Other long-tailed birds, Shenzhouraptor and Jixiangornis (Ji et al., 2002a, 2002b),
from the Jehol are similar to Jeholornis and may prove to be junior synonyms (Zhou,
pers. comm. 2008) pending detailed studies. Another taxon, Dalianraptor cuhe (Gao and
Liu, 2005) also from the Jiufotang Formation, can be distinguished from Jeholornis by
the smaller forelimb/hindlimb ratio, much longer alular digit, and different phalangeal
proportions of manual digit III, though these taxa were likely closely related and the
56 
holotype of the former (DNHM D2139) could benefit from additional preparation and
study. Three other long-tailed specimens have been described: Jinfengopteryx elegans (Ji
et al., 2005), an incomplete skeletal tail (Lü and Hou, 2005), and the Late Cretaceous
Yandangornis longicaudus (Cai and Zhao, 1999). Jinfengopteryx has been reinterpreted
as a troodontid (Turner et al., 2007a) and the two other specimens cannot be assigned on
the basis of the fragmentary material currently available.

Zhongornis haoae
The transition from long bony tail to pygostyle was, until the recent discovery of
Zhongornis haoae from the Early Cretaceous Yixian Formation (125 Ma) of northeastern
China (Gao et al., 2008), very poorly known. The only known specimen is small and
interpreted as a juvenile; teeth are absent, the coracoid is short, the manual phalangeal
formula is 2-3-3-x-x (autapomorphy) and the tail is composed of 13-14 differentiated
caudal vertebrae (autapomorphy). Zhongornis is the only known bird to possess a
reduced number of caudal vertebrae, yet lack a pygostyle; instead the distal four
vertebrae, morphologically the same as preceding caudals, appear tightly ankylosed. The
discovery of Zhongornis suggests that in at least one lineage of early bird the short tail
was achieved first through the reduction in number rather than size of caudal vertebrae
(Gao et al., 2008).

57 
Confuciusornithidae
Confuciusornithidae, composed of three genera (Confuciusornis,
Changchengornis, and Eoconfuciusornis), represent the possibly the earliest known
occurrence of a horny beak within Aves (Chiappe et al., 1999; Zhang et al., 2008b).
Confuciusornis sanctus is known mostly from the Early Cretaceous Yixian Formation
(also reported from the slightly younger Jiufotang Formation; Dalsatt et al., 2006). There
are several species of Confuciusornis, yet only C. sanctus and C. dui have sufficient
diagnostic support to be considered valid (Chiappe et al., 2008). Changchengornis
hengdaoziensis, is known from a single specimen from the Yixian Formation (Ji et al.
1999), and differs from Confuciusornis in its smaller size and shorter and more curved
beak (Chiappe et al. 1999). Eoconfuciusornis zhengi comes from the oldest member of
the Jehol Group, the Dabeigou Formation (131 Ma), and has more basal morphologies,
such as a short coracoid, and the absence of lateral depressions on thoracic vertebrae, as
well as lacks a number of specializations such as the large fenestra piercing the
deltopectoral crest of the humerus (Zhang et al., 2008b).
The skull of confuciusornithids, in addition to possessing a massive horny beak
and no teeth, have fully enclosed supra- and infratemporal fenestrae (diapsid
morphology; Chiappe et al. 1999). As in Archaeopteryx, the shoulder bones of these
birds are fused into a rigid scapulocoracoid, a condition more primitive than that of the
long-tailed Rahonavis and Jeholornis. The furcula is robust without a hypocleideum, as
in Archaeopteryx, the ossified sternum is flat and quadrangular, lacking the keel and
caudal trabeculae present in more advanced birds (although some specimens do have a
58 
faint ridge that could have anchored a deeper cartilaginous carina; Chiappe et al., 1999)
and the synsacrum is formed by seven sacral vertebrae as in Sapeornis and some
enantiornithines (more than Archaeopteryx and Rahonavis). The forelimb approaches the
length of the hindlimb, as in Archaeopteryx, and has primitive proportions in that the
hand is longer than the humerus, which is longer than the ulna-radius; the hand retains
three claws. The number of gastralia is reduced from Archaeopteryx (Chiappe et al.,
1999). The compound bones in the robust hindlimbs were fully formed; the short tail
ends in a robust and straight pygostyle. As in other basal birds, confuciusornithids
possessed essentially modern plumage; they evolved a propatagium, the lift-generating
skin fold joining the shoulder and wrist, and remarkably long flight feathers hint at lower
wing-loading values and thus more advanced flight (Chiappe et al., 1999; Sanz et al.,
2000). A pair of long streamer-like feathers are variably preserved extending from the tail
region in specimens of C. sanctus (Chiappe et al., 1999, 2008; Zhang et al., 2008b). This
intraspecific difference has been hailed as evidence of sexual dimorphism (Feduccia,
1996; Hou et al., 1996; Zhou and Zhang, 2004) in which specimens with streamer-like
feathers are interpreted as males that died during lekking (male reunions for competitive
display). This hypothesis is not supported by a recent morphometric study in which no
statistical correlation between size distribution and the presence or absence of streamer-
like feathers was found, indicating that if these feathers are sexual characteristics, they
are not correlated with gender specific size difference, one of the most common sexually
dimorphic traits (Chiappe et al., 2008).

59 
Sapeornithidae
Another clade of pygostylians from the Jehol Biota (Zhou and Zhang, 2002b;
Yuan, 2008; Chiappe, 2007), this group includes the largest known Early Cretaceous
bird, Sapeornis chaoyangensis from the Jiufotang Formation (Zhou and Zhang, 2002b,
2003). Two other sapeornithids have been named from the Jiufotang Formation,
Sapeornis angustis (Provini et al., in press) and Dydactylornis jii (Yuan, 2008), however
their validity, mostly related to differences in relative proportions compared to Sapeornis
chaoyangensis (Yuan, 2008; Provini et al., in press) requires further study. The
sapeornithid skull is relatively short with rostrally restricted robust conical premaxillary
teeth. A large postorbital indicates at least a complete supratemporal fenestra is present.
The articulation between the scapula and the short coracoid is mobile. No specimen
preserves an ossified sternum, suggesting that, like Archaeopteryx, the sternum may have
been cartilaginous. Like other basal birds, the furcula of Sapeornis is very robust with a
wide-interclavicular angle, but unlike Archaeopteryx and confuciusornithids bears a small
hypocleidium. The forelimb is elongate, approximately 1.5 times the length of the
hindlimb, despite more derived proportions, with a humerus shorter than the ulna-radius.
The deltopectoral crest is pierced by a large proximal foramen, as in advanced
confuciusornithids and basal bird Zhongjianornis yangi (Chiappe et al., 1999; Zhou et al.,
2009). The hand of Sapeornis is reduced relative to confuciusornithids and Zhongornis; it
is subequal to the humerus in length with only two unguals. The pelvic bones of
Sapeornis remained unfused; the pubis is longer than the ischium, fused over its distal
third and ending in a boot-like expansion. The tail is composed of 6-7 free caudals
60 
followed by a small pygostyle more comparable to advanced ornithuromorphs than other
basal pygostylians.

Ornithuromorpha
This massive clade can be defined as the common ancestor of Patagopteryx and
neornithines and all taxa in between (Chiappe, 1995); a large number of Mesozoic taxa
filling a variety of niches have been collected from all over the world, spanning the entire
Cretaceous.

Basal Ornithuromorpha. The earliest record of the clade, in the Early Cretaceous Yixian
Formation of the Jehol, already records a small diversity of disparate taxa (i.e.
Yixianornis, Hongshanornis, Archaeorhynchus). Before the numerous complete
specimens from the Jehol, basal ornithuromorphs were known from primarily
fragmentary specimens of thus ambiguous phylogenetic placement (i.e. Patagopteryx,
Vorona, Ambiortus). Basal ornithuromorphs possess several derived features associated
with the advancement of flight, while remaining fairly unmodified in other regions of the
body (i.e. the skull). The skull is similar to Archaeopteryx and enantiornithines – unfused
with a fairly small premaxilla, however no postorbital has ever been preserved; teeth are
present in most taxa although edentulousness likely evolved several times within the
clade (i.e. Archaeorhynchus; Zhou and Zhang, 2006b). The thoracic girdle nears the
modern condition; the furcula forms a narrow U-shape and lacks a hypocleideum in all
known specimens. The coracoid is strut-like and possesses a procoracoid process (i.e.
61 
Gansus); the sternal margin is wide and bears an incipient lateral process (i.e. Gansus,
Yixianornis). The scapula is long – though in no taxon does it exceed the humerus in
length – and tapered, with a small acromion process. The sternum is much larger than in
more basal taxa; it is craniocaudally elongate, distally bearing a pair of fenestrae (i.e.
Songlingornis, Yanornis, Yixianornis, Gansus). The keel is well-developed, projecting
past the rostral margin (i.e. Yixianornis), as in some extant birds. The humerus is shorter
than the ulna; the humeral head is globose, and distally the condyles are bulbous. The
manus is typically fully fused and ungual claws are reduced (though still present); the
first phalanx of the major digit is craniocaudally expanded and dorsoventrally
compressed.
Distally, the pelvic girdle in some taxa is fairly primitive, with partially
retroverted and distally contacting pubes, which may or may not be expanded into a boot
(i.e. Hongshanornis, Yanornis) whereas the pubes are long, thin, and parallel to the ilium
and ischium in Apsaravis, which may be a basal ornithurine (Clarke, 2004). The hindlimb
has a diversity of proportions relative to the forelimb; in one clade the hindlimbs are
fairly elongate, possibly indicating a wading ecology (i.e. the hongshanornithids;
O’Connor et al., in press). The tibiotarsus is fully fused and clearly possesses two
cnemial crests in some taxa (i.e. Gansus). The tarsometatarsus is fully fused lacking
sutures, and possesses an intercotylar eminence. The rudimentary hypotarsus is
developed as a large, smooth, caudally projecting surface.
Integument is advanced; alulae and fan-shaped feathered tails are preserved in
several specimens (i.e. Hongshanornis, Yixianornis).
62 
Ornithurae. Only Ichthyornis and hesperornithiforms are considered ornithurines here;
previous analyses have placed Gansus and Apsaravis as basal ornithurines (Clarke et al.,
2006; You et al., 2006), however recent analyses, which include new morphological data
on the former taxon, have placed the species outside the ornithurine clade (O’Connor et
al., 2009). Hesperornitiformes are a group of large, flightless, foot propelled diving birds
and represent one of the most diverse clades of Mesozoic birds known. Their fossils are
collected primarily from Late Cretaceous deposits (Enaliornis from the Early Cretaceous;
Galton and Martin, 2002) and have been found all over the world, apparently limited to
the Northern hemisphere (Dyke et al., 2006). These birds have advanced features of the
cranium that suggest, like modern birds, their skulls were kinetic (Buhler et al., 1988); the
jaws however, retain numerous large teeth (Gregory, 1952). The forelimb is largely
reduced to a humerus and an ulna; the coracoid is robust and trapezoidal (Marsh, 1880;
Galton and Martin, 2002). The pelvic girdle is fully fused with an elongate post-
acetabular wing of the ilium and long thin parallel pubes and ischium (Marsh, 1880;
Martin and Cordes-Person, 2007). These birds possess a large, proximocranially
projecting cranial cnemial crest, and a highly modified tarsometatarsus in which
metatarsal IV is enlarged and metatarsals II and II are plantarly displaced (Marsh, 1880;
Dyke et al., 2006; Martin and Cordes-Person, 2007).
Ichthyornis dispar, another toothed Late Cretaceous bird known from North
America (Marsh, 1872), is typically resolved more advanced than hesperornithiforms
(Clarke et al., 2006; You et al., 2006; Zhang et al., 2008b; Zhou et al., 2009), often
forming a more exclusive clade with Aves, Carinate (Clarke, 2004; Zhang et al., 2008b).
63 
The rostrum is elongate and full of teeth. The acromion process on the coracoid is very
small, not projecting cranially past the articular surface for the coracoid (Clarke, 2004).
These birds were volant, with elongate forelimbs relative to their hindlimbs. The
deltopectoral crest of the ulna is thin and slightly concave caudally, but the strong cranial
projection of more advanced birds is absent. The manus is advanced, fully fused, with a
well-developed extensor process on the alular metacarpal (Clarke, 2004). The first
phalanx of the major digit bears a distocaudal projection (Steggman’s process); the digit
ended in a claw (Clarke, 2004). Distally, a well-defined brachial scar is present on the
cranial surface; caudally a well-developed olecranon is absent. The tibiotarsus bears
fairly small (compared to some extant birds) cnemial crests; distally the extensor groove
is caudally demarcated but lacks an ossified bridge. The tarsometatarsus bears a well-
developed intercotylar eminence and proximal and distal vascular foramen. Several
features, such as the presence of a dorsal supracondylar process on the distal humerus
suggest this taxon may be aquatic (Clarke, 2004).

Neornithes. Until recently, the Cretaceous record of modern birds consisted primarily of
fragmentary specimens (i.e. Cimolopteryx, Graculavis, Teviornis; Hope, 2002;
Kurochkin et al., 2002) of dubious phylogenetic placement. Even early descriptions of
enantiornithines, prior to the naming of the clade itself, placed such taxa as Gobipteryx
and Alexornis within neornithines (Elzanowski, 1974; Brodkorb, 1976). More recently, a
far more complete post-cranial specimen was uncovered from Late Cretaceous deposits
in Antarctica (Noriega and Tambussi, 1995; Clarke et al., 2005). Vegaavis iaai is
64 
assigned to Anseriformes, lending support to inferences supporting major neornithine
radiations (such as the galliform – anseriform split) occurred in the Cretaceous (van
Tuinen and Hedges, 2001; Feduccia. 2003; Clarke et al., 2005). The humerus is long and
the deltopectoral crest is deflected cranially. Both the ilioschiadic fenestra and obturator
foramen are present. Distally, the tibiotarsus possesses a fully ossified supratendinal
bridge. The specimen displays a fully formed hypotarsus with four crests, the medial of
which projects farther plantarly, enclosing three canals, a morphology consistent with
Anatidae (ducks).

v. Conclusions
This chapter cannot encapsulate all the arguments and proposed alternatives that
surround the debate on avian origins. Given the focus of this project, fairly deep within
the avian tree, the relationships outside Aves are almost unimportant. Understanding the
morphology of closely related non-avian maniraptorans, however, can help to better
understand the overall trajectory of avian evolution. The morphologies presented for each
group are incomplete, especially for such groups as Dromaeosauridae and
Ornithuromorpha, which are diverse and speciesous. These groups have also grown
considerably within the past decade, and new groups that may or may not be very closely
related to the base of the avian tree have only appeared in the past few years (months at
the time this is written!). Given that new morphological information continues to pour
from the fossil record, what is understood about basal avians and the avian sister-group is
highly subject to change. Like-wise, the cladistic method will continue to produce
65 
phylogenetic hypotheses of fluctuating hypotheses as new morphological information,
states and combinations of characters are uncovered and character lists and data matrices
are expanded. For this reason and those detailed above, phylogenetic hypotheses should
be interpreted with caution.
Hypotheses regarding the trajectory of evolution within the avian clade are also
difficult to summarize given the wealth of new clades that have appeared in the last
decade alone. The known distribution of morphologies throughout the clade continues to
change drastically (i.e. the recent discovery of basal bird Zhongjianornis; Zhou et al.,
2009). ‘Traditionally accepted’ relationships regarding basal birds in particular have
begun to collapse in light of new evidence (i.e. the placement of pygostylian Sapeornis as
more basal than long-tailed bird Jeholornis; Zhou et al., 2009). The continuing discovery
of new forms poses an exciting challenge to those who seek to uncover the relationships
of affected clades, i.e. Enantiornithes.
66 
CHAPTER 3: TAXONOMIC REVIEW

i. Introduction
Like many other groups of fossil vertebrates, the diverse Enantiornithes requires
taxonomic revision. A large number of the described taxa lack clear and valid character-
based diagnoses founded on rigorous comparisons and phylogenetic analyses and are thus
likely nomina dubia. Numerous fragmentary and dubious taxa obfuscate cladistic
analyses and thus some taxonomic revision is required prior to systematic review. Below,
the fossil birds Cathayornis yandica and Sinornis santensis from the Cretaceous of China
are used as examples, to argue that this problem is largely the result of inadequate
taxonomic practices (i.e. diagnosis, holotype material, and comparison). Fragmentary
taxa and those lacking clear diagnoses are reviewed and recommendations on their
validity are made.

ii. Taxonomic Practices as Applied in Paleontology
Vertebrate paleontology is a science that will always be plagued with doubts,
assumptions and missing data. Our knowledge of taxa and their morphology is limited
by available fossil material, compromised by the processes of death, fossilization, and
diagenesis. It has long been understood that the naming of vertebrate fossil taxa is
especially subjective because differential characteristics can be based only on preserved
morphology, observationally variable between workers (Amadon, 1963; Eldredge and
Cracraft, 1979): one person examining a fossil may view it as ‘considerably different’ in
67 
morphology compared to someone else. Although rules apply to this process just as they
do across all zoology (i.e. ICZN, 2000), an absence of congruency in research methods
even within dinosaur paleontology is still prevalent (e.g. Dodson, 1990; Benton, 1998,
2008; Taylor, 2006). The proliferation of potential synonyms, homonyms and nomina
dubia has been especially evident in the study of Mesozoic birds as recent years have
seen an explosion in the numbers of known fossils leading to an exponential rise in
numbers of named taxa since the mid-1990s (Fountaine et al., 2005; Chiappe and Dyke,
2007). The vast majority of new named avian taxa come from the Cretaceous of China,
where thousands of specimens have been unearthed apparently just in the last two
decades (Zhou and Zhang, 2006a; He, 2007).
The proliferation of named fossil bird taxa, and fossil vertebrates in general, is a
problem that can be rectified via a unified effort amongst paleontologists. Problems arise
as a result of: (1) Use of inadequate, fragmentary and undiagnostic holotype material (i.e.
resulting in nomina dubia - taxa that cannot be distinguished from others); (2) Inadequate
comparisons of new taxa with those already described (i.e. resulting in the subsequent
erection of junior synonyms); (3) Differences in interpretation of fossils (i.e. perhaps
based on observed morphological differences or via a taphonomic effect); and (4)
Variation in species definitions (i.e., basing a new taxon on the fact that it comes from a
different locality to other similar forms).
The well-known Chinese fossil enantiornithine birds Cathayornis yandica and
Sinornis santensis are both represented by fairly complete specimens yet there has been
debate over their status as distinct taxonomic entities. Largely this debate has occurred
68 
because of inadequacies in the original descriptions and because clear diagnostic
characters had not been presented. Close inspection reveals important morphological
differences indicating that these two taxa are clearly distinct from one another and should
remain separate taxa.
Despite the guidelines put forth by the ICZN (Nomenclature ICoZ, 2000), large
numbers of taxa of fossil birds have been described with inadequate diagnoses (Hou,
1997a; Li et al., 2006) or published in book chapters that lack adequate peer review (He,
2007). Others have been described based on specimens in private collections,
unavailable to the scientific community, and thus rendering any interesting data they may
have to contribute useless (Dalingheornis; Zhang et al., 2006). The most recent example
of this worrying trend is the description of a new, small enantiornithine bird from the
Crato Formation of Brazil (Naish et al., 2007), potentially the oldest fossil bird known
from Gondwana (Close et al., 2009).
The biggest problem of all is the erection of taxa based on largely incomplete
material (i.e. Explorornis, Lectavis, Martinavis; Panteyelev, 1998; Chiappe, 1993;
Walker et al., 2007). For whatever reason scientists are compelled to erect taxa from
fragmentary material, it is up to the scientific community as reviewers to prevent
undiagnosible or comparable specimens from being named. When taxa are based on
private material, or are for other reasons invalid, the scientific community should unify in
excluding these ‘taxa’ when discussing the clade they are purported to belong to. This
will hopefully discourage the continued practice of the erection of such taxa (i.e.
Dalingheornis, Zhang et al., 2006). While it is very important to describe new material,
69 
erecting a new genus based on a bone fragment or publishing information that can never
be verified does little to help clarify enantiornithine diversity and relationships.
Within the highly mobile living flying vertebrates - birds and bats - it has long
been known that large numbers of biological species exist that are indistinguishable from
one another based on osteology alone (Amadon, 1963). Taxa differentiate themselves
through mating behaviors, vocalizations, habitat and integument. These species are
regarded as one as they are indistinguishable to paleontologists. This is unavoidable in
the fossil record, but this also means that within birds, a large amount of diversity is
encapsulated within a very small amount of osteological disparity. Therefore, birds and
other flying vertebrates should be studied with care, and small osteological differences
should not be disregarded.
With no way to differentiate species other than bones and rare soft tissues (i.e.
integument being reasonable within Aves) we argue that vertebrae paleontologists should
use only such characters to discern taxa from a given geological unit. As has been done,
differentiation based on inferred geological age or geographic separation makes
assumptions about a species range or success. Such assumptions are for obvious reasons
inherently weak; the error associated with dating sediments is typically large and limiting
an extinct taxon based on knowledge of an extant analogue bears no validity other than a
proposed possibility. However, based on comparisons with geographic ranges of similar
(diet, ecology, size, etc) modern taxa or average species duration through time may be
used as valid arguments for erecting a new taxon. Such arguments should only be made
when they can be justified and well supported by cited data. Finally, given the
70 
uncertainty regarding geologic and geographic data associated with many Chinese
enantiornithines, these methods should be used with caution and only when the
appropriate data is not only available but also reliable.

iii. Taxonomic Issues as applied within the Enantiornithines
Enantiornithes is the most specious known lineage of Mesozoic birds (Chiappe,
2002; Chiappe and Dyke, 2007; Dyke and Nudds, 2009) with approximately 60 species
named, and in China hundreds, if not thousands, of undescribed specimens (pers. obs.).
Despite this apparent diversity the taxonomy of enantiornithines is riddled with thorny
issues: a third of named species are based upon extremely fragmentary, sometimes non-
overlapping, fossil material (Table 3.1; e.g. six named species from the Cretaceous of
Uzbekistan based on coracoid fragments; Panteleyev, 1998). The extremely rapid
succession of discoveries from China in recent years has resulted in publications dealing
with strikingly similar specimens sometimes appearing almost simultaneously, as was the
case with S. santensis and C. yandica (Zhou et al., 1992; Sereno and Rao, 1992; see also
Hou and Chen, 1999; Ji and Ji, 1999; Zhou and Zhang, 2001; Gong et al., 2004).
Because detailed comparisons have often been absent, diagnostic distinctions between
‘species’ have often remained unclear or are unverifiable from publications (i.e. through
photographs and figures) (e.g. Zhang et al., 2005; Li et al., 2006; Gong et al., 2008).
These taxonomic issues have been further propagated as specimens in Chinese museum
collections are labeled, even assigned as new species, within genera that may later prove
invalid. Because enantiornithine birds are usually small and morphologically uniform,
71 
like their extant perching passerine counterparts, small morphological differences may go
unobserved and multiple ‘real’ species may be regarded under one taxon (Martin and
ZHou, 1997a; Zhou, 2002). Resolution is required so that studies of enantiornithine
biology, phylogenetics and lineage dynamics can proceed (Chiappe and Walker, 2002;
Chiappe et al., 2007).

iv. Cathayornis yandica vs. Sinornis santensis
These issues discussed above are illustrated using one particularly controversial
example of the two named enantiornithines Sinornis santensis (BNHM BPV 538a,b) and
Cathayornis yandica (IVPP V9769) (Sereno and Rao, 1992, Sereno et al., 2002, Zhou et
al., 1992). The first two named enantiornithine birds from China, their publications
appeared almost simultaneously. Since C. yandica was named, three additional species
have been added to the genus, C. caudatus, C. aberransis (IVPP V10917 and V12353),
and C. chabuensis (BMNH-Ph00010). Published diagnoses on the former are poor and do
not provide character-based tools with which to differentiate them from other taxa (Hou,
1997a). The overall poor preservation of C. caudatus and C. aberransis, makes it
difficult to determine the presence of anatomical details or make morphological
comparisons to other taxa and it is believed they should be regarded as nomina dubia (see
below). However, these specimens were not studied in the firsthand making it premature
to make strong recommendations at this time; furthermore, preparation of the fossil could
potentially reveal additional information (removing bone to create casts). The more
recently described C. chabuensis (Li et al., 2008) provides clear distinctions between the
72 
new specimen and C. yandica as well as other birds from the same locality (Otogornis;
Hou, 1994).
In museums across China, a large but unknown number of specimens have been
referred to C. yandica (Martin and ZHou, 1997a; Zhou and Hou, 2002; pers. obs.): one of
these referred specimens (IVPP V10916) was later assigned to a new genus and species,
Eocathayornis walkeri (Martin and ZHou, 1997a; Zhou, 2002). In the second publication
to describe S. santensis, a book chapter, C. yandica was synonymized under the former
(Sereno et al., 2002), which had appeared in print slightly earlier. However, in another
chapter in the same book, C. yandica was regarded as separate from Sinornis (Zhou and
Hou, 2002). Synonymy was not strongly supported (or refuted) empirically in either
chapter and thus C. yandica and S. santensis are still treated as distinct taxa by some (Li
et al., 2006; Chiappe et al., 2006) and as synonyms by others (Cau and Arduini, 2008).

S. santensis and C. yandica Compared
Although the holotype specimens of S. santensis and C. yandica do come from
different localities within the Early Cretaceous Jiufotang Formation, upper Jehol Group
(120 Ma; Zhou, 2006), like many Jehol birds, these specimens were not collected by
scientists and so published locality information varies (c.f. Zhou and Hou, 2002; Zhou
and Zhang, 2006a). While the exact locality data is unknown, publications consistently
place these specimens less than 20 km apart, with Chaoyang City as the closest major
geographic indicator (Zhou and Hou, 2002; Sereno et al., 2002; Zhou and Zhang, 2006a).
S. santensis was discovered just west of Shengli, near Chaoyang city in northwestern
73 

Figure 3.1. A, IVPP V9769, holotype of Cathayornis yandica; B, BNHM BPV538,
holotype of Sinornis sinensis (from Sereno and Rao, 1992).
74 
Liaoning Province while the holotypes of all the Cathayornis species were collected just
south of Boluochi, also near Chaoyang City (Hou, 1997a; Zhou and Hou, 2002).
Although the mode of preservation is similar in both specimens, both preserved
primarily as voids, the information discernable differs greatly between the two holotypes
(Fig. 3.1). The holotype of C. yandica (IVPP V9769) consists of a slab and counterslab
so that both views are available for many elements (although largely disarticulated and
incomplete) (Fig. 3.1A) while S. santensis is preserved in lateral view also in a slab and
counterslab largely articulated but incomplete (BNHM BPV 538a,b) (Fig. 3.1B). The
holotype of C. yandica (IVPP V9769) includes a well-preserved skull but lacks feet and
the pelvic girdle is incomplete and disarticulated. In contrast S. santensis includes both
feet and the pelvic girdle but has a poorly preserved partial skull. The characters
originally used to diagnosis S. santensis are thus difficult to assess in C. yandica and vice
versa.
Despite the limited amount of overlap in elements several elements can be
compared. A number of apparent differences in preserved anatomy between the two
specimens are interpreted as due to their preservation (see below). However, a number of
other anatomical features are not and there is clear, distinctive morphological variation in
three areas of the skeleton, indicative of taxic differentiation.

Hand. The hand of both taxa is similar (Fig. 3.2A, B): S. santensis and C. yandica have
small claws on both the alular and major digits of their hands and have short alular digits
that do not distally surpass the distal end of the major metacarpal. The proximal
75 

Figure 3.2. A, carpometacarpus of Cathayornis yandica; B, hand of Sinornis santensis; C,
postacetabular ilium of C. yandica; D, postacetabular ilium of S. santensis.
76 
carpometacarpus was considered to be unfused in S. santensis as opposed to fused in C.
yandica, however this character is unclear and cannot be coded in both taxa due to
preservation (Fig. 3.2A, B). The morphology of the first phalanx of the minor digit
differs between taxa (contra Sereno et al., 2002): in C. yandica this bone is clearly
straight, rectangular to trapezoidal, tapering distally (Fig. 3.2A) while in S. santensis this
phalanx is curved with a concave ventral margin (Fig. 3.2B). The morphological
disparity of this phalanx between taxa was noted by Sereno et al. (2002) but it was not
considered that this could distinguish the two taxa.

Pelvis. Sinornis santensis and C. yandica also clearly differ from one another in the
preserved morphology of the postacetabular wing of the ilium (Fig. 3.2C, D). The pelvic
girdle of S. santensis is nearly entirely preserved in full articulation in left lateral view
(Fig. 3.2D), missing only the preacetabular wing of the ilium. The dorsal margin of the
postacetabular wing of the ilium is dorsally convex while the ventral margin is slightly
concave so that the entire post-acetabular wing is slightly curved in a caudoventral
direction (Fig. 3.2D). In contrast, although both ilia are preserved, the pelvic girdle of C.
yandica (IVPP V9769) is incomplete and disarticulated (Fig. 3.2C). The right ilium is
complete in this specimen, preserved near the right distal humerus, while the left
(associated with the disarticulated pelvic girdle and hindlimb) is missing its proximal
third (Fig. 3.2C). The void of the right ilium forms an impression of the lateral surface
but the morphology remains unclear due to overlap with other elements. The
postacetabular process of the left C. yandica ilia has a straight dorsal margin with a
77 
ventrally concave ventral margin and is directed caudally (Fig. 3.2C). This process tapers
caudally but has a blunt distal margin, whereas in S. santensis this termination forms a
sharper point (Fig 3.2D). A three-dimensionally preserved enantiornithine from the
slightly younger Xiagou Formation (CAGS-IG-05-CM-06) possesses a nearly complete
and fully articulated pelvic girdle, and displays the same straight morphology as C.
yandica which results in differences in the shape of the ‘ilioschiadic fenestra’ between S.
santensis and the Xiagou enantiornithine. This indicates that the morphology seen in C.
yandica is not preservational.

Tarsometatarsi. Both C. yandica and S. santensis have a plantarly excavated
tarsometatarsus formed by keel like medioplantar and lateroplantar margins of
metatarsals II and IV respectively. The metatarsals in C. yandica are arranged in a single
horizontal plane while the trochlea of metatarsals II and IV of S. santensis are displaced
plantarly. The distal ends of the metatarsals in C. yandica however, are not preserved in
the holotype specimen (well preserved in a referred specimen IVPP V9936) and thus this
difference is ambiguous.

Pygostyle. The pygostyles of S. santensis and C. yandica are morphologically very
similar; Sinornis santensis has the typical enantiornithine pygostyle, which is dorsally
forked with ventrolaterally directed processes that rapidly diminish distally (contra
Sereno et al., 2002; see Chiappe et al., 2007). Under close inspection the poorly
preserved pygostyle of C. yandica is also dorsally forked and tapers sharply in
78 
mediolateral width distally. The pygostyles of the two taxa, however, differ in length
with respect to their overall body size, which can only be considered a true
morphological difference and thus a diagnostic character: the pygostyle of C. yandica is
nearly 25% longer than that of S. santensis.

Differentiating S. santensis and C. yandica
In terms of preserved characters that can be used to formulate a taxonomic
diagnosis, S. santensis (BNHM BPV 538) differs from C. yandica (IVPP V9769) in that:
(1) the first phalanx of the minor digit is curved (straight in C. yandica); (2) the pelvic
girdle is nearly fully fused (unfused in C. yandica); (3) the post-acetabular wing of the
ilium is curved (straight in C. yandica); (4) the distal ends of metatarsals II and IV are
plantarly displaced (in the same plane in C. yandica); and (5) the pygostyle is shorter (3/4
the length of that of C. yandica).
The additional small differences observed between S. santensis and C. yandica
are interpreted here as the result of or obscured by poor preservation. For example, the
scapula of S. santensis is relatively broad for much of its length; the distal third is marked
by a slight expansion. This morphology appears absent in C. yandica in which the
scapular shaft appears much narrower for its entire length. This could be a result of the
angle in which the scapula is preserved, with S. santensis being preserved in lateral view
and C. yandica being preserved in dorsolateral view, the width of the shaft angled into
the slab. The transverse processes of the free caudal vertebrae in S. santensis appear
longer than those of C. yandica however the caudals in the latter are not well preserved.
79 

Differentiating Cathayornis aberransis, C. caudatus and C. chabuensis
The ability to differentiate and diagnose IVPP V9769 and BNHM BPV 538 may
be in large part due to their preparation. Bones were removed to create clean voids and
molds and casts were made for study. While many taxa below are recommended nomina
nuda, future preparation of some specimens may prove their validity. This may very well
be the case for the holotypes of C. aberransis and C. caudatus. These specimens were
not examined first hand and published data is limited. On the basis of the poor quality of
their published diagnoses (Hou, 1997a) these two taxa should be considered nomina nuda
until further preparation and study is completed. In cases such as this - when a new
specimen potentially may represent a new species but the material is sparse or a specimen
requires further preparation, reservations should be made. While new material should be
described when it becomes available, it is more parsimonious to wait for diagnosable
material before erecting a new taxon. Currently, the information available on IVPP
V12353 and IVPP V10917, the only known specimens of C. aberransis and C. caudatus
respectively, cannot be accurately compared with the majority of known specimens (see
below for a detailed discussion of each specimen), and thus do not contribute to the
overall understanding of enantiornithine taxonomy. The holotype of C. chabuensis is
distinguished from C. yandica by the slight distolateral projection of the outer sternal
trabeculae, as well as the relatively more caudal restriction of the keel (Li et al., 2008),
however, the published photographs and illustrations prevent verification of the
anatomical details described for C. chabuensis.
80 

v. Fragmentary Taxa
Twelve species of enantiornithine have been erected on bone fragments (less than
one complete element), and an additional seven taxa have been named from a single
bone. Some of these taxa possess obvious autapomorphies that readily distinguish them
from other specimens (Yungavolucris, A. archibaldi), however, the degree to which
fragmentary species can be compared with other members of the clade is extremely
limited. Fragmentary specimens and taxa with missing data can still contribute
phylogenetically significant information (Kearny and Clark, 2003; Wiens, 2003),
however the data available from a specimen should be evaluated in terms of how it will
contribute towards taxonomic understanding, and taxa should only be erected when
diagnosable material is available. All species known from less than a single bone come
from the Uzbekistan Bissekty Formation (Table 3.1). These twelve taxa are evaluated
based on available literature; based on the material and available information, of the
twelve species eleven are here considered nomina dubia (see Table 3.1).

Coracoid Fragments
Six species are named entirely from coracoid fragments (following Panteyelev,
1998 and Kurochkin, 2003): Abavornis bonaparti (TsNIGRM NTS 56/11915),
Catenoleimus anachoretus (PO-4606), Explorornis nessovi (PO-4819), Enantiornis
walkeri (PO-4825, Explorornis walkeri per Panteyelev, 1998), Enantiornis martini (PO-
4609, Incolornis martini per Panteyelev, 1998), and Incolornis silvae (PO-4604). Four
81 
other coracoid fragments were identified as enantiornithines to varying taxonomic levels
(PO-4605 – Abavornis sp.; PO-4818 and PO-4817 – Explorornis sp. 1 and 2; PO-4821 -
Alexornithiformes indet.) and are also reevaluated here. The material is highly
fragmentary (Fig. 3.3) and largely non-overlapping, or eroded in such a way that
differences are ambiguous (delicate features lost to abrasion). While there may be some
slight differences between individual bones, and there likely does exist among the
material more than a single species, the fragments provide too little comparative material
to be able to determine unequivocally if a difference is not a preservational artifact, or if
the head of a coracoid called one species is not synonymous with the partial corpus
fragment used to erect another. For example, following Panteleyev (1998) the holotypes
of Incolornis silvae (PO-4604, Fig. 3.3E) and “I. martini” (PO-4609, Fig. 3.3F) are
represented by a coracoid neck and head respectively; there is no overlap between the
two specimens, yet they are assigned to the same genus. PO-4604 differs from other
Bissekty coracoid necks in that it possesses a small mediodorsally projecting triangular
projection just distal to the coracoid head, similar to Protopteryx (Zhang and Zhou,
2000). Unfortunately, the specimen does not definitively preserve enantiornithine
morphologies and its taxonomic assignment to the clade is questionable (here regarded as
incertae sedis); PO-4609 is laterally compressed and the acrocoracoid, glenoid and
scapular facet are approximately aligned, an enantiornithine morphology, but preserves
no autapomorphies. PO-4609 was returned to the genus Enantiornis by Kurochkin
(2003), despite the fact the figures lack an obvious acrocoracoidal tubercle, as in E. leali.
Size is often an apparent distinction between taxa, however growth in enantiornithines
82 

Figure 3.3. Uzbekistan coracoid fragments (from Panteylev, 1998): A, PO 4819
(Explorornis nessovi); B, PO 4818 (Explorornis sp.); C, PO 4825 (Enantiornis walkeri);
D, PO 4606 (Catenoleimus anachoretus); E, PO 4604 (Incolornis silvae); F, PO 4609 (I.
martini); G, TGNIGRM NTS 56/11915 (Abavornis bonaparti); H, PO 4605 (Abavornis
sp.); I, PO 4821 (Alexornithiformes indet.).
83 
and other basal birds is prolonged relative to advanced birds and therefore size alone is
not a reliable indicator of specific differences (Chinsamy et al., 1995; Senter and Robins,
2003; Chiappe et al., 2008).
These coracoid fragments were all originally described by Nessov (1992) but
assigned at the clade level only; taxonomic assignments came later and have shifted
between researchers (Nessov and Panteleyev, 1993; Panteleyev, 1998; Kurochkin, 2003).
On the basis of published material, it seems most parsimonious to follow Nessov (1992)
and assign the coracoids, where possible, at the clade level only (Table 3.1). Abavornis
bonaparti, Catenoleimus anachoretus, Enantiornis walkeri, E. martini, E. nessovi, and I.
silvae are all here considered nomina dubia. After reassessment of the coracoid
fragments, PO-4821 (Fig. 3.3I; formerly Alexornithiformes indet.), PO-4606 (Fig. 3.3D;
formerly Catenoleimus anachoretus) and PO-4604 (formerly I. silvae) are considered
incertae sedis as their inclusion in the enantiornithine clade is questionable. These
specimens are so fragmentary they reveal little to no morphological information and thus
were not included in the cladistic analysis. TsNIGRM NTS 56/11915 (Fig. 3.3G;
formerly A. bonaparti), PO-4605 (Fig. 3.3H; formerly Abavornis sp.), PO-4609 (formerly
E. martini), PO-4917 (formerly Explorornis sp. 1), PO-4818 (Fig. 3.3B; formerly
Explorornis sp. 2), PO-4819 (Fig. 3.3A; formerly E. nessovi) and PO-4825 (Fig. 3.3C;
formerly Enantiornis walkeri) are referred to Enantiornithes indet. (Table 3.1).

84 
Table 3.1. Fragmentary taxa and their revised assignment based on this study.
85 
Synsacral Fragments
Three fragmentary taxa are known entirely from portions of the synsacrum
(Zhyraornis kashkarovi, Z. logunovi, and Lenesornis maltshevskyi); this element is
commonly preserved among Early Cretaceous Chinese enantiornithines, but most
commonly preserved flattened and visible only in dorsal or ventral view. There are only
two known enantiornithine synsacri that are three-dimensionally preserved, and disparity
between their morphologies, as well as the distribution of morphologies among
ornithothoracines makes comparison and taxonomic assignment difficult. The holotypes
of Z. kashkarovi (TsNIGRI 42/11915) and Z. logunovi (PO-4600; Nessov, 1984) are not
readily distinguishable; the differences suggested by the diagnosis provided by
Kurochkin (2003) cannot be confirmed from published figures (Nessov, 1984, 1992). The
specimens (TsNIGRI 42/11915, PO-4600) are morphologically different from other
enantiornithine synsacri yet whether they belong within the clade at all is uncertain. The
genus was originally described as an ichthyornithiform but, based on comparison with the
synsacrum of Gobipteryx (PIN-4492-1), was later assigned to Enantiornithes based on the
shared presence of a dorsally convex surface, transverse processes of equal size and
distribution in dorsal view, and the presence of enlarged costal facets on the 3-4
th
sacral
vertebrae (Kurochkin, 1995; Kurochkin, 2003). The dorsoventral curvature is reported in
Gobipteryx PIN-4492-1, but absent in the El Brete synsacrum (PVL-4041-4). The
synsacri of Rapaxavis and Pengornis appear straight but are preserved embedded in
single slabs making it difficult to determine unequivocally if this is an artifact of
preservation. The synsacrum of the Late Cretaceous flightless ornithothoracine
86 
Gargantuavis philoinos (Buffetaut and Le Loeuff, 1998) and some modern birds (tawny
owl) show this curvature. The transverse processes of equal size and distribution are
difficult to confirm since they are largely not preserved, however, the relative spacing
and size of the transverse processes in ornithuromorphs is also fairly consistent. Nothing
in this diagnosis directly suggests this taxon belongs within Enantiornithes. The proximal
articular surface of the synsacrum in Zhyraornis is equal in width and height and
concave, similar in Gobipteryx but also Ichthyornis (Clarke, 2004) and Gargantuavis
(Buffetaut and Le Loeuff, 1998). A dorsal spinous crest is present along the entire length,
as in PVL-4041-4, Pengornis, and Gargantuavis. However, in Gargantuavis, Pengornis,
and other enantiornithines, the crest is low along the entire length. In Gansus, Ichthyornis
and Zhyraornis, the crest is prominent, diminishing caudally. A ventral groove, like that
present in several enantiornithines (Rapaxavis, Gobipteryx, Concornis), is reportedly
absent in Zhyraornis and PVL-4041-4, shallow and questionable in Ichthyornis, but
present in Gargantuavis. Zhyraornis bears large, deep excavations on the lateral surface
of the sacrals that diminish distally; excavations are present in PVL-4041-4 but much
shallower and less defined. Seven vertebrae are reportedly preserved in TsNIGRI
42/11915, the more complete of the two specimens. This number is typical for
enantiornithines but fewer than any known ornithuromorph. A total of seven to nine
vertebrae are present, estimated from published photos (Fig. 5a-c, Nessov, 1984)
however it is very difficult to determine how many sacrals are present; the synsacrum
appears fully fused and the cranial and caudal surfaces are poorly preserved. Based on the
preserved morphology and comparison with other known Mesozoic bird synsacri, it is
87 
premature to assign Zhyraornis to Enantiornithes. Based on the fragmentary nature of Z.
kashkarovi and Z. logunovi, the taxa should be regarded as nomina dubia (Table 3.1). The
morphology as interpreted here suggests that a placement in Ornithuromorpha may be
more fitting, consistent with more recent hypotheses by Kurochkin (2006).
Little information is available on L. maltshevskyi (Ichthyornis maltshevskyi,
Nessov, 1986; Kurochkin, 1996), the third enantiornithine known from synsacrum
material. The holotype specimen (PO-3434) was reassigned to the enantiornithines after
comparison with Gobipteryx and other material (Kurochkin, 1995, 2003). This specimen
possesses a ventral groove as in Gobipteryx and is dorsoventrally bowed as in Zhyraornis
(Ornithuromorpha). This taxon is here considered a nomen dubium pending new available
information and reassigned to Aves incertae sedis (Table 3.1).

Sazavis prisca (PO-3472; Nessov and Jarkov, 1989)
Known only from a poorly preserved distal fragment of a right tibiotarsus from
the Bissekty Formation (Late Turonian - Conacian), this specimen resembles the
tibiotarsi of other enantiornithines and basal birds: the medial condyle is wider than the
lateral (the plesiomorphic condition within Aves) and projects farther cranially (also
Rahonavis and Confuciusornis). It cannot be determined from the photographs if the two
condyles were separated by an intercondylar incisure, similar to Gobipteryx (PIN-4492-1,
formerly Nanantius valifanovi following Chiappe et al., 2001) from the Barun Goyot
Formation (Late Campanian). The distinguishing characteristic of the specimen is the
transverse paracondylar expansion (absent in Confuciusornis and Patagopteryx), only
88 
medially expanded in Gobipteryx. This morphology resembles that of an Early
Cretaceous Xiagou enantiornithine (CAGS-05-CM-006, CAGS-04-CM-006); in this
specimen the medial condyle is round and wider than the lateral in width, while the
lateral is triangular, tapering medially. The poor preservation of the lateral condyle in
Sazavis prevents further comparison. Based on the combination of the fragmentary and
poor preservation of the only known specimen and the paucity of available information,
this taxon should be considered a nomen dubium.

Kizylkumavis cretacea (Nessov, 1984)
Represented by a distal left humerus (TsNIGRI 51/11915), the specimen strongly
resembles the North American Late Cretaceous Alexornis (Brodkorb, 1976) strongly
supporting its taxonomic assignment to the enantiornithines. The distal end bears
paracondylar expansions and the distal margin is strongly angled, as in Martinavis,
Gurilynia, and Alexornis. The condyles are strap-like and the dorsal condyle is
transversely oriented, as in other enantiornithines. Both Alexornis and TsNIGRI 51/11915
share the presence of a well-developed dorsal epicondyle on the craniodorsal margin. The
two taxa are comparable in size and morphology cannot readily be distinguished from the
published material. Based on the fragmentary nature of the holotype, the taxon is
regarded as a nomen dubium.

89 
Gurilynia nessovi (Kurochkin, 1999)
The holotype of this taxon consists of the proximal third of a left humerus (PIN-
4499-12), however a distal left humerus (PIN-4499-14) was assigned as the paratype and
a proximal fragment of a left coracoid (PIN-4499-13) was also assigned to the genus
(Kurochkin, 1999). Kurochkin (2003) later suggested that the assignment of the coracoid
to the genus is unsubstantiated and the genus is evaluated here based on the humeral
material only. Gurilynia shares a number of morphologies with humeri from El Brete
(Martinavis and E. leali) strongly supporting its taxonomic assignment to the
enantiornithines; the specimen is distinct from all species of Martinavis in that the
proximal margin of the humeral head is not as deeply concave, and does not rise ventrally
and dorsally as steeply. Enantiornis leali possesses a more distoventrally located ventral
tubercle (more distal in the latter) and a thicker proximal humerus. In both Martinavis
and E. leali, the impression for the m. coracobrachialis cranialis is circular, and lacks the
distinct ventral margin present in Gurilynia. The paratype (PIN-4499-14) differs from
Kizylkumavis in that the dorsal (caudodorsal) margin only possesses a small bump for the
attachment of the m. extensor metacarpi radialis, and lacks the well-developed dorsal
epicondyle present in the latter. The genus can be diagnosed as having the following
unique combination of humeral morphologies: proximal cranial surface concave and
caudal surface convex; proximal margin convex on the midline, rising dorsally and
ventrally; deltopectoral crest projecting proximally to the same level as the humeral head;
cranial margin shallow capital incision; proximoventrally restricted ventral tubercle; and
oval impression for the m. coracobrachialis cranialis demarcated ventrally by a defined
90 
ridge. Despite its fragmentary nature, Gurilynia shows characters known only to occur
within enantiornithines as well as unique morphologies that distinguish it from other
known taxa. However, because it is so fragmentary, it cannot be resolved in cladistic
analysis (see Chapter 12).

vi. Inadequate Diagnoses
Following the description of taxa based from fragmentary holotype material, the
erection of taxa with inadequate diagnoses is the second leading taxonomic problem
within enantiornithines. One study has suggested that the many poorly preserved taxa be
synonymized under Cathayornis (i.e. Longchengornis, Cuspirostrisornis; Zhou et al.,
2008b). Many of these taxa may be valid taxa, but they cannot be determined as such
based on the published information. Several of these taxa were studied first hand and
revised diagnoses are provided below. Others were inaccessible due to communication,
funding or other restraints; for these taxa, discussions of the published material are
provided. The holotypes and published specimens of taxa addressed here are typically
nearly complete (Table 3.2), yet the small amount of information that can be gleaned
from the short publications that describe them often does not include apomorphies or
unique morphologies cannot be confirmed unequivocally due to preservation and the
quality of preparation and photographs. Given the current information available, taxa
such as Largirostrornis (Hou, 1997a) represent functional nomina dubia. Detailed
morphological studies of these taxa will most likely support their status as distinct taxa,
as has been shown for some genera (Dapingfangornis).
91 

Table 3.2 All Chinese enantiornithines currently considered invalid.
92 
Valid Taxa
Alethoalaornis agitornis (from LPM-B00017 – Li et al., 2007). This taxon is named
from five nearly complete specimens all from the Jiufotang Formation of western
Liaoning. During firsthand study of this taxon, only a single referred specimen (LPM-
B00017, formerly LPM-00040; Li et al., 2007) was available for study (Fig. 3.4).
Because the published information (Li et al., 2007) is based mostly on the holotype, some
morphologies cannot be addressed, however the following observations and amendments
can be made to the published diagnosis and description.
In the published diagnosis the beak is described as long and pointed (Li et al.,
2007), a morphology observed in the ornithuromorph Hongshanornis (Zhou and Zhang,
2005). In specimens LPM-00009 (this collection number is now assigned to a specimen
of Confuciusornis, new collection number unknown; pers. obs.) and LPM-00038 the
preserved portion of the rostrum forms a point; in the former, the premaxillae are
articulated with each other (likely fused at least proximally) and displaced so that the true
morphology of the beak is unknown. In LPM-00038, it is possible the skull is in ventral
view; the quality of the photograph prevents assessment of most morphologies. In
specimen LPM-B00017 the premaxilla is preserved in ventrolateral view; the rostral
portion appears low (dorsal and ventral margins nearly parallel) but the angle and quality
of preservation prevents an unequivocal interpretation of the element. Preservation of all
specimens prevents an accurate assessment of rostral length. The cervicals are described
as heterocoelic; in LPM-B00017 the cervicals are poorly preserved and in articulation
making this difficult to determine. Two or three pairs of teeth are described, but it is not
93 

Figure 3.4. A referred specimen of Alethoalaornis agitornis (LPM B00017, formerly
LPM 00040); scale bar equals one cm.
94 
mentioned in which bones (premaxilla, maxilla or dentary). The premaxilla and maxilla
both bear peg-like teeth typical of small enantiornithines as in C. yandica, lacking the
distinct caudal curvature of Eoenantiornis; the exact number cannot be determined.
LPM-B00017 is preserved in dorsal view, preventing assessment of the furcula
and sternum diagnostic characters; an elongate hypocleidium however, is typical of Early
Cretaceous enantiornithines, but a well-projected carina is only known in the Late
Cretaceous Neuquenornis (Chiappe and Calvo, 1994). The coracoid is described as
possessing a wide sternal margin; in LPM-B00017 the sternal margin is approximately
40% of the omal-sternal length, typical of most enantiornithines from the Jehol
(sympatric ornithuromorphs such as Yanornis and Songlingornis possess wide sternal
margins).
A well-developed capital incision and pneumatic foramina are described on the
humerus. In LPM-B00017 the pneumotricipital fossa appears rudimentary, smaller than
that of C. yandica and much smaller than the well-developed fossae of El Brete humeri.
An actual foramina piercing the ventral tubercle as in some specimens from El Brete
(PVL-4035, 4020) is absent. The capital incision separates the ventral tubercle, as in all
enantiornithines, however the incision is shallow, as in other Early Cretaceous taxa, not
the deep groove of Late Cretaceous forms (Enantiornis, Martinavis). The diagnosis,
metacarpal formed, or the introductory statement, “carpometacarpus developed basically”
does not diagnose and specific morphology (Li et al., 2007). The carpometacarpus is at
least partially fused proximally, but the exact degree is unclear due to preservation. The
95 
presence of two small claws on the carpometacarpus is also typical of enantiornithines
(Dapingfangornis, Eocathayornis, Eoenantiornis).
On the distal tarsometatarsus, the trochlea are described as ending distally at the
same level; in LPM-B00017, metatarsal III is longer than metatarsals II and IV, which are
subequal in length. In the introduction the pedal digits are described as equal in length (Li
et al., 2007). However, in LPM-B00017 the third digit is clearly the longest, followed by
IV then II. The final diagnostic character provided, pedal claws very long (and described
as uncurved in the introduction), is also unsubstantiated. The claws in LPM-B00017 are
all longer than any pedal phalanx, but this is another feature typical of Early Cretaceous
enantiornithines. The claws display curvature typical of sympatric enantiornithines (less
recurved in Dapingfangornis). The claw of digit III, however, appears less recurved than
the remaining unguals.
A long pygostyle cannot be confirmed in LPM-B00017 (pygostyle incomplete);
what appears to be a complete pygostyle is preserved in LPM00053 (incomplete in LPM-
00032) and measurements were taken from the published photo (pygostyle approximately
12 mm). Whether this specimen is truly the same species as the holotype or LPM-B00017
cannot be determined here; regardless, the relative pygostyle to tibiotarsus length
indicates that proportions (pygostyle/tibiotarsus ≅ 0.47) are comparable to other similar
Jehol birds (approximately 0.52 in Dapingfangornis) and much different than the truly
robust pygostyle present in longipterygids (0.80 in Longipteryx - IVPP V12552).
Based on observations of LPM-B00017, the following is provided as a possible
diagnosis for Alethoalaornis agitornis. Small enantiornithine bird with the unique
96 
combination of the following morphologies: low and delicate spinous crest on dorsal
surface of synsacrum; coracoid with convex lateral margin and sternal margin slightly
ventrally concave; sternolateral corner of coracoid distal to mediosternal corner (sternal
margin angled); sternum with lateral trabeculae projecting distally farther than the
xiphoid process; humerus with pneumotricipital fossa rudimentary and deltopectoral crest
tapering distally; alular digit short, approximately half the length of the major metacarpal;
ungual phalanx of alular digit larger than that of the major digit; tibiotarsus proximal
surface angled so that medial margin is elevated with respect to the lateral margin; pedal
ungual of digit III less recurved than digits II and IV; proximal half of pedal unguals with
laterally projecting ridges.
Given that there have been no direct observations made on the holotype, paratype
and other referred material, this diagnosis is premature. Alethoalaornis agitornis is here
considered valid and distinct, but requires further morphological study (and preparation
of the known material). Since the diagnosis does not match observations in LPM-
B00017, it is possible this specimen is not referable to Alethoalaornis agitornis, or that
the original diagnosis is inaccurate.

Dapingfangornis sentisorhinus (LPM-B00027 – Li et al., 2006). This taxon is based on
a single specimen (LPM00039) from the Jiufotang Formation (Fig. 3.5). The only
description of this taxon mentions an unusual nasal morphology (Li et al., 2006). The
taxon is diagnosed as, “the individual in medium to small size, with a distinct thorn-like
crest on the middle of the nasal, high feathered crown, sharp rostrum, relatively larger
97 

Figure 3.5. The holotype of Dapingfangornis sentisorhinus LPM-B00027 (formerly LPM
00039; Li et al., 2006).
98 
distance between teeth, flat frontals and long dentary, heterocoelous cervical vertebrae, a
well-developed sternum with a long posterolateral process, a short process and a well-
developed keel, well-developed down feathers, and two long tail feathers” (Li et al.,
2006). The overall poor preparation of the specimen makes boundaries between bones
obscure and difficult to determine (the specimen bears a glossy coat of glue that fills up
cracks and makes delicate and subtle details and individual margins between bones
indiscernible). However, the preservation of the specimen overall is excellent in that the
bones still partially retain their original three-dimensional shape.
Since a nasal crest is unknown in any other enantiornithine, the skull was closely
re-examined. The skull of this specimen is very difficult to interpret; cranial bones are
particularly thin and delicate and thus details are completely obscured by the glue. The
region where the supposed nasal crest projects dorsally is particularly difficult to
interpret; there are clearly bones underlying the nasal corpus, possibly the lacrimal, and
no specific identifications can be made. Given the preservation of this region, a nasal
crest cannot be confirmed although at this time, it also cannot be entirely refuted.
However, given the poor preservation of the feature and the absence of such a process in
all other known enantiornithines, this character should be regarded with caution until new
material is available.
The rostrum is described as pointed; the dorsal portion of the premaxilla is poorly
preserved and thus the true morphology is unknown. The presence of a long dentary as a
diagnostic character is confusing. The dentary is approximately 30-50% longer than the
surangular, typical of most enantiornithines with the exception of the longipterygids.
99 
However, the caudal half of the dentary is strongly concave, as in the latter. The spacing
between aveoli appears typical of other enantiornithines. The published number of teeth
is higher than what was observed; it appears four were present in the premaxilla (typical
of toothed birds), at least three in the maxilla (but nowhere close to the six published),
and seven teeth are counted in the dentary. The frontals are poorly preserved and largely
incomplete and thus whether they are truly “flat” cannot be determined.
The cervicals are poorly preserved and it cannot be determined if they were fully
heterocoelic. The sternum possesses two pairs of trabeculae (as in C. yandica, Rapaxavis,
Eocathayornis, Alethoalaornis). The outer trabecula ends approximately at the same level
as the xiphoid process, not surpassing it as in Rapaxavis and C. yandica. The outer
trabecula bears a distal expansion but it cannot be determined if it was a simple fan, as in
C. yandica, or forked, as in Rapaxavis.
The feathers that outline the dorsal margin of the skull do not distinguish
themselves in length or morphology from other body contour feathers. The morphology
of the elongate tail feathers cannot be compared to the only other published specimen to
possess such feathers (Protopteryx) since they are incomplete in the latter.
None of the characters provided by Li et al. (2007) diagnose the specimen and therefore a
new diagnosis is provided. A small enantiornithine bird with the unique combination of
the following characters: caudal half of dentary ventrally concave; omal tips of furcula
dorsally expanded; keel not bifurcated proximally; inner trabecula of sternum well-
developed and strongly curved medially; circular fossa and circular scar for insertion for
m. coracobrachialis cranialis on proximocranial surface of humerus absent; rectangular
100 
deltopectoral crest less than shaft width; intermetacarpal space present (though narrow);
major digit ungual larger than alular digit ungual; astragalus and calcaneum fused to each
other and the tibia with ascending process of astragalus forming a raised surface on the
craniodistal tibiotarsus; flat proximal articular surface of the tibiotarsus; medial surface of
medial condyle of tibiotarsus deeply excavated by a pit-like fossa; medial rim of
metatarsal III trochlea projecting distally further than lateral; hallucal claw larger than
those of digits II and III; digit IV claw smaller than those of I, II and IV; proximal half of
pedal unguals with laterally projecting ridges; and curvature of pedal claws weak. As
mentioned, this specimen would benefit from further preparation. After the glue has been
removed, new details may be discernible and the issue of the nasal crest may be resolved.
Until then, all nasal characters are regarded as missing data.

Paraprotopteryx gracilis (STM-V001 – Zheng et al., 2007). This recently described
taxon drew immediate attention for its preservation of a previously unknown tail
morphology (four display feathers). The species is known from a single specimen (STM-
V001) from the Yixian Formation of Hebei, China. The only publication is short and
poorly illustrated, and thus while contributing to the diversity of known enantiornithine
tail feathers, provides little morphological information (Zheng et al., 2007). The validity
of the species is evaluated based on the publication. The provided diagnosis is as follows:
scapula long; length of coracoid 2.5 times the [sternal] width; interclavicular angle less
than 40˚ and hypocleideum three-fourths the length of the clavicular rami; inner trabecula
of sternum longer and more robust than the outer trabecula; alular digit with largest
101 
manual claw, ending distally level with distal end of major metacarpal; minor metacarpal
thinner than major metacarpal; first phalanx of major digit longer than the second;
carpometacarpus fused proximally, unfused distally; tibiotarsus unfused; pedal claws
strong and curved; pygostyle long bearing four ribbon-like tail feathers with distal
expansions (Zheng et al., 2007). Several of these features are true for all enantiornithines
(minor metacarpal thinner than major metacarpal, first phalanx of major digit longer than
the second). The scapula does not appear long; it is shorter than the humerus and
approximately 150% the length of the coracoid, typical of other enantiornithines. The
furcula is extremely poorly preserved and the interclavicular angle appears slightly wider
than reported (45-50˚); a hypocleideum approximately ¾ the length of the clavicular rami
is typical among enantiornithines (C. yandica, Dapingfangornis, Hebeiornis). What is
interpreted in the publication as the outer trabecula of the sternum appears to be a sternal
rib, and the ‘inner’ trabecula the true outer trabecula of the sternum. However, without
firsthand study of the specimen, this cannot be determined for certain. The size of the
alular digit and claw, also present in Eoenantiornis, may be an informative character in
combination with other morphologies. Most enantiornithines have some degree of fusion
proximally (completely unfused carpal and metacarpal bones are known) and are unfused
distally. The absence of fusion between the tibia and proximal tarsals is also known
among several enantiornithines (Rapaxavis, Protopteryx, DNHM D2950/1). The pedal
claws appear be fairly straight with curved horny sheathes (as in Shanweiniao).
The plumage is the most interesting aspect of this specimen, given that there is no
true morphological data. Unfortunately, there is reason to doubt the observed
102 
morphology, given the history of Chinese fossil forgeries (Chiappe et al., 1999; Zhou et
al., 2002) and the inconsistencies between the inner and outer feathers. Paired tail
feathers are known in several specimens (Protopteryx, DNHM D2844 ½, CAGS-07-CM-
001) and a fan-like tail composed of more than four rectrices has also been described
(Shanweiniao), though at the time, Paraprotopteryx was the first described
enantiornithine with more than two long tail feathers. There are preservational differences
that warrant closer inspection of these tail feathers before they are accepted as a true and
diagnostic morphology. The medial pair of feathers appear similar to those preserved in
CAGS-07-CM-001 and Dapingfangornis; the ribbon-like portion bears a longitudinal
‘stripe’ and the distal end expands and differentiates into barbs. The lateral pair of
feathers, however, do not bear any of the actual darkened carbon trace of the feather.
Their shape is demarcated by a change in color in the matrix. The contour feathers that
surround the body and wing impressions are all represented by a reddish-brown
carbonized remains. The light and dark matrix that distinguishes the lateral pair of
feathers is also found surrounding some of the bones and in varying patches on the slab,
suggesting they are preparational artifacts. The main slab clearly shows four feathers,
while in the counter slab, only the medial pair are clear.
There is evidence from the publication that Paraprotopteryx is a valid taxon; the
holotype has a combination of features unknown in other similar enantiornithines:
humeral deltopectoral crest less than shaft width (equal to shaft width in C. yandica,
Otogornis and Hebeiornis); alular digit ending slightly distal to distal end of major
metacarpal (longer in Protopteryx, shorter in Eocathayornis) and bearing the largest
103 
manual claw (subequal to major digit ungual in Alethoalaornis and Dapingfangornis);
and manus subequal to humerus in length (shorter in Eoenantiornis). However, without
further detailed investigation of this specimen to elucidate in particular the morphology
of the proximal humerus, the furcula and sternum, as well as the rest of the post-crania
and integument, this taxon contributes far more missing information than it does useful
data.

Functional Nomina Dubia
Cathayornis aberransis (IVPP V12353 – Hou et al., 2002). The single specimen (IVPP
V12353) known for this species comes from the Jiufotang Formation of northeastern
China; the specimen was studied from published photos of the slab and counterslab (Hou
et al., 2002; Hou, 2003). Following the English diagnosis provided by Hou in his book,
Fossil Birds From China (2003), this taxon was diagnosed by the presence of a crest
between the two frontals with processes on the frontal sides, many teeth in the maxilla, a
distally developed sternal carina, sternal outer trabecula distally ending proximal to the
distal end of the xiphoid process (“sternum lateral process no longer than posterior
process”), humerus shorter than ulna, and a distally fused pubis.
The diagnosis is obviously weak, with characters such as the humerus shorter than
ulna plesiomorphic to Ornithothoraces. From the photographs alone, most characters
mentioned in the diagnosis can be disregarded. The frontals are unfused, their contact on
the midline here interpreted as the crest mentioned by Hou (2003); the mentioned
processes cannot be identified. The frontals appear comparable to other enantiornithines,
104 
narrow proximally, vaulted and expanded caudally with caudoventrally concave margins.
The maxilla is not readily identifiable from the photographs, though a portion of the
dentary is visible, bearing 3-4 teeth; it cannot be determined if this is what was
interpreted as the maxilla, but regardless, without a specific number or range, this
character is not very diagnostic given that all known Chinese enantiornithines bear teeth.
The morphology of the sternum is also unclear and it cannot be determined if an outer
trabecula as even present, let alone where it ended distally relative to the xiphoid process.
The distal ends of the pubes are clearly non-contacting and thus while likely joined in a
symphysis in life (evident from the expanded distal ends), were not fused.
Further preparation (generate molds and casts) and detailed study are required to
determine if this specimen represents a distinct taxon and thus C. aberransis is here
considered a nomen dubium.

Cathayornis caudatus (IVPP V10917 – Hou, 1997a). This taxon was studied from
published photos of the slab and counterslab (Hou, 1997a; Hou et al., 2002; Hou, 2003).
The only known specimen comes from the Jiufotang Formation, Liaoning, China.
Following the English diagnosis provided by Hou (2003), the taxon was diagnosed as a
small Cathayornis species with a transverse groove between the frontal and parietal,
more than three teeth in the dentary, and a short bony tail lacking a pygostyle. Based on
the relative lengths of the femur and tibiotarsus, IVPP V10917 is only 2-5% smaller than
C. yandica (IVPP V9769), so the new specimen is essentially the same size as other
Cathayornis. The presence of a transverse groove or comparable structure has not been
105 
identified from photographs. Three teeth can be easily seen in the dentary; preservation
and the spacing of the teeth suggest at least five total were present. Dentary teeth are
present in all enantiornithines with the exception of the Late Cretaceous Gobipteryx. It is
unclear from photographs what was interpreted as the unfused caudal vertebrae (Hou,
2003), however a fully fused and typical enantiornithine pygostyle is clearly visible in
one of the slabs (Hou et al., 2002; counterslab in Hou, 2003) overlapping the sternum and
pelvic elements. Further preparation and study of IVPP V10917 will likely also prove C.
caudatus a valid taxon, but based on the available material and the published diagnosis,
this taxon is considered a nomen dubium.

Cuspirostrisornis houi (IVPP V10897 – Hou, 1997a). The species, from the Jiufotang
Formation (Liaoning, China) is known from a single specimen in slab and counterslab
(IVPP V10897; Hou, 1997a). Only the counterslab (impression of the dorsal surface) was
studied firsthand; the specimen is partially disarticulated and preserved as voids, which
retain some bone fragments. The elements of the proximal skeleton largely overlap,
obscuring details of the thoracic girdle and limb. Features that may differentiate the
specimen from other known taxa, such as the presence of an alular process on the alular
metacarpal, are impossible to discern unequivocally. Removal of the remaining bone
fragments and making casts for study would likely elucidate the morphologies of this
specimen. This taxon represents a nomen dubium pending further study and preparation.

106 
Jibeinia luanhera (GH-001 – Hou, 1997a). The only known specimen of this species
was reported lost (Zhang et al., 2004) and since there has been no report that the
specimen has resurfaced, based on this alone, the species is a nomen dubium. GH-001 is
from the Yixian Formation in Hebei Province, China and is reportedly similar to
Hebeiornis from the same region (Xu et al., 1999; Zhang et al., 2004). The specimen was
studied from published photos (Hou, 1997a; Hou et al., 2002) alongside which a short
diagnosis is offered in English. The bird is described as differing from Confuciusornis
(the only other known bird from Hebei at the time) in that it is smaller, possesses sharp
teeth, a well-developed sternum, unfused carpometacarpus (also in Hebeiornis), and three
manual claws (only two appear present). This diagnosis, though differentiating GH-001
from Confuciusornis, does not diagnosis the taxon within enantiornithines, nor does it
distinguish it from other known Hebei enantiornithines (Hebeiornis). From photographs,
a few features may distinguish the specimen from Hebeiornis. For example, the outer
trabecula of the sternum appear to splay laterally, while the inner processes curve towards
midline; in Hebeiornis the lateral sternal margins are more or less parallel to the long axis
of the sternum, and inner trabecula are poorly developed, however this element is poorly
preserved. The proportions of the skeletal elements are comparable between specimens,
and both possess a relatively short pygostyle (approximately 30% the length of the
tibiotarsus). Until GH-001, the only known specimen of Jibeinia, resurfaces, the taxon
should be considered a nomen dubium.

107 
Largirostrornis sexdentornis (IVPP V10531 – Hou, 1997a). The single specimen
known for this genus was studied from photographs of the slab and counterslab (Hou,
1997a); the English diagnosis provided by Hou (2003) separates the specimen based on
the relatively larger size of the skull compared to other birds from the Boluochi locality
(Jiufotang Formation; Liaoning, China). The specimen appears distinct from the
photographs, bearing a unique sternal morphology in which the sternum is narrow with
elongate outer trabeculae with large distal expansions. IVPP 10917 (C. caudatus) also
possesses comparable large expansions; their morphology cannot be compared as the
lateral half is overlapped by other elements in IVPP V10531, however the overall
morphology of the sternum differs between specimens, the former being shorter and
wider (estimated width to length ratio of 0.81 in IVPP 10917 compared to 0.65 in IVPP
V10531). IVPP V10531 is preserved partially in three-dimensions as evidenced by the
deep concavity of the sternum in dorsal view whereas the sternum in IVPP V10917 has
been flattened and thus the relative width of the latter may be preservational. The
morphology of the skull elements and tarsometatarsus appear comparable to C. yandica;
detailed morphological work is required to properly address the validity of this taxon.
Pending new information, this specimen is considered a nomen dubium.

Longchengornis sanyanensis (IVPP V10530 – Hou, 1997a). The only known specimen
of this taxon, IVPP V10530, is an incomplete individual from the Jiufotang Formation,
northeastern China preserved entirely as voids in a single slab (Hou, 1997a). The
specimen is missing the cranium, sternum, and ilia. The pygostyle is very large retaining
108 
discernible morphologies in the proximal elements. A firsthand analysis suggests that,
together with other interesting morphologies such as the width of the sternal margin of
the coracoid, this taxon may be unique. However, given the quality of the specimen,
details are not discernible from the voids and it is impossible to make a concrete
diagnosis. Until the morphology of this specimen is studied in detail, it is here considered
a nomen dubium.

vii. Some Additional Taxonomic Recommendations for Enantiornithes
Boluochia zhengi (IVPP V9770 – Zhou, 1995)
Close morphological inspection of Boluochia zhengi (Zhou, 1995) from the
Jiufotang Formation of Liaoning, China revealed numerous morphological similarities
with the contemporaneous Longipteryx chaoyangensis suggesting a close relationship
between the taxa; unfortunately, Boluochia is very incomplete and poorly preserved so
that there is limited comparable information (Fig. 3.6A). The two taxa cannot be
differentiated except in size, the former being smaller than the known range of the latter,
and slight differences in the morphology of the tarsometatarsus. Several smaller
longipterygids are known and comparisons with these taxa are included. Boluochia is
known from a single slab (IVPP V9770) that only preserves part of the skull and sternum,
the caudal half of the axial skeleton, the pelvic girdle and hindlimbs; the caudal half of
the skeleton is largely overlapping and obscured. Longipteryx is described from two
nearly complete specimens (IVPP V12352 and V12552) and additional material is known
(Zhang et al., 2000; pers. obs.). Boluochia is preserved as voids whereas in all
109 
Longipteryx specimens the bones are preserved. Despite the highly fragmentary and
poorly preserved nature of the Boluochia holotype, it reveals morphologies identical to
those of Longipteryx, while differentiating itself from related taxa, Longirostravis,
Rapaxavis and Shanweiniao.
The premaxilla of Boluochia is missing the caudal ends of the nasal processes but
is otherwise complete (Fig. 3.6B). As in Longipteryx, the dorsal and ventral margins of
the rostral portion are nearly parallel, forming a long imperforate region before diverging
into nasal and maxilla processes. The maxillary process is long and tapers sharply and the
nasal process is a robust bar, both features present in Longipteryx. Recurved teeth are
present in Boluochia but their size and degree of curvature are unclear. These
morphologies are shared by other longipterygids as well (less clear in Shanweiniao and
Longirostravis).
The pygostyle is the only vertebral element clearly preserved in both taxa, and is
shaped typical of other enantiornithines with the proximal dorsal fork, ventrolaterally
projecting lateral processes and a tapered distal end (Chiappe et al., 2002a). What is
distinct about the pygostyle in both taxa is its unusual size and robustness. The pygostyle
is shorter than the tarsometatarsus in Longirostravis, approximately equal to the in length
in Shanweiniao, and 10% longer in Rapaxavis. In Boluochia and Longipteryx, the
pygostyle is 20% longer than the tarsometatarsus and very robust.
Only the distal half of the sternum is preserved in Boluochia; the xiphoid process
and strap-like outer trabecula are consistent with Longipteryx, however the bulb-like
distal expansions of the latter are not preserved. They are also not preserved in the
110 

Figure 3.6. A, holotype of Boluochia zhengi (IVPP V9770); B, camera lucida drawing of
boxed region. Anatomical abbreviations, pmx: premaxilla; np: nasal processes of
premaxilla; tth: teeth; stn?: sternum?.
111 
juvenile Longipteryx (IVPP V12552) and the sternum is extremely poorly preserved in
Boluochia. In Longirostravis the medial margin of the outer trabecula is strongly concave
and the xiphoid process expands slightly and has a flat distal margin.
The pelvic girdle is preserved in near articulation at the level of the acetabulum
in both Boluochia and Longipteryx. Only the postacetabular ilium is clear in either; it is
triangular, tapering distally. The proportions of the ischium and ilium are comparable,
whereas the ischium is proportionately longer in Rapaxavis. In both Boluochia and
Longipteryx, the pubis curves caudodorsally so that the ventral margin is concave; the
distal end bears a boot-like expansion that is long, tapered distally and oriented nearly
perpendicular to the long axis of the pubis.
The morphology of the tarsometatarsus in both taxa is unique from other known
enantiornithines in which the metatarsal III is longest, followed by IV and II. In
Boluochia and Longipteryx, IV slightly exceeds III in length, followed by metatarsal II.
Longirostravis, Rapaxavis and Shanweiniao possess a similar morphology; in these
specimens, metatarsal III is longer than IV, which exceeds II in distal projection.
Boluochia differs from Longipteryx in that the distal end of metatarsal IV is deflected
laterally so that the metatarsals III and IV do not abut for the distal 1/5 of their lengths.
This is not considered a diagenetic artifact based on the similar appearance of both right
and left tarsometatarsi. In Longipteryx, the metatarsals, though unfused, contact for their
entire length, even in the juvenile specimen (IVPP V12252).
Boluochia is indistinguishable from Longipteryx in a number of morphologies
including longipterygid apomorphies such as the elongate imperforate rostral portion of
112 
the premaxilla and the robust pygostyle. The taxon is thus considered a longipterygid (see
Chapter 12 for phylogenetic hypotheses based on cladistic analysis).

Liaoxiornis delicatus (NIGPAS 130723/GMV 2156 – Hou and Chen, 1999)
The holotype specimen, (formerly Lingyuanornis parvus; Ji and Ji, 1999), has
recently been considered a nomen dubium based on its uncertain ontogenetic status and
absence of diagnosable characters (Chiappe et al., 2007). The specimen is poorly
preserved, with the bones preserved as rusty stains. Its small size is the most obvious and
only distinguishing character, however if the specimen is considered a subadult based on
the presence of pits and scars on the bone surface, the absence of compound bones and a
fully fused sternum, the small size of the specimen should also be regarded as
ontogenetic. While the absence of compound bones and a completely ossified sternum
are not good indicators of sub-adulthood within enantiornithines (pers. obs.), the
incomplete ossification of the periosteal surface remains only known within juveniles.
However, a large number of specimens have been collected from northern China, all very
similar to Liaoxiornis, suggesting that this taxon may be valid (Zhou pers. comm.) and
possibly even paedomorphic. Pending publication of new specimens, Liaoxiornis is
considered a nomen dubium following Chiappe et al. (2007). Until it can be determined
through histological analysis that Liaoxiornis is an adult or subadult, the unique features
present in the holotype cannot be separated from those subject to ontogenetic change.

113 
Hebeiornis fengningensis (Xu et al., 1999)
Similar to the case with Liaoxiornis and Lingyuanornis, the specimen commonly
known as Vescornis hebeiensis (Zhang et al., 2004) received a prior publication under the
binomial Hebeiornis fengningensis (Xu et al., 1999). Both taxa are clearly based on the
same specimen (Fig. 2 in Xu et al., 1999; Fig. 2 in Zhang et al., 2004); although the
photograph in the earlier publication is very poor, not allowing for morphological details
to be discerned, it is clearly the same specimen based on the position of the preserved
elements of the bird and the location of cracks in the slab. Xu et al. (1999) provide a brief
description and discussion in Chinese, and erects the name Hebeiornis fengningensis.
The specimen was later redescribed with no mention of the prior publication and the
name Vescornis hebeiensis was erected for the specimen (Zhang et al., 2004). There is
no apparent reason why the first publication was considered invalid, as the specimen is
figured, named and diagnosed. It is true that the diagnosis in the later publication actually
provides means to differentiate the specimen, however this alone is not justification for
considering a taxon a nomen dubium. If such was the case, since a true diagnosis is
provided above for Dapingfangornis, it could also be argued that a new binomial could
be erected, or when C. caudatus and Largirostrornis are restudied, renaming them would
also be valid. Were no further information published on Hebeiornis, indeed the species
would be considered a nomen dubium. However, Zhang et al. (2004) provide clear
justification for the separate taxonomic identity of specimen NIGP-CAS-130722 and
since the specimen had been named prior, Vescornis is invalid and junior synonym to
Hebeiornis. Zhang et al. (2004) suggested that Hebeiornis (Vescornis) may prove to be a
114 
junior synonym of Jibeinia luanhera (Hou, 1997a) but that the only known specimen of
the latter had been lost and was therefore unavailable for detailed comparison. Based on
what can be discerned from the photographs of the slab and counterslab of GH-001
(holotype of Jibeinia luanhera), there is no strong evidence to refute this suggestion.
However, given that the holotype of Jibeinia luanhera has still not resurfaced, this taxon
is considered a nomen dubium (see above). Should the specimen resurface, the name may
take priority over Hebeiornis fengningensis.

Aberratiodontus wui (LHV-001 – Gong et al., 2004)
A poorly preserved specimen (LHV001a/b) was described as a diapsid
enantiornithine and given the name Aberratiodontus wui (Gong et al., 2004). Though not
accessed first hand, based on the information discernible from the publication, this
species is invalid. From the photographs (Gong et al., 2004, figure 1), the furcula of
Aberratiodontus is U-shaped and broad, appearing to lack a hypocleidium; the scapula is
curved distally; and the proximal humeral head is convex. Zhou et al. (2008) further note
the presence of a large cranial cnemial crest. These morphologies are more consistent
with an ornithuromorph bird, a conclusion also reached through recent cladistic analysis
(Cau and Arduini, 2008), and Aberratiodontus is here considered a junior synonym of
Yanornis in concurrence with previous work (Cau and Arduini, 2008; Zhou et al., 2008a).

115 
Liaoningornis longidigitrus (IVPP V11303 – Hou, 1997b)
This taxon widely is considered to be a member of the clade Ornithuromorpha
(Clarke et al., 2006; Zhou and Zhang, 2006). The holotype and only known specimen is
largely incomplete, the most characteristic morphology being the strange sternum. The
bone is shaped like a spade – trabeculae are absent and the caudal margin expands to
form a slightly caudally concave margin perpendicular to the longitudinal axis of the
sternum. The ventral surface bears a low keel that diverges distally forming a distinct
ventrally projecting labum on the caudal margin.
At the time this incomplete specimen was described, only a few ornithuromorph
specimens were known (a foot from Gansus, and the incomplete and poorly preserved
Chaoyangia; Hou and Liu, 1984; Hou and Zhang, 1993) none of which preserved sternal
material and thus morphological comparisons could not be made on which to base the
systematic position of the specimen. Liaoningornis was assigned to Ornithurae, although
this taxonomic assignment was never rigorously supported by morphological characters
(the only possible character presented by Hou, 1997b which might support this
identification is the presence of a broad sternal margin of the coracoid however this is not
clearly preserved in the specimen). Since the taxon was described, it has not been
extensively restudied. The recent explosion of diversity has resulted in a fairly complete
understanding of early ornithuromorph sterna, as most recent discoveries preserve this
element (the holotypes of Yixianornis, Yanornis, Hongshanornis, Longicrusavis and
Archaeorhynchus, and new specimens of Gansus). The morphology of Early Cretaceous
ornithuromorph sterna is fairly conservative with all specimens possessing a
116 
craniocaudally elongate rectangular, largely imperforate sternum with a pronounced
ventrally projecting carina. The morphology of Liaoningornis would represent a
significant departure from other taxa. Instead it bears a strong resemblance to the bizarre
sternum of the Spanish Early Cretaceous enantiornithine Eoalulavis hoyasi (Sanz et al.,
1996), and lacks clear ornithuromorph morphologies such as the presence of two cnemial
crests or a well-developed intercotylar eminence on the proximal tarsometatarsus. Recent
cladistic analyses have all differed in the placement of this taxon (You et al., 2006; Zhou
and Zhang, 2006), however morphological comparison most strongly aligns this
specimen with enantiornithines; further investigation and additional material may place
this taxon within the clade.

viii. Terminology
Enantiornithine vs. Enantiornithian (-ean)
Recent publications have substituted the term “enantiornithean” in lieu of
enantiornithine (Harris et al., 2006; Morschhauser et al., 2009); the clade name,
Enantiornithes, is unaffected. However, enantiornithine is maintained throughout this
document and avian paleontologists are encouraged to do the same. The logic for the
proposed change in nomenclature is based the correct Latin ending of the typified name
for a clade ending in ‘-es’ such as Enantiornithes; as in Aves, the correct ending is –ian,
as in avian (note the correct ending is not –ean, contra Harris et al., 2006), but members
of Enantiornithes are called enantiornithines (-ine). The ending of a particular clade does
not affect its scientific status, and thus this minor inaccuracy (and several others, such as
117 
ornithurine and neornithine) persisted for twenty-five years before being addressed. One
proposed benefit for this change, the ending –ine is typically used for subfamilies ending
in –inae, and thus if a subfamily named ‘Enantiornithinae’ was erected, than the typified
name would be enantiornithine and mass confusion may ensue. However, for over two
decades within the scientific community enantiornithine has been used with high
consistency between researchers and has become colloquial. Given this stability,
changing the ending of the typified name simply because of a minor technical inaccuracy
seems counter productive to the goal of overall consistency and congruency between
taxonomists and systematists. Stability and common understanding are of greater
scientific importance than correct Latin, especially in light of the large number of taxa
whose names no longer rely entirely upon this ancient language. As science becomes
truly an international community, language differences between researchers are likely to
result in strange taxonomic names; as long as there is stability between these terms,
however, this should not affect the science. Changing enantiornithine to ‘enantiornithian’
does nothing to increase the current taxonomic stability of the clade; rather, one would
expect the change in terminology to result in confusion and inconsistency as researchers
differentially choose to follow different terminologies. Despite seeking to ‘correct’ the
literature, the revision published by Harris et al. (2006) is also incorrect (enantiornithean
rather than –ian), a mistake that is later rectified by the authors (J. Harris pers. comm.).
The original goal may have been to rectify the current taxonomy, but the unfortunate
result is confusion where there previously was none; for example, those who did switch
to enantiornithean (Morschhauser et al., 2009), will now be given the choice to change
118 
again to enantiornithian, while enantiornithine is maintained all the while by others (Zhou
et al., 2008a; O’Connor et al., 2009). There are now three terms permanently in the
literature where there previously was one common term; there are no benefits associated
with changing the nomenclature that can be discerned.
While in the future, it is always recommended that publications, when using
Latin, should do so correctly, there are far more important aspects of publications that
should be regulated (quality of diagnosis, description, verifiability of morphologies
through photographs or illustrations, etc.), which actually create large taxonomic
problems when unaddressed (as discussed above). Trivial inconsistencies, such as this
one, that if corrected do not contribute any positive effect to the science of the clade, but
rather are detrimental to studies (by creating unnecessary confusion and inconsistency
between researchers), are best left alone. The term enantiornithine is perpetuated here in
the largest study ever conducted on the clade in order to maintain taxonomic stability. To
mention the most obvious example of the accepted use of a typified name despite its non-
compliance with the rules of Latin, members of the order Primates are referred to as
primate, not primatian.

Aves vs. Avialae
One example of how changing terminology can result in systematic confusion is
the erection of the term Avialae by Gauthier (1986) for the clade that includes
Archaeopteryx and modern birds, here referred to as Aves. In this application of Avialae,
Aves is used for the crown-group of birds, here named Neornithes. The reasoning behind
119 
this change in nomenclature is to maximize the amount of information available for Aves
(in terms of soft tissue and other lines of information rarely or poorly preserved in fossil
taxa) in phylogenetic systems (Padian and Chiappe, 1998; Padian et al., 1999). The
colloquial term ‘birds,’ however, still refers to the same group of taxa as before, which
are now avialans. This shift in nomenclature was picked up by several research groups
and is currently widespread throughout the literature (Huang et al., 2002; Xu et al., 2002;
Clarke, 2004; Turner et al., 2007a).
There are several problems associated with changing the nomenclature of a major
group, such as Aves. The new usage of Aves is confusing for the simple reason that Aves
translates to ‘birds’ in Spanish and Portuguese, and thus in countries where these
languages are used, all avialans are called ‘birds’ colloquially (‘aves’), and thus some
‘birds (‘aves’) are excluded from the clade Aves. Furthermore, this shift in definition
excludes many taxa that have traditionally been considered part of Aves (Archaeopteryx,
Ichthyornis, Hesperornis); changing the name of this clade affects over one hundred
years of taxonomic stability in the literature (Padian and Chiappe, 1998). Regardless of
the usefulness of this change for phylogenetic systems, the current confusion more than
twenty years after the change was proposed is argument enough that changing stable
taxonomic nomenclature is irresponsible within taxonomy and systematics (and thus
enantiornithines is maintained, although this proposed change is of a much lesser scale
than is discussed here).
Padian (1997) created further confusion when he redefined Avialae as the stem
group, including all maniraptorans more closely related to modern birds than
120 
Deinonychus (and thus including taxa such as Anchiornis and Epidexipteryx); in this
usage, basal avialans (those outside the avian node) are not considered ‘birds’ (Padian et
al., 1999). This application of Avialae is also wide spread (Padian, 1997; Senter, 2007;
Xu et al., 2009b). Currently, throughout the literature depending on which nomenclature
is preferred, Avialae and Aves have two very different definitions which results in
confusion between publications and when discussing phylogenetic results (see Chapter
2). Congruency is of upmost importance in discussion to promote common understanding
and facilitate collaborative research; the proposed changes to ‘Aves’ have in no way
facilitated this and thus the new terminology is not adopted here, nor is it recommended
that it continue to be used, or changes of this nature again be proposed without a very
careful assessment of its contribution to scientific understanding.

ix. Conclusions
It was common methodology for early fossil systematists to erect new taxa on the
basis of very fragmentary holotypic material. Combined with a rapid rate of discovery in
recent years, enantiornithine taxonomy has many problems. Following a review of
enantiornithine material, 23 species are considered nomina dubia (two to ten taxa
variably considered invalid prior to this study) based on the inability of a specimen to
differentiate itself from other known species based on available information. Eleven of
these species are known only from highly fragmentary specimens and five cannot be
diagnosed from the paucity of available information. For future taxonomic clarity,
researchers are urged to only erect new taxa on the basis of accessible, diagnosable and
121 
comparable material. Recent publications are showing a trend towards more responsible
taxonomy, supporting many of the suggestions provided here for the erection of new
taxa, which suggests that this form of taxonomic review may not again be necessary for
this clade.

122 
CHAPTER 4: SKULL MORPHOLOGY

CHAPTER 4 ABSTRACT – Enantiornithines are the most specieous avian clade in the
Mesozoic, with a fossil record that spans throughout the Cretaceous, however with less
than half of known taxa preserving skull material, our understanding of their cranial
morphology remains incomplete. The current knowledge of enantiornithine skull
anatomy is reviewed and the range of morphologies known for each of the main cranial
elements is discussed. The typical enantiornithine skull retains numerous ancestral
features such as the lack of fusion among bones, the presence of a postorbital, a primitive
quadrate with a single headed otic process, an unforked dentary, and teeth. The
postorbital in at least one taxon is unreduced suggesting the existence of a complete
infratemporal fenestra and thus a diapsid skull as in confuciusornithids. The rostrum is
well known and shows considerable variation, typical of theropods, however in terms of
rostral proportions, enantiornithines are extremely limited within the modern bird
spectrum. Although Late Cretaceous skull material is extremely fragmentary, when
compared to Early Cretaceous material it reveals a trend towards more derived
morphologies in younger taxa. The foramen magnum in all taxa points caudally
indicating the ‘flexed’ type skull morphology may not have evolved in this group.
Enantiornithine teeth show considerable diversity in numbers, size, morphology and
placement ranging from taxa with large teeth found throughout the jaws to taxa with
small, rostrally restricted teeth to the fully edentulous. Despite limited preservation of
skull material, a number of trophic specializations can be deduced from the range of
123 
preserved morphologies further hinting at the morphological and ecological diversity of
the Cretaceous Enantiornithes.

i. Introduction
Until the recently, little has been understood about the enantiornithine skull. The
discovery of dozens of nearly complete skeletons from the Early Cretaceous Jehol Group
of northern China has helped to elucidate the postcranial anatomy of Enantiornithes while
their cranial anatomy has remained poorly known. Taphonomically, the skull is the first
part of the avian skeleton to detach from the body (Davis and Briggs 1998) and thus
headless specimens are common (Sanz et al., 2002). The largely complete specimens
from the Jehol Group almost all preserve skull material. However, despite the presence of
preserved skull material, most of the early specimens collected reveal little information;
preservation is primarily in 2-D and the bones are often torn between two slabs, crushed
and/or disarticulated.
Reconstructions of the enantiornithine skull are few, which can be attributed to
early preservational limitations. The only major attempts to construct the enantiornithine
skull are that of Martin and Zhou (1997) and Sanz et al. (1996). The reconstruction of
Martin and Zhou (1997) based on Cathayornis yandica (IVPP V9769, IVPP V10896, and
IVPP V10916 – the latter now the holotype of Eocathayornis walkeri, Zhou and Zhang,
2002) lacks a postorbital and possesses unsubstantiated lacrimal and premaxilla
morphology. The second reconstruction, that of the Montsec hatchling (LP 4450) is more
accurate. However, both these reconstructions are based on single taxa, and little has been
124 
done to find common morphological ground between all enantiornithines. The discovery
of exceptionally preserved specimens such as Eoenantiornis buhleri, Longipteryx
chaoyangensis, Pengornis houi and new specimens of Gobipteryx minuta provide new
insight on how the enantiornithine skull was constructed and how it varied among taxa
(Hou et al., 1999; Zhang et al., 2000; Zhou et al., 2008a; Chiappe et al., 2001). Data
extracted from nearly thirty specimens with skull material allows for a partial
reconstruction of the basic enantiornithine skull and common morphologies begin to
emerge.
The phylogenetic placement of Enantiornithes in the avian tree, though well
established, it is based primarily on postcranial synapomorphies rather than features of
the skull. From the morphology of basal bird crania, it can be inferred that the most
recent ornithoracine common ancestor retained a primitive toothed skull with an overall
lack of bone fusion, a postorbital bone and a squamosal unincorporated into the
braincase, and that the development of a toothless beak and an enlarged premaxilla in
several avian lineages including Enantiornithes is the result of convergent evolution
(Chiappe et al., 1999; Zhou and Zhang, 2006b). Therefore, studies of enantiornithine
skull morphology also have the ability to reveal significant information about the timing
and sequence of the evolution of morphologically modern ecological specializations in a
lineage parallel to that of modern birds.

125 
ii. Material
Approximately 60 species of enantiornithines have been named (including several
potential synonyms); of these, 24 preserve skull material (Table 4.1). An additional four
unnamed juveniles (Sanz et al. 2001; Chiappe et al. 2007) preserve crania and will be
discussed in this review. This study relies almost entirely on Asian material and this
should be recognized as a major bias of any enantiornithine study; more than 90% of the
specimens come from the Jehol Group which records a time interval spanning
approximately 11 Ma (ca. 131-120 Ma) and representing a single geographic area (Yang
et al., 2007; He et al., 2006; Zhou, 2006).
The best skull material belongs to Gobipteryx, specimen IGM-100/1011 from the
Campanian Barun Goyt and Djadokhta Formations (Chiappe et al. 2001). Though only
preserving the rostral half of the skull, IGM-100/1011 boasts three-dimensional
preservation and provides the most reliable information on the enantiornithine palate.
Additional Gobipteryx skulls (ZPAL-MgR-I/12, ZPAL-MgR-I/32, PIN 4492;
Elzanowski, 1976, 1977; Kurochkin, 1996) are known, however the material is
compromised (diagenetically recrystallized) or largely incomplete. The Jehol Group has
produced six specimens with well preserved skulls: IVPP V11537 - the holotype of
Pengornis (Zhou et al. 2008), IVPP V15336 - the holotype of Eoenantiornis (Zhou et al.
2001), DNHM D2522 - the holotype of Rapaxavis pani (Morchhauser et al. 2009),
DNHM D2950/1 - a new taxon, LPM 00039 - the holotype of Dapingfangornis
sentisorhinus (Li et al. 2006 – unfortunately, this specimen is poorly prepared and glue
obscures most features) and two referred specimens of Longipteryx, IVPP V12552
126 
Table 4.1 Current published enantiornithine material separated into Early and Late
Cretaceous collections.
127 
(Chiappe et al., 2007) and DNHM D2889. Other largely complete though poorly
preserved skulls include IVPP V12325 - the holotype of Longipteryx (Zhang et al. 2000),
IVPP V11309 - the holotype of Longirostravis hani (Hou et al. 2004), NIGP-CAS
130722 - the holotype of Hebeiornis fengningensis (Xu et al., 1999; Zhang et al. 2004),
IVPP V11665 - the holotype of Protopteryx fengningensis (Zhang and Zhou, 2000), IVPP
V9769 - the holotype of C. yandica (Zhou et al. 1995) and LPM 00009, LPM 00038 and
LPM B00017 (published as LPM 00040), three specimens of Alethoalaornis agitornis (Li
et al., 2008). This study relies primarily on the morphology from these specimens but
includes details discerned from two-dozen other specimens (Table 4.1), including several
that are undescribed (DNHM D2836, DNHM D2510/1, DNHM D2567/8, DNHM
D2952/3, DNHM D2884 ½ , DNHM D2130, DNHM D2566). The holotype of
Dalingheornis liwei (CNU VB2005001) is in a private collection (Z-H. Zhang pers.
comm.), and the skull of the Paraprotopteryx gracilis holotype (STM V001) does not
belong to the main slab (Zheng et al., 2007), thus these taxa are listed in Table 4.1 as
published with skull material but not included in this morphological review.
Outside Asia, the published record of enantiornithine skull material is limited to a
nearly complete juvenile specimen from the La Pedrera de Rubies Lithographica
Limestones, Lleida, Spain (LP 4450; Sanz et al. 1997), and a partial brain case belonging
to the holotype of Neuquenornis volans from the Rio Colorado Formation of Neuquén,
Argentina (MUCPv-142; Chiappe and Calvo, 1994). A partial mandible from the Lecho
Formation, El Brete, Argentina (PVL 4698) has been suggested to be enantiornithine
based on the absence of any other avian material from the locality (Chiappe and Walker,
128 
2002). Currently there are no synapomorphies that support the placement of this
specimen within the group and thus it will not be included in this review. The Late
Cretaceous record of enantiornithine skull material consists of material known for
Neuquenornis and Gobipteryx.
Despite the serious limitations of the material in terms of temporal and
geographical distribution, even the few known specimens record a large range of
morphologies and specialization, and some major evolutionary patterns can be discerned.

iii. Morphology
Anatomical nomenclature mainly follows Baumel and Witmer (1993) here and
throughout this document; certain structures not cited therein follow Howard (1929).
While the Latin terminology used by Baumel and Witmer (1993) is retained for muscles
and ligaments, osteological structures are described using the English equivalents of the
Latin terms.

Cranium
The rostrum, orbit and braincase in all enantiornithine taxa appear aligned in the
same plane in lateral view (Fig. 4.1). All known foramen magnums are directed caudally
indicating that these birds had ‘extended’ type skull morphology (Marianelli, 1928; Van
der Klaauw, 1948). All well-preserved skulls indicate enantiornithines were typically
mesorostrine (sensu Busbey, 1995) with the rostrum typically contributing to around 50%
of the total skull length. Longipterygid enantiornithines (e.g. Longirostravis, Longipteryx,
129 

Figure 4. 1. Camera lucida drawings of select enantiornithine skulls with cranial elements
color-coded to highlight morphological disparity. A, Pengornis houi IVPP V15336; B,
Cathayornis yandica IVPP V9769; C, Eoenantiornis buhleri IVPP V11537; D,
Rapaxavis pani DNHM D2522; E, DNHM D2950/1; F, Longipteryx chaoyangensis IVPP
V12552; and G, Gobipteryx minuta IGM 100-1011. All scale bars equal one cm.
130 

Figure 4.1, Continued.
131 

and others), though not longirostrine (sensu Busbey, 1995), represent a significant
departure from other enantiornithines, and an excursion into new morphospace, with the
average rostrum being 65% of the skull length.

Premaxilla. This element varies considerably through the clade in degree of fusion,
relative lengths of the nasal and maxillary processes, degree of facial contribution,
morphology of the articulations with the nasal and maxilla, and dentition. The
premaxillae range from being completely unfused to one another (e.g. Pengornis; Fig.
4.1A) to being fused rostrally (nasal processes remain unfused) (e.g. Eoenantiornis,
Longipteryx, Gobipteryx; Fig. 4.1C,F,G), and in some cases (e.g. IVPP V10897 –
formerly the holotype of Cuspirostrisornis, see Chapter 3), these bones appear to be fully
fused.
The prenarial portion of the premaxilla ranges from low with the dorsal and
ventral margins nearly parallel (e.g. Boluochia, Longipteryx), to high with the dorsal
margin strongly angled caudodorsally forming a skull with a more robust rostrum (e.g.
DNHM D2950/1; Fig. 4.1E). The prenarial region is usually short and thus small (e.g.
Longirostravis, Eoenantiornis), but in some taxa it is long (e.g. Longipteryx) and massive
(e.g. Gobipteryx). The premaxilla typically bears four teeth as in most nonavian
theropods and other basal birds (e.g. Archaeopteryx, Sapeornis). Teeth are absent in
Gobipteryx—thus far the only known edentulous enantiornithine. The nasal (frontal)
processes are shorter than those of modern birds, typically extending only to the level of
the caudal margin of the nares (e.g. DNHM D2950/1) and not reaching the frontals.
132 
Although the morphology is not limited to this group (present also in Gobipteryx), the
longipterygids all possess elongate nasal processes that extend nearly to the level of the
caudal margin of the antorbital fenestra (e.g. Rapaxavis, Longirostravis, Shanweiniao).
The articulation of the premaxillae with the nasals is typically wedge-like,
extending for approximately 50% of the length of the nasal (e.g. DNHM D2950/1, C.
yandica, Rapaxavis; Fig. 4.1E,B,D).
The premaxilla is often perforated with small nutrient foramina along the facial
margin (e.g. Longirostravis, Pengornis, Eoenantiornis, Longipteryx). In the presumably
beaked Gobipteryx, the premaxilla bears a pair of dorsal grooves in which the nutrient
foramina are located (Elzanowski, 1977; Chiappe et al., 2001). The maxillary process is
typically short so that the facial contribution of the premaxilla is restricted rostrally in
most taxa (e.g. Pengornis, Eoenantiornis, Gobipteryx). However, the three-dimensionally
preserved skulls of Gobipteryx (Chiappe et al., 2001) show that the maxillary process of
this taxon extends for approximately half the length of the rostrum but a portion of this is
laterally obscured by the overlapping premaxillary process of the maxilla. While the
condition in Gobipteryx suggests that the visible portion of the maxillary process of taxa
preserved in two-dimensions such as Eoenantiornis may extend farther caudally, the
disarticulated premaxilla of IVPP V10897 indicates that in at least some taxa, the
maxillary process of this bone was indeed short. In Longipteryx, a long and tapering
maxillary process that is fully exposed laterally shows that the premaxilla of this taxon
also contributed to nearly half the facial margin (IVPP V12552). Not surprising, the taxa
having a more extensive contribution of the premaxilla to the facial margin (e.g.
133 
Longipteryx and Gobipteryx) also possess a larger prenarial region. Very little is known
about the details of the premaxilla-maxilla contact. In Gobipteryx it is complex; the
maxillary process of the premaxilla tightly fits in a dorsal groove defined by the
premaxillary process of the maxilla (Chiappe et al. 2001).

Nasal. The nasal varies in relative length, width, and morphology of the maxillary
process. The nasals are typically elongate bones that contact each other—however, the
long nasal processes of the premaxilla of Longipteryx may have completely separated
both nasals. The premaxillary (internarial) process of the nasal is sharply tapered. The
maxillary process of the nasal is not present in all taxa. The maxillary process, when
present, is typically short—shorter than the premaxillary process—and also sharply
tapered (e.g. Eoenantiornis, C. yandica). The maxillary process is longer than the
premaxillary process in at least Gobipteryx. In Longipteryx, the maxillary process is
reduced so that it does not extend ventrally beyond the caudodorsal margin of the nares,
while in other taxa (e.g. DNHM D2950/1, Rapaxavis, Shanweiniao), the process is
completely absent (Fig. 4.1D,E).
The mediolateral width of the nasal corpus varies from very narrow (e.g. DNHM
D2950/1, Longipteryx, Rapaxavis) to broad (e.g. Eoenantiornis, C. yandica).
Taphonomic biases not withstanding, estimated nasal width to length ratios vary from
0.04 in taxa such as Rapaxavis, to 0.22 in C. yandica (IVPP V9769). Caudally, the nasal
articulates with the lacrimal and the frontal. In Pengornis and LP 4450, the articulation
with the lacrimal extends over the caudal half of the lateral margin of the nasal. While the
134 
shape of the articulation with the frontal remains unclear, the caudal margin of the nasal
is typically rounded (Longipteryx, C. yandica, DNHM D2950/1).

Maxilla. The maxilla is not as well known as the premaxilla. It varies mainly in dentition,
relative lengths of the premaxillary, jugal, and nasal processes, and fenestration. The
typical maxilla contributes to a majority of the facial margin, has premaxillary and jugal
processes (the jugal process here refers to the ramus of the maxilla that extends from the
rostral margin of the antorbital fossa to the articulation with the jugal) of subequal length,
and bears teeth (e.g. DNHM D2950/1, Gobipteryx, Hebeiornis, Pengornis). Gobipteryx
and the longipterygids represent the only known examples in which the maxilla lacks
teeth. When present, the number of teeth varies from 5-6 to 11. The longipterygid
Rapaxavis further departs from the typical morphology, possessing a premaxillary
process three times longer than the jugal process (Fig. 4.1D). Conversely, in some taxa
(e.g. LP 4450) the premaxillary process is shorter than the jugal process, although there
are no known taxa in which the latter is considerably longer than the former.
The nasal process (ramus) is typically thin and caudally directed, separating the
nares from the antorbital fenestra. The caudal portion of the nasal process of Pengornis
forms a fenestrated recessed bony wall that medially lines the rostral third of the
antorbital fossa. The recessed nasal process and accessory antorbital fenestra, less clearly
preserved in DNHM D2889 and suggested to be present in C. yandica (Martin and Zhou,
1997), may have a broader distribution but preservational biases in two-dimensional
specimens make this difficult to determine (including the presence of this condition in C.
135 
yandica). The nasal process of the maxilla is reduced in Gobipteryx, only contributing to
the caudoventral margin of the nares, and thus lacking the above-mentioned recessed
bony wall. In Pengornis, the caudodorsal end of its well-developed nasal process forms a
fork presumably for the articulation with the lacrimal in which the ventral ramus projects
considerably beyond the dorsal ramus (Fig. 4.1A). Whether the nasal process of the
maxilla articulated with the lacrimal in other taxa is not clear due to the poor preservation
of the latter bone in most specimens, yet the elongate nasal process of some taxa (e.g.
DNHM D2950/1, LP 4450, Longipteryx) suggests that this condition may have had a
wider distribution.

Lacrimal. The morphology of this bone is clear in only two specimens: Pengornis (IVPP
V15336; Fig. 4.1A) and LP 4450. In these specimens, the lacrimal is T-shaped as in most
non-avian maniraptorans. The dorsal rami are tapered and angled so that the rostral ramus
is rostroventrally directed and the caudal ramus is oriented caudodorsally. In the
Pengornis holotype, the dorsal margin is strongly concave between the two rami defining
a small foramen with the lacrimal and the nasal. The dorsal margin of the nasal also
appears slightly concave in LP 4450, however the nasal is broken along the lacrimal
contact making it impossible to determine if a fenestra was present. In LP 4450, the
descending (ventral) ramus of the lacrimal appears to form a mediolaterally broad sheet
descending perpendicularly to the long axis of the skull; the distal end, not preserved in
Pengornis, expands into a broad articulation with the jugal. Eoenantiornis may exhibit a
unique lacrimal morphology, depending on the reinterpretation of the structure identified
136 
as the nasal process of the maxilla by Zhou et al. (2005). In this alternative view, the
caudal half of the skull is interpreted as pushed forward covering most of the left maxilla
so that only the caudal end of this bone is visible in lateral view (Fig. 4.1C). The nasal
process of Zhou et al. (2005) is thus regarded as the lacrimal. If this is the case, the
lacrimal of Eoenantiornis is a thin, rostroventrally angled S-shaped bone with an
expanded ventral ramus and a caudally tapering dorsal ramus, a design significantly
different from the T-shaped bone described above.

Jugal. In most taxa the jugal appears to be a simple rod-like element lacking a postorbital
process (e.g. C. yandica, Pengornis, Rapaxavis). This bone is best preserved in LP 4450.
In this specimen, the rostral end articulates with both the maxilla and lacrimal,
contributing to the caudoventral corner of the antorbital fenestra. The caudal end is
forked, with the dorsal ramus longer and more robust than the ventral ramus, a condition
similar to that in Archaeopteryx. This morphology also appears to be present in DNHM
D2950/1 (Fig. 4.1A).

Postorbital. This element—absent among modern birds—is retained within
Enantiornithes but is only definitively preserved in three specimens: LP 4450, the
Pengornis holotype, and DNHM D2950/1 (Fig. 4.1A,E). In LP 4450 and DNHM
D2950/1 the postorbital exhibits a typical T-shaped design but in Pengornis the
caudodorsal (squamosal) ramus is either absent or broken. The postorbital of these
specimens shows considerable variation in size and morphology. In DNHM D2950/1 it is
137 
large and broad, with a straight and tapered jugal process that possibly enclosed a
complete infratemporal fenestra. In contrast, in Pengornis and LP 4450 the bone is much
smaller, with a rostrally deflected, splint-like jugal process that fails to reach the jugal. In
LP 4450 and DNHM D2950/1 the dorsal margin of the postorbital is concave, suggesting
it contributed to the margin of a supratemporal fenestra. The rostrodorsal (frontal) ramus
is larger than the caudodorsal ramus in LP 4450; in DNHM D2950/1 the disarticulated
postorbital cannot be oriented unequivocally, however one ramus is much more robust
than the other, and has a more dorsal position.

Squamosal. The only known squamosal is preserved in LP 4450. It is a small triradiate
bone that unlike modern birds, is unincorporated into the braincase. In lateral view it has
a broad descending process and a small caudally directed process. The third process
articulated with the dorsocaudal ramus of the postorbital and contributed to the caudal
margin of the supratemporal fenestra.

Quadrate. The quadrate is preserved in several taxa (Rapaxavis, Pengornis, LP 4450,
DNHM D2950/1, Eocathayornis, Protopteryx, Gobipteryx), but unfortunately few
morphological details are known. The mandibular process appears bicondylar in all
specimens, with the medial condyle larger than the lateral condyle. As in other basal birds
and non-avian theropods, the orbital ramus appears broad (e.g. Gobipteryx), lacking the
tapered morphology of ornithurines. The caudal surface is excavated. Some quadrates are
pierced by a foramen, which may be an indication that the bone was pneumatic; the
138 
location of this pneumatopore is difficult to ascertain but it is located caudally in DNHM
D2950/1 and Pengornis (Fig. 4.1A,E).

Frontal. Completely unfused in most taxa, the frontals are rostrocaudally elongate,
narrow rostrally and largely expanded caudally (e.g. C. yandica, DNHM D2951,
Pengornis, DNHM D2511). They form a majority of the dorsal margin of the orbit; in
Pengornis, this portion of the lateral margin of the frontal forms a slight laterally
projecting surface. Best evidenced in Neuquenornis the frontals contact on the midline
forming a longitudinal suture; the caudal margin of each frontal is rounded forming a
caudally convex suture with the parietals.

Parietal. These bones are unfused to each other and the rest of the braincase (e.g.
Dapingfangornis, Pengornis, Eocathayornis). They are vaulted and oval in shape. The
parietals are smaller and rostrocaudally shorter than the frontals. In Neuquenornis, the
medial portion of both parietals contributes to a dome-like structure located between the
interfrontal suture and the central occiput. The parietals of Neuquenornis also form a
gentle nuchal crest along their margin with the occiput.

Supraoccipital. This bone is completely fused to the exoccipital bones in all known
specimens (Neuquenornis, Hebeiornis and DNHM D2950/1; Fig. 4.2) and thus the
precise lateral margin of this bone is unclear. The midline vaults into a cerebral
eminence, which is most prominent in DNHM D2950/1 (Fig. 4.2A,B). In this taxon the
139 
dorsal margin of the supraoccipital is horizontal, forming right angles with the lateral
margins. The supraoccipital forms the dorsal margin of the foramen magnum. In DNHM
D2950/1 this forms a ventrally obtuse angle that defines the dorsal margin of a
pentagonal foramen magnum.

Exoccipital. The exoccipitals may (Neuquenornis) or not (Hebeiornis, DNHM D2950/1)
be fused to the basioccipital (Fig. 4.2). In DNHM D2950/1 the exoccipitals form the
lateral and complete ventral margin of the foramen magnum; the medial margins slope
medioventrally giving the foramen magnum a pentagonal shape. The exoccipitals bear
mediolaterally long excavations on either side of the foramen that shallow laterally, and
based on location, may possibly be homologous to the external opening of the ophthalmic
canal (ostium canalis ophthalmici externi) of modern birds. In the same location,
Neuquenornis possesses a foramen interpreted as for the external occipital vein (Chiappe
and Calvo, 1994). In DNHM D2950/1 the exoccipitals extend laterally, forming long and
slightly tapering paraoccipital processes.
The dorsal half of the occipital condyle is formed by the exoccipitals in DNHM
D2950/1; they contact on the midline but remain completely unfused, each forming
approximately a quarter of the condyle. In Hebeiornis, the basioccipital accounts for a
majority of the occipital condyle; the exoccipitals each bear a small flange that
contributes to a small portion of the foramen magnum and possibly the occipital condyle
(Fig. 4.2E,F; Zhang et al., 2004).
140 

Figure 4.2. Enantiornithine basicrania, photographs and camera lucida drawings. A,B,
DNHM D2950/1; C,D, Neuquenornis volans MUCPv 142; E,F, Hebeiornis fengningensis
NIGPCAS 130722. Anatomical abbreviations: b, basioccipital; cp, cerebral prominence;
fh, foramen n. hypoglossus; fm, foramen magnum; fo, foramen for the external occipital
vein; oc, occipital condyle.
141 
Ventral and lateral to the occipital condyle in Neuquenornis there is a vertical
depression that contains two foramina, one located above the other (Chiappe and Calvo,
1994). Between the basioccipital and right exoccipital in DNHM D2950/1 lies a bone
fragment with two foramina; this bone is interpreted as a piece of the exoccipital, and
defines a concave margin between the paraoccipital processes and the basioccipital. The
larger of the two foramina is circular; the second much smaller elliptical foramen is
located just medial to the former. The openings in both taxa are interpreted as the canals
for the hypoglossus nerve; their position in the exoccipital is consistent with that of
modern birds (Zusi, 1993). A similar location for the hypoglossus nerve is reported in
Gobipteryx (ZPAL-MgR-I/33; Elzanowski, 1981).

Basioccipital. This bone varies in degree of fusion with other occipital bones, and degree
of contribution to the occipital condyle. The basioccipital is unfused to the exoccipitals in
Hebeiornis and DNHM D2950/1, but fully fused in Neuquenornis. The dorsal most
portion of this bone contributes to the occipital condyle in all known taxa (Hebeiornis,
DNHM D2950/1), as in modern birds. Ventral to the occipital condyle, the basioccipital
expands giving this bone an overall trapezoidal appearance (Hebeiornis, DNHM
D2950/1). The basioccipital forms ventrolaterally projecting basal tubera, which define a
strongly concave ventral margin (DNHM D2950/1).

Foramen magnum and occipital condyle. The foramen magnum is mediolaterally wider
than it is dorsoventrally tall (Hebeiornis, DNHM D2950/1; Fig. 4.2). Its shape ranges
142 
from round (Neuquenornis) to pentagonal (DNHM D2950/1). The foramen magnum is
much larger than the occipital condyle (Neuquenornis, Hebeiornis, DNHM D2950/1) but
the exact proportion varies widely from three (DNHM D2950/1) to eight times the size of
the latter (Neuquenornis).

Palatal bones. The only information available on the enantiornithine palate comes from
Gobipteryx (Elzanowski, 1995; Chiappe et al., 2001) and no new information is presented
here. In the enantiornithine palate, the premaxilla does not contact the rostral end of the
fused vomers, which are instead contacted by the maxilla. This results in a horse-shoe-
shaped rostral opening that connects the palatal vault and oral cavity. Just caudal to this
opening lies the choana, which lies below the caudal margin of the nares, rostral to its
position in modern birds. The fused vomers form a slender rod-like element forming the
palatal midline; rostrally it contacts the maxilla and the palatine, a paddle-shaped bone.
The pterygoids are robust, forked rostrally and did not contact the vomers (Chiappe et al.,
2001). An Archaeopteryx-like ectopterygoid has been suggested for Gobipteryx by
Elzanowski (1995). A possible ectethmoid has also been identified in this taxon (Chiappe
et al., 2001).

Cranial Fenestrae
The external nares are typically elliptical and longer than the antorbital fenestra,
and the orbit is the largest of the cranial openings, as in modern birds. The antorbital
fossa is filled by a large fenestra in most taxa. The external nares and antorbital fenestra
143 
are not separated by a large space, so that the caudal margin of the external nares usually
approaches and sometimes overlaps the rostral margin of the antorbital fenestra.
Maxillary fenestrae homologous to those of non-avian theropods appear to be absent,
although the homology of an accessory fenestra in the maxilla of Pengornis remains
uncertain. An enclosed supratemporal fenestra is known in some taxa. Likewise, a fully
separated infratemporal fenestra may have existed in at least one taxon (DNHM
D2950/1), although this fenestra appears to be partially connected to the orbit in most
(Pengornis, LP 4450). Additional pneumatic foramina are known to occur (Pengornis).

External nares. The nares vary in the bones that form them, position, and shape. The
nares are typically holorhinal, rostrocaudally elongate and elliptical (e.g. Eoenantiornis,
C. yandica). The opening is bounded rostrally, rostrodorsally and typically
rostroventrally by the premaxilla; in some longipterygids it appears that the majority of
the ventral margin of the nares is formed by the maxilla. The nasals form the dorsal
margin of the nares and depending on the development of their maxillary process, they
contribute to the caudodorsal and caudal margins (e.g. Eoenantiornis, Gobipteryx, C.
yandica, DNHM D2889). The maxilla forms the caudoventral margin and contributes to
the caudal and caudodorsal (e.g. DNHM D2950/1, Rapaxavis) margins of the nares in
varying degrees depending on the morphology of the maxilla-nasal contact. In most taxa,
the nares are contained within the rostral third of the skull. An exception is represented
by the longipterygids in which the nares are retracted and appear to be schizorhinal. The
latter condition is also known outside the longipterygids (DNHM D2950/1). The
144 
proportions between length and height also vary among taxa. Most typically, the nares
are elliptical—the length is several times the height—but in the retracted nares of the
Late Cretaceous Gobipteryx these two dimensions are subequal. The shape of the
longipterygid nares is difficult to ascertain but it appears that these openings are very
narrow and slit-like.

Antorbital fossa. In most taxa, the antorbital fossa appears to be entirely excavated by a
large antorbital fenestra (e.g. DNHM D2950/1, LP 4450) however in at least two taxa
(e.g. Pengornis, DNHM D2889) the fossa is rostrally lined by a recessed medial wall of
the maxilla—in Pengornis, the antorbital fenestra is approximately two-thirds the size of
the antorbital fossa. The antorbital fossa and fenestra are typically triangular with
subequal length and height. The relative contribution of the maxilla, nasal, and lacrimal
to the antorbital fossa is unclear for most taxa. In Pengornis and DNHM D2950/1 the
maxilla forms the rostral margin and rostral half of the dorsal margin; the lacrimal forms
the remaining half of the dorsal margin, thus excluding the nasal from participating in the
fossa. However, in Gobipteryx, the maxillary contribution is limited to a small
rostroventral corner of the fossa, while most of the rostral and possibly dorsal margins are
formed by the nasal (the lacrimal contribution remains unknown). The jugal contributes
to the caudoventral corner of the antorbital fossa in LP 4450. In Pengornis, the maxilla is
pierced by a single accessory foramen. The foramen is small and elliptical, located in the
rostrodorsal corner of the fossa; its size and placement suggest it may not be homologous
to either of the accessory fenestrae (maxillary and promaxillary) of Archaeopteryx and
145 
non-avian theropods, which are more ventrally located (Elzanowski, 2002; Norell et al.,
2006).

Temporal fenestrae. The preservation of a T-shaped postorbital indicates the presence of
a fully demarcated supratemporal fenestra formed by the frontal, parietal, postorbital, and
squamosal (Pengornis, DNHM D2950/1, LP 4450). The elongate jugal process of the
postorbital of at least one specimen (DNHM D2950/1) suggests the presence of a
completely enclosed infratemporal fenestra, and thus a fully diapsid skull. However, the
reduced postorbital of other specimens indicates that in most taxa the infratemporal
fenestra converged with the orbit (Pengornis, LP 4450). The elongate postorbital bone in
DNMH D2950/1 is disarticulated making it difficult to ascertain with absolute certainty if
this bone fully separated the infratemporal fenestra from the orbit, especially given the
absence of a postorbital process on the jugal or a preserved quadratojugal. The jugal
process of the postorbital in this specimen is very long (more than three times the length
of the proximal rami), suggesting the postorbital would have almost completely delimited
an infratemporal fenestra. Based on the position of the postorbital in articulated
specimens, if the postorbital were to contact a bone distally in DNHM D2950/1, it likely
be the medial or lateral surface of the jugal, a very different articulation from the long
overlapping contact between the postorbital and postorbital process of the jugal in non-
avian theropods and some other basal birds (Confuciusornis; Chiappe et al., 1999).

146 
Additional fenestrae. In Pengornis the nasal and lacrimal form a small fenestra. This
feature, not preserved in any other enantiornithine, is inferred to be pneumatic based on
the extensive pneumaticity that characterizes the nasolacrimal region of birds and non-
avian theropods (Witmer, 1997). Pengornis also possesses an additional small
rostrocaudally elongate oval foramen that pierces the nasal at the level of the rostral
margin of the antorbital fenestra.

Mandible
There is a general lack of fusion between the dentary and postdentary bones, and
the dentaries are typically not fused into a mandibular symphysis; the only specimen with
fusion between mandibular bones is the Late Cretaceous (Gobipteryx ZPAL-MgR-I/12;
Elzanowski, 1977). The degree of mandibular fenestration is unclear, but all known adult
mandibles are imperforate.

Dentary. The dentary varies in morphology and dentition. This bone is most commonly
unfused, toothed, and straight with an unforked ventrally sloping caudal articulation with
the surangular (e.g. Longipteryx, C. yandica, Alethoalaornis, DNHM D2950/1; Fig. 4.1).
Caudally, the ventral margin of the dentary often expands ventrally at the level of the
lacrimal while the dorsal margin remains straight (e.g. Hebeiornis, DNHM D2950/1,
Eocathayornis). In the longipterygids Longirostravis, Rapaxavis and Longipteryx, the
dentary is overall slightly concave ventrally. Gobipteryx reportedly differs from Early
Cretaceous enantiornithines in that the mandibular bones are nearly completely fused
147 
(dentaries strongly ankylosed in IGM -100/1011; Chiappe et al., 2001) and the caudal
articulation of the dentary is forked, as in more advanced birds (Elzanowski, 1977),
however, these specimens reportedly have undergone some diagenetic recrystallization.
Dentary teeth range from absent (Gobipteryx; Fig. 4.1G) to rostrally restricted
(Longipterygidae) to present throughout (e.g. Pengornis, C. yandica, DNHM D2950/1).
The number of teeth ranges from low in the longipterygids to 6-7 in the typical
enantiornithine (e.g. Hebeiornis, DNHM D2950/1) with an estimated thirteen teeth
marking the known upper limit (Pengornis; Zhou et al., 2008a).

Surangular. Usually unfused to the dentary, this bone is typically much shorter than the
dentary, robust and straight (e.g. Rapaxavis, Hebeiornis, DNHM D2510/1). The
articulation with the dentary is long and slopes rostrodorsal – ventrocaudally so that the
rostral third of the surangular tapers to a blunt tip rostrodorsally (e.g. Dapingfangornis,
Longipteryx, Protopteryx). No coronoid bone is known but Gobipteryx ZPAL-MgR-I/12
and Rapaxavis possess a rounded coronoid process on the dorsal margin of the
surangular.

Angular. Often difficult to differentiate from possible hyoid bones (Rapaxavis,
Longirostravis), the angular appears to be a thin, straight and rod-like element that forms
the ventrolateral margin of the postdentary portion of the mandible (e.g. Shanweiniao,
DNHM D2567/8). The angular is slightly curved so that it is convex ventrally in some
148 
taxa (e.g. Hebeiornis, Longipteryx). The rostral end is wider than the caudal end in lateral
view (e.g. Hebeiornis, Longipteryx, DNHM D2567/8).

Splenial. This bone is usually not preserved in view but in a few specimens it is unfused
and disarticulated so that it is visible (e.g. Hebeiornis, Dapingfangornis). In Hebeiornis,
the bone is more than half the length of the dentary. The ventral margin of this bone is
slightly concave ventrally. The dorsal margin defines the apex of an obtuse triangle; the
rostral ramus is twice the length of the caudal ramus and tapers more sharply. In
Archaeopteryx the rostral and caudal rami are closer to subequal in length, although the
rostral ramus is still longer (Elzanowski, 2002).

Prearticular and articular. Preserved in Hebeiornis, the prearticular is rostrally lancet-
shaped (rostral ramus is tapered sharply) as in Archaeopteryx (Elzanowski, 2002),
differing from the rounded margin in neornithines. The articular is preserved in LP 4450
but no information can be discerned.

Mandibular fenestrae. Completely perforated rostral and caudal mandibular fenestrae
are only known in LP 4450, although since the specimen is a juvenile it is difficult to
ascertain to what degree this is the result of incomplete ossification (Sanz et al., 1997). In
this specimen, the fenestrae are elongate ovals. The rostral fenestra retains the ancestral
condition in which the ventral margin is formed by the angular, as in nonavian dinosaurs
(as opposed to the dentary of modern birds; Sanz et al. 1997). In Gobipteryx (ZPAL-MgR
149 
I/12), a small, depressed area on the rostral-most surangular is reported to correspond to
the rostral mandibular fenestra while the caudal fenestra is reduced to a small foramen
(Elzanowski 1977); however, the extent to which the alleged rostral fenestra perforates
the mandible is unclear. GMV-2158 also possesses a single fully perforate caudal
(surangular) fenestra (Chiappe et al., 2007); the mandibular fenestra of this juvenile is
relatively smaller than that of LP 4450 and round. Thus, the only two specimens with
fully perforate mandibular fenestrae are juveniles (Sanz et al., 1997; Chiappe et al.,
2007); the absence of mandibular fenestrae in specimens of adult enantiornithines could
suggest their presence in these specimens reflects their ontogenetic stage. However,
similar structures are absent in other juvenile specimens GMV-2159 and GMV
2156/NIGP-130723 (Chiappe et al., 2007).

iv. Discussion
Enantiornithines display a unique mosaic of basal and derived characters,
reflecting their phylogenetic position and the scale of their Cretaceous evolutionary
radiation. However, the pattern of character loss or retention in certain areas of the
skeleton is intriguing. Within the skull, most notable is the lack of derived characters
relative to more basal birds such as Archaeopteryx. Instead, in many details the skull
bears strong similarity to this basal taxon; enantiornithines still retain teeth, a postorbital
bone, a quadrate with a single headed otic process and bicondylar mandibular process, a
complete osseous bar separating the orbit and antorbital fenestra, a small premaxilla,
unfused skull bones, and the apparent absence of kinetic features. The absence of teeth
150 
and presence of a caudally forked dentary – features otherwise common to modern birds
and present in Apsaravis (Clarke and Norell, 2002) but also present in the basal
pygostylians Confuciusornis (Chiappe et al., 1999) – are only known in a single Late
Cretaceous taxon (Gobipteryx), suggesting an overall trend towards more advanced
morphologies in at least one lineage. The absence of anatomically modern features in
Early Cretaceous enantiornithines is not unique to this one avian lineage, but rather
plesiomorphic of basal birds. Sapeornithids and confuciusornithids, basal pygostylians
also from the Jehol Biota, share the presence of a postorbital, a squamosal unincorporated
into the braincase, absence of fusion, and an unforked dentary (forked in Confuciusornis);
both these groups have either reduced (Sapeornis) or lost their dentition
(confuciusornithids). Even the skulls of some sympatric Jehol ornithuromorphs are also
highly unfused, have small premaxillae, teeth, and unforked dentaries (Yanornis,
Hongshanornis), though no ornithuromorph is known to retain a postorbital bone and the
skulls of more advanced taxa are considerably less massive than those of basal species
(Jeholornis, Sapeornis, Confuciusornis). The absence of derived features in the skulls of
early birds with advanced flight features, such as an alula, strut-like coracoid, and
reduced manual digits, emphasizes that the refinement of powered flight dominated early
avian evolution. Despite the conservative nature of the enantiornithines skull morphology
relative to more basal taxa and the absence of detailed morphologies preserved among a
large number of specimens, variation within the group can be discussed at the level of
skull shape and fenestration. Enantiornithine dentition and trophic specialization are also
diverse relative to other sympatric avian clades and are also discussed below.
151 
Fenestration
The main cranial fenestrae in enantiornithines are very similar to those of
Archaeopteryx, with large external nares and orbits as in modern birds, as opposed to the
small external nares (relative to the antorbital fenestra) of dromaeosaurs and
confuciusornithids (Chiappe et al., 1999; Norell et al., 2006). At least one enantiornithine
is known to possess an additional foramen in the antorbital fossa (Pengornis IVPP
V15336). Its rostrodorsal position, however suggests it may not be homologous to the
accessory maxillary fenestrae located in the antorbital fossa of Archaeopteryx,
Dalianornis cuhe (Gao and Liu, 2005) and non-avian theropods. Basal pygostylians
Sapeornis and Confuciusornis also possessed an accessory maxillary foramen, though
this feature is unknown in birds more advanced than enantiornithines. In Confuciusornis,
the round shape of the foramen and its position suggest it may be the maxillary fenestra
of non-avian theropods though the homology is uncertain (Witmer, 1997; Chiappe et al.,
1999). In Sapeornis the preservation is unclear and it cannot be determined if there is one
or two accessory foramen present, or their possible homology. This ‘accessory foramen’
and others are known within at least one taxon indicating that, like other closely related
taxa, enantiornithines had evolved pneumatic features.
Modern birds, having lost their postorbital bone, no longer possess fully isolated
supra- and infratemporal fenestrae. Basal birds like Confuciusornis that possess a diapsid
skull are considered to have secondarily derived the primitive condition (Chiappe et al.,
1999), an inference supported by the presence of a reduced postorbital in Archaeopteryx
(Elzanowski, 2002). While the postorbital is a bone rarely preserved, in enantiornithines
152 
it also appears to be typically reduced (Pengornis, LP 4450). The postorbital in DNHM
D2950/1, however, suggests that this bone may have rostrally enclosed an infratemporal
fenestra in at least one enantiornithine taxon. The jugal morphology in this specimen
suggests the postorbital would have contacted the medial or lateral surface of the jugal
bar, a different configuration from the long articulation of the postorbital and postorbital
process of the jugal in non-avian theropods and confuciusornithids. This does support the
hypothesis that the condition in DNHM D2950/1 is also secondarily derived. However,
the presence of a large postorbital in Sapeornithidae, Confuciusornithidae and some
enantiornithines (e.g. DNHM D2950/1), as well as in non-avian theropods (Ostrom,
1969; Clark et al., 2002; Xu et al., 2002), suggests that a large postorbital is the
plesiomorphic avian condition and the postorbital in archaeopterygids may have been
reduced during the evolution of the clade.

Skull Morphology
Modern birds have two general skull types: extended and flexed (Marianelli,
1928; Van der Klaauw, 1948). While the skull type is associated with the position of the
brain, rotated in flexed type skulls with a ventrally directed foramen magnum, it can be
determined osteologically from the position of the foramen magnum. In extended type
skulls the skull units are aligned in lateral view and the foramen magnum is directed
caudally. In the flexed type skull, the skull units are decoupled, not limited to the same
plane in lateral view, and the foramen magnum is ventrally located (Marugán and
Buscalioni, 2006). The avian skull is incredibly diverse in terms of form and proportion,
153 

Figure 4.3. Ternary diagram depicting the range of skull proportions within Archosauria.
The most reliable enantiornithine measurements have been added to the dataset (yellow)
for comparison. Enantiornithines cluster approximately within the center of neornithine
morphospace. B, braincase; O, orbit; R, rostrum (modified from Marugan-Lobon and
Buscalioni, 2003).
154 
however, a number of morphologies are limited to the flexed type of skull leading to the
hypotheses that the flexed morphology is derived within Aves and that the evolutionary
decoupling of the skull units within the group facilitated the evolution of a wider
range/spectrum of morphologies. The rotation of the brain most likely occurred after the
ornithoracine split, within the lineage towards modern birds. Currently there is no
evidence that enantiornithines or any other basal bird developed a flexed type skull; all
three preserved enantiornithine basicrania – belonging to taxa of substantially different
size, morphology and geologic age – possess caudally directed foramen magna
(Hebeiornis, Neuquenornis, DNHM D2950/1). Taxa in which the skull is well-preserved
in lateral view all show the skull units aligned in a single plane. This suggests that during
the evolution of Enantiornithes the brain remained un-rotated. This conclusion is
equivocal, based on the limited available information, but even without the rotation of the
brain, the range of morphological variation observed in modern birds was not necessarily
impossible for enantiornithines to achieve. However, if enantiornithines did not develop
flexed type skulls, the development of morphologies comparable to those of modern
flexed type skulls would likely have involved developmental pathways different from
those in modern birds.
Several enantiornithines were measured and added to the archosaur skull
geometry morphoset by Marugán-Lobon and Buscalioni (2003) in order to determine
how the clade compares to neornithines and other archosaurs (Fig. 4.3). The range of
enantiornithine craniomorphospace is based on a sample size of only five taxa (several of
which are longipterygids, thus the sample size is biased towards longer rostra); obviously
155 
more cranial material is known, however only five specimens could be measured. Given
the preservation of fossil specimens (disarticulated, compressed, damaged, and or
incomplete), it is impossible to measure as accurately as with modern specimens. The
measurements presented are considered best estimates, even in the best preserved
specimen (Pengornis); thus, it is premature to make detailed inferences about variation
and proportions and these results will have to be explored further when more well-
preserved specimens are available. Currently, all five enantiornithines fall approximately
within the known range of avian mesorostrine archosaur morphospace – the only slight
outlier is the poorly preserved Protopteryx IVPP V11665. Archaeopteryx and
Confuciusornis were plotted in order to determine if basal bird skull geometry is
conservative; the two taxa plot distinct from each other and enantiornithines.
Archaeopteryx and Confuciusornis differ in that the latter has a smaller orbit relative to
the latter. They also fall within the range of extant mesorostrine birds. Enantiornithines
form a cluster in the center of the archosaur spectrum, and vary in proportions of all skull
units, not just the rostrum. The braincase and orbit show the most variation however these
measurements are much more difficult to take than the rostrum length and this is
considered an artifact of preservation.
The rostrum is the most variable skull unit within Theropoda, and the same holds
true for avian as well as non-avian taxa (Marugán-Lobon and Buscalioni, 2003). There
are obvious functional constraints on the orbit and the postorbit (to house and protect the
eye and brain), while the rostrum is relatively free to respond to selective pressures and
evolve a wide range of morphologies associated with specialized trophic function.
156 
Following the terminology for rostral proportions set forth by Busbey (1995) and
maintained by Marugán-Lobon and Buscalioni (2003), the archosaur skull is broken into
three categories according to rostral proportions: brevirostrine (30-50%), mesorostrine
(50-70%), and longirostrine (70-90%).
Archaeopteryx, Confuciusornis and the enantiornithines fall in the mesorostrine
range (Fig. 4.3), suggesting that the mesorostrine condition is basal within Aves, as it is
for all Archosauria (Marugán-Lobon and Buscalioni, 2003). Though few skulls are
preserved well enough to measure accurately, observations and measurements indicate
that taxa typically possess skulls that are approximately 50% rostrum. The longipterygid
clade represents an enantiornithine incursion into new morphospace, with rostral
proportions approaching and exceeding 60% skull length. Currently, there are no
enantiornithine or other Mesozoic avians unequivocally known to have possessed a
brevirostrine or true longirostrine skull, suggesting that brevirostrality is a derived
condition within Aves.

Dental Variation
A majority of enantiornithine taxa, for which cranial material is known, possess
teeth, with the exception being the Late Cretaceous Gobipteryx minuta (Elzanowski,
1974). Taxa vary considerably in the morphology of the teeth, their number, and where
they are located. With the exception of LP 4450 (Sanz et al., 1997) and PVL 4698
(Chiappe and Walker, 2002), all specimens are from the Early Cretaceous Jehol Group.
Even within this single geologic unit, a diversity of dental morphologies can be
157 
recognized; teeth vary in terms of number, morphology, and relative size (Fig. 4.4). Teeth
are typically similar to that of Archaeopteryx (Elzanowski, 2002): simple, conical,
slightly constricted at the base, recurved, and without serrations (Hebeiornis, C. yandica,
Eocathayornis, LP 4450). The degree of caudal curvature is typically relatively low, with
the occlusal tip of the tooth located just caudal to the midpoint of the alveolus (C.
yandica, Pengornis, GMV 2158, DNHM D2950/1). In taxa in which teeth are more
strongly recurved the occlusal tip reaches the caudal margin of the tooth socket
(Eoenantiornis), and in extreme taxa, projects beyond it (Longipteryx).
Teeth range in size from very small, reduced peg-like teeth (Longirostravis) to the
large, robust teeth of DNHM D2950/1. Tooth size relative to body size varies
considerably as well; the teeth of Longirostravis are the same size as those of Pengornis,
despite the fact the latter specimen is several times the size of the former. The teeth of
DNHM D2950/1 are proportionately the largest and most robust known within
enantiornithines; the teeth are fat with circular cross sections. They taper rapidly into a
slightly caudally deflected tip. This taxon represents one extreme in hypsodonty within
the clade. The other extreme is exemplified by the low crowned teeth of Pengornis. It is
suggested that the teeth of this specimen bear wear facets and evidence for primitive-style
tooth replacement, with teeth replaced throughout the organism’s life span (Zhou et al.,
2008a). This detail is difficult to verify and could equally likely represent heterodonty or
differential preservation. Currently there are no known enantiornithines who clearly
preserve a resorption pit or newly erupting replacement teeth, and therefore evidence for
dental replacement – although likely – remains elusive.
158 
Trophic Specialization
The diversity of recognized dental patterns, such as the longipterygids, which
possess rostrally-restricted dentition, suggests a great deal of trophic specialization.
Stomach contents are known from two specimens, the holotypes of Eoalualvis and
Enantiophoenix (Sanz et al., 1996; Dalla Vecchia and Chiappe, 2002). Eoalualvis
preserves the remains of arthropods associated with the visceral region while
Enantiophoenix is associated with bits of amber scattered among the skeletal elements,
and is interpreted as a sap-eater (Dalla Vecchia and Chiappe, 2002). Neither preserves
any skull material, and thus morphologies of the rostrum and teeth associated with such
diets cannot be determined. No enantiornithine is known to preserve gastroliths, which
are wide-spread among sympatric ornithuromorphs (Zhou and Zhang, 2005; You et al.,
2006; Zhou et al., 2004).
Without stomach contents, dietary inferences for fossil taxa are weak, however
the following interpretations are based on tooth morphology and observations of related
taxa. The teeth of Archaeopteryx are interpreted as too weak for crushing hard foods and
the taxon is interpreted as a general insectivore, limited to small arthropods with softer
cuticles (Elzanowski, 2002). The tooth morphology in a number of enantiornithines is
largely consistent with Archaeopteryx, however a number of taxa depart from this
morphology thus indicating specialization for a unique niche. Longipteryx, Pengornis,
and DNHM D2950/1 represent the most extreme deviations from the typical tooth
morphology, within the clade. The teeth of DNHM D2950/1 are the relative largest and
most robust known for enantiornithines; this taxon is interpreted as having a
159 

Figure 4.4. Size and morphological variation within enantiornithine dentition.
160 
duraphageous diet, utilizing food items unavailable to other birds of a similar size.
Longipterygids all possess rostrally restricted dentition, and most taxa bear very small,
reduced teeth; Longirostravis has been suggested to be mud-prober, using its delicate
rostrum to retrieve worms and other soft-bodied organisms from the littoral substrate
(Hou et al., 2004). The teeth of Longipteryx are large, recurved, and slightly laterally
compressed, features associated with increased predatory capability. The rostral
restriction of the teeth together with their morphology indicates Longipteryx may have
been piscivorous. The numerous small teeth of Pengornis are blunt, brachydont, and may
bear wear facets (Zhou et al., 2008a); low-crowned teeth, however, are not consistent
with a diet of abrasive food items. The morphology of the teeth of Pengornis are more
consistent with a diet consisting of soft-shelled arthropods from the Jehol lake system.

Cranial Kinesis
The absence of a complete jugal-postorbital bar in some enantiornithine taxa
indicates that cranial kinesis was at least possible. Without jugal and postorbital contact,
the jugal is free to rotate forward and thus elevate the skull as in modern birds.
Osteologically, kinesis can be determined by identifying thinned regions of bone,
representing bending zones, or true mobile hinges such as a frontal-nasal hinge, where
the movement occurs. All modern birds possess some form of cranial kinesis and are able
to move their upper jaw with respect to the lower jaw to some degree (Zusi, 1984).
Among modern taxa there are many forms of kinesis (amphikinesis, prokinesis, and
rhynchokinesis), which reflect where the bending occurs within the rostrum (Zusi, 1984).
161 
These different types of kinesis are associated with different specialized trophic
functions; for example, rhynchokinesis (rostrally located bending zone) is common
among (although not limited to) the longirostrine shore birds, Scolopacidae, and aids the
removal of food items from the substrate as well as the capture of planktonic prey (Zusi,
1984; Estrella and Masero, 2007).
It has been observed within Neornithes that all schizorhinal skulls are
rhynchokinetic, though not all rhynchokinetic skulls are schizorhinal (Zusi, 1984).
Longirostravis, a purported mud-prober (Hou et al., 2004), has schizorhinal nostrils, as
does the closely related Rapaxavis; together with the absence of a preserved postorbital in
these specimens, it is possible that the skulls of these taxa may have been capable of
rhynchokinesis. Unfortunately, the incomplete and 2-D preservation of these taxa and
most other enantiornithine specimens makes it impossible to determine if bending zones
were present. No cranial hinges have been reported or observed in any specimen of
enantiornithine. The nature of the postorbital-jugal contact in taxa such as DNHM
D2950/1 is unknown but it can be suggested that some enantiornithines may have been
incapable of cranial kinesis, as in the confuciusornithids (Chiappe et al., 1999).

Evolutionary Trends
The Late Cretaceous record of enantiornithine skull material is extremely limited
compared to that of the Early Cretaceous; as a result, any inferences made regarding
trends in enantiornithine evolution through time are inherently weak. Despite this, the
obvious trends that present themselves should be noted. An increase in the degree of
162 
fusion between skull bones is apparent, evidenced by the highly fused basicranium of
Neuquenornis. The complete loss of teeth within Enantiornithes is only known in a Late
Cretaceous taxon (Gobipteryx), but occurred much earlier in other lineages of Mesozoic
birds (Confuciusornithidae, Ornithuromorpha; Hou et al., 1995; Zhou and Zhang, 2006b).
The increased fusion and loss of teeth can both be considered derived features, consistent
with morphologies present in modern birds, and thus a weak, general trend from more
basal to derived features is observed during enantiornithine evolution. This trend is also
observed in the postcrania, with an increase in size and degree of fusion in compound
bones such as the tarsometatarsus in the Late Cretaceous (Chiappe and Walker, 2002).
The well-sampled Jehol avifauna, however, indicates that by the Early Cretaceous,
enantiornithines were already incredibly diverse in form and function.

v. Conclusions
The skull is one of the most difficult regions of the skeleton to understand for
preservational reasons, however over the past decades the number of specimens with
some skull material have accumulated and several generalizations can be inferred
regarding the enantiornithine skull archetype. Enantiornithines possessed skull
morphology comparable to that of Archaeopteryx; the presence of teeth and a postorbital,
absence of fusion, and unforked caudal articulation of the dentary are all considered fairly
basal features. Within this basic model, enantiornithines show a range of variation
including tooth morphology, rostral length, degree of fenestration, and the morphology of
several elements (i.e. maxilla, nasal). Enantiornithine skull morphology is more diverse
163 
than is known for sympatric ornithuromorphs, which are admittedly poorly known.
Material from the Late Cretaceous is rare and thus any inferred evolutionary trends are
weak; however, the best known Late Cretaceous material suggests the acquisition of
more derived morphologies comparable to more advanced avians (absence of teeth, large
premaxilla, greater fusion). Unfortunately, many areas of the skull, such as the palate, are
very poorly known and in terms of cladistic analysis the skull represents the most
uninformative skeletal region for this clade.
164 
CHAPTER 5: POST-CRANIAL MORPHOLOGY

i. Introduction
Before the discovery of Enantiornithes, there existed a conspicuous gap in the
record of the evolution of the modern avian form between the primitive Archaeopteryx
and advanced ornithurine Ichthyornis. The discovery of the first enantiornithine partial
skeleton (Neuquenornis) provided an intermediate between the morphology of long-tailed
birds and ornithurines, and the subsequent flood of specimens from China have helped to
create a better understanding of avian evolution. As discussed in the previous chapter, the
enantiornithine skull is similar to Archaeopteryx, with extended type morphology
(caudally directed foramen magnum) and mesorostral proportions. The skull elements
typically remain highly unfused, retaining primitive bones, teeth and proportions. A
majority of the more derived characters that place enantiornithines higher in the avian
phylogeny and support their monophyly are found in the postcranial skeleton (Chiappe,
2002). Many of the features that support the placement of Enantiornithes as sister group
to Ornithuromorpha are related to the enhancement of flight, for example, a strut-like
coracoid articulating with the scapula through localized facets (scapulocoracoid present
in Archaeopteryx, Confuciusornis, Changchengornis). Despite the presence of features
associated with advanced flight, many of the osteological modifications, while similar to
structures in modern birds (i.e. strut-like coracoid, sternum with keel), differ considerably
in the details of their morphology. This suggests that while enantiornithines may have
165 
been capable fliers, their flight mechanism was intrinsically different from that of modern
birds.
The number of nearly complete enantiornithines known has nearly doubled since
the last morphological review was conducted on the group (Chiappe and Walker, 2002)
although the new material is primarily limited to the Early Cretaceous. Identifying
synapomorphies that can be determined across the enantiornithine clade is hindered by
preservational differences between the world’s main collections. The three-dimensional
nature of the disassociated elements from the El Brete collection and collections from
France and Uzbekistan preserve structures such as the acrocoracoidal tubercle, dorsal
coracoidal fossa or an excavated posterior trochanter on the femur. These enantiornithine
features are largely unidentifiable in the crushed and two-dimensional specimens from
China. These specimens, however, are far more complete, revealing new morphological
information, which includes, as mentioned in the previous chapter, skull material. The
great temporal range spanned by the clade (over 60 My separates the earliest and latest
enantiornithine record), and the enormous diversity of the group, having independently
evolved locomotor and trophic specializations, only further fetters the identification of
new enantiornithine synapomorphies and increases the spectrum of known morphologies.
The goal of this chapter is not to provide a complete review of every detail of
enantiornithine morphology, but rather to describe features typical of the enantiornithine
post-cranial skeleton while providing ranges for elements that show the most variation.
Chapters 6 – 8 provide complete descriptions of three separate taxa. These provide
complete, detailed case studies of enantiornithine morphology, including comparison
166 
with other taxa to further elucidate the full range of morphologies currently recognized
within the clade. Chapters 6 and 7 provide examples of two taxa that have been
hypothesized to be closely related, the longipterygids Shanweiniao and Rapaxavis, while
Chapter 6 details the morphology of another more disparately related taxon (DNHM
D2950/1), thus providing a picture of both inter- and intraclade diversity. These
descriptions also highlight the different and varying amounts of information that can be
discerned from every unique specimen, which hinders comparison and cladistic analysis.

ii. Description
Axial Skeleton
Most cervical series are incomplete, however preserved necks are composed of
approximately nine (e.g. Sinornis, LP 4450) to eleven (e.g. Eoenantiornis, Pengornis)
elements. The two isolated midcervical vertebrae from el Brete, PVL 4050 and 4057, and
the cervicals in Pengornis are elongate, their lengths approximately 150% their widths,
while most Jehol enantiornithines have cervicals in which the length only slightly
exceeds the width (e.g. DNHM D2950/1, Eoenantiornis). Cervical vertebrae usually
possess incipient heterocoely if at all (absent in Eoalulavis and Iberomesornis), with only
the cranial surfaces of the anterior elements of the series heterocoelic (e.g. Longipteryx,
Longirostravis, PVL 4050, Pengornis); however the degree to which heterocoely is
present is obscured by the incomplete preservation of most specimens. Sharply tapered
costal processes are present in varying degrees of fusion (unfused in DNHM D2950/1;
fused in PVL 4050 and 4057). Cervical central are compressed so that the ventral surface
167 
is keeled (e.g. Pengornis, Hebeiornis). No specimen possesses cervicals with observable
pneumatopores.
The thoracic vertebrae are spool-like, with tall neural spines, and deep lateral
excavations on the vertebral body (e.g. Concornis, Neuquenornis, Protopteryx) that
perforate the vertebral body in some specimens (e.g. PVL 4051). The intervertebral
articulations are amphicoelous. Compared to other birds, the parapophyses are more
centrally located (except in Pengornis). No taxon is known to possess a notarium. The
synsacrum, only partly fused in some taxa (e.g. Hebeiornis) is typically composed of
approximately seven (e.g. Protopteryx, Pengornis, Rapaxavis, Longipteryx) or eight (e.g.
Cathayornis, Concornis; Chiappe and Walker, 2002) vertebrae. The synsacrum in some
taxa possesses a ventral groove (e.g. Rapaxavis, Concornis, Gobipteryx). Dorsally, the
spinous crest is low and approximately the same height its entire length (Longirostravis,
Pengornis, PVL 4032-3) as opposed to the high and caudally tapering crest of more
advanced birds (e.g. Gansus, Ichthyornis). The synsacrum is unfused from the pelvic
girdle in most taxa (e.g. Cathayornis, Pengornis; fused in PVL 4032-3), although the
transverse processes of the caudal-most sacral vertebrae are often laterodistally directed
and expanded (e.g. Cathayornis, Pengornis). No more than eight free caudals precede the
pygostyle (e.g. Sinornis, Iberomesornis, six in Rapaxavis). These vertebrae retain
elongate transverse processes, approximately equal to the centra width in length (e.g.
Concornis, DNHM D2950/1), that decrease in length distally (e.g. Rapaxavis). Short
haemal arches are present on the caudals of some taxa (e.g. Boluochia, Concornis) and
absent in others (e.g. Halimornis). The pygostyle (Fig. 5.1) is large and straight, equal to
168 

Figure 5.1. Enantiornithine pygostyles: A, Hebeiornis in ventral view; B, Iberomesornis
in lateral view. C-F, the typical modified enantiornithine morphology: C,
Dapingfangornis in lateral view; D, Rapaxavis in ventral view; and E, Halimornis in
dorsal view.
169 
or exceeding the combined length of the free caudals (e.g. Iberomesornis, Protopteryx,
IVPP 10530). Enantiornithines possess a unique morphology in which the element is
forked proximally, with a pair of ventrolateral processes that extend for most of the
length before the bone constricts distally (e.g. Halimornis, Longipteryx, Cathayornis,
Dapingfangornis, Longirostravis, Rapaxavis; Fig. 5.1C-F). A simple, triangular, tapering
pygostyle is present in some taxa (e.g. Hebeiornis, Gobipteryx; Fig. 5.1A). The pygostyle
of Iberomesornis is unique (Fig. 5.1B); it is very long and individual vertebrae can be
discerned proximally. The number of fused caudals composing the pygostyle has been
estimated to be 10 – 15 based on this taxon (Sanz and Bonaparte, 1992), however,
inferring the number of incorporated vertebrae is premature given the lack of data on
pygostyle formation in modern birds, and evidence from the fossil record that suggests a
reduction in the number of caudals preceded fusion in at least one line of Mesozoic birds
(Gao et al., 2008).

Thoracic Girdle
The coracoid (Fig. 5.2) is strut-like, excavated dorsally, with a straight
acrocoracoid. The proximal end is laterally compressed so that the acrocoracoid process,
scapular cotyla and glenoid facet are nearly aligned in dorsal view (e.g. Enantiornis,
Eoalulavis, M192, PO 4819 – formerly Explorornis). A peg-like acrocoracoidal tubercle
is present just proximal to the scapular articulation (e.g. PO 4819, Enantiornis, M192;
Fig. 5.2E,F). In no taxa is there a well-developed procoracoid process as in modern birds,
but Protopteryx possesses a similarly positioned triangular medial projection (Fig. 5.3)
170 

Figure 5.2. Enantiornithine coracoids (not scaled): A-C in ventral view, D-F in dorsal
view. A, Concornis; B, DNHM D2950/1; C, Rapaxavis; D, PVL 4034; E, M 192; F,
Enantiornis PVL 4035.
171 
that may have functioned similarly (Zhang and Zhou, 2001); Elsornis possesses a slight
swelling in the same location (Fig. 5.3C; Chiappe et al., 2006). In many taxa, the n.
supracoracoideus does not pierce the coracoid, but is inferred to pass medially (e.g.
Longirostravis, Iberomesornis); in taxa where the supracoracoideum nerve foramen
pierces the coracoid, the foramen lies in a medial groove (e.g. Eoalulavis, Eoenantiornis).
The dorsal fossa ranges from broad and shallow (e.g. Alethoalaornis, Cathayornis) to
deep (e.g. Enantiornis, Neuquenornis). A similar, deep impressio m. sternocoracoideus
is found in some modern ground birds (e.g. Turnicidae, Rallidae, Rhynochetidae), with
both highly pneumatized and apneumatic coracoids. The deep concavity of this surface in
enantiornithines may have functioned to increase the surface area for muscle attachment,
compensating for the relatively narrow corpus; the deepest fossae are associated with the
narrowest coracoids (e.g. Enantiornis, M192, Neuquenornis). The position of the
supracoracoideum nerve foramen relative to the dorsal fossa varies between specimens,
piercing either above the fossa (e.g. Enantiornis) to within it (e.g. Neuquenornis). The
lateral margin is typically convex (e.g. Eoalulavis, Concornis, PVL 4034), but the degree
of convexity present varies, producing a variety of different morphologies (Fig. 5.2) and
is even absent in some (e.g. Longipteryx, Rapaxavis). The width of the sternal margin
varies significantly relative to the proximodistal length. In some taxa the coracoid
expands rapidly so that the corpus is a wide fan attached to a slim proximal neck and the
sternal margin exceeds half the proximodistal length (e.g. Pengornis and Longipteryx). At
the opposite extreme, the sternal width is less than one third the total length so that the
coracoid resembles an elongate acute triangle (e.g. Enantiornis, Enantiophoenix,
172 

Figure 5.3. Medial processes and procoracoid processes (indicated by arrows) in
Ornithothoraces. A, Protopteryx (from Zhang and Zhou, 2004); B, Protopteryx as
reconstructed here; C, Elsornis; D, Gansus; E, Aquila.
173 
Neuquenornis, M192). As previously mentioned, taxa with narrow coracoids possess
deeper dorsal excavations compared to those with wider sternal margins, suggesting that
post-mortem compression could be exaggerating the shallowness of the dorsal fossa and
the width of the coracoid in slab specimens from China. However, the morphology of
Alethoalaornis and Enantiornis are clearly distinct and despite crushing, there is evidence
for a relatively deep dorsal coracoidal fossae in at least one slab specimen from China
(DNHM D2567/8). The sternal margin is usually straight (e.g. Rapaxavis, Eoalulavis),
but is concave in some specimens (e.g. PVL 4037, M192), and can be strongly angled so
that the sternolateral margin projects farther than the medial margin (e.g. M192,
Concornis). No lateral process is present in any taxon; the coracoid of Protopteryx
expands laterally proximal to the sternal margin and has been described as a lateral
process (Zhang and Zhou, 2000), but the morphology is more comparable to the distally
restricted convexity of the lateral margin present in some taxa (e.g. Concornis,
Eoalulavis) more than the discrete lateral process of modern birds and basal
ornithuromorphs (e.g. Gansus, Yanornis, Ichthyornis).
The scapula is straight and shorter than the humerus, typically possessing a large
cranially projecting acromion process. The acromion preserves a wide range of
morphologies; most commonly it appears long, straight and untapered (e.g. Eoalulavis,
Longipteryx, DNHM D2950/1) though in some taxa it is costolaterally wide and spatulate
(e.g. Cathayornis, Enantiornis, Halimornis), and in one taxon (Pengornis) the acromion
is hooked, like that of Apsaravis and some neornithines (e.g. Kittiwake, Herring Gull). A
small and tapered acromion is also known for several specimens (e.g. Enantiophoenix,
174 
Eocathayornis, CAGS-05-CM12) but even when reduced, the process projects further
cranially than the articular surface for the coracoid (as opposed to Ichthyornis). Visible in
three-dimensional specimens, the proximal surface of the scapula bears a pit-like
depression between the acromion and glenoid, which may have articulated with the
acrocoracoidal tubercle present on the coracoid (e.g. PVL 4035, Enantiornis) – this is the
mistaken “backwards” articulation of the coracoid and scapula that earned the
enantiornithines their name, the “opposite birds.” The scapular blade is typically straight
and the distal end is blunt (e.g. Longipteryx, DNHM D2950/1), rather than curved and
tapered (scimitar-like) as in Jeholornis and ornithuromorphs. At least one specimen
possesses a unique midshaft ‘kink,’ so that in lateral view the scapula ventrally defines an
obtuse angle (Elsornis). The costal surface of the scapular blade is excavated in some
taxa (e.g. Enantiornis, Elsornis, Halimornis, Neuquenornis).
Compared to the U-shaped furculae of more advanced birds (Ornithuromorpha),
the enantiornithine furcula (Fig. 5.4) is most commonly Y-shaped with relatively straight
rami (e.g. Elsornis; as opposed to the strong dorsal curvature present in advanced
ornithuromorphs) and an elongate hypocleidium often more than half the length of the
rami (e.g. Cathayornis, Protopteryx, Rapaxavis, Hebeiornis). The clavicular symphysis is
typically short (e.g. Longipteryx; Fig. 5.4B), but in some taxa the clavicles form a broad
symphysis that becomes the hypocleidium distally (e.g. Shanweiniao; Fig. 5.4C). The
hypocleidium ranges from very small (Neuquenornis) to 2/3 or more the length of the
furcular rami (e.g. Eoalulavis, Cathayornis, Elsornis, IVPP 10530). In many taxa, the
cross section of the furcula rami is L-shaped so that the bone is excavated dorsolaterally
175 

Figure 5.4. Furcular variation across enantiornithines: all in ventral view except D and E.
A, Eoalulavis; B, Longipteryx; C, Shanweiniao; D, DNHM D2567/8; E, Noguerornis; F,
DNHM D2950/1.
176 
(e.g. Longipteryx, Concornis, Elsornis). In dorsal view, the keeled medial margins of the
rami converge and form a ridge that runs down the hypocleidium (DNHM D2568; Fig.
5.4D). The hypocleidium is also keeled ventrally in some specimens (e.g.
Dapingfangornis, DNHM D2950/1). A tubercle, possibly for muscle attachment, is
present on the hypocleidium in Eoalulavis (Fig. 5.4A) and DNHM D2568; this could also
be pathological in origin (Sanz et al., 2002).
The imperforate region of sternum (Fig. 5.5) is short compared to the sterna of
ornithuromorphs (e.g. Yixianornis, Songlingornis); this element is inferred to be present,
but cartilaginous in Archaeopteryx and other basal birds (ossified in Confuciusornis). A
fully ossified sternum is present in most enantiornithines though a few taxa possess
strange morphologies that are interpreted as the result of incomplete ossification of this
element in the adult (e.g. Eoenantiornis, Eoalulavis). Typically, the sternum is
quadrangular with a rounded cranial margin (e.g. Cathayornis, Longirostravis), and
dorsally concave (DNHM D2567/8). The keel shows a range from low and restricted to
the caudal half (e.g. Dapingfangornis, Hebeiornis), to large and cranially projecting (e.g.
Neuquenornis). In some taxa the keel is cranially forked, a morphology unique to
enantiornithines (e.g. Elsornis, Concornis). Typically two pairs of sternal trabeculae are
present with the inner trabecula very small and the outer trabecula distally expanded (e.g.
Longipteryx, Cathayornis, Concornis). These distal expansions vary from largely absent
(e.g. Hebeiornis) to simple (e.g. Longipteryx, Concornis) or complex (e.g. Rapaxavis,
Longirostravis). The lateral sternal margins are straight; no specimen is known to possess
distinct costal facets or a strong ‘zyphoid’ process (Clarke et al., 2006) as in
177 

Figure 5.5. Sternal variation among enantiornithines; all in ventral view (except E). A,
Longipteryx; B, Concornis; C, Eoalulavis; D, Longirostravis; E, DNHM D2567/8; F,
Eoenantiornis; G, Rapaxavis; H, Elsornis.
178 
Confuciusornis (Chiappe et al., 1999) and ornithuromorphs (Yixianornis, Gansus; Clarke
et al., 2006; You et al., 2006), although a caudolaterally projecting process is present at
the level of the proximal end of the outer trabecula in some specimens (e.g. DNHM
D2568, Cathayornis, Protopteryx). Distally, the sternum typically ends in a simple,
untapered xiphoid process (e.g. Longirostravis, Protopteryx, Rapaxavis). Fenestrae
perforating the caudal half of the sternum such as those present in some contemporaneous
ornithuromorphs (e.g. Yixianornis, Yanornis, Songlingornis) and in neornithines are
absent.

Thoracic Limb
The humerus (Fig. 5.6) is very diagnostic of the group; as in more primitive taxa,
the humerus is twisted so that the proximal and distal ends are expanded in different
planes, but the degree of torsion varies (Chiappe et al., 2007). The proximal surface is
cranially concave, while the caudal surface is convex (e.g. Enantiornis, Martinavis,
Gurilynia); the degree of concavity varies (Chiappe et al., 2007) and one taxon possesses
a globose morphology more similar to that of more advanced taxa (Pengornis; Fig. 5.6A).
In cranial view, the proximal margin is concave at the midpoint, rather than convex as in
more advanced birds. In some taxa the humerus is long and thin (e.g. Concornis; Fig.
5.6D) where in others it is more robust and sigmoidal (e.g. Cathayornis, Eoenantiornis).
The proximocranial surface bears a circular fossa on the midline (e.g. Cathayornis,
Enantiornis, Hebeiornis); proximoventral to this fossa, a poorly developed transverse
ligamental groove in present in some taxa (e.g. Concornis, Halimornis, Pengornis). On
179 

Figure 5.6. Humeral variation within Enantiornithes. A, Pengornis (caudal view); B,
Cathayornis (cranial); C, Eocathayornis (caudal); D, Concornis (cranioventral); E, F,
Elsornis in caudal and cranial view; G, H, Martinavis in cranial and caudal view; I, J,
Enantiornis in caudal and cranial view.
180 
the cranial surface, dorsodistal to the circular fossa, some specimens possess a distinct
scar for the m. coracobrachialis cranialis (e.g. Gurilynia, Martinavis). The bicipital crest
is cranially developed but the degree of projection varies from low (e.g. DNHM D2950/1,
Rapaxavis) to hypertrophied (e.g. Enantiornis, Concornis). In most taxa, the crest bears a
pit shaped fossa on its craniodistal (e.g. Eoalulavis, Enantiornis) or ventrodistal surface
(e.g. Martinavis, Dapingfangornis) presumably for muscle attachment (Chiappe and
Walker, 2002). This fossa bears similar topography (craniodistal in Yanornis martini,
ventrodistal in Apsaravis ukhaana, absent in Yixianornis grabaui) in basal
ornithuromorphs, but is caudodistally located in neornithines. Clarke (2004) suggested
this fossa maybe the attachment site of a tendon of the m. biceps brachii, the aponeurosis
of which covers the bicipital region in modern birds (Vanden Berge and Zweers, 1993).
The deltopectoral crest projects dorsally, is typically shaft width, imperforate, and tapered
distally (e.g. Eoenantiornis, Pengornis, Martinavis), though in some taxa, the crest ends
more abruptly (e.g. Concornis, Protopteryx, Enantiornis). On the caudal surface, the
ventral tubercle is separated by a capital incision, which is very deep (e.g. Martinavis;
Fig. 5.6G,H) and perforated in some taxa (e.g. Enantiornis, PVL 4020). Several taxa
possess a well-developed pneumotricipital fossa (e.g. Cathayornis, Enantiornis,
Martinavis, Neuquenornis) but only one specimen possesses what is interpreted as a
distinct pneumotricipital foramen (PVL 4022). If this is correct, the humerus in at least
one taxon was pneumatized by the clavicular air sac as in modern birds (Chiappe and
Walker, 2002).
181 
Distally, the humerus is craniocaudally compressed (e.g. Martinavis, Elsornis)
with strap-like condyles (e.g. Rapaxavis, Martinavis). The dorsal condyle is usually
transversely oriented (e.g. Alexornis, Cathayornis, Dapingfangornis). In some
‘euenantiornithines’ the humerus is transversely expanded (e.g. Enantiornis, M.
cruzyensis, PVL 4025); in others, this paracondylar expansion occurs primarily dorsally
(e.g. Eocathayornis, M. vincei, CAGS-IG-04-CM-023). The distal margin is typically
angled relative to the long-axis of the humeral shaft; this ranges from weak (e.g.
Pengornis, PVL 4025, Neuquenornis) to strongly angled with a distally expanded flexor
process (e.g. Alexornis, M. vincei, Eoalulavis). A wide olecranon fossa is common (e.g.
Martinavis, Cathayornis, Eoalulavis), but a distinct, textured brachial scar on the cranial
surface or tricipital grooves on the caudal surface are absent (e.g. Martinavis, Eoalulavis,
Alexornis).
The ulna-radius (antebrachium) is at least as long as the humerus except in the
flightless Elsornis; the shaft of the ulna is bowed proximally (straight in Noguerornis)
and typically twice the thickness of the straight radius (e.g. Concornis, Eoalulavis,
DNHM D2950/1). The ulnar cotylae are separated by a groove in some taxa (e.g.
Concornis, Eoalulavis) but not in others (e.g. Elsornis, Enantiornis). Remige papillae
(quill knobs) are absent in all known taxa (present in the Late Cretaceous Rahonavis,
some modern birds and non-avian theropods; Forster et al., 1998; Turner et al., 2007b)
though they are reported to be present in an undescribed avisaurid from the Late
Cretaceous of North America (Hutchison, 1993). The thin, straight radius is often
182 
longitudinally excavated by a groove on the caudoventral surface (e.g. Eoenantiornis,
Gobipteryx).
The carpometacarpus ranges in degree of fusion from absent (e.g. DNHM
D2950/1 – possibly ontogenetic) to nearly complete, most commonly approaching
complete fusion proximally but remaining unfused distally (e.g. Enantiornis,
Longirostravis, Neuquenornis). In all taxa, the minor metacarpal projects distally beyond
the distal end of the major metacarpal, except Protopteryx in which the minor metacarpal
projects as far as the major. The intermetacarpal space is either absent (e.g.
Alethoalaornis, DNHM D2950/1) or narrow (e.g. Dapingfangornis, Sinornis).
Proximoventrally, the minor metacarpal is contiguous with a tubercle (e.g. Cathayornis,
Longipteryx, Enantiornis) in the location of the pisiform process of advanced birds (e.g.
Ichthyornis, Neornithes). The tubercle is undercut by a supratrochlear fossa in some (e.g.
Enantiornis, Pengornis). The alular metacarpal is typically rectangular (e.g.
Cathayornis, Eoenantiornis, Longipteryx, DNHM D2950/1), though it has a semi-lunate
profile in some taxa (e.g. Hebeiornis, Longirostravis, Neuquenornis). A well-developed
extensor process is present in one specimen (PVL 4020) but in no specimen is an alular
process clearly present.
Both the alular and major digits are typically clawed (e.g. Protopteryx,
Longipteryx, Sinornis), though at least one taxon has lost all manual claws (Rapaxavis).
The alular digit ranges from long and robust, exceeding the major metacarpal in distal
extent (e.g. Longipteryx, Protopteryx), to highly reduced into a single splint-like phalanx
(e.g. Rapaxavis). In most taxa, the alular digit is short, distally ending proximal to the
183 
distal end of the major metacarpal, bearing a claw subequal to that of the major digit (e.g.
Concornis, Dapingfangornis, Eocathayornis). The first phalanx of the major digit is of
normal non-avian shape (lacking the dorsoventral expansion present in ornithuromorphs
Yixianornis and Hongshanornis), and phalanges decrease in length distally (e.g.
Eoenantiornis, Hebeiornis, DNHM D2950/1). The minor digit is reduced, composed of
two phalanges, the distal of which is extremely reduced to a small splinter of bone (e.g.
Protopteryx, Longipteryx, Eocathayornis); this second phalanx is either lost or not
preserved in some taxa (e.g. Rapaxavis, Eoalulavis). The first phalanx is straight in some
taxa (e.g. Cathayornis, Concornis, Hebeiornis), but bowed in others (e.g. Eoalulavis,
Sinornis).

Pelvic Girdle
The pelvic girdle ranges from unfused (e.g. Cathayornis, DNHM D2950/1) to
nearly complete fusion at the level of the acetabulum with sutures discernible (e.g.
CAGS-IG-04-CM-007, Sinornis); in the Late Cretaceous PVL 4032-3 the pelvic elements
appear completely fused. The ilia are rounded and broad proximally, tapering caudally
(e.g. Sinornis, Longirostravis). In most taxa the dorsal crests of the ilia approach each
other on the midline but do not contact (e.g. Alethoalaornis, Gobipteryx, Longirostravis).
The crests contact on the midline in one El Brete specimen (PVL 4041-4), as well as in
Hesperornis and modern birds. The ilium in some taxa bears a triangular, laterally
projecting supracetabular tubercle (dorsal antitrochanter per Sereno et al., 2002) on its
dorsal margin (e.g. PVL 4032-3, Sinornis). This process forms a laterally projecting
184 
flange along the dorsal margin of the post-acetabular ilium that diminishes distally (e.g.
Sinornis, PVL 4032-3). The antitrochanter is a prominent caudodorsally projecting
triangular process on the caudodorsal margin of the acetabulum (e.g. PVL 4032-3,
CAGS-05-CM-006, Sinornis). The acetabulum ranges from partially occluded as in
Archaeopteryx and Patagopteryx (e.g. CAGS-05-CM-006) to fully perforated (e.g.
Sinornis, PVL 4032-3).
The ischium has a dorsal process which contacts (but is not fused to) the ilium
medially demarcating an ilioschiadic fenestra (e.g. Sinornis, CAGS-05-CM-006) not
homologous to that of neognaths (Chiappe and Walker, 2002). No obturator process is
present; distal to the dorsal process the ischium is typically strap-like (straight, subequal
in width with a blunt caudal margin; e.g. DNHM D2950/1, Cathayornis) but curved and
tapered in others (e.g. Sinornis, Eoenantiornis). Distally, the ischia are known to contact
in one taxon (Noguerornis); the distal ends of these bones approach each other in
Concornis, but appear unfused.
The pubes are typically retroverted at approximately a 45˚ angle (e.g. Sinornis,
CAGS-05-CM-006) though they appear subvertical in CAGS-05-CM-04. The pubes
range from straight (e.g. Eoenantiornis, DNHM D2950/1) to caudodorsally concave (e.g.
IVPP V10530, CAGS-05-CM-04); in CAGS-05-CM-006 the pubes are straight
proximally with a slight ventral bend at the distal third. The pubes, though often distally
unfused (e.g. Longipteryx, Rapaxavis), contacted distally, forming a short symphysis (e.g.
Concornis). In most taxa, the distal end is expanded into a boot that projects
185 
perpendicular to the pubic shaft (e.g. Longipteryx, Boluochia, DNHM D2950/1) though
in some specimens, no expansion is present (CAGS-05-CM-006, CAGS-06-CM-012).

Pelvic Limb
The femur typically is craniocaudally bowed, the head separated from the shaft by
a distinct neck (e.g. Longirostravis, Pengornis, PVL 4037). A hypertrophied posterior
trochanter excavates the proximolateral surface forming a shelf-like structure (Eoalulavis,
Neuquenornis, Protopteryx, M193). The distal end lacks a patellar groove on the cranial
surface in most taxa (e.g. PVL 4036) however a long groove appears present in CAGS-
04-CM-006. The popliteal fossa is a shallow excavation, bound distally but lacking an
ossified bridge. A well-developed fibular crest is absent (poorly developed in
Halimornis). Just proximal to the lateral condyle in some taxa the lateral margin bears a
caudally projecting flange (e.g. Neuquenornis, Concornis, PVL 4037).
The tibia and distal tarsals are usually fused into a tibiotarsus (Fig. 5.7) in most
taxa (e.g. Lectavis, Soroavisaurus, Nanantius) though the sutures are distinguishable in
some (e.g. Gobipteryx, CAGS-04-CM-006) and fusion is absent in others (e.g. DNHM
D2950/1, Iberomesornis, Rapaxavis) – the latter morphology may prove to be
ontogenetic. The proximal end of the tibiotarsus ranges from circular (e.g. Concornis,
Soroavisaurus) to ovoid (e.g. Lectavis) and is typically flat (e.g. Gobipteryx, Lectavis)
though several taxa show an inclined surface so that the lateral proximal margin is distal
to the medial proximal margin (e.g. Cathayornis, Nanantius, Soroavisaurus).
Unfortunately, the femora are not well known in these taxa, and corresponding
186 

Figure 5.7. Enantiornithine tibiotarsi. A, Nanantius in medial and cranial view (from
Molnar, 1986); B, CAGS-04-CM-006 in medial and cranial view; C, D Soroavisaurus
PVL 4030 and PVL 4033 in cranial view (from Chiappe and Walker, 2002); E, Lectavis
in cranial and medial view (from Chiappe, 1993).
187 
modifications are not known. The tibiotarsus bears a single cnemial crest, which is
typically low and craniolaterally positioned (e.g. Neuquenornis, Soroavisaurus). One
taxon may possess a crest that projects strongly cranially (CAGS-04-CM-006; Fig. 5.7B)
though the crest in this specimen does not project proximally beyond the articular
surface, a morphology common in the cranial cnemial crest of ornithuromorphs (Gansus)
and living birds. The single crest present in Enantiornithes is interpreted as the ancestral
lateral cnemial crest of modern birds (Chiappe, 1996). The fibular crest projects laterally
and extends for approximately one third the tibiotarsus. Distally, the condyles range
from round and bulbous (e.g. Dapingfangornis) to tapered medially forming an hourglass
(e.g. Lectavis, Nanantius) to narrow, proximodistally elongate and separated by a narrow
proximodistally oriented intercondylar incisure (e.g. Soroavisaurus; Fig. 5.7C). The
proximal margin of the condyles is sharply incised (e.g. Cathayornis, Soroavisaurus,
Nanantius, CAGS-04-CM-006). The medial condyle is often much larger than the lateral
condyle (e.g. Nanantius, Soroavisaurus, Lectavis), the plesiomorphic condition in Aves,
though in several taxa the condyles appear subequal (e.g. Longipteryx, Dapingfangornis).
The medial surface of the medial condyle possesses a central, circular pit-like fossa
(depressio epicondylaris medialis) in several specimens (e.g. CAGS-04-CM-006,
Dapingfangornis, Gobipteryx, Nanantius). The lateral surface is shallowly excavated
(depressio epicondylaris lateralis) across the entire surface (e.g. CAGS-04-CM-006,
Sinornis, Soroavisaurus); dorsal to this fossa there exists a small tubercle for muscle
attachment (e.g. Lectavis, CAGS-04-CM-006).
188 

Figure 5.8. Enantiornithine tarsometatarsi: A, Boluochia; B, Yungavolucris (from
Chiappe, 1993); C, CAGS-04-CM-007; D, Avisaurus archibaldi (from Chiappe, 1993).
189 
The tarsometatarsus is characteristically fused proximally and tightly ankylosed
distally with the individual metatarsals fully distinguishable (Fig. 5.8). In some taxa,
fusion between the distal tarsals and metatarsals, and thus a true tarsometatarsus, is
absent (e.g. DNHM D2950/1, Iberomesornis, Rapaxavis) although this may also prove to
be ontogenetic (see Chapter 9). No metatarsal V is preserved in any taxon (present in
more basal birds and Vorona). Metatarsals II-IV are aligned in the same plane
proximally, lacking the plantar displacement of metatarsal III present in ornithuromorphs.
In some avisaurids, the dorsal surface of metatarsal III is strongly convex, projecting
dorsally farther than the equivalent surfaces in metatarsals II and IV (e.g. A. archibaldi,
Neuquenornis, Soroavisaurus). There is huge variation in the relative length and
thickness among the metatarsals indicating great ecomorphological diversity. In the
typical enantiornithine tarsometatarsus, III is the longest, followed by IV and then II, and
metatarsal IV is mediolaterally thinner than metatarsals II and III (e.g. Avisaurus,
Soroavisaurus, Longirostravis, Hebeiornis). The greatest excursion from this
morphology is the Late Cretaceous Yungavolucris from El Brete (Fig. 7.8B); in this
taxon, metatarsal II is shorter than III and IV, and its trochlea is expanded so that it
exceeds the mediolateral width of that of III and IV combined. Proximally, an
intercotylar eminence is not strongly developed. Plantarly, a hypotarsus is absent, though
Lectavis has developed a caudal projection that may be similar though unlikely
homologous (Chiappe, 1993). In some taxa, the plantar surfaces of metatarsals II and IV
project more plantarly than metatarsal III forming a plantar excavation (e.g. A.
archibaldi, Lectavis, Neuquenornis). The proximal half of metatarsal II often bears a
190 
tubercle, presumably for the attachment of the m. tibialis cranialis, on the dorsal surface
(e.g. Pengornis, Enantiophoenix, Soroavisaurus), a condition also known in
Confuciusornis and dromaeosaurs (Chiappe and Walker, 2002). The tubercle varies in its
distance from the proximal end, from just below the proximal surface (Lectavis) to just
distal to midshaft (A. gloriae), but is typically approximately located a third of the way
down the shaft from the proximal end (e.g. A. archibaldi, Shanweiniao, Soroavisaurus).
The placement of the tubercle on the surface of the metatarsal ranges from the medial
(e.g. A. gloriae, Soroavisaurus) to lateral (e.g. Rapaxavis, Yungavolucris) surface and is
most commonly located on the dorsal surface (e.g. A. archibaldi, Gobipteryx, Hebeiornis,
Lectavis). No true proximal or distal vascular foramen is known though the distal end of
Yungavolucris demarcates an intertarsometatarsal opening between metatarsals III and
IV. Distally, the trochlea of metatarsal II is often wider than the trochlea of III and IV
(e.g. Yungavolucris, Eoenantiornis, Hebeiornis); the trochlea of metatarsal IV is typically
poorly developed and undifferentiated (e.g. Yungavolucris, Avisaurus). Avisaurids have
an unusual morphology in which the lateral half of trochlea II and medial half of III
project strongly distally and plantarly (e.g. Neuquenornis, Soroavisaurus, A. archibaldi).
Metatarsal I occupies a range of morphologies (Fig. 5.9) from very simple and
straight (e.g. Rapaxavis; Fig. 5.9A), to the extreme J-shape of avisaurids (e.g.
Neuquenornis, Soroavisaurus; Fig. 5.9C,D). Most commonly, the metatarsal I is shaped
like an inverted P, articulating on the medial or medioplantar surface of metatarsal II (the
two morphologies cannot be distinguished unequivocally in specimens without some
three-dimensional preservation), with the articular facet for the digit nearly parallel to
191 

Figure 5.9. Select enantiornithine metatarsal I: A, Rapaxavis in craniomedial view; B,
DNHM D2950/1 in medioplantar view; C, Neuquenornis in medial view (from Chiappe,
1993); D, Soroavisaurus in medial view (from Chiappe, 1993).
192 
that for metatarsal II (e.g. Pengornis, Concornis, Iberomesornis). In specimens that
clearly articulate medioplantarly (those not completely flattened), the articular facet for
metatarsal II is concave, wrapping around the medioplantar surface of metatarsal II (e.g.
Sinornis, CAGS-05-CM-006). The articular surface for the first phalanx of digit one
appears nearly parallel to the plantar surface of the tarsometatarsus so that the hallux is
interpreted as completely reversed (Sinornis, CAGS-05-CM-006). The J-shape metatarsal
I of avisaurids refers to the profile of the bone in medial view; the caudally directed
ramus is almost half the length of the metatarsal shaft. The proximal ramus is
mediolaterally compressed and the lateral surface is flat, articulating with the medial
surface of metatarsal II. The caudally directed ramus is slightly expanded distally into a
trochlea for articulation with the first digit, so that the hallux is fully reversed and the two
articular surfaces of metatarsal I occupy define a 90˚ angle (e.g. Neuquenornis,
Soroavisaurus). A similar condition is observed in DNHM D2950/1 (Fig. 5.9B) and
CAGS-IG-04-CM-007 but the caudal ramus is much shorter and lacks the extreme
mediolateral compression in Soroavisaurus (PVL 4048). In specimens with a fairly
straight metatarsal I morphology (i.e. Rapaxavis; Fig. 5.9A), it is unclear if the hallux
was fully reversed; it is possible in such taxa the hallux was medioplantarly directed. A
heterodactyl enantiornithine has been reported (Zhang et al., 2006); regardless of the fact
the specimen is in a private collection and thus a nomen nudum, the interpreted
morphology is unsubstantiated given the poor preservation of the foot.
The pedal phalangeal formula is 2-3-4-5-x; digit II is often robust and digit III is
usually the longest. The proportions of phalanges within and between digits varies,
193 
though not to the degree observed in modern birds, with most specimens displaying a
generalist foot morphology like other basal birds (Hopson, 2001). Enantiornithines are
envisioned to be small arboreal perching birds (e.g. Eoenantiornis, Hebeiornis), a
conclusion that is typically not supported by distinct pedal proportions. The exception is
Rapaxavis in which the phalanges elongate slightly distally as in modern perching birds
(Hopson, 2001). The pedal claws are typically uniform in size, though some are known to
possess a robust hallux (e.g. Neuquenornis, Soroavisaurus) or a reduced digit IV ungual
(e.g. Hebeiornis, CAGS-05-CM-006) and the preservation in one taxon suggests strong
heterogeneity may be present (DNHM D2950/1).

iii. Amendments to published data
Boluochia zhengi (Zhou, 1995)
This taxon, known from a single specimen (IVPP V9770) can be distinguished
from other enantiornithines by the unique morphology of its tarsometatarsus, in which the
metatarsals end approximately at the same level. Metatarsal II is slightly shorter than III,
which is slightly shorter than IV; the distal sixth of metatarsal IV deflects laterally
leaving a deep cleft between the distal ends of III and IV. Metatarsal IV is deflected
comparably on both sides and thus this is interpreted as a true feature rather than the
slight distal disarticulation of metatarsal IV. Another unique morphology is the hooked
tip of the premaxilla, a morphology common among modern birds of prey but thus far
only known in Boluochia within Mesozoic birds. This morphology, however, is
challenged; the preservation of Boluochia is poor and the skull is largely incomplete and
194 
difficult to interpret. The bone identified as the premaxilla could also be argued to be the
dentary, though it is here also interpreted as the premaxilla. The rostral portion of the
bone appears poorly preserved, but the voids make it difficult to interpret. The hook is
interpreted as the rostral-most premaxillary tooth. The dorsal bulge of the rostral portion
of the premaxilla has a rough margin compared to the smooth and straight margins that
characterize all other parts of the bone, and could represent abrasion or crushing. The
imperforate region of the premaxilla is low and elongate and the maxillary process is long
and tapered, as in Longipteryx (see Chapter 3 for further discussion on the taxonomic
validity of Boluochia and comparison with Longipteryx).

Eoenantiornis buhleri (Hou et al., 1999)
The original description of Eoenantiornis reconstructed the sternum as lacking
lateral trabeculae, resembling the sterna of some juvenile specimens GMV 2159 and
GMV 2156 (Hou et al., 1999). The redescription of Eoenantiornis interpreted the sternum
as similar to those of other enantiornithines with two pairs of trabeculae: the outer ending
approximately at the same level of the xiphoid process with a distal expansion, with the
inner short and minimally developed. The preservation of the sternum in Eoenantiornis is
very clear, except for the outer trabeculae which are very difficult to discern and
incomplete. This paper follows the Hou et al. (1999) interpretation of this bone; what
Zhou et al. (2005) interpret as the distal end of the right outer trabecula, is here
reinterpreted as the distal end of the right humerus. This interpretation is supported by the
position of the distal left humerus, which is located at approximately the same level as
195 
what is interpreted here as the distal right humerus, as well as by the differential
preservation between the ‘sternal trabecula’ and the sternal body itself. The sternum is
proportionately different but similar in morphology to that of “Liaoxiornis” and other
juvenile specimens in which the sternum is represented by a small flat body with a
rounded cranial margin, no trabeculae, ending in a xiphoid process (Chiappe et al., 2007).
In these specimens, the sternal margin of the coracoids are much wider than their
respective articular surfaces on the cranial margin of the sternum and thus the latter bone
is considered to be incompletely ossified, and attributed to the well-supported juvenile
status of the specimens (porous periosteal surface, distal ends of long bones incompletely
ossified, large orbit relative to skull). Since there are no other indicators that
Eoenantiornis is a subadult, this is interpreted as the true morphology of Eoenantiornis;
however it is suggested that the sternum may have bore cartilaginous outer trabeculae.
One other enantiornithine, Eoalulavis hoyasi, does not possess a fully ossified sternum in
the adult; the sterna of these two taxa differ greatly in morphology.

iv. Conclusions
The diversity of enantiornithine morphology makes it difficult to encapsulate the
complete range of conditions present or make generalizations about the clade. However,
the differences briefly outlined above provide a general understanding of the
enantiornithine skeleton a well as the elements that vary more than others, and how they
differ from other groups of birds. Reflecting the size of the clade, enantiornithines show a
wide range of morphologies, in addition to specializations associated with locomotor or
196 
trophic specializations. The incredible morphological diversity makes it difficult to create
hypotheses regarding the order of character acquisition and identify synapomorphies of
the clade, especially given the incomplete nature of Late Cretaceous specimens.
The following chapters are case studies of enantiornithine anatomy meant to
further reconstruct the morphology of these birds. The three taxa described are all from
the same Early Cretaceous geologic unit (Jehol Group) and thus represent a fairly narrow
view of enantiornithine diversity; however, morphological differences between taxa from
a single time and locality further emphasize the high degree of enantiornithine diversity.
The described taxa represent two closely related forms and a third non-related taxon,
therefore creating a picture of enantiornithine inter- and intraclade diversity. These
specimens also exemplify the differential preservation between specimens, even from the
same geologic unit, the information that is subsequently available for each specimen, and
how this hinders morphological comparison between taxa and attempts at phylogenetic
hypotheses.
197 
CHAPTER 6: THE MORPHOLOGY OF DNHM D2950/1, A WELL-PRESERVED
SPECIMEN FROM THE QIAOTOU FORMATION OF NORTHEASTERN CHINA

CHAPTER 6 ABSTRACT – The morphology of a new species of enantiornithine bird from
northeastern China is described based on a single specimen. The new specimen
possesses several enantiornithine synapomorphies but is unique from other known
species. The specimen has a well-preserved skull that reveals new information about
enantiornithine cranial morphology. The new taxon possesses a large postorbital with a
long tapering jugal process indicating that some enantiornithines may have had a fully
diapsid skull, as in Confuciusornis. The tooth morphology of the specimen is unique and
likely represents a previously unknown trophic specialization within Enantiornithes.

i. Introduction
The Lower Cretaceous deposits in northeastern China have held an important role
in revealing enantiornithine diversity by producing more complete specimens than any
other region in the world (Zhang et al., 2003). Many of these specimens, however
complete, are poorly preserved with the bones split between two slabs, thus as the known
diversity of enantiornithines has rapidly increased, many anatomical details, especially
those regarding the skull, vertebral column and pelvic girdle, have remained enigmatic.
Here we describe a new well-preserved specimen from the older Qiaotou
Formation, a unit stratigraphically lower than the Yixian Formation of the Jehol Group (Ji
et al., 2005). The exact age of this formation is currently under study (Ji et al., 2005) and
198 
it is unknown if it correlates with the Dabeigou Formation, the oldest unit of the Jehol
Group, from which the primitive enantiornithine Protopteryx is known (Zhang and Zhou,
2000; Zhou, 2006). A Late Jurassic age has been suggested for the formation (Ji et al.,
2005), suggesting DNHM D2950/1 may prove to be the oldest enantiornithine record to
date. The new specimen represents a new taxon and contributes to our understanding of
enantiornithines by increasing known morphological diversity, providing new anatomical
information, and expanding the known range of trophic specialization.

ii. Systematic Paleontology
Aves Linnaeus, 1758
Pygostylia Chiappe, 2002
Ornithothoraces Chiappe, 1995
Enantiornithes Walker, 1981
N. sp. (Figs. 6.1, 2)
Holotype
A nearly complete and largely articulated individual preserved in a slab (DNHM D2950;
Figs. 6.1A, 2A) and counter slab (DNHM D2951; Figs. 6.1B, 2B). The bones are
primarily preserved in DNHM D2951 (DNHM - Dalian Natural History Museum) and
are exposed mainly in ventral view. The manus are preserved in DNHM D2950 along
with voids of the remainder of the skeleton. Feathers are preserved as carbonized traces
concentrated around the head, wings and tail. Despite the lack of fusion present in several
of the compound bones (absence of tibiotarsus and carpometacarpus), this specimen is
199 

Figure 6.1. Photograph of A, DNHM D2950; B, DNHM D2951.
200 
considered not to be an early juvenile based on the size and proportions of the skull and
orbit and the absence of any pitted periosteal surfaces, and is here regarded as an
subadult/adult.

Locality and Horizon
Senjitu Area, Fengning County, Hebei Province, China. Qiaotou Formation, Late Jurassic
- Early Cretaceous (Ji, 2004; Ji et al., 2005).

Diagnosis
Medium sized enantiornithine bird with the following unique combination of characters:
narrow nasal lacking maxillary process; postorbital with elongate, straight jugal process;
robust teeth with circular cross-sections and slightly recurved apices (autapomorphy);
omal tips of furcula expanded; distal third of coracoid lateral margin convex; sternum
with fan-shaped expansion of outermost trabecula; unreduced and unfused manus with
claws on the alular and major digits; dorsally projecting tubercle on caudodorsal surface
of semilunate carpal; strap-like ischium lacking obturator process; pubis bearing boot-like
distal expansion; J-shaped metatarsal I with laterally directed facet for the articulation
with metatarsal II and caudally oriented facet for the articulation with digit I.

201 
iii. Anatomy
Skull
The skull is preserved primarily in DNHM D2951 with voids in DNHM D2950.
The skull is preserved primarily in right lateral view, although the external basicranium is
also visible due to the largely disarticulated nature of the postorbital region (Fig. 6.3A).
There are four robust teeth present in the premaxilla, typical of theropods and other
toothed birds, such as Sapeornis and Eoenantiornis (Zhou and Zhang, 2002; Zhang et al.,
2004). Based on the tooth distribution, the premaxilla is interpreted as restricted rostrally
forming only a small portion of the facial margin. The nasal processes of the premaxilla
(syn. frontal process; Baumel and Witmer, 1993) are relatively short, extending beyond
the rostral margin of the antorbital fenestra but not reaching the level of the lacrimal. The
distal third of the nasal processes forms a wedge-like articulation with the nasals. The
nasals are long and narrow, expanding caudally; a maxillary process is absent.
The maxilla has a long and slender dorsal process that extends caudodorsally to
contact the nasal. Unlike the condition preserved in Pengornis (Zhou et al., 2008a), the
maxilla of DNHM D2950/1 appears to lack a recessed medial wall within the antorbital
fenestra. The maxilla possesses at least four teeth (Fig. 6.3B).
The jugal is a straight bar, forked distally, as in Archaeopteryx and the Montsec
nestling (Sanz et al., 1997; Elzanowski, 2002). There is no evidence of a postorbital
process on the jugal and no quadratojugal is preserved.
The postorbital is T-shaped with a large tapering jugal process, as opposed to the
reduced postorbital in the Montsec nestling and Pengornis; the bone is disarticulated so it
202 
cannot be determined unequivocally whether or not it contacted the jugal. While the
postorbital clearly did not fully separate the infratemporal fenestra from the orbit in the
former taxa, the length of the jugal process of the postorbital in DNHM D2950/1 suggests
some contact or overlap was present. Given the distribution of elongate postorbitals
outside Ornithothoraces (Sapeornis, Confuciusornis), the morphological variation within
Enantiornithes, and the apparent absence of a postorbital within Ornithuromorpha
(Ichthyornis, Hesperornis), it is difficult to determine if the elongate jugal process in
DNHM D2950/1 is a derived morphology (Chiappe et al., 1999). The absence of a large
postorbital process on the jugal indicates that the condition in other non-avian theropods,
in which the two bones articulated for an extended length, was not present. The presence
of a bony postorbital bar in DNHM D2950/1 would preclude this taxon from any form of
cranial kinesis, present in all modern birds.
The quadrate is preserved in caudal view; the caudal surface is excavated, similar
to that of Archaeopteryx, and perforated by a pneumatic foramen as in Pengornis and the
Montsec nestling. The medial condyle of the mandibular process of the quadrate is much
larger than the lateral condyle.
The frontals are craniocaudally long, slender rostrally, caudally expanding into
domed structures. The parietals are oval and vaulted; they are unfused to the frontals and
occipital bones. The basicranium is preserved disarticulated and caudoventral to the
rostrum and orbit. The occipital bones are fully fused with the exception of the
basioccipital and where the two exoccipitals meet on the midline to each form a dorsal
quarter of the occipital condyle. The supraoccipitals form a cerebral prominence, more
203 
pronounced than that of Neuquenornis (Chiappe and Calvo, 1994). Large fossae excavate
the exoccipital lateral to the foramen magnum; ventrally the exoccipital bears two
foramina. These may represent the canales n. hypoglossi (XII), the location of which in
modern birds typically opens through the exoccipital (Zusi, 1999). The foramen magnum
is a pentagonal opening, mediolaterally wider than it is craniocaudally tall, and more than
four times the size of the occipital condyle. The basioccipital forms the caudal half of the
occipital condyle; basal tubera project caudolaterally giving the basioccipital a ventrally
concave caudoventral margin.
Both dentaries are preserved in lateral view. There were at least seven teeth in
each dentary (Fig. 6.3C). The caudal-most tooth is smaller than the rest. A row of
nutrient foramina runs parallel to the dorsal margin of the dentary, possibly for the veins
that supplied the robust teeth. The dentary is straight; caudal to the dentigerous region,
the ramus expands ventrally. The articulation with the surangular appears unforked,
typical of other Early Cretaceous enantiornithines, such as Eoenantiornis and
Shanweiniao (O’Connor et al., 2009).
The cranial and dentary teeth are nearly the same in size and morphology, with
the one exception noted in the dentary (Fig. 6.3B,C). The teeth are bulbous with a
circular cross section near the root. Distally they bulge slightly along the rostral margin
and then taper quickly into a slightly caudally directed point.

204 

Figure 6.2. Camera lucida drawings of A, DNHM D2950; B, DNHM D2951. Anatomical
abbreviations: al, alular metacarpal; al I, alular phalanx I; al II, alular phalanx II; cau,
caudal vertebra; cor, coracoid; crv, cervical vertebra; den, dentary; dt, distal tarsals; ebc,
external basicranium; fem, femur; fro, frontal; fur, furcula; hum, humerus; ili, ilium; isc,
ischium; jug, jugal; ma, major metacarpal; ma I, major digit phalanx I; ma II, major digit
phalanx II; ma III, major digit phalanx III; mi, minor metacarpal; mi I, minor digit
phalanx I; mtI, metatarsal I; nas, nasal; par, parietal; pcl, pedal claw; pmx, premaxilla; po,
postorbital; pph, pedal phalanx; pub, pubis; qd, quadrate; rad, radius; rib, ribs; sca,
scapula; scl, scleral; stn, sternum; sur, surangular; syn, synsacrum tbt, tibiotarsus; tmt,
tarsometatarsus; tth, thoracic vertebra; uln, ulna.
205 

Figure 6.2., Continued.
206 
Axial Skeleton
The cervical series is incomplete; seven vertebrae, including the atlas and axis, are
preserved. The atlantal hemi-arches appear unfused. The post-axial cervicals are
disarticulated and displaced so that both dorsal and ventral surfaces are visible. The
cranial most post-axial cervicals appear incipiently heterocoelous. The prezygapophyses
project cranially beyond the articular surface; the postzygapophyses are elongate, twice
as long as the prezygapophyses (Fig. 6.3G). The postzygapophyses become more robust
distally through the series. Ventrally, the posterior cervicals possess carotid processes and
a small ventral process but appear unkeeled. Costal processes are unfused to the vertebral
bodies; they are robust proximally, tapering sharply at their distal ends (Fig. 6.3H).
The amphyplatan thoracic vertebrae have elongate and spool-like centra, typical
among enantiornithines (Chiappe and Walker, 2002; Fig. 6.3F). The vertebrae possess
tall neural spines very similar to those of Iberomesornis (Sanz and Bonaparte, 1992); the
postzygapophyses are slightly longer than the prezygapophyses, and both extend beyond
the caudal/cranial margin of the centrum. The parapophyses are centrally located and the
centra bear a deep lateral groove, both features typical of enantiornithines (Chiappe and
Walker, 2002).
The number of vertebrae fused into the synsacrum cannot be discerned (Fig. 6.3I).
The incorporated vertebrae possess transverse processes that increase in length and width
distally; the processes expand distolaterally so that the ends of the distal-most transverse
processes contacted each other as in Pengornis. A single free caudal is preserved; the
207 
transverse processes are elongate, equal in length to the centrum width (Fig. 6.3I). No
pygostyle is preserved.
No uncinate processes are preserved; several slender disarticulated elements near
the pelvic girdle are interpreted as gastralia (Fig. 6.3I).

Thoracic girdle
The strut-like coracoids are flattened making it impossible to determine whether
they bore a dorsal fossa as in some enantiornithines (Eoenantiornis, Neuquenornis; Fig.
6.3E,H). The acrocoracoid process is small and rounded; a procoracoid process is absent
as in other enantiornithines with the exception of Protopteryx (Zhang and Zhou, 2000;
Chiappe and Walker, 2002). The medial margin of the right coracoid appears to have a
groove (Fig. 6.3H) but it is impossible to determine if it is perforated by the foramen
supracoracoideum, as in many other enantiornithines (Chiappe and Walker, 2002). The
lateral margin is strongly convex along the distal quarter as in Concornis (Sanz et al.,
1995); a lateral process is absent. The sternal margin is straight and slightly less than half
the omal-sternal length.
The scapula is long, approximately 50% longer than the coracoid (Fig. 6.3H). The
scapular blade is straight and the distal end is blunt. The acromion (Fig. 6.3E) is long and
straight, as in Eoalulavis, Elsornis, and Shanweiniao (Sanz et al., 1996; Chiappe et al.,
2007).
The furcula is Y-shaped with an interclavicular angle of approximately 50˚ (Fig.
6.3E,H). The omal tips curve dorsally (visible in the right ramus) and bear bulb-like omal
208 

Figure 6.3. Detail photographs of DNHM D2950/1. All scale bars represent one cm: A,
skull in right lateral view; B, upper dentition; C, lower dentition; D, left manus; E,
thoracic girdle, slab 0; F, thoracic vertebrae; G, cervical vertebrae; H, thoracic girdle, slab
1; I, pelvic girdle.
209 
expansions in dorsal view (left ramus) as in Shanweiniao. The rami fuse over a broad
area; the suture forms a ventral ridge that is visible along the entire length of the
hypocleidium. The hypocleidium is long, approximately 70% the length of the rami; it is
keeled dorsally and tapers distally. It cannot be determined if the furcula was laterally
excavated as in other enantiornithines, such as Longipteryx, and Eoenantiornis (Zhang et
al., 2000).
A large piece of the left sternum is preserved allowing a reconstruction of this
structure (Fig. 6.3H). The rostral margin is rounded but the lateral corner is not preserved.
The sternum ends in a simple xiphoid process, which is preserved as a void in both slabs
(Fig. 6.3H). The sternum possesses at least one trabecula interpreted as the outer (lateral
process) trabecula of other enantiornithines, e.g. Shanweiniao, Longipteryx, and
Concornis. It extends laterodistally from the rostrolateral margin of the sternum, as in
Concornis, and ends in a simple fan-shaped expansion that is leveled with the end of the
xiphoid process. The region between the outer trabecula and the xiphoid process is badly
broken so it cannot be determined with any degree of certainty whether an inner trabecula
(medial process) was present. A small groove in the void of the sternum rostral to the
xiphoid could represent a shallow keel (DNHM D2950).

Thoracic limb
The humerus is straight with a moderate deltopectoral crest, less than half the
shaft width (Fig. 6.2, 3). The crest extends for one-third the length of the humerus before
it ends abruptly (as opposed to gradually reducing until absent). The proximal cranial
210 
surface is convex and the caudal surface is concave; the midline of the proximal surface
is concave as in other enantiornithines (Chiappe and Walker, 2002). The bicipital crest
does not appear to project strongly cranially. Similar to the condition in Pengornis, the
ventral tubercle is separated by a shallow capital incision, unlike the deep groove that
separates the ventral tubercle in the El Brete enantiornithines (Chiappe and Walker,
2002). The distal end of the humerus is poorly preserved; the condyles are located on the
cranial surface as in other ornithothoracine birds. The distal margin does not appear
angled ventrally as in some enantiornithines, e.g. Alexornis, Eoalulavis, and Hebeiornis
(Brodkorb, 1976; Zhang et al., 2004).
The ulna is proximally bowed and more robust than the straight distal half (Figs.
6.1, 2). Remige papillae (quill knobs) are absent. Proximally, the olecranon process is
small; distally, the dorsal condyle is large and rounded in profile. The radius is straight
and approximately half the shaft width of the ulna—there is no evidence of the
longitudinal sulcus present in some other enantiornithines (Chiappe and Walker, 2002).
A single proximal carpal is preserved; it cannot be determined if it is the ulnare or
radiale. Two distal carpals are present, interpreted as the semilunate and carpal x
(Chiappe et al., 2007); these remain free from the metacarpal bones, not fusing to form a
carpometacarpus (Fig. 6.3D). The semilunate carpal has a semi-rounded profile with a
straight cranial margin. The caudodorsal surface of the semilunate bears a dorsally
projecting tubercle. Carpal x is rectangular, and located proximal to the minor
metacarpal, fitting with a notch on the caudodistal corner of semilunate carpal. A free
carpal x is known in juvenile enantiornithines, and Longipteryx possesses distal carpals
211 
fused to each other but not the metacarpals (Chiappe et al., 2007). DNHM D2950/1
shares the basal condition of Archaeopteryx with carpals and metacarpals fully unfused in
adults (Wellnhofer, 1974).
The proximal ends of the alular and major metacarpals are nearly aligned. The
alular metacarpal is less than ¼ the length of the major metacarpal; it is wedge-shaped so
that the cranial margin is angled craniocaudally, with the thicker end of the metacarpal
articulating with the digit. The alular digit ends level with the distal end of the major
metacarpal as in Eoenantiornis, Longipteryx, and Eoalulavis. The first phalanx is slightly
bowed and tapers distally. The distal end possesses deep extensor pits and articulates with
a recurved claw. The major metacarpal is robust and increases in craniocaudal thickness
distally. The first phalanx is slightly less than half the length of the major metacarpal; it is
robust and bar like, with a straight cranial margin and slightly convex caudal margin. The
second phalanx is much shorter than the proximal one; it is wedge-shaped, tapering
distally. The third phalanx is a recurved claw, slightly smaller than that of the alular digit.
The minor metacarpal is thinner than the major metacarpal but approximately the same
length. The proximal end of the minor metacarpal is distal to that of the major
metacarpal, offset by the carpal x, so that its distal end projects beyond that of the major
metacarpal, a synapomorphy of enantiornithines (Chiappe and Walker, 2002). The
proximal and distal ends of the minor metacarpal firmly abut the major metacarpal but
the minor metacarpal is slightly bowed, creating a sliver of intermetacarpal space. The
first phalanx of the minor digit is small, less than ½ the length and width of the first
212 
phalanx of the major digit. It is unclear if there is a second phalanx; if present, it would
have been greatly reduced. The minor digit does not possess a claw.

Pelvic girdle
The pelvic girdle is incomplete and entirely disarticulated (Fig. 6.3I). The
preacetabular wing of the ilium is missing on both sides; the postacetabular wing appears
to be broad proximally and tapered distally but the distal half is covered by the ischium
(DNHM D2951). Both ischia are well preserved and in medial view (Fig. 6.3I). The
ischium is approximately half the length of the pubis. Proximally, the ventral process for
articulation with the pubis is much larger than the corresponding dorsal process for the
ilium. The ischium bears a large proximodorsal process but no obturator process. The
ischiadic wing is strap-like and blunt, as opposed to curved and tapered as in Sinornis
(Sereno et al., 2002).
The pubis is disarticulated indicating that the distal ends were not fused, however
the presence of an articular facet on the distal medial surface indicates the two bones
were in contact. The pubes are approximately the same length as the femur and nearly
twice the length of the ischia; they are slightly bowed in lateral view and laterally
compressed with an oval cross-section (Fig. 6.3I). The proximal ends are broad
preserving the articulations for the ischium (convex) and the ilium. Distally, the pubis
possesses a boot-like expansion as in many other basal birds, e.g. Archaeopteryx,
Eoenantiornis, Pengornis, and Yanornis (Zhou and Zhang, 2001).

213 
Pelvic limb
Only the right femur is preserved; the bone is straight but very incomplete and
obscured by the tibia (Fig. 6.3I). The rounded head of the femur is visible at the edge of
the slab. A single incomplete tibia, associated with the right side, is preserved over-
lapping the femur revealing no anatomical information. No fibula is preserved.
The proximal tarsals (astragalus and calcaneum) are fused to each other but not
the tibia (Fig. 6.1, 2, 3I). The astragalus possesses a large sheet-like ascending process
that tapers proximally. A single triangular distal tarsal is preserved free near the
proximal end of the right metatarsals.
Both tarsometatarsi are poorly preserved, one below the pelvic girdle and limb
and the other under the skull (Figs. 6.1, 2). A displaced and disarticulated metatarsal I
along with two claws and a phalanx are preserved in DNHM D2950. The metatarsal I is
J-shaped with a flat laterally directed facet for articulation with metatarsal II and a
caudally directed articular facet for the first phalanx so that the hallux is fully reversed.
Metatarsal III appears to be the longest, followed by metatarsal IV, which is slightly
longer than metatarsal II, but preservation of the distal end of the tarsometatarsus makes
all interpretations equivocal.
The first phalanx of digit I is longer than that of digit II. The second phalanx of
digit II is incomplete but longer than the first. The first phalanx of digit III is the longest
phalanx preserved. The proximal phalanx of digit IV is short, half the length of the
proximal phalanx of digit III. The isolated phalanx is exposed plantarly and deeply
excavated. The two isolated claws clearly do not belong to the manus, as they are larger
214 
and not as recurved as the claws of the wing. The claws differ in size, one being
approximately 150% the size of the other, indicating that the pedal claws were not
uniform in size. The larger of the preserved claws bears a pronounced laterally projecting
longitudinal ridge that extends from the proximal third of the ungual and tapers caudally;
this feature, seen in some ornithomimids, is also present in Rapaxavis and Shanweiniao
but is much more pronounced in the DNHM D2950/1 (Makovicky et al., 2004;
Morschhauser et al., 2009; O’Connor et al., 2009). In the two longipterygids, the ridge
only extends the middle third of the claw and does not project laterally as strongly as in
DNHM D2950/1. The pedal claws preserve long, recurved horny sheaths.

Integument
Feathers are primarily preserved in DNHM D2950 (Fig. 6.1A); there are two
incomplete remiges associated with the right wing and traces of body coverts preserved
throughout, especially around the pectoral girdle and skull.

iv. Discussion
The tooth morphology of DNHM D2950/1 represents a departure from that of the
more typical enantiornithine, whose teeth resemble those of Archaeopteryx (Elzanowski,
2002); teeth are placed throughout the premaxilla, maxilla and dentary, conical with
slightly recurved apices (the apex ends just caudal to the midpoint of the base), slightly
constricted at the base, and without serrations, as in Hebeiornis, and Cathayornis (Zhou,
1995), and the Montsec nestling. Taxa from the Jehol biota, however, have revealed a
215 
large diversity of dental morphologies and patterns. Longipteryx represents one extreme
in the spectrum of caudal curvature, with the apex of the tooth projecting beyond the
caudal margin of its corresponding alveolus (Zhang et al., 2000). Other atypical
morphologies include the reduced peg-like teeth of Longirostravis and Shanweiniao and
the low-crowned rounded teeth of Pengornis (Hou et al., 2003; Zhou et al., 2008a;
O’Connor et al., 2009). The teeth of DNHM D2950/1 are considerably more robust than
the typical enantiornithine, which may be indicative of increased strength and durability,
an adaptation for crushing hard materials such as insects. This morphology is most
similar to that of the recently described Pengornis, although in the latter, the teeth are
proportionately much smaller, far more numerous and have much lower crowns (Zhou et
al., 2008a).
While the exact diet of DNHM D2950/1 and the function of its teeth remain
speculative, the specimen documents a previously unknown tooth morphology unique
among Mesozoic birds. Coupled with the unusually elongate postorbital, DNHM
D2950/1 represents a considerable departure from the typical enantiornithine skull
morphology, indicating that DNHM D2950/1 likely occupied a distinct niche within the
clade, utilizing food items unavailable to other taxa.
216 
CHAPTER 7: MORPHOLOGICAL DESCRIPTION OF SHANWEINIAO COOPERORUM,
A NEW LONGIPTERYGID ENANTIORNITHINE FROM NORTHERN CHINA

CHAPTER 7 ABSTRACT – The complete morphology of a new species of enantiornithine
bird, Shanweiniao cooperorum, from the Lower Cretaceous Yixian Formation of
northeastern China is described. The new specimen possesses several enantiornithine
synapomorphies as well as the elongate rostral morphology (rostrum equal to or
exceeding 60% the total length of the skull) of the Chinese early Cretaceous
enantiornithines, Longipteryx chaoyangensis and Longirostravis hani. The discovery of
this new specimen highlights the diversity of the trophically specialized clade,
Longipterygidae. Shanweiniao provides new information on the anatomy of
longipterygids, and preserves a tail morphology previously unknown to enantiornithines,
with rectrices closely arranged to form a surface. This supports the hypothesis that
enantiornithines were strong fliers and adds to the diversity of known tail morphologies
of these Cretaceous birds.

i. Introduction
Since their establishment as a clade less than three decades ago, Enantiornithes
has become the most specieous group of Cretaceous birds known to science. Though
diverse, enantiornithines are morphologically very similar, and in this respect, often
compared to the modern passerines (Chiappe, 2007). Although their cranial morphology
is not well known because the skull is missing, crushed, or fragmentary in most
217 
specimens, available data shows that most of these birds possess relatively short rostra,
approximately 50% of the total skull length. However, four enantiornithines from the
Lower Cretaceous (~125-120 Ma) Jehol () Group deposits of northeastern China
(Swisher et al., 2002; Zhu et al., 2007), are known to possess a relatively elongate
rostrum: Longipteryx chaoyangensis (Zhang et al., 2000), Longirostravis hani (Hou et al.,
2004), Rapaxavis pani (Morschhauser et al., 2009; Chapter 8) and Shanweiniao
cooperorum (O’Connor et al., 2009). These taxa share several characteristics (elongate
rostrum [here defined as a preorbital length equal to or exceeding 60% of the total skull
length]; upper dentition limited to the premaxilla; lower dentition restricted to the rostral
tips of the dentaries; dentary long, slender, and ventrally concave) (Hou et al., 2004;
Zhang et al., 2000), which suggests they form a monophyletic group of trophically
specialized enantiornithine birds (Chiappe et al., 2006; O’Connor et al., 2009). The new
taxon, Shanweiniao cooperorum, reveals integument previously unknown within the
clade.

ii. Systematic Paleontology
Aves Linnaeus, 1758
Pygostylia Chiappe, 2002
Enantiornithes Walker, 1981
Longipterygidae, Zhang et al. 2000
Shanweiniao cooperorum (Figs. 7.1,2; O’Connor et al., 2009)
218 

Figure 7.1. Holotype (DNHM D1878/1) of Shanweiniao cooperorum. A, photo; B,
camera lucida drawing. Anatomical abbreviations: al, alular metacarpal; al I, first
phalanx, alular digit; al II , second phalanx alular digi; ang, angular; cau, caudal
vertebrae; cmc, carpometacarpus; cor, coracoid; crv, cervical vertebrae; den, dentary;
fem, femur; fur, furcula; hum, humerus; ili, ilium; jug, jugal; ldn, left dentary; mac, major
metacarpal; ma I , first phalanx, major digit; ma II, second phalanx, major digit; max,
maxilla; mi I, first phalanx, minor digit; mt I, metatarsal one; nas, nasal; pmx, premaxilla;
pub, pubis; pyg, pygostyle; qd?, possible quadrate, ; rad, radius; rdn, right dentary; rib,
ribs; sca, scapula; scl, sclerotic ring; stn, sternum; sur , surangular; syn, synsacrum; tbt,
tibiotarsus; thv, thoracic vertebrae; tmt, tarsometatarsus; tth, teeth, , ; uln , ulna; I - IV,
pedal digits; I-(1 - 5) pedal phalanges.
219 

Figure 7.2. Holotype (DNHM D1878/2) of Shanweiniao cooperorum. A, photo; B,
camera lucida drawing. See Figure 7.1 caption for anatomical abbreviations.

220 
Holotype
A nearly complete and largely articulated adult individual preserved in a slab (Fig. 7.1)
and counterslab (Fig. 7.2). The bones contained in the slab, DNHM D1878/1, are exposed
primarily in ventral view, while those in the counterslab, DNHM D1878/2, are mainly
exposed in dorsal view. Feathers are preserved as carbonized traces concentrated around
the head, wings, and tail.

Locality and Horizon
Lingyuan, Liaoning Province, China. Dawangzhangzi Bed, middle Yixian Formation,
Lower Cretaceous (Swisher et al., 2002).

Diagnosis
Shanweiniao cooperorum is a longipterygid enantiornithine that possesses the unique
combination of the following characters: elongate cranium that is 62% rostrum (64% in
Longipteryx; 60-64% in Longirostravis; 65% in Rapaxavis); second phalanx of manual
major digit reduced and wedge-shaped (as in Longirostravis and Rapaxavis; unreduced in
Longipteryx); omal one-third of the clavicular rami dorsally curved; acute (40˚)
interclavicular angle (70˚ in Longipteryx; 55˚ in Longirostravis and Rapaxavis);
clavicular symphysis broad, exceeding the hypocleidium in length (short in Longipteryx,
Longirostravis and Rapaxavis); sternum with simple distal expansions of the lateral
trabeculae (similar to Longipteryx; forked in Rapaxavis; branching, moose-horn
morphology in Longirostravis); intermembral index (humerus + ulna/femur + tibia) of
221 
1.23 (Longipteryx = 1.48-1.51; Longirostravis = 1.07; Rapaxavis = 1.09); tarsometatarsus
with metatarsal III longest and cranially convex, closely approached in length (in order)
by metatarsals IV and II (as in Longirostravis and Rapaxavis; IV longest in Longiptyerx);
pedal unguals relatively unrecurved with large, curved keratinous sheaths; tail composed
of at least four elongate rectrices.

iii. Anatomy
Skull
The skull is preserved in lateral view (Fig. 7.3). It is elongate and delicate. The
rostrum (measured from the rostral margin of the orbit to the rostral margin of the
premaxilla) constitutes 62% of the total skull length, slightly less than the percentage in
Longipteryx and Rapaxavis (estimated at 64% and 65% respectively), and within the
range estimated for Longirostravis, 60-64%. The rostralmost tip of the skull is obscured
where it abuts wing bones, but the presence of alveoli and small teeth can be confirmed
in the premaxilla, indicating that this bird shares with Longipteryx, Longirostravis and
Rapaxavis an edentulous maxilla but dentigerous premaxilla. A lone tooth can be
identified near the rostral portion left of the dentary (Fig. 7.3), but there is no evidence of
either teeth or alveoli along the majority of the length of the dentaries, indicating that
mandibular teeth, if present, were also restricted to the rostral portion of the dentary, as in
Longipteryx, Longirostravis and Rapaxavis. The proximally restricted teeth and overall
delicate and elongate nature of the skull suggests that Shanweiniao may also have
occupied the mudprobing niche of Longirostravis (Hou et al., 2004). Distal
222 
rhynchokinesis is often associated with this ecological adaptation, however preservation
makes it difficult to determine if Shanweiniao (or Longirostravis) possessed this
specialization.
The mandibles are straight (Fig. 7.3), lacking the ventral curvature present in
Longipteryx, Longirostravis and Rapaxavis. Both dentaries are visible in DNHM
D1878/2; the left mandible is preserved in lateral view; a lateral groove paralleling the
tomial edge is marked with small, oval foramina. The right mandible is preserved in
medial view; although crushed, the articulation between the dentary and surangular is
visible. Fragments of thin, curved bones interpreted as the angular bones are preserved
below the mandible and above the right dentary (Fig. 7.3). In DNHM D1878/1, the distal
end of the left dentary is visible; the caudal end shows the caudoventrally slanted and
tapered ancestral condition (unforked), seen in Archaeopteryx lithographica (Elzanowski,
2001) as well as in Longipteryx, Hebeiornis fengningensis and Eoenantiornis buhleri
(Zhang et al., 2004; Zhou et al., 2005).
The frontal processes of the premaxilla are long, approaching 50% the length of
the skull, but the ends are not preserved and their caudal extent cannot be ascertained.
The jugal bar is preserved but displaced dorsally, obscuring the morphology of the
antorbital fenestra. The proximal end of the jugal is covered by the broken and displaced
proximal end of the left dentary. The external nares appear to be retracted caudal to the
rostralmost one-third of the skull. A curved bony margin preserved rostral to the orbit is
interpreted as the displaced caudal margin of the nares. The exact size, shape, and relative
223 

Figure 7.3. Skull of Shanweiniao cooperorum in left lateral view. A, photo; B, camera
lucida drawing. See Figure 7.1 caption for anatomical abbreviations.
224 
position of the nares and antorbital fenestra cannot be determined. A sclerotic ring is
preserved, but the number of individual ossicles is impossible to discern.

Axial Skeleton
Approximately ten poorly preserved but articulated vertebrae are preserved in
ventral (DNHM D1878/1) and dorsal (DNHM D1878/2) view extending from the base of
the skull to a point near the interclavicular symphysis (visible in DNHM D1878/1). The
last vertebra appears to be associated with a long rib and is thus interpreted as a thoracic
vertebra. The exact position of the cervico-thoracic transition is difficult to determine due
to the poor preservation where the vertebrae intersect the pectoral girdle. The cervical
series (eight or nine preserved plus an atlas, for a minimum of nine total) appears to be at
least partially heterocoelous: in the seventh cervical, the cranial articular surface is visible
and transversely concave. Nevertheless, the exact degree of heterocoely present
throughout the cervical series cannot be determined. A small tubercle present on the
dorsal margin of cervical five is interpreted as a spinous process. The postzygapophyses
of the cervical vertebrae are well developed and project caudally beyond the vertebral
body by a distance that exceeds one-third the vertebral bodies total length. The shorter
prezygapophyses extend cranially half the lengths of their caudal counterparts. Cervicals
five, six, and seven preserve thin, elongate caudally directed ribs. The longest (cervical
five) approaches the length of the vertebra. Two poorly preserved thoracic vertebrae are
preserved distal to the sternum in DNHM D1878/2.
225 
A portion of the synsacrum is displaced caudally between the two femora and
exposed in ventral view in DNHM D1878/1 (Fig. 7.2). The piece consists of two or three
fused vertebrae; the transverse processes are long, equal to the width of the vertebral
body, and project perpendicular to the axis of the synsacrum. The distal ends of the
transverse processes are wider than the proximal portion. A groove preserved along the
midline is interpreted as a ventral sulcus, present also in Rapaxavis.
The pygostyle is broken; proximally, the right side bears a process reminiscent of
the dorsal fork present in enantiornithine taxa such as Longipteryx and Halimornis
thompsoni (Chiappe et al., 2002a). The distal margin is broken, although it was clearly
constricted, as in Longipteryx, Rapaxavis, and Halimornis. In DNHM D1878/2, a pair of
keel-like processes are visible running parallel down the midline of the pygostyle;
preservation makes it difficult to ascertain in what view the pygostyle is preserved, so
these processes cannot be definitively correlated to the paired ventral keels seen in the
pygostyle of Halimornis (Chiappe et al., 2002a). The number of vertebrae constituting
the pygostyle likewise cannot be determined.
Short, parallel sternal rib segments are preserved on either side of the sternum.
Visible thoracic rib segments appear to lack ossified uncinate processes on both slabs.
Gastralia, however, are present, preserved disarticulated between the sternum and the
pelvis.

226 

Figure 7.4. Reconstruction of ‘longipterygid’ sterni. A, Shanweiniao cooperorum; B,
Longirostravis hani; C, Longipteryx chaoyangensis.
227 
Thoracic girdle
Both coracoids, preserved in articulation with the sternum, are strut-like. The
sternal margin of each is concave as in Longipteryx, not straight as in Longirostravis and
Rapaxavis. The lateral margin is straight to slightly concave, as in Longirostravis and
Longipteryx, not strongly convex as in some enantiornithines (e.g., Concornis lacustris;
Sanz et al., 1995). In DNHM D1878/2, a slight depression embays on the dorsal surface
of the coracoid. This depression is weak, unlike the deep fossae present in some other
enantiornithine taxa (Chiappe and Walker, 2002) and the basal ornithuromorph Apsaravis
ukhaana (Clarke and Norell, 2002). The coracoid neck is simple, lacking a procoracoid
process, as in other enantiornithines. No supracoracoideus nerve foramen is visible.
In ventral view (DNHM D1878/2), the right scapula is preserved in articulation
with the right coracoid such that the blade is covered by the coracoid. It possesses a
robust and elongate acromion as in the Spanish enantiornithine Eoalulavis hoyasi (Sanz
et al., 2002). In DNHM D1878/1 the scapular blade is exposed in costal view; it is long
and straight, with no visible groove like those reported in the enantiornithine material
from El Brete, Argentina (Chiappe and Walker, 2002). The scapula exceeds the coracoid
in length; the distal end is blunt, tapering only very slightly.
The furcula of Shanweiniao, preserved in DNHM D1878/1, is narrow and Y-
shaped. The morphology and exact length of the long, poorly preserved hypocleidum
relative to the rami cannot be determined, though it is clearly at least one-third the length
of either ramus. The rami are each approximately as long as the coracoid. The omal one-
third of each ramus is curved dorsally and the omal tip slightly expanded. The caudal end
228 
of the clavicles fuse over a broad area so that the symphysial portion of the furcula is
nearly the same length as the hypocleideum unlike other longipterygids in which the
symphysis is restricted. The interclavicular angle is acute, describing an angle of
approximately 40˚, which is much smaller than those of Longirostravis (55˚) and
Longipteryx (70˚).
The sternum is preserved in dorsal view (DNHM D1878/2) but badly broken (Fig.
7.2). The proximal portion is displaced along a small crack that runs diagonally through
the element, offsetting the proximal portion of the right humerus as well (DNHM
D1878/2). The cranial margin of the sternum appears to be rounded. A large, well-
preserved piece clearly shows the morphology of the right lateral and medial trabeculae,
as well as the morphology of the midline, which allows a confident reconstruction of its
overall morphology (Fig. 7.4). The distal end of the right lateral trabecula is slightly
broken, but the morphology appears to have been relatively simple: straight with the
distal end only slightly expanded. The cross-sectional profile of each lateral trabecula
appears to change from dorsoventrally oval proximally to spatulate at the distal end, but
this may be a preservational artifact. The branching, “moose-antler morphology” of
Longirostravis remains an autapomorphy of that taxon. The medial trabeculae are smaller
than the lateral trabeculae (~one-third the length); their axes are slightly angled medially
with respect to the lateral trabeculae and sternal midline. The caudal margin of the
sternum forms a relatively long xiphoid process, which projects slightly farther caudally
than the lateral trabeculae, unlike Longirostravis and Rapaxavis in which the lateral
trabeculae project furthest. Distally as in the lateral trabecula, the xiphoid process
229 
expands slightly, and its distal margin is straight. The distal end of the sternum, like
Longipteryx, Longirostravis and Rapaxavis, is imperforate, as opposed to the condition in
several ornithuromorph taxa (e.g., Yixianornis, Yanornis, and Songlingornis linghensis;
Clarke et al., 2006).

Thoracic Limb
The humerus is only partially preserved on both sides. The proximal tip of the
right humerus is preserved in DNHM D1878/2, broken and displaced; its head displays
the typical enantiornithine condition: concave on the midline, rising dorsally and
ventrally. The left humerus, preserved in pieces in both slabs, indicates that the
deltopectoral crest was weak, transversely measuring less than the width of the shaft. The
distal margin (right humerus DNHM D1878/1) is angled, but not as strongly as in some
enantiornithines (e.g., Longipteryx, Rapaxavis, Alexornis; Brodkorb, 1976).
The ulna and radius are nearly equal in length. The ulna is robust, approaching the
width of the humeral shaft. The ulna is slightly bowed, creating a proximal interosseous
space between it and the radius that closes distally. The dorsal and ventral condyles and
the carpal tuberosity are visible on the distal end of the left ulna (DNHM D1878/2). The
two condyles are weakly developed and not separated by a deep sulcus; the dorsal
condyle appears to form a semilunate ridge. The carpal tuberosity (also visible on the left
side of DNHM D1878/2) is prominent and not separated from the ventral condyle by an
incisure as in some neornithines (e.g., Cathartes).
230 
The radius is straight and half the width of the ulna. The presence of a
longitudinal groove cannot be determined.
A cup-shaped structure preserved between the ulna, radius and underlying
metacarpal bones is interpreted as the carpal trochlea of the carpometacarpus. An
indeterminate fragment located dorsolateral to the right manus in DNHM D1878/2 may
represent at least part of the ulnare or radiale.
The manus of Shanweiniao is reduced, as in Longirostravis and Rapaxavis; based
on the available specimen, it appears to be 2-2-1-x-x but is likely to have been 2-2-2-x-x,
as in Longirostravis, which has two phalanges in the minor digit (personal observation),
the second being extremely reduced. The alular digit is covered proximally by the ulna
and radius. The distal half of the first phalanx of the alular digit is straight (DNHM
D1878/2). A fragment in DNHM D1878/1 is interpreted as the second phalanx; it is
reduced and wedge-shaped, approximately the same size as the lone preserved minor
digit phalanx. The major digit possesses two phalanges, lacking the large claw present in
Longipteryx. The first phalanx is cylindrical and not dorsoventrally expanded as in more
advanced birds (e.g., Gansus yummenensis, Neornithes; You et al., 2006). The distal
phalanx is wedge-shaped and tapers distally. The single preserved phalanx of the minor
digit is cylindrical in shape and approximately the same size as the distal phalanx of the
major digit. The relative lengths of the metacarpals and the degree of fusion present in the
carpometacarpus cannot be determined.
231 

Figure 7.5. Left tarsometatarsus of Shanweiniao cooperorum in dorsal view. A, photo; B,
camera lucida drawing. See Figure 7.1 caption for anatomical abbreviations.
232 
Pelvic Girdle
The pelvic girdle is preserved primarily in DNHM D1878/2, including portions of
both ilia and pubes (Fig. 7.2). Details of the preacetabular wings of the ilia are not clear.
The right acetabulum contains the broken head of the right femur. The pubic peduncle is
long, but it cannot be ascertained if the new taxon shares the same laterally compressed
and hooked condition seen in Longirostravis and Longipteryx. The postacetabular wing
of the left ilium, preserved in lateral view, is directed slightly ventrally, rendering the
ventral margin concave. The distal end tapers, as in Longipteryx, Rapaxavis and other
enantiornithines (e.g., Eoalulavis, Cathayornis yandica; Zhou, 1995; Sanz et al., 2002).
The ventral margin of the ilium bears a large, rounded antitrochanter. The delicate, rod-
like pubis is short, approximately equal to the femur in length, but more than twice the
length of the postacetabular wing of the ilium. The pubes together form a caudally
directed V, indicating that they were likely retroverted. The distal ends, not preserved,
approach each other as if to form a short pubic symphysis.

Pelvic Limb
The hindlimb is shorter than the forelimb. The intermembral index (ImI,
measured as the sum of the lengths of the humerus and ulna divided by the sum of the
lengths of the femur and tibiotarsus) measures approximately 1.23, intermediate between
Longipteryx (ImI = 1.5) and Longirostravis (ImI = 1.07). In DNHM D1878/2, the left
femur is preserved in ventral view and the right femur in lateral view. The proximal
portions of both femora are preserved in DNHM D1878/1. The femur is shorter than the
233 
tibiotarsus and longer than the tarsometatarsus. The femur is slightly bowed
craniocaudally; the head is round and directed at an angle of 90° from the shaft. The
trochanteric crest is separated from the femoral head by a distinct neck and projects
farther proximally than the femoral head. Distally, both a fossa for the insertion of the
capital ligament and a patellar groove are absent. In lateral view, the femur lacks the crest
present in some enantiornithines (e.g., the El Brete material; Chiappe, 1996). A
tibiofibular crest is also absent.
Both tibiotarsi are preserved in DNHM D1878/2. Each is more than double the
length of the tarsometatarsus. The right tibiotarsus is preserved in lateral view and the left
in caudal view. The lateral condyle is visible on the distal end of the right tibiotarsus. A
faint fibular crest is visible 4 mm from the proximal end of the right tibiotarsus. The
fibula is preserved in articulation with the left tibiotarsus in DNHM D1878/2. Its
proximal end is wedge shaped. The void of the left fibula in DNHM D1878/1 indicates
the bone extended for at least half the length of the tibiotarsus.
The feet are primarily preserved in dorsal view in DNHM D1878/1 and in plantar
view in DNHM D1878/2, although voids of the dorsal view are also preserved in DNHM
D1878/2. The tarsometatarsus is short and proximally fused, with suture lines visible
distally. Proximally, an intercotylar eminence is absent. The metatarsals are subequal in
mediolateral width. Distally, the third metatarsal extends farthest but is closely
approached by the fourth. The second metatarsal is the shortest, but it approaches the
metatarsal IV in length: the distal end of metatarsal II surpasses the proximal end of the
trochlea of metatarsal IV. Metatarsal I, preserved in lateral view, is reversed and
234 
transversely compressed with a convex dorsal margin; whether it was straight or J-shaped
cannot be determined. Metatarsal I articulates low on the tarsometatarsus, as in
Longipteryx and Rapaxavis. A dorsal tubercle on metatarsal II lies approximately 3 mm
from the proximal end of the tarsometatarsus. As in Longipteryx, it appears to be located
more on the dorsal surface as opposed to the lateral surface of metatarsal II (e.g.
Apsaravis; Clarke and Norell, 2002). Metatarsal III is transversely convex in dorsal view.
In DNHM D1878/2, the left tarsometatarsus is preserved in caudoventral view, and it is
clear that a hypotarsus is absent.
The feet are visible on both sides of both slabs; the left foot in DNHM D1878/1
preserves the most information (Fig. 7.5). The pedal phalangeal formula is 2-3-4-5-x. The
first phalanx of the hallux is longer and more slender than the proximal phalanges of
digits II-IV. In each digit, the penultimate phalanx is longer than the preceding phalanges.
The total length of each digit, except the hallux, exceeds the length of the
tarsometatarsus. The first phalanx of the second digit is approximately two-thirds the
length of the penultimate phalanx, which is the longest phalanx in the entire foot. The
two proximal phalanges of digit III are approximately equal to each other and shorter
than the proximal phalanx in digit II. The penultimate phalanx in digit III is shorter than
that of digit II. The proximal three phalanges in digit IV are subequal and each is
approximately half the length of the penultimate phalanx. The claws of all the pedal
digits (including the hallux) are large, subequal in size and triangular in shape, lacking
both strong degrees of curvature and strong flexor tubercles. The ungual of digit II,
including its keratinous sheath, nearly exceeds the length of the preceding two phalanges
235 
combined. A longitudinal crest on the central portion of the claw is visible in the best-
preserved unguals (left digits II and IV on DNHM D1878/1 and digit III in DNHM
D1878/2) and is also present in Rapaxavis and ornithomimid theropods (e.g.,
Struthiomimus altus, Harpymimus okladnikovi; Makovicky et al., 2004). Horny sheaths
are preserved, giving the claws a sickle shape. The sheaths appear to lack the distal
constrictions interpreted as wear facets seen in some climbing birds (e.g., Picoides;
personal observation).

Integument
Carbonized traces of feathers are preserved throughout the specimen. Wing
feathers are present, but the exact number of primaries and secondaries is difficult to
determine. The outermost contour (presumed to be a primary) is estimated at 82 mm,
measured from the impression of the right wing in DNHM D1878/1.
Tail rectrices are preserved in both slabs and are most clearly visible in DNHM
D1878/1. Four rachises are clearly discernable, indicating the presence of four vaned,
long and slender rectrices. The feathers are incomplete, missing their proximal and distal
ends. The vanes of these rectrices are parallel to one and another and directed toward the
pygostyle. The outline of the right wing is complete in DNHM D1878/1 and does not
overlap the rectrices. The vanes of the wing feathers are also directed at a different angle
from that of the tail feathers, further supporting that these feather impressions do not
represent wing elements. Because the distal most ends are not preserved, it cannot be
determined if the rectrices were graded, as in Yixianornis. Upper- and under-tail covert
236 
feathers are also preserved on the lateral margins of the pygostyle. See Chapter 10 for a
discussion of enantiornithine rectricial morphologies.

iv. Discussion
This holotype specimen of Shanweiniao cooperorum shows several distinct
morphologies associated with longipterygids (i.e. elongate rostrum, robust pygostyle) and
a unique aerodynamic tail morphology making it an important specimen, but is otherwise
poorly preserved. An early phylogenetic analysis lent support to morphological
inferences that this new specimen is related to Longirostravis and Longipteryx (O’Connor
et al., 2009). As in DNHM D2950/1, DNHM D1878 ½ is preserved in two slabs but
many individual bones are broken between both slabs, not presenting bone surfaces as in
the former specimen. This greatly affects the amount of information available from the
specimen for cladistic analysis, and the certainty in which some information can be
scored. This specimen, although complete, preserves fewer detailed morphologies than
DNHM D2950/1 (previous chapter) and translates into a greater amount of missing data
when scored for cladistic analysis. The phylogenetic placement of specimens with higher
amounts of missing data are more vulnerable to changes in character or taxon sampling,
relative to well known specimens. Additional discoveries of Shanweiniao will certainly
elucidate the morphology of the taxon, and may also affect how the taxon is resolved in
phylogenetic analysis (see Chapter 12).

237 
CHAPTER 8: A REDESCRIPTION OF THE HOLOTYPE OF RAPAXAVIS PANI (AVES:
ENANTIORNITHES) AFTER PREPARATION

i. Introduction
Recently, yet another new genus of enantiornithine was described from the
Jiufotang Formation of northeastern China; the holotype of Rapaxavis pani (DNHM
D2522) is one of the best-preserved and most complete enantiornithines described to date
(Morschhauser et al., 2009). Unfortunately, the specimen did not receive proper
preparation prior to study (Fig. 8.1; Morschhauser et al., 2009), and thus many details
incorporated in Chapters 4, 5 and 12 were not clear at the time of the original study or
were interpreted differently in published data (Morschhauser et al., 2006; Morschhauser
et al., 2009). This specimen is important for several reasons; it is one of few well-
preserved Chinese specimens contained in a single slab and therefore has the potential to
reveal new information about enantiornithine anatomy. It also preserves an intriguing pair
of unidentifiable ossifications first observed in this specimen and later identified in
Concornis. These paired bones present an interesting biological puzzle that requires
further investigation. Increasing the amount of morphological data available for
individual taxa can ameliorate the results of cladistic analysis by augmenting the
accuracy, precision, and completeness of the data for this OTU. In addition, this
specimen has a well-preserved skull worthy of description that contributes to our
understanding of the cranial morphology of the clade.
238 
Rapaxavis belongs to the most diverse clade of Early Cretaceous enantiornithines,
Longipterygidae (synonyms: Longirostravisidae, Longipterygithidae; Zhou and Zhang,
2006a), which is currently known to consist of four taxa (Zhang et al., 2000; Hou et al.,
2003; Morschhauser et al., 2009; O’Connor et al., 2009; see Chapters 7 and 12). The
group is characterized by cranial modifications associated with trophic specialization,
namely an elongate rostrum. The rostral proportions that characterize this clade represent
a distinct departure from the typical enantiornithine, which may have facilitated the
diversification of the group (Chapter 4). Further investigation of this clade will help to
create a better understanding of higher-level enantiornithine diversity as well as trophic
specialization.
The original study of the specimen preceded any form of preparation (Fig. 8.1).
The specimen was later prepared by an amateur, during which the fossil was damaged
(Gao pers. comm.; O’Connor pers. obs.); after preparation by this unnamed individual, a
preparator from the Natural History Museum of Los Angeles, Aisling Farrell, attempted
to mitigate the affects of the first preparation (Fig. 8.2). The specimen was studied before
and after its preparation, and thus a complete description of the animal, including details
both originally hidden in matrix as well as those lost, is provided.

ii. Systematic Paleontology
AVES Linnaeus, 1758
ENANTIORNITHES Walker, 1981
LONGIPTERYGIDAE Zhang et al., 2000
239 
RAPAXAVIS PANI, Morschhauser et al., 2009

Holotype
DNHM D2522, a nearly complete, near completely articulated adult individual preserved
in a single slab of buff tuffaceous shale (Fig. 8.1,2). The bones are preserved primarily in
ventral view. No feathers are preserved.

Type Locality and Horizon
Lianhe, Chaoyang, Liaoning Province, China. Lower Cretaceous Jiufotang Formation
(Swisher et al., 1999, 2002).

Amended Diagnosis
The morphology of the outer trabecula (caudolateral process) of the sternum is differently
interpreted here, however the morphology is still unique (proximally straight and distally
forked). The number of sacral vertebrae is six or seven, and the number of sacrals and
caudals is not known to be diagnostic of enantiornithines (though it does vary). An
alternative diagnosis is proposed in the format preferred here. A small longipterygid
enantiornithine bird characterized by the unique combination of the following
morphological characters: rostrum approximately 60% skull length; teeth rostrally
restricted; premaxillary process of maxilla approximately three times longer than the
jugal process; nasals lacking maxillary process, external nares schizorhinal; furcula with
short interclavicular symphysis and interclavicular angle of 50˚; coracoid lateral and
240 

Figure 8.1. Photograph of DNHM 2522 before preparation.
241 

Figure 8.2. Photograph of DNHM 2522 after preparation.
242 
sternal margins straight; coracoidal facets of sternum defining an obtuse angle of
approximately 110˚; sternal lateral trabecula distally forked; first phalanx of alular digit
and second phalanx of major digit reduced to sharply tapering triangular splints (all
manual claws absent); femur 80% the length of the ‘tibiotarsus’; and penultimate pedal
phalanges longer than preceding.

iii. Description
Skull
The skull (Fig. 8.3) is crushed and preserved in right lateral view. The premaxilla
is similar to Longirostravis; the maxillary process is long but relative to the length of the
facial margin its contribution is restricted rostrally. The maxillary process of the
premaxilla articulates laterally with the maxilla; the exact length of this articulation is not
clear due to overlap and the delicate nature of this process. The premaxillary process of
the maxilla tapers rostrally while the premaxilla tapers caudally (Fig. 8.3C). The
premaxilla preserves three teeth, which are large compared to Longirostravis but still
much smaller than those of Longipteryx. All teeth are restricted rostrally, as in other
longipterygids, located in the premaxillary corpus, before the premaxilla splits into
maxillary and nasal processes. The rostral half of the rostrum appears imperforate but the
external nares are slit-like (schizorhinal), and may have been quite long but, due to the
slight disarticulation of cranial elements; the external nares is only visible where it
widens distally in the caudal half of the rostrum. The nasal (frontal) processes of the
premaxilla are elongate and appear to extend to the level of the frontals, excluding the
243 

Figure 8.3. A, detail photograph of the skull of DNHM 2522 before preparation, B, after
preparation, and C, camera lucida drawing. Anatomical abbreviations: den, dentary; jug,
jugal; max, maxilla; nas, nasal; pmx, premaxilla; qd, quadrate; sur, surangular.
244 
nasals from the midline or dorsal margin of the skull. The nature of the premaxillary
articulation with the frontals is unclear but the premaxilla clearly reached beyond the
rostral margin of the orbit. The nasal processes are unfused along their entire lengths but
it is unclear if the premaxillae were fused rostrally. The nutrient foramina present in
Longirostravis and interpreted as indicative of a horny beak (Hou et al., 2003) appear
absent in Rapaxavis, contra Morschhauser et al. (2009), however the bone surface is not
well preserved in this region.
The maxilla forms a majority of the facial margin; the articulation with the
premaxilla is elongate. The caudodorsally directed nasal process is very delicate and
appears not to be lined medially by a recessed bony wall as in Pengornis (Zhou et al.,
2008a). The premaxillary process is much longer than the jugal process (approximately
three times). The caudal articulation with the jugal is unclear. The strap-like jugal,
preserved with the rostral end slightly displaced dorsally (figured in Morschhauser et al.,
2009), was lost during the preparation of this specimen (Fig. 8.3A). As in other
longipterygids, the maxilla appears edentulous; nutrient foramina are also absent from the
maxilla.
The nasals are exposed in two views, the right in lateral view and the left in
ventral view (Fig. 8.3B,C). The nasals appear to lack a maxillary process; they are
elongate, rostrally tapering to a needle-like point and caudally expanding to form a
rounded caudal margin. The medial margin, which formed an unfused articulation with
the lateral margin of the nasal process of the premaxilla, is straight. The nasals extended
245 
for the caudal half of the premaxilla. The nasal may have been perforated caudally by a
small, rostrocaudally elongate oval foramina, as in Pengornis (pers. obs.).
The orbit and postorbital regions are poorly preserved. No lacrimal is identifiable.
A small L-shaped bone may represent the quadratojugal or the distal end of the jugal. It
appears to contact a triangular bone that may represent a postorbital. The bone in
question is triangular, broad proximally, with a dorsally concave margin. It tapers
ventrally towards the contact with the L-shaped bone.
A quadrate is preserved, displaced towards the cervicals (Fig. 8.3B,C). We
interpret the bone as in caudal view; if this is correct, then a pneumatic foramina is
absent. The otic process is single headed; the medial condyle of the mandibular process is
approximately twice the size of lateral condyle. The quadrate appears similar to that of
Pengornis; interpretations of the bone are equivocal but if correct, the quadrate in these
taxa are bowed craniocaudally (appear straight in Eocathayornis, DNHM D2950/1).
The frontals are rostrocaudally elongate, and may have articulated rostrally with
the premaxilla and or nasals. Although not entirely clear, the caudoventral margin forms
a ventrocaudally concave unfused contact with the parietals. The parietals are petal
shaped with the tapered margin creating a small orbital contribution.
The mandibular bones remain unfused. The dentary and surangular are both
straight. Mandibular fenestrae are absent. Two teeth are preserved in the dentary.

246 

Figure 8.4. Select camera lucida drawings of DNHM D2522 exposed in ventral view: A,
synsacrum; B, distal caudals and pygostyle.
247 
Axial Skeleton
The cervicals preserve little information and the thoracic vertebrae are mostly
covered by the sternum (Fig. 8.2). Given the articulated and flattened nature of the
cervicals, whether or not the articulations are heterocoelic cannot be determined (contra
Morschhauser et al., 2009). A few disarticulated thoracic vertebrae reveal elongate spool-
like centra with amphyplatan articular surfaces. The synsacrum is composed of six or
possibly seven fully fused vertebrae (Fig. 8.4A; six in Morschhauser et al., 2009); this
element appears dorsoventrally flattened distally. The lateral processes of the fused
vertebrae enlarge caudally, but do not appear to contact. A ventral groove persists along
the entire surface but is more pronounced on the third to fifth vertebrae. The cranial
articular surface is only slightly concave; the caudal articular surface appears flat, but this
is not entirely clear.
There are six free caudals; the lateral processes exceed the centrum in
mediolateral length. The articular surface is approximately equal in size to the nerve
foramen. The caudals bear a small neural spine; lateral processes appear to become
increasingly caudally deflected distal in the series.
The pygostyle (Fig. 8.4B), preserved in ventral view, is excavated which we
interpret as the presence of ventrally directed lateral processes, as in the longipterygids
and other enantiornithines (Halimornis, Cathayornis, Dapingfangornis; Chiappe et al.,
2002a; pers. obs.). Where the caudal excavation ends, the pygostyle constricts
mediolaterally in a step-like fashion, before forming a bluntly tapered caudal margin, also
consistent with longipterygids and some other enantiornithines (Chiappe et al., 2002a;
248 
Sereno and Rao, 1992; Hou et al., 2003). A dorsal fork, also characteristic of
enantiornithine pygostyle morphology (i.e. Halimornis, Cathayornis, Longipteryx) cannot
be determined. The relative size and robustness of the pygostyle is also consistent with
longipterygids.

Thoracic girdle
The furcula is V-shaped; an elongate hypocleidium nearly 50% the length of the
furcular rami was lost during preparation (Fig. 8.1,2). The clavicular symphysis is short,
as in Longipteryx. The ventral margin of the furcula does not form a keeled surface or
bear a ventral ridge as in some enantiornithines (Dapingfangornis, DNHM D2950/1;
pers. obs.). The omal tips taper bluntly and slightly longer than originally published (Fig.
8.5A,B; omal tips covered in matrix).
The lateral margin of the strut-like coracoid is essentially straight, as in
Longipteryx and Iberomesornis, lacking the strong convexity that typically characterizes
enantiornithines (Chiappe and Walker, 2002). A procoracoid process is absent, as in most
enantiornithines (Chiappe and Walker, 2002). No medial groove or supracoracoiduem
nerve foramen is visible. The dorsal surface of the coracoid may have been slightly
excavated, as evidenced by a slight convexity of the ventral surface, but a deep dorsal
fossa like that of Enantiornis was definitely absent (Chiappe and Walker, 2002). The
short sternal margin is straight. The basic shape of the coracoid body is a triangle; the
inner angle formed by the medial and sternal margins is slightly more acute than the
249 

Figure 8.5. A, B, close up of thoracic girdle before and after preparation; C, D, close up
of sternum left outer trabecula before and after preparation; E, F, close up of left
tarsometatarsus before and after preparation.
250 
lateral, however a distinct median process (angulus medialis; Baumel and Witmer, 1993)
is not considered present (contra Morschhauser et al., 2009).
Only the left scapula is preserved and only the proximal half is visible in medial
view. The acromion is large and straight with kidney shaped articular surface; the
tubercle described on the acromion (Fig. 8.5A; Morschhauser et al., 2009) with matrix
removed is reinterpreted as the dorsomedial margin of the articular surface of the
acromion (Fig. 8.5B). The scapular blade appears to have a costal excavation, as in
Elsornis (Chiappe et al., 2007).
The sternum is quadrangular; the rostral margin is a caudally obtuse angle (110˚)
defined by the coracoidal sulci. There is no rostral midline notch as in Eoalulavis (Sanz et
al., 1996). The coracoidal sulci are adjacent, separated by a distance no greater than half
the width of the sternal margin of the coracoid. There are no costal facets visible; five
sternal ribs are preserved tightly associated on the left side (four on right), however they
are associated with numerous other rib fragments and the total number of sternal ribs may
have been greater (5-7). The lateral margin of the sternum is straight; the outer trabecula
is strongly forked distally. A third process is described on the outer trabecula by
Morschhauser et al. (2009); they correctly postulated that this may represent a displaced
fragment of bone, however still considered the morphology an autapomorphy of the
taxon. Preparation reveals that the third process is a small rib fragment (Fig. 8.5C,D). The
inner trabecula is small and triangular. The caudal margin forms a wide V from the
medial margin of the inner trabecula before constricting to a short xiphoid process. The
distal ends of the outer trabeculae extend caudally beyond the xiphial region. The
251 
sternum bears a short ridge that diverges cranially, reminiscent of the keel in some
enantiornithines (Chiappe et al., 2007; Zhou, 2002). Alternatively, this may be a
diagenetic artifact, resultant from the underlying thoracic vertebrae as the ridge is only
preserved diverging left (considered absent, Morschhauser et al., 2009).
The thoracic girdle of this specimen includes an additional pair of ossifications of
indeterminant function and homology. These ossifications are acute triangles, located
lateral and dorsal to the articulation of the coracoids with the sternum (Fig. 8.6A). The
surface of these elements is porous (Morschhauser et al., 2009); even after preparation
there is still matrix embedded on the surface, evidence of the numerous small pits on the
surface of these bones. Since this element is new and no previous information is known
on its origin or function, it cannot be determined if the porous surface is indicative of
incomplete ossification or simply the nature of the element in this taxon.

Thoracic limb
The humeri are both preserved in cranial view (medial view, Morschhauser et al.,
2009). The proximal margin in cranial view is concave on the midline, rising dorsally and
ventrally, as in other enantiornithines (Chiappe and Walker, 2002). The bicipital crest
forms a cranial projection relative to the shaft, but is not hypertrophied as in other
enantiornithines (i.e. Eoalulavis, E. leali). The deltopectoral crest is narrow, less than
shaft width, and tapers distally; it appears projected dorsally, contra Morschhauser et al.
(2009). Distally, the dorsal condyle is smaller than the ventral, which is a transversely
252 

Figure 8.6. A, close up of pectoral region of DNHM D2522; B, close up of pectoral
region of Concornis lacustris LH-2814.
253 
elongate oval. The distal margin is angled relative to the shaft width, but not as strongly
as in some taxa (i.e. Alexornis).
The ulna is robust, subequal to the humerus in length and approaching it in
mediolateral width. The bone is bowed proximally and straight distally. The ventral
cotyla is slightly concave. The radius is rod-like, and nearly half the mediolateral width
of the ulna. A large triangular bone preserved in articulation with the ulna on both sides is
interpreted as the ulnare (as in Morschhauser et al., 2009).
The degree of proximal fusion of the carpometacarpus is difficult to discern but
the individual bones can for the most part be distinguished suggesting they were not
completely fused. Distally, the major and minor metacarpals are clearly unfused.
Proximally, the semilunate carpal does not overlap with the rectangular alular metacarpal.
The major metacarpal is thicker than the minor metacarpal; the two bones closely abut for
their entire length. As in other enantiornithines (i.e. Longipteryx, Pengornis, Hebeiornis),
the minor metacarpal is contiguous with the pisiform process forming a ridge on the
ventral surface of the carpometacarpus (described as the major metacarpal diving under
the minor proximally; Morschhauser et al., 2009). The minor metacarpal projects distally
further than the major metacarpal, a synapomorphy of enantiornithines. Distally, the
minor metacarpal bears a small tubercle on the caudal margin.
The digits of Rapaxavis are extremely reduced; the alular digit consists of a single
short phalanx that tapers distally, ending far proximal to the distal end of the major
metacarpal. The major digit possesses only two phalanges; the first is “normal” and
cylindrical in shape. The second tapers distally and appears to have a semi-keeled cranial
254 
margin. The minor digit consists of a single phalanx; it is wedge-shaped, approximately
half the width and thickness of the first phalanx of the major digit. The hand of
Longirostravis is disarticulated and incomplete (alular digit not preserved) and thus it
cannot be ascertained for certain if their manual morphology is the same (contra
Morschhauser et al., 2009); the manus in the latter taxon is however clearly reduced.

Pelvic girdle
The pelvic girdle was completely unfused. Both ilia are preserved in medial view
(interpreted as lateral view by Morschhauser et al., 2009); the right is disarticulated and
slightly displaced. The preacetabular process of the ilium has a broad, rounded cranial
margin. The postacetabular process of the ilium is strap-like and less than half the
thickness of the preacetabular process. The caudal margin is not preserved on either side,
but it is estimated the postacetabular process was shorter than the preacetabular process
by 25-35%.
The ischium is long, two-thirds the length of the pubis. The iliac peduncle is
narrow and longer than the broad pubic peduncle. It possesses a stout dorsal process,
visible on the right ischium, located on the proximal dorsal margin of the shaft; it cannot
be determined if this process contacted the ilium as in some other enantiornithines
(Chiappe and Walker, 2002). As in other enantiornithines, there is no obturator process
(Chiappe and Walker, 2002). The ischia are strap-like for most of its length (contra
Morschhauser et al., 2009). The distal end is covered but the two ischia curve medially
the distal quarter, appearing to contact. In medial view (visible on the right) the ischium
255 
appears to have possessed a laterally directed ventral flange that extended the distal half
of the bone. The pubes are unfused to each other but curve medially and would have
formed a short symphysis; the distal end is expanded into a small boot as in some
enantiornithines and most basal birds (i.e. Longipteryx, Confuciusornis, Archaeopteryx).
Morschhauser et al. (2009) describe the pubes as kinked but it appears they are
caudodorsally concave throughout their length, rather than forming a distinct kink (Fig.
8.2).

Pelvic limb
The femur is long, more than ¾ the length of the tibiotarsus (80%), and bowed
craniocaudally. The femora are both preserved in medial view (right in craniomedial
view) with the lateral margin embedded in the slab making it difficult to describe the
morphology of the trochanters. The ‘tubercle on the trochanter’ described by
Morschhauser et al. (2009), appears to have been artifact of the incomplete removal of
matrix along the craniolateral margin of the right femur. The femoral head is separated
from the shaft by a distinct neck; with the current preparation it appears a fossa for the
femoral origin of m. tibialis cranialis was absent.
There is no true tibiotarsus – the proximal tarsals are fused to each other but not to
the tibia, as in DNHM D2950/1 (may be ontogenetic, see Chapter 9). Contra
Morschhauser et al. (2009), no cnemial crests are preserved and if they were present,
were poorly developed. As observed by Morschhauser et al. (2009) the distal fifth of the
tibia bears a shallow cranial sulcus. The sulcus appears to be oriented distomedially; a
256 
similar morphology has been observed in a Xiagou enantiornithine (CAGS-04-CM-006)
and interpreted as the retinaculum extensorus (Baumel and Witmer, 1993). The distal
condyles are subequal in size and taper towards each other; the lateral surface of the
lateral condyle may have had a lateral epicondylar depression, as in CAGS-04-CM-006
and Lectavis (Chiappe, 1993). The fibula is triangular, fat proximally, swiftly tapering to
a splint, and only extending for the proximal third of the tibia.
A true tarsometatarsus is also absent as in DNHM D2950/1; the distal tarsals are
fused together but remain free from the metatarsals, also present in DNHM D2950/1.
Proximal fusion between the metatarsals was reported (Morschhauser et al., 2009);
although the metatarsals are preserved in tight articulation they are here interpreted as
entirely unfused (Fig. 8.5E,F). Fusion of the tarsometatarsus is subject to ontogenetic
change and given the unknown developmental stage of DNHM D2522, it cannot be
determined if this is the true morphology of the taxon or a juvenile feature of the
specimen. Proximally, metatarsal II bears a poorly developed tubercle in its dorsolateral
surface, contacting metatarsal III. Metatarsal III is slightly thicker than II and IV, which
are subequal. Metatarsal III is the longest, closely followed by metatarsal IV, which is
longer than metatarsal II. The distal trochlea of metatarsal III is slightly wider than that of
the other metatarsals. The sulci on the cranial surface of the distal end of metatarsals II-
IV is observed and also concluded to represent crushing (Morschhauser et al., 2009).
Metatarsal I is straight in medial view and medially concave in cranial view (not
a J-shaped metatarsal characteristic of some enantiornithines, i.e. Neuquenornis; contra
Morschhauser et al., 2009) and between a quarter to a third the length of metatarsal III.
257 
The hallux is long and slender. The first phalanx of the second digit is short and robust;
the penultimate phalanx is long, approximately equal in length to the first phalanx of the
hallux. The third digit is the longest in the foot; the proximal two phalanges are subequal.
The penultimate phalanx is 50% longer than the preceding phalanx. The first three
phalanges of the fourth digit are approximately equal and the shortest phalanges in the
foot. The penultimate phalanx is nearly double the length of preceding phalanx. These
pedal phalangeal proportions are consistent with an arboreal lifestyle (Hopson, 2001;
Morschhauser et al., 2009). All claws are hooked, broad proximally then curving distally.
They possess laterally projecting ridges, also present in some other enantiornithines
(Shanweiniao) and oviraptorosaurs (O’Connor et al., 2009). All pedal claws bear long
horny sheaths.

iv. Discussion
Unidentified Thoracic Ossifications
The paired structures of unknown significance reported in Rapaxavis are also
known in Concornis (Fig. 8.6B). Contra Morschhauser et al. (2009) the ossifications are
also paired; they are poorly preserved so their exact morphology cannot be discerned but
their placement, dorsolateral to the coracoid sternum articulation, is comparable to
Rapaxavis. The paired nature of these elements in this specimen is not surprising given
the bilateral symmetry of birds and their paired nature in Rapaxavis. While the degree of
ossification among compound bones is a weak assessment of ontogenetic stage, the fact
the thoracic ossifications have a porous texture in Rapaxavis, but not in Concornis
258 
(surface texture appears comparable to other elements), may suggest this specimen is a
juvenile (Concornis is considered a late stage subadult based on histology; Cambra-Moo
et al., 2006), an interpretation supported by the absence of fusion in the compound bones
of the hindlimb. The nature of these structures is yet unknown but is further evidence of
the disparity between the flight apparatus of modern and enantiornithine birds.

Phylogenetic Placement and Longipterygid Diversity
The specimen, DNHM D2522, has already been included in a large cladistic
analysis (O’Connor et al., 2009). This analysis provides support for a longipterygid clade
composed of Longipteryx, Longirostravis, Shanweiniao and Rapaxavis (O’Connor et al.,
2009). Not surprisingly, within this clade, Longirostravis and Rapaxavis form a more
exclusive relationship, as suggested by Morschhauser et al. (2009); DNHM D2522 was
originally considered to be a new specimen of Longirostravis (Morschhauser et al.,
2006). The longipterygid clade is known from both the Yixian and Jiufotang formations
of the Jehol Group, northeastern China. Though Rapaxavis is considered more closely
related to Longirostravis, it comes from the younger Jiufotang Formation while
Longirostravis is from the middle Yixian Formation. The presence of the more basal
Longipteryx in the younger Jiufotang Formation suggests the presence of a great deal of
undiscovered diversity within the clade, a conclusion reached by Hou et al. (2003) and
subsequently confirmed by the discovery of two new longipterygids (Morschhauser et al.,
2009; O’Connor et al., 2009). Still, these new discoveries are more derived than
Longipteryx; Rapaxavis indicates that the Longirostravis lineage persisted into the
259 
Jiufotang, while Shanweiniao increases our known diversity. The presence of such
primitive morphologies in Longipteryx that are absent in the other taxa suggest that there
existed longipterygids with morphologies similar to Longipteryx (i.e. unreduced manus)
in the Yixian, yet undiscovered.

Ontogenetic age of DNHM D2522
The absence of fusion and fairly rough surface of the bones (preservation and
preparation making it difficult to determine clear pits) in specimen DNHM D2522 may
suggest that it represents a subadult individual (Morschhauser et al., 2009). As is
particularly evident in other specimens (DNHM D2950/1; see Chapter 6), given
unknowns regarding enantiornithine growth (see Chapter 9), any inferences regarding the
ontogenetic stage of DNHM D2522 should await histological analysis of this specimen.
The morphology of Rapaxavis pani is described as preserved in the only known
specimen, however ontogeny may affect features, such as fusion. In the absence of any
well-documented growth series, to what degree fusion and proportions may change is
unknown within enantiornithines. A juvenile Longipteryx (IVPP V12353) suggests that
DNHM D2522 may fuse compound bones later in ontogeny, but not increase greatly in
size.

v. Conclusions
Further preparation has revealed new morphologies and consistent with the desire
to expand available morphological information, this taxon is redescribed. If new
260 
information was not made available, a majority of systematists would derive
morphological data for their data matrix from Morschhauser et al. (2009), which would
differ from the information now revealed by the specimen post-preparation. For example,
to accommodate the original interpretation of the morphology of the sternal trabeculae,
characters would have to be modified. It is easy to envision how differences in available
information can lead to disparity between comprehensive studies that utilize such taxa.
Information regarding Rapaxavis pani could benefit from further preparation of the
holotype and the discovery of new specimens and thus the presented morphology, limited
by personal observation and interpretation, may be subject to change. As new information
becomes available, published data should be continually updated and incorporated into
cladistic analyses, which will continue to refine the resultant phylogenetic hypotheses.

261 
CHAPTER 9: ENANTIORNITHINE LIFE HISTORY

i. Introduction
Enantiornithines are often compared to living birds (Neornithes), their closest
extant relatives, in order to make inferences about ontogeny, ecology and function. This
assumes that enantiornithines and neornithines are biologically very similar, likely based
on the appearance of some advanced, modern morphological features at the
ornithothoracine node. While sharing similar features of the modern flight apparatus
(i.e., furcula with hypocleideum, modern wing proportions, keeled sternum), as more
information becomes available on enantiornithine biology, it becomes increasingly clear
that these birds had unique life histories different from more advanced birds and also
from non-avian dinosaurs (Padian et al., 2001; Erickson et al., 2007). A few exceptional
discoveries of enantiornithines document nearly every ontogenetic stage, from embryo to
adult; however, these finds are rare and often difficult to interpret. From these
specimens, aspects of enantiornithine embryonic and postnatal development can be
inferred and have begun to reveal the unique life history of enantiornithines. However
given the paucity of information at this time, inferences about growth and strategy are
only weakly documented.

ii. Egg Size and Morphology
Enantiornithine oology is a relatively restricted field of research, a consequence of
the fragility of the egg and subsequent paucity of specimens in the fossil record (Hayward
262 
et al., 2000). Eggshell fragments of purported enantiornithine affinity have been reported
from the Gobi Desert of Asia (Elzanowski, 1981; Mikhailov, 1991; Kurochkin, 1996), the
Rio Colorado Formation of Argentina (described only as ornithothoracine; Schweitzer et
al., 2002), and the North American Kaiparowits Formation (Bray, 2002). Of these, the
only specimens that are likely to actually belong to enantiornithines and not interpreted as
diagenetically altered (Mikhailov, 1997) are those from Argentina (Schweitzer et al.,
2002; Grellet-Tinner et al., 2006). In addition, a well preserved in ovo enantiornithine
embryo is known from the Jehol Group of China (Zhou and Zhang, 2004); this specimen
preserves most of the outline of the egg, but no shell. While the material is limited,
advanced techniques (i.e. scanning electron microscopy) allow a great deal of knowledge
regarding enantiornithine egg morphology to be retrieved.
The Argentine eggs are from the Late Cretaceous Bajo de la Carpo continental
sandstone member of the Rio Colorado Formation, Neuquén, Argentina, which is
reportedly Campanian in age (Dingus et al., 2000). Eggs and egg fragments are abundant
from this unit (Grellet-Tinner et al., 2006); the specimens reported by Schweitzer et al.
(2002) include one egg containing a partially articulated embryo (MUCPv-284).
Several morphological characters suggest that these Argentine embryos are
enantiornithine birds although previous publications only bracket the specimens as
phylogenetically within Ornithothoraces but outside Ornithuromorpha (Fig. 9.1A;
Schweitzer et al., 2002; Grellet-Tinner et al., 2006). The presence of a strut-like coracoid
suggests these birds are ornithothoracine (Enantiornithes + Ornithuromorpha), while the
presence of a dorsal process on the ischium (absent in advanced ornithuromorphs) and
263 
the absence of a cranially directed deltopectoral crest on the humerus (present in
neornithines), places the embryos basal within this clade. The embryos also possess a
dorsolaterally excavated furcula (with an L-shaped cross-section), which is only known
to occur within Enantiornithes (Chiappe and Walker, 2002); the proximal location of the
dorsal process of the ischium is also consistent with their placement within this clade
(this process is distally located in basal ornithuromorphs; Clarke et al., 2006). Currently,
a majority of phylogenetic hypotheses place only the enantiornithines outside
Ornithuromorpha, within Ornithothoraces (see Chapter 11; Clarke et al., 2006; Cau and
Arduini, 2008; Zhou et al., 2008a; O’Connor et al., 2009) and therefore these specimens
are inferred to belong to Enantiornithes. The early ontogenetic state of these individuals
prevents further diagnosis at the genus or species level.
An enantiornithine placement for the Argentine embryos is argued in spite of the
fact that one recent analysis places Confuciusornis as the outgroup to enantiornithines
within Ornithothoraces (Zhou and Zhang, 2006b); these specimens can be excluded from
Confuciusornithidae on the absence of a quadrangular and perforated deltopectoral crest
of the humerus. Yet another analysis resolves Ornithothoraces as a polytomy between
Vorona, Enantiornithes and Ornithuromorpha (You et al., 2006). Although there is no
comparable material between Vorona and the Argentine eggs, most analyses resolve the
former within basal Ornithuromorpha (Clarke et al., 2006; Cau and Arduini, 2008; Zhou
et al., 2008a). Indeed, even if the specimens later prove to be from another group of birds
that hold such a phylogenetic position, the fact that they are phylogenetically close to
enantiornithines suggest that they may have shared comparable eggshell morphology.
264 
These Argentine specimens are extremely informative, revealing a majority of what is
known about basal ornithothoracine eggshell morphology. As a result it is important to
keep in mind the incredible diversity of enantiornithines; these Argentine specimens
represent only one morphology within a particular lineage of birds that lived during the
Late Cretaceous.
The Argentine eggs, like modern birds, lack any ornamentation on the surface of
the shell, such as that present in most non-avian theropods and other non-avian dinosaurs
(Schweitzer et al., 2002; Mikhailov, 1997). The egg is oval but not symmetrical (Fig.
9.1A); this shape is polarized so that the two ends are not equal and the egg tapers in one
direction. This is interpreted as indicative of the presence of an air sac, a feature present
in modern birds and some non-avian dinosaurs closely related to birds (i.e., Troodon
formosus, Phuk Phuk eggs, and others; Varricchio and Jackson, 2004; Buffetaut et al.,
2005; Grellet-Tinner et al., 2006). Other non-avian theropods, which based on egg
morphology are more disparately related to modern birds, also have eggs in which some
asymmetry is observed and thus a proto-air sac is inferred to have been present (i.e.,
Deinonychus antirrhopus and Citipati osmolka; Grellet-Tinner et al., 2006).
As in modern birds, the Argentine eggs possess three crystallographic layers (Fig.
9.1B; also present in Phuk Phuk eggs; Grellet-Tinner et al., 2006), and appear to possess
a thin carbonaceous cuticle also consistent with modern birds (also present in unidentified
eggs from the Two Medicine Formation; Varricchio and Jackson, 2004). Non-theropod
dinosaurs and those non-avian reptiles that lay hard-shelled eggs (e.g., turtles, crocodiles)
have eggs that are composed of a single crystallographic layer (Grellet-Tinner, 2005),
265 

Figure 9.1. A, a reconstruction of the egg size of the Rio Colorado Formation eggs
(Schweitzer et al., 2002), and the preserved elements that suggest these eggs are
enantiornithine. Anatomical abbreviations: cor, coracoid; hum, humerus; isc, ischium. All
scale bars are one cm. B, schematic drawing of the cross-section of the eggshell showing
the three crystallographic layers and their relative thicknesses.
266 
whereas theropod dinosaurs such as Deinonychus antirrhopus and Citipati osmolka, taxa
near the dinosaur-bird transition, possess aprismatic eggshells (referring to the
morphology when the shell unit originating at the membrana testacea is visible only
through the first crystallographic layer, layer boundaries distinguishable) composed of
two layers (Grellet-Tinner, 2005). The eggs of the troodontid Troodon formosus, part of a
clade believed to be very closely related to birds (Forster et al., 1998; Benton, 2004) are
believed to have a true air sac (based on inferences from the asymmetry of their eggs),
lack obvious surface ornamentation (Grellet-Tinner et al., 2006; striations reported by
Varricchio et al., 2002), and have prismatic contacts (shell unit originating at the
membrana testacea visible throughout eggshell, layers indiscernible) between the two
eggshell layers, all features consistent with modern birds; whether a third layer is present
or not is controversial (Varricchio et al., 2002; Varricchio and Jackson, 2004; Grellet-
Tinner et al., 2006).
In the Argentine eggs, the first layer is perforated by vesicles, has a indistinct
prismatic contact with layer two and accounts for nearly half the total eggshell thickness
(Fig. 9.1B); in modern birds the second layer exceeds the first in thickness. Layer two is
roughly 70% the thickness of layer one in these specimens and has vesicles of increased
number and size, while layer three is thin (approximately half the thickness of layer two)
and amorphous, with relatively few vesicles. The boundary between layers one and two is
distinct and thus aprismatic. The Argentine eggs can be distinguished from neornithine
eggs by differences in the relative thickness of these layers, with layer one greatly
exceeding the thickness of layer two (Grellet-Tinner, 2005).
267 
The presence of a thick layer one relative to layer two is also present in the Phuk
Phuk eggs, however these eggs differ from the Argentine eggs in that all contacts are
prismatic and the surface bears ornamentation, otherwise unknown among avians
(Grellet-Tinner et al., 2006). The Argentine eggs are similar to those of modern birds,
asymmetrical, smooth, with three distinct layers with at least one prismatic contact; they
differ from those of modern birds in the relative proportions of the layers and the absence
of a prismatic contact between layers two and three. Given that their phylogenetic
placement is uncertain, these differences cannot be attributed solely to their
enantiornithine affinity, however the morphology of the embryonic material and the
eggshell, the phylogenetic placement of enantiornithines, and the eggshell morphology of
related taxa suggest that enantiornithines would also have possessed eggshell with three
layers.
In terms of other known enantiornithine eggshell, in ovo embryonic skeletons of
Gobipteryx were described from the Khermiyn-Tsav locality, Barun Goyot Formation
(Elzanowski, 1981) and only later assigned to enantiornithines (Martin, 1983).
Subsequently, hundreds of small ‘bird’ eggs from the Barun Goyot and Djadokhta
Formations, from which Gobipteryx is also known, have been attributed to this taxon
(Mikhailov, 1997). While the morphology of the embryos is clearly enantiornithine
(Martin, 1983), their taxonomic assignment within this clade remains controversial
(Kurochkin, 1996), even if they may well belong to Gobipteryx (Kurochkin, 2003). The
eggs come in two size distributions, and thus have been assigned to two different ootaxa
(i.e., Gobioolithus minor and G. major; Mikhailov, 1996) comprising the smaller form
268 
from the Barun Goyot Formation at Khermiyn-Tsav, and the larger form from the Barun
Goyot and Djadokhta Formations (Mikhailov et al., 1994) at other localities within the
southern Gobi Desert. The eggshell is otherwise comparable, and may suggest the
presence of two taxa (Kurochkin, 2004). Complete clutches with uncrushed, intact eggs
are preserved at the Bayn-Dzak locality of the Djadokhta Formation indicating the birds
nested on the ground as in modern megapodes and non-avian dinosaurs (Sabath, 1991;
Norell et al., 1995). Furthermore, the presence of numerous egg ‘layers’ at the
Khermiyn-Tsav locality suggests nesting site fidelity among these birds (Sabath, 1991;
Mikhailov et al., 1994).
Interpretations of the microstructure of these eggs differ widely between
published accounts (i.e., prismatic vs. aprismatic, the number of layers) and the eggs are
reportedly heavily recrystallized and diagenetically altered making them very difficult to
interpret (Mikhailov, 1991, 1997; Mikhailov et al., 1994). Nevertheless, the “Gobipteryx”
eggs have been described as small, smooth, ovoid and asymmetrical (Mikhailov et al.,
1994) consistent with morphologies observed in the Argentine eggs (Schweitzer et al.,
2002). The reported thickness of eggshell ranges from 100 – 200 microns (for the smaller
form) to 200 – 400 microns for the larger specimens (Mikhailov et al., 1994). Original
publications described the eggshells as prismatic with two layers (Mikhailov, 1991), but
later it was considered that the interpretation of the eggshells as prismatic might be
incorrect (Mikhailov, 1997). The identification of only two layers does not exclude the
presence of a third layer, considering the preservation of these specimens. However,
since the Argentine eggs with which these are compared are not even definitively
269 
enantiornithine, inferences regarding possible causes for the observed differences are
inappropriate; any conclusion from the current available information is premature.
Aprismatic eggshell composed of two layers has been attributed to the taxon
“Nanantius valifanovi” (= Gobipteryx minuta, [Chiappe et al., 2001]) based on the co-
occurrence of eggshell fragments at the site that yielded “N. valifanovi” (Kurochkin,
1996; Grellet-Tinner and Norell, 2002). However, because the specimens inferred to have
been contained within these eggs are not neonates, although they not fully grown, this
association is unwarranted. As discussed above, the eggshells and skeletal elements
themselves have been recrystallized, which may have obscured features such as
microscopic eggshell layers (Kurochkin, 1996). With no full-grown and relatively
complete specimens of Gobipteryx, it is impossible to estimate the mass of this taxon to
compare with estimated egg volumes.
The eggshells reported from the Late Cretaceous Kaiparowits Formation in
southern Utah have been published in abstract form only (Bray, 2002) and their
morphology was not described. In order to identify these eggs as enantiornithine, in ovo
material, or strongly associated skeletal elements would have had to been collected
together with eggshell because the nature of enantiornithine shell morphology is still
highly controversial. In addition, the presence of an undescribed avisaurid theropod from
the formation (Hutchison, 1993) may also have influenced the taxonomic assignment of
any thin, smooth eggshell collected. Thus, pending new information on these specimens
nothing further can be inferred; published statements about enantiornithine eggshell from
the Kaiparowits Formation are dubious.
270 
A single enantiornithine embryo is known from the Jehol deposits of northeastern
China, preserved in the confines of its egg (Zhou and Zhang, 2004) – but eggshell is not
preserved (Fig. 9.2C). The Liaoning embryo (IVPP V14238), as it is called, is inferred to
be an enantiornithine based on the presence of teeth, a V-shaped furcula (an
enantiornithine synapomorphy), a strut-like coracoid (an ornithoracine synapomorphy)
with a convex lateral margin (common among enantiornithines; Chiappe and Walker,
2002), and a metacarpal III that exceeds II in distal projection (another synapomorphy of
Enantiornithes; Chiappe and Walker, 2002). While not studied firsthand, these features
are discernible from the published photograph, and the systematic assignment of this
specimen is not questioned here. The specimen is not complete, however more than half
the outline of the egg is preserved, indicating it was probably asymmetrical.
Unfortunately the Liaoning embryo is not complete enough to allow for an
accurate estimate of egg size and there is no associated adult material or way to
determine the taxonomic affinity of the embryo at the binomial level. Despite the lack of
direct evidence, several inferences can be made about enantiornithine egg size relative to
body mass based on morphological limitations. The pelvis of enantiornithines differs
greatly from that of modern birds in such a way that it has been inferred that this former
clade could not have developed the same range of egg size to body mass ratios as the
latter based on morphological constraints (Dyke and Kaiser, 2008). In the pelvis of
enantiornithines the individual pubes contact distally forming a short distal symphysis
(e.g. Gobipteryx), which in many taxa is expanded into a boot (e.g. Eoenantiornis,
Longipteryx, Pengornis). This condition is present in most basal birds and non-avian
271 

Figure 9.2. Early Cretaceous subadult birds from Liaoning, China. A, GMV 2159; B,
GMV 2158; C, embryo IVPP V14238; D, ‘Liaoxiornis delicatus’ GMV-2156. All arrows
indicate remiges and rectrices (in A).
272 

theropods, with exceptions including advanced members of the bird-like theropod clade
Alvarezsauridae (Chiappe et al. 2002b), in which distally non-contacting pubes
convergently evolved with those of modern birds. The presence of distally contacting
pubes places a restriction on the size of the oviduct and thus the egg itself relative to
overall body size (Dyke and Kaiser, 2008). Based on this inference, enantiornithine eggs
would be expected to be small relative to adult body size compared to some modern
birds. Although smaller eggs are commonly associated with altricial development (Starck
and Ricklefs, 1998), this not the developmental mode inferred for enantiornithines (see
below), suggesting unique developmental pathways in the clade relative to modern birds.

iii. Development and Parental Care
In Neornithes there are two forms of development: altricial, in which the neonate
hatches with a high degree of dependence on the parents for nourishment, protection and
insulation, and precocial, in which the bird hatches relatively self-sufficient, capable of
foraging for itself (Starck and Ricklefs, 1998). Within the diversity of Neornithes, there
exists a complete spectrum from one extreme to the other; the super-precocial megapode
birds can fly soon after hatching, while highly altricial birds, such as parrots and
songbirds, are born naked and blind, and completely dependent on the care of their
parents (Starck and Ricklefs, 1998). There are several lines of evidence that can be used
to infer the mode of development from the fossil record, and thus, the hatchling strategies
of Enantiornithes. Growth rates, egg size (discussed above), degree of ossification at
hatching and integument can all be used as clues to infer how these birds developed. As
273 
discussed above, enantiornithine embryos, as well as fossil embryos of nearly any animal,
are extremely rare, even more so than the remains of their eggs.
The ‘Gobipteryx’ embryos (ZPAL-MgR-I/33-34, 88-91) were described as being
osteologically highly advanced and as such were inferred to be super-precocial
(Elzanowski, 1981). Of the most complete specimens, ZPAL-MgR-I/33 was described as
uncalcified at the time of death, resulting in deformation and artificial fusion of the
specimens while ZPAL-MgR-I/34 is interpreted as representing a later stage of
development based on its higher degree of ossification (Elzanowski, 1981). This
specimen even displays higher degrees of ossification than some modern precocial birds
at the hatching stage (Elzanowski, 1981), such as the presence of ossified epiphyses of
the ulna and radius (cartilaginous in hatchlings of many birds) and a fully developed
humerus (deltopectoral crest cartilaginous in precocial hatchlings) (Elzanowski, 1981).
The forelimb proportions (ulna > humerus) of these embryos are also suggestive of
advanced flight capabilities and a ‘notarium’-like structure, which aids flight by bracing
the chest against forces generated by the wing, is described in ZPAL-MgR-I/34
(Elzanowski, 1981). The presence of well-ossified flight apparatus relative to the
hindlimbs in an enantiornithine embryo was interpreted as providing evidence that these
birds were super-precocial, born capable of flight and foraging as in the extant
megapodes (Elzanowski, 1981). The presence of a ‘notarium,’ otherwise unknown
among enantiornithines, and greater degrees of fusion than is typical of modern precocial
birds suggests these specimens may have been diagenetically altered (Schweitzer et al.,
2002). Since no firsthand observations have been made on this material no comment can
274 
be made on the accuracy of either interpretation; regardless, neither the degree of
ossification present (Starck and Ricklefs, 1998) nor the fossilization of ossifications at the
long bone epiphyses (Geist and Jones, 1996) correlates well with developmental mode
(Starck and Ricklefs, 1998).
The Liaoning embryo (Fig. 9.2C), though not associated with a nest or an adult,
still presents clues to its developmental mode. Long rectricial feathers are visible,
indicating that this bird would have hatched fully or nearly fully fledged, a characteristic
highly consistent with precocial development (Starck and Ricklefs, 1998). Integument
alone, however, is not enough to support an inference of super-precociality (Elzanowski,
1981). While the super-precocial megapodes are the only living birds known to hatch
fully fledged, there are many other precocial species, including some anseriforms (ducks
and geese) and charadriiforms (plovers, gulls, and terns), that hatch nearly fledged but
receive some parental care (Starck and Ricklefs, 1998) and thus are not considered to be
super-precocial. This distinction, between fully-fledged and nearly fledged, is impossible
to determine unequivocally given the state of preservation in the Liaoning embryo and is
further complicated by the lack of an accurate method to determine the ontogenetic state
of a neonate; depending on the stage of the embryo’s development, it may or may not be
expected to develop additional integument (Ricklefs and Starck, 1998).
A number of very small, presumably early juvenile, enantiornithines have also
been collected from the Jehol deposits of China (Ji and Ji, 1999; Hou and Chen, 1999;
Chiappe et al., 2008). The first of these is ‘Liaoxiornis delicatus’ (Fig. 9.2D; Hou and
Chen, 1999; ‘Lingyuanornis parvus’ - Ji and Ji, 1999; Chiappe et al., 2007; Zhou and
275 
Zhang, 2007; see Chapter 3). The validity of ‘Liaoxiornis’ is debated (see Chapter 3); the
early ontogenetic stage of the holotype suggests to some that its small size, one of its
diagnostic characteristics, is due to its sub-adult status (Chiappe et al., 2007). The
specimen is inferred to be a juvenile based on the presence of a relatively large orbit
relative to the skull, a lack of fusion between compound bones (a character that is
admittedly quite weak based on the wide range in the degree of fusion present within the
clade Enantiornithes) and the presence of grooves and pits in the external surface of the
bone (indicative of incomplete ossification, a juvenile feature in modern birds). The slab
and counterslab preserve the shape of the wing as a dark stain, which may have been
artificially enhanced (Chiappe et al., 2007).
More recently, two more juvenile enantiornithines were described from China
(Chiappe et al., 2007). Both preserve feather impressions (faint in GMV-2158; Fig.
9.2B); one, GMV-2159, clearly preserves the impression of wings and tail in which
pennaceous primary and secondaries can be discerned (Fig. 9.2A). These specimens from
China possess remiges indicating they were fledged despite their early developmental
stage (Chiappe et al., 2007). Fledging early during postnatal development before adult
size is achieved is indicative of precocial development (Starck and Ricklefs, 1998) but
since the exact age of the juveniles at the time of death cannot be determined, the degree
of precociality that can be inferred is ambiguous.
Several juvenile specimens are also known from Lower Cretaceous Spanish
Lagerstatten (Sanz et al., 1997; Sanz et al., 2001). A regurgitated pellet containing four
subadult birds was collected from the Las Hoyas locality (Sanz et al., 2001). The pellet
276 
preserves long, fully developed, asymmetrical flight feathers; while it cannot be
determined precisely which of the four skeletons these belong to, all four specimens are
juvenile enantiornithines. The Montsec hatchling (LP 4450) also preserves feathers,
despite its juvenile ontogenetic stage (Sanz et al., 1997). These feathered Spanish
juveniles further suggest that enantiornithines were precocial.
While feathers themselves are not unusual in a subadult neornithine, flight
feathers typically don’t develop until the animal is ready to fledge; this is either prior to
or soon after hatching in a super-precocial or precocial bird, or when development is
nearly complete, as in altricial birds (Ricklefs et al., 1980; Starck and Ricklefs, 1998).
Since all these specimens are clearly juvenile and development is incomplete, the
presence of flight feathers can be interpreted as a precocial feature. The fact that nearly
every specimen of juvenile enantiornithine preserves feathers suggests that as a clade
these birds were precocial.
Egg size in modern birds has been correlated with developmental mode (Ricklefs
and Stark, 1998), with larger eggs associated with precocial hatchlings and smaller eggs
typical of altricial hatchlings. Within the modern altricial – precocial spectrum, there is a
corresponding range of egg size to body mass ratios, the extreme being the Kiwi
(Apteryx), which lays an egg up to 25% its body mass (Davies, 2002). The Liaoning
embryo preserves long feathers suggesting it was precocial, however, without an
associated adult, it is difficult to identify what species it belongs to, and thus, there is no
way to estimate the adult terminal body mass. Consequently, egg size to body mass ratios
cannot be used to infer the developmental mode of the Liaoning embryo. As discussed
277 
earlier, the restriction on egg size as a result of the distally contacting pubis in
enantiornithines and other basal birds suggests that the evolution of a super precocial
developmental mode would have been highly constrained relative to modern birds.
Histological studies suggest that enantiornithines possessed a unique growth trajectory
(Starck and Chinsamy, 2002; Cambra-Moo et al., 2006), unlike those of modern birds,
which also suggests precocial development and may have helped to accommodate
morphological constraints associated with this developmental strategy.
Histological studies on the bone microstructure of a ‘Gobipteryx’ embryo
(Elzanowski, 1981; Chinsamy and Elzanowski, 2001) reveals a morphology structurally
different from the microstructure of adult enantiornithines (Fig. 9.3A,D,E; see below).
Unlike the cross-sections of adult enantiornithine bone which are composed entirely of
organized, slow forming, parallel-fibered bone, the ‘Gobipteryx’ embryo (Fig. 9.3A;
ZPAL MgR - I/90) consists entirely of rapidly formed, vascular fibrolamellar bone
(Chinsamy et al., 1994; Chinsamy and Elzanowski, 2001). This has lead to the
interpretation that enantiornithines developed rapidly during the embryological stages,
but slowed after hatching as locomotor activities assumed (Chinsamy and Elzanowski,
2001). Locomotor activity, particularly flight, is costly, yet the presence of rectrices and
thoracic limbs with volant proportions suggests young enantiornithines were fully mobile
and may have been airborne. The evidence that rapid growth was required to obtain these
structures, and that these growth rates were later lost suggests enantiornithines grew
rapidly as embryos, were born independent, and then experienced slow post-natal growth
278 

Figure 9.3. Cross-sections of enantiornithine femora: A, ‘Gobipteryx’ ZPAL-MgR-/90;
B, Concornis LH-2814; C, MACN-S-01; D, PVL-4273. Hypothetical enantiornithine
growth strategies: E, rapid embryological growth followed by prolonged, slow,
interrupted growth, as inferred from ‘Gobipteryx’ embryo ZPAL-MgR-/90 and Lecho
femora MACN-S-01 and PVL-4273; F, rapid growth until adult or near adult-size
followed by slow, interrupted growth as inferred from LH-2814; G, intermediate rapid
growth phase (followed by slow, interrupted growth) as interpreted from histological
analyses and the known distribution of sampled fossils. Placement of specimens in E-G
indicate inferred ontogenetic position in the given hypothesis.
279 
as a consequence of the energy consumed for locomotion (Fig. 9.3E; Chinsamy and
Elzanowski, 2001). Additional histological data makes it difficult to determine if this is
accurate for the entire clade or even within subclades (see below).
Phylogenetic analyses of modern birds suggest that precociality is primitive for
Neornithes, and altriciality is basal for neognaths, with precociality independently rising
several times within the more derived clade (Cracraft, 1988; Sibley and Ahlquist, 1990;
Hackett et al., 2008). A phylogenetic analysis of parental care characters suggested that
paternal care is the ancestral state of Neornithes (McKitrick, 1992) with bi-parental care
ancestral to Neognathae, but lost several times within. Crocodiles were used as the
outgroup in this analysis and no evidence from fossil taxa, which at the time was
admittedly scarce, was included.
Recent discoveries of troodontid and oviraptorid dinosaurs associated with nests
have allowed for comparisons between clutch size and volumes compared to extant birds
(Varricchio et al., 2008). In this study, regression analyses revealed that the attributes of
the clutches of these fossil theropods most closely resemble those of modern birds with a
paternal care system (contra Wesolowski, 1994), such as the ratites. Bi-parental care is
thus considered a derived condition of neognaths (McKitrick, 1992; Varricchio et al.,
2008).
Altricial chicks require bi-parental care and are only found among the neognaths
(though altriciality, as well as bi-parental care, has been lost to varying degrees within
this massive clade). Analyses of both systems, altriciality and parental care, suggest that
these two characters evolved at the same point (with the origin of Neognathae, which
280 
includes a majority of all extant birds). The form of parental care in enantiornithines is
unknown, however based on evidence from the fossil record and the phylogenetic
placement of the clade, it is likely they developed precocially, and had predominantly
paternal care as in closely related non-avian dinosaurs (Varricchio et al., 2008) and basal
neornithines (paleognaths; Davies, 2002; McKitrick, 1992).

iv. Growth and Ontogeny
All modern birds have rapid growth rates typically faster than those of mammals;
within the precocial-altricial spectrum of developmental strategies there is a range of
growth rates, with altricial chicks having the fastest, typically reaching maturity within a
few weeks (Starck and Ricklefs, 1998). Given that the latter developmental strategy is
inferred to have evolved within the neornithine clade itself (see above), even the growth
rates of precocial birds are relatively faster than most mammals (Varricchio et al., 2008).
Dinosaurs have historically been viewed as growing slowly like primitive reptiles,
however dinosaurs are now known to have sigmoidal growth curves like other vertebrates
and some grew very quickly (Erickson et al., 2001). Without the aid of some modern
techniques (i.e. histological analysis), the origin of the avian growth rates, whether within
the clade or within its non-avian outgroup was unclear.
Within dinosaurs, there is a wide range of growth patterns and strategies (Starck
and Chinsamy, 2002). Though well-sampled ontogenetic series are available for some
taxa (ex Tyrannosaurus rex, Psittacosaurus), these series are complicated by
misinterpretations of ontogenetic differences as true morphological species distinctions
281 
(e.g. Nannotyrannus – Currie et al., 2005). Another way to determine the age and growth
rate of an organism is from histological analysis and thus can aid taxonomic assessments
as well as reveal ontogenetic stage and growth rates. When bone grows at different rates,
it forms a different structure; rapid growth is characterized by fibrolamellar type bone in
which the vascular canals are arranged in a disorderly fashion. Lamellar bone results
from slower growth, forms an organized parallel arrangement and is often avascular
(Francillon-Vieillot et al., 1990; Chinsamy et al., 1995; Chinsamy-Turan, 2005). Some
studies suggest that bone structure may not be an accurate reflection of growth rates
(Starck and Chinsamy, 2002); bone growth is related to metabolism, terminal size, and a
number of other factors, and is highly susceptible to external environmental factors
(Starck and Chinsamy-Turan, 2002). In addition, as bone grows, it restructures itself and
often absorbs older bone tissue, thus erasing key information for understanding growth
during the entire life of the individual. These are factors to keep in mind when using
histology to make inferences about growth rates or the age of a specimen.

Growth in Non-avian Theropods
Dinosaurs have historically been regarded as having slow, constant growth as in
primitive reptiles but recent studies show that dinosaur growth rates are accelerated
relative to the condition in modern non-avian reptiles, with sigmoidal growth curves with
an exponential growth phase and determinate growth (Erickson et al., 2001; Chinsamy-
Turan, 2005; de Ricqlès et al., 2008). During the rapid growth phase of their lives,
fibrolamellar tissue is deposited on the periphery of the bone (the Outer Circumferential
282 
Layer or OCL); when full size is achieved, a thin layer of lamellar bone is deposited.
Most taxa, such as Tyrannosaurus rex and Troodon formosus, like mammals and unlike
most modern birds, apparently did not achieve full size within a single growth period and
the rapid growth phase lasted several years in some taxa. In such taxa, organisms
experience cyclical periods of rapid growth in which haversian fibrolamellar bone is
deposited followed by seasonal periods of arrested growth until skeletal maturation is
achieved and growth slows (Varricchio, 1993; Chinsamy and Elzanowski, 2001; Starck
and Chinsamy, 2002; Erickson et al., 2004; Erickson et al., 2007). When growth is
interrupted, a dark line of lamellar bone known as a line of arrested growth (LAG) forms.
The presence of such LAGs (or annuli representing periods of slower growth) suggests
that the organism did not reach full size within a single year; LAGs occur annually in
living organisms and thus, they are assumed to also represent annual cycles among
extinct organisms (de Ricqlès, 1976; Chinsamy et al., 1995). In most cases, energetic
considerations and inferences on growth trajectories also suggest that these animals
reached reproductive maturity before attaining full size, another departure from modern
birds (Erickson et al., 2007). Dinosaur growth rates vary depending on adult size (faster
rates in larger taxa), but no non-avian dinosaurs are known to have achieved growth rates
comparable to altricial neognaths or even as high as that of the blue whale, the largest
known vertebrate of all time (Erickson et al., 2001; Erickson et al., 2004; Erickson et al.,
2006). At least some large dinosaurs grew at comparable rates and had similar life
trajectories to large mammals and precocial birds (Erickson et al., 2001; Ricklefs, 2007).
Non-avian dinosaurs represent a huge radiation and even within theropods different
283 
growth strategies are recognized. Some theropods, including Herrerasaurus and
Allosaurus, show no evidence of LAGs, indicating they had uninterrupted growth (Starck
and Chinsamy, 2002), though whether they achieved adult size within a year, like modern
birds, is uncertain.

Growth in Extant Birds
Modern birds grow exceptionally fast, most of them reaching adult size in a single
uninterrupted period of growth, typically less than a year (Starck and Ricklefs, 1998;
Bourdon et al., 2009). Their bone microstructure reveals three distinct layers; the thickest
and primary layer consists of rapidly formed vascularized fibrolamellar bone, with a thin
layer of lamellar bone on either side which gets deposited when adult size is achieved
(Francillon-Vieillot et al., 1990; de Ricqlès, 1991; Starck and Chinsamy, 2002;
Chinsamy-Turan, 2005). The OCL forms slowly throughout adulthood after the rapid
growth phase and often records tightly packed LAGs that do not appear to correlate well
with specimen age (de Ricqlès, 1980; Chinsamy et al., 1995). In small birds especially
(due to cortical thickness which is low in all birds) bone is often completely resorbed and
restructured during adulthood, removing evidence of an early period of rapid growth
(Ponton et al., 2004; Cambra-Moo et al., 2006; contra Chinsamy et al., 1995).
The fastest relative growth rates known among extant animals are in altricial
birds, however recent studies indicate that this unique growth strategy and rapid growth
rates can be interpreted as a highly modified dinosaurian condition (Padian et al., 2001).
Relative to taxa such as Tyrannosaurus, within Neornithes the exponential or rapid
284 
growth phase of the curve is very short, occurring typically within a year. This could be
related to the reduction in size within the clade relative to outgroups; however, while size
is reduced and thus time required to reach full size is reduced, growth rates are still
relatively elevated (given differences in the adult mass between taxa). Maniraptorans, the
group of theropods inferred to include birds (see Chapter 2), show a marked decrease in
size relative to other theropods (Turner et al., 2007a), yet their growth rates are still
estimated to be slower than those of precocial birds (Erickson et al., 2001), and thus the
evolution of modern avian growth rates is inferred to have occurred during the evolution
of Aves itself.

Growth Rates in Mesozoic Birds
Ornithurines, such as Ichthyornis dispar, Hesperornis regalis and virtually all
neognaths, do not normally preserve LAGs (Chinsamy et al., 1998; Stark and Chinsamy,
2002; Bourdon et al., 2009), indicating that by the Late Cretaceous, ornithurines had
already achieved modern avian type growth in which adult size is achieved in a single
uninterrupted period of growth, inferred to be less than a year. No LAGs interrupt the
deposition of fibrolamellar bone in the basal Jehol pygostylian, Confuciusornis (Zhang et
al., 1998; de Ricqlès et al., 2003), which has been interpreted as evidence that these birds
grew rapidly, comparable to modern birds of their size (de Ricqlès et al., 2003).
Morphometrics studies, however, reveal a bimodal distribution, which is considered at
odds with this hypothesis, and is used to infer a multi-year development with an
intermediate, very rapid exponential growth phase as in non-avian dinosaurs (Chiappe et
285 
al., 2008). The apparent absence of LAGs in Confuciusornis is explained by bone
remodeling, given that the histologically sampled specimens fall within the largest end of
the size spectrum (i.e., early phases of growth which could potentially show LAGs are
not preserved). More histological studies of Confuciusornis are needed but it is possible
that developmental plasticity of growth rates within birds (Starck and Chinsamy, 2002)
may have produced a unique growth strategy within this clade (see Bourdon et al., 2009
for modern examples).
Basal ornithuromorph Patagopteryx preserves a single LAG, which is followed
by another rapid growth phase in which fibrolamellar bone is deposited (Chinsamy et al.,
1994). The development of basal ornithuromorphs, like non-avian dinosaurs, required
more than a year, and thus the specific developmental strategy of modern birds appears to
have evolved only within derived members of this clade.

Growth in Enantiornithines
El Brete Femora. The first histological analysis of enantiornithines was based on two
presumably adult femora from the Late Cretaceous Lecho Formation (Chinsamy et al.,
1994). Unlike the primarily fibrolamellar bone preserved in an enantiornithine embryo,
ornithuromorphs and Confuciusornis, the cross-sections show thick parallel-fibered bone
tissue (slow growth), with very little or no fibrolamellar type (Fig. 9.3C,D). Given that
even in modern birds, rapidly formed bone can be lost with age, the absence of
fibrolamellar bone could represent an age related bias (Cambra-Moo et al., 2006). This is
considered unlikely based on the medullary resorbtion, which encroaches the parallel-
286 
fibered bone, indicating this bone was deposited before age-related restructuring began.
The morphology of this bone differs from, though is similar to, lamellar bone. It is
avascular but interpreted as having a faster rate of deposition than lamellar bone,
intermediate between the former and the fibrolamellar type (Chinsamy et al., 1995).
These two specimens preserve four (MACN-S-01) and five (PVL-4273) LAGs
interrupting deposition of the parallel-fibered bone (Fig. 9.3C,D); these lines differ from
those found in the OCL of modern birds (closely and evenly spaced) in that they are
widely and variably spaced. This is interpreted as evidence enantiornithines grew slowly
for prolonged periods of time greater than those of basal ornithuromorphs and also
suggests growth rates were variable (Chinsamy et al., 1994; Chinsamy et al., 1995). The
absence of fibrolamellar bone between periods of arrested growth (LAGs) in these
enantiornithines differentiates them from the bone structure of more advanced birds and
non-avian theropods.

‘Gobipteryx’ Embryo. Cross sections from different enantiornithines reveals histological
differences associated with ontogenetic stage within the clade. As discussed above,
histological analysis of ZPAL MgR - I/90, a late stage embryo (or hatchling – Chinsamy
and Elzanowski, 2001) revealed a cortex entirely composed of fibrolamellar bone (Fig.
9.3A; Chinsamy and Elzanowski, 2001). The presence of fibrolamellar bone in an
extremely young specimen, but its absence in specimens at least four years old (MACN-
S-01), suggests that this bone gets completely resorbed and restructured during the post-
natal development of enantiornithines (Chinsamy and Elzanowski, 2001).
287 
The hypothesis enantiornithines may have been precocial (see above) is further
supported by evidence of rapid embryological growth compared to rates in adults.
Locomotor activity, especially flight, slows a hatchling’s growth by consuming energy,
and thus extant precocial chicks have slower postnatal growth than altricial chicks (Starck
and Ricklefs, 1998); therefore, slower post-natal growth rates (relative to embryological
growth) would be consistent with a precocial development (Chinsamy and Elzanowski,
2001; Ricklefs and Starck, 1998). Based on the differences in bone structure (and thus
inferred growth rates) between juvenile and adults, enantiornithines were interpreted as
having a growth strategy with early rapid growth followed by a period of slow protracted
growth (in exchange for locomotor independence) until adult size is achieved (Fig. 9.3E;
Chinsamy and Elzanowski, 2001). This strategy differs from most modern precocial
chicks in that post-natal growth rates are relatively much slower and adult size is not
achieved within a single year. However, if enantiornithines grew rapidly as embryos
followed by years of slow and prolonged growth, specimens considered to belong to the
same species would be expected to occupy a range of sizes. There are few
enantiornithines known from multiple specimens, and this condition is not strongly
apparent in the few examples thus far available (Longipteryx).

Concornis lacustris. Histological analysis of the presumed ‘adult’ holotype specimen of
Concornis lacustris (LH-2814) from the Early Cretaceous of Spain reveals a morphology
intermediate between that of the Gobipteryx embryo and the Lecho Formation femora
(Cambra-Moo et al., 2006). The majority of the cortical thickness in LH-2814 consists of
288 
parallel-fibered bone containing two or three LAGs, fewer than in the Lecho femora,
however the inner layer shows remaining fibrolamellar bone (Fig. 9.3B; Cambra-Moo et
al., 2006). This specimen was interpreted as an adult when originally described, based on
the complete periosteal ossification and proportions of the limbs (Sanz et al., 2002) and
the specimen is still considered to be developmentally very close to skeletal maturity.
Cambra-Moo et al. (2006) reinterpreted this specimen as one that died nearing adulthood,
when its fibrolamellar bone was presumably in the process of being absorbed and
restructured. This reinterpretation fits well with speculations by Chinsamy and
Elzanowski (2001) regarding slowing of growth and subsequent restructuring of bone in
enantiornithines, however this specimen is regarded as nearly full size, whereas the
precocial features of the few enantiornithine embryos and juveniles suggested that growth
slowed much earlier (after hatching, with slow growth towards adulthood) as a result of
the energetic constraints of precocial flight (Fig. 9.3E; Chinsamy and Elzanowski, 2001).
Based on the presence of fibrolamellar bone but the high percentage of parallel-fibered
bone (OCL approximately 50% of cortical thickness), Concornis lacustris (but not
necessarily all lineages of enantiornithines) is interpreted as having grown quickly after
hatching but entered a slowed growth phase upon nearing adult size (Fig. 9.3F; Cambra-
Moo et al., 2006), much later than inferred from Gobipteryx (Fig. 9.3E; Chinsamy and
Elzanowski, 2001).

Possible Interpretations of the Data. The small number of published studies prevents
drawing any major conclusions regarding the growth strategy of enantiornithines as a
289 
whole. The sectioned enantiornithine specimens are temporally, geographically and likely
phylogenetically disparate further weakening any conclusions drawn from all three
studies. Troodontids and neornithines are known to have diverse growth patterns (Starck
and Ricklefs, 1998; Erickson et al., 2007) subject to environmental pressures (Starck and
Chinsamy, 2002); given that enantiornithines are also quite diverse, the same could prove
true within the clade. Based on the given evidence, it cannot be equivocally discerned
across the clade what developmental strategies were employed by the enantiornithines,
however there still exist hypotheses or possible interpretations of the data.
The differences in bone microstructure between enantiornithines at different
ontogenetic stages has led to the interpretation that this group may have had rapid
embryological growth in order to develop flight structures (highly ossified thoracic
girdle, feathers) and proportions by hatching, followed by slow post-natal growth in
which parallel-fibered bone is deposited and the vascularized bone of the neonate is
restructured (Fig. 9.3E; Chinsamy and Elzanowski, 2001). LH-2814, the Concornis
lacustris holotype, is inferred to have died during the slow growth phase, which may
have taken several years given the number of LAGs preserved, while the Lecho
Formation femora had already completely resorbed the fibrolamellar bone of their early
ontogeny (although the LAGs are interpreted as having been deposited prior to age
related structural remodeling; Chinsamy et al., 1995) and may or may not have still been
growing. The degree of development in the ‘Gobipteryx’ embryos and inference that
growth slows when locomotor activity begins led to the interpretation that growth slowed
290 
very early in enantiornithines, possibly earlier than known in other birds (Chinsamy and
Elzanowski, 2001).
In the case of Concornis lacustris, this taxon is envisioned to have maintained
rapid growth during early post-natal development (days to weeks), only slowing when
near-adult size was achieved (Fig. 9.3F; Cambra-Moo et al., 2006). This may offer an
explanation for the small size of most enantiornithines, such as Concornis and even
Longipteryx, which is larger than most Jehol enantiornithines with the exception of
Pengornis. However, some Late Cretaceous Lecho Formation enantiornithines are quite
large (Soroavisaurus, Lectavis) and Confuciusornis, which preserves rapidly formed
fibrolamellar bone structure in even the largest specimens, is much larger than the typical
Jehol enantiornithine (comparable in size to Pengornis). This interpretation of the growth
strategy of LH-2814, however, does not fit a precocial model, which would suggest
altriciality either evolved outside Neornithes or twice within Aves. The current
distribution of known specimens at varying ontogenetic stages also does not support such
an inferred growth strategy; juveniles are relatively well sampled, which would not be
expected if maturity was rapidly acquired.
The absence of growth series within a single species prevents assessing inferred
growth curves; however, the absence is also in itself significant. It would be expected
that growth strategies in enantiornithines would be reflected in the size range of
specimens and distribution of specimens within that range. Archaeopteryx is known from
several specimens and represents a size range of approximately 150% (Yalden, 1984;
Elzanowski, 2002). Size differences in Archaeopteryx have been interpreted as species
291 
differences (Wellnhofer, 1993; Elzanowski, 2002) however studies suggest that the size
range represents a growth series and that all morphological differences between
specimens can be explained through ontogeny (Houck et al., 1990; Senter and Robins,
2003). If the size range is indeed within a single species, then Archaeopteryx likely grew
over prolonged periods of time, as in other non-avian theropods.
In the case of enantiornithines, there are only obvious juveniles and adult
specimens known. While the study of Concornis reveals that not all ‘adult’
enantiornithines specimens are completely mature, there are no obvious size ranges
observed within a single species. This issue is complicated by the fact that only few
species are definitively known from more than one specimen (Longipteryx and
Gobipteryx) with taxonomic assignments for many specimens unclear. Longipteryx is
known from several complete specimens and one is considered a subadult (Zhang et al.,
2000; Zhou pers. comm.); the juvenile (IVPP V12552) is approximately 93% the size of
the holotype (differences based on relative lengths of elements, which range from 90-
95%, with 93% representing the mode). Additional specimens have been loosely referred
to Longipteryx sp. (DNHM D2889 and D2566); morphologically there are no obvious
differences, however preservation of these specimens is poor making it difficult to take
accurate measurements or identify detailed morphologies. Given the preservation of these
unstudied specimens, inferences about enantiornithine growth should await well-
documented populations. Regardless, without histological analysis, the size difference
between IVPP V12325 and IVPP V12552 can be interpreted in support of either
proposed growth strategy (slow post-natal growth, or rapid post-natal growth). If the
292 
latter was true and the period of ontogeny spent as an obvious juvenile was short, then it
would be unlikely that such a large number of juveniles would have been collected
(Chiappe et al., 2007); furthermore, juvenile specimens of ornithuromorphs are unknown
from the Jehol (more advanced birds are inferred to have developed faster and thus spent
short periods of time at subadult size). This would, however, lend support to the
hypothesis that Liaoxiornis may be a valid taxon distinguishable by is small size and not
a juvenile (Hou et al., 2002).
If these specimens are regarded as juveniles (as they are here), the data for
enantiornithines suggests that the group experienced two phases of rapid growth, the first
as embryos, and the second approximately during the second or third year of life, perhaps
to achieve sexual maturity (Fig. 9.3G). This supports the bimodal distribution of small
juvenile and adult enantiornithines and fits the histological observations of the few
sampled specimens. The juvenile Longipteryx (IVPP V12325) could thus be interpreted
as nearing the end of this second rapid growth phase. However, the dearth of evidence is
stressed and further evidence is required to make justified inferences about the clade. A
intermediate exponential growth phase is also inferred for Confuciusornis based on the
observed bimodal size distribution of known specimens (Chiappe et al., 2008). Inferences
regarding Confuciusornis differ from those for enantiornithines in that both size clusters
appear to be adult and fibrolamellar bone structure is present in both (de Ricqlès et al.,
2003; Chiappe et al., 2008). Histological analysis of IVPP V12325 and V12552 could
help to better understand growth in at least the longipterygid clade.
293 
While it is unclear the exact shape of enantiornithine growth curves; the thickness
of parallel-fibered bone and space between LAGs in the outer cortex of some
enantiornithines (Chinsamy et al., 1994, 1995) indicate that enantiornithines were not
simply restructuring bone tissue after the rapid growth phase, but growing slowly, unlike
most extant birds but similar to some paleognathus birds (Bourdon et al., 2009).
Differences in growth strategy may have been a factor in the survival of enantiornithines
(Zhang et al., 2000; Starck and Chinsamy, 2002). Despite their diversity and advanced
flight capabilities, enantiornithines go extinct at the Cretaceous-Paleogene boundary,
alongside all other non-avian dinosaurs. Their growth pattern, while not well understood,
clearly differed from that of modern birds. Differences in growth are correlated strongly
with energy consumption (Starck and Chinsamy, 2002) and therefore may have been a
factor in the extinction of the enantiornithines.

Morphological Changes during Ontogeny
For reasons related to growth strategies discussed above and an absence of growth
series, it is difficult to infer skeletal changes in morphology related to ontogeny. This is
further complicated by preservation and uncertain taxonomy, which can confuse
ontogenetic changes with taxonomic difference. Longipteryx is known from several adult
specimens (Zhang et al., 2000; Zhou pers. comm.) and one specimen interpreted as a
juvenile (IVPP 12552). There appears to be a greater degree of fusion present in the adult
specimen; in the juvenile the proximal and distal tarsals remain unfused from the tibia
and metatarsals, respectively (fused in IVPP V12325). The absence of fusion in
294 
compound bones is inferred to be evidence that a given specimen is not an adult,
however, DNHM D2950/1 appears to be an adult based on size, proportions of the orbit
to skull, and the absence of pitted periosteal bone surface but lacks fusion in all
compound bones. Thus, it is no longer clear how fusion relates to ontogeny within
enantiornithines; histological analysis of species with unfused compound bones may help
to clarify whether this feature is ontogenetic or a true feature of some species. This
character should be used in caution in diagnoses and ontogenetic inferences. Both
Longipteryx specimens, however, share numerous autapomorphies (such as fusion
between the semilunate carpal and carpal x which are then free from the metacarpals;
Chiappe et al., 2007) suggesting that they belong to the same species and that within at
least this lineage, fusion correlates with ontogeny. Given that the subadult is
approximately 90% the size of a presumably adult specimen, fusion of compound bones
can be interpreted as a feature that develops fairly late in the skeletal ontogeny of
Longipteryx. As in the smaller or subadult Archaeopteryx (i.e. Eichstätt specimen) and
some other non-avian theropods, juvenile Longipteryx (IVPP V12552) has relatively
more recurved and laterally compressed teeth relative to the presumably adult holotype
IVPP 12325 (Senter and Robins, 2003). Proportions do not appear to significantly differ
between specimens, although differential preservation prevents a completely accurate
assessment; this is also not surprising given the fact that IVPP V12552 is nearly the same
size as IVPP V12325 (estimated to be 93% the size of the holotype).
Another apparent ontogenetic feature is the presence of mandibular fenestrae, thus
far only known in juvenile specimens (Elzanowski, 1981; Chiappe et al., 2007). Although
295 
no adult is known of the Montsec hatchling (LP 4450), the only enantiornithine with two
fully perforated mandibular fenestrae (Sanz et al., 1997), the absence of such a feature in
all (inferred to be) adult specimens suggests this feature may be subject to ontogeny, and
ossify towards adulthood.

v. Conclusions
As in other groups, preserved information regarding the early stages of
enantiornithine life history is meager. Given the diversity of the clade, it is difficult to
draw conclusions from a handful of specimens of uncertain phylogenetic affinity. Based
on the overall phylogenetic placement of Enantiornithes, the possible morphologies and
strategies can be bracketed, and together with information from a few exceptional
specimens, the ontogenetic history of enantiornithines begins to unveil.
While undeformed eggs definitively of enantiornithine affinity are unknown,
identified specimens suggest that the eggshell of enantiornithines may have been
prismatic with two or three distinct layers. The egg itself would have been small, based
on the morphology of the enantiornithine pelvis and restriction of the oviduct,
asymmetrical with an air sac, and with a smooth shell. The degree of development
present in late stage embryos, and the proportions and presence of feathers in young
juveniles suggests that precociality may be plesiomorphic for the clade. Precociality is
inferred to be the plesiomorphic condition for Neornithes and Aves as a whole.
Growth rates and curves in enantiornithines are unclear, however sections of adult
femora reveal differences between the morphology of these birds and extant taxa. At least
296 
some enantiornithines experienced a rapid growth phase together with a prolonged phase
of slow growth that lasted more than a single year. How these phases fit within the
overall life history of these birds is unclear. Rates of growth cannot be determined,
however for at least part of their growth these enantiornithines grew much slower than
more advanced taxa. Given this inference, there are obvious complications for comparing
these taxa to the modern precocial – altricial spectrum. If enantiornithines grew for
periods up to five years, then even an altricial hatchling may be expected to leave the
parents before reaching adult size. This is an example of how trying to directly compare
enantiornithines to modern birds can often limit hypotheses.
There is little information regarding specific morphological changes related to
ontogeny other than increased degrees of fusion and ossification, and a slight change in
tooth morphology, as in Archaeopteryx and some non-avian theropods.
This review highlights several areas that require further research. Histological
analysis of many more specimens will help not only to reveal growth strategies and rates,
but also clarify the true variation in characters such as those related to fusion and
taxonomic status of some specimens (i.e. IVPP V12552).

297 
CHAPTER 10: INTEGUMENT

i. Introduction
The preservation of advanced feather structures in the earliest birds and some
non-avian theropods suggests that enantiornithines would have had comparable if not
more derived integument. Archaeopteryx was first identified as a bird largely by its large
asymmetric pennaceous remiges; the morphology and distribution of wing feathers in this
taxon and other primitive birds (Confuciusornis) is considered essentially modern
(Chiappe et al., 1999; Elzanowski, 2002; Chuong et al., 2003; Zhang F-C. et al., 2006).
Bilaterally symmetric pennaceous feathers have a wide distribution within the avian
outgroup (Ji et al., 1998; Ji et al., 2001; Norell et al., 2002) and aerodynamic feathers
(asymmetrical pennaceous feathers), as well as flight related structures such as the alula
not present in Archaeopteryx, are known in at least one non-avian theropod (Zhang F-C.
et al., 2006). The identification of at least one enantiornithine feather type not present in
modern birds, though apparently present in other Mesozoic birds, and the wide and
variable distribution of different feather morphologies within theropods suggests that the
evolution of neornithine integument is more complicated than suggested by
Archaeopteryx and warrants further investigation.
The early record of enantiornithines, the El Brete material, Neuquenornis, the
first Chinese enantiornithines and isolated material from North America (Walker, 1981;
Brett-Surman and Paul, 1985; Sereno and Rao, 1992; Zhou et al., 1992; Chiappe and
Calvo, 1994; Varricchio and Chiappe, 1995) did not preserve any integument. The
298 
discovery of the exceptionally well-preserved Spanish enantiornithines in the late 90’s
and the continuing surge of feathered birds from China helped to literally flesh out our
interpretation of the enantiornithine plumage. The available material reveals not only the
wings of these birds, but also the tail and additional structures that are important for
inferring enantiornithine flight capability and integumentary advancement.
Unfortunately, this information is almost entirely restricted to the Early Cretaceous, yet
the advanced characters observable in these early birds suggests that Late Cretaceous
forms would have had comparable if not more advanced integument.
This chapter provides a comprehensive review of feather structures (wing, tail,
alula) and morphologies preserved within the clade, including information from several
unpublished specimens. Several enantiornithines are known to possess feathers unlike
those of any modern bird; these are discussed in terms of the unique molecular pathways
they are inferred to represent and how they affect our interpretation of the evolution of
basal bird integument.

ii. Material
Approximately half the named Jehol enantiornithines are preserved with feathers
(Table 10.1; Hou et al., 1999; Zhang and Zhou, 2000; Zhang et al., 2000; Hou et al.,
2004; Li et al., 2006; Zheng et al., 2007; O’Connor et al., 2009). The differential
preservation that results in the absence or presence of feathers between Liaoning
specimens is not fully understood, however feathered specimens are relatively more
abundant in the older Yixian Formation leading to the hypothesis that the higher
299 

Table 10.1. List of enantiornithine material with feathers incorporated in this review;
includes current published material as well as four unpublished specimens from the
DNHM and two from CAGS.
300 
frequency of volcanic eruptions—and thus greater volume of pyroclastic sediments—
during the deposition of this unit helped to promote feather preservation (Zhou and
Zhang, 2006a). Outside China, there are several specimens from the Spanish Lagerstätten
at Las Hoyas and Montsec that preserve feathers (Lacasa-Ruiz, 1986; Sanz and
Buscalioni, 1992; Sanz et al., 1996; Sanz et al., 1997; Sanz et al., 2001), and one
specimen from Lebanon (Dalla-Vecchia and Chiappe, 2002). Feathers have also been
reported from the Crato Member of the Santana Formation in Brazil (Naish et al., 2007),
however while one specimen is reported to be an enantiornithine, this claim is weakly
supported and unverifiable as the specimen is in a private collection. No feathers from
this formation are unequivocally known to belong to enantiornithines and for this reason
are not included in this view. Only feathers associated with skeletons and thus
definitively known to be enantiornithine are discussed here. Table 10.1 lists all published
material with feathers and unpublished material included in this study.

iii. The Wing
The preservation of the wing in no known enantiornithine specimen is
exceptional, as in several specimens of Archaeopteryx; Eoalulavis preserves beautiful
feathers but they are incomplete and their true lengths cannot be determined. Several
Chinese specimens preserve a partial outline of the wing, but the number or exact length
of individual feathers cannot be discerned (Eoenantiornis, “Liaoxiornis,” Protopteryx,
Dapingfangornis, Shanweiniao, DNHM D2884; Table 10.2). The most information that
301 
 Table 10.2. Enantiornithine specimens preserving wing integument. Basal birds for
comparison. Measurements in mm.
302 
can be derived from these specimens is usually a lower limit on the number of feathers
and length of the longest preserved primary (primaries vary in length with position).
Though the paucity of specimens with concrete morphological data prevents in
depth comparison with other groups, wing morphology appears comparable to that of
modern birds. Asymmetrical remiges can be identified in several specimens (i.e.
Longirostravis, Concornis, Protopteryx); their presence is unsurprising given the
presence of essentially modern aerodynamic feathers in basal birds and some non-avian
theropods (Chiappe et al., 1999; Christiansen and Bonde, 2004; Xu et al., 2003). The
number of primaries preserved in Eoalulavis (eight) is close to the number in modern
birds (typically ten, nine in some passerines; Proctor and Lynch, 1993). This is lower
than the number in Archaeopteryx (twelve; Elzanowski, 2002) although the wing in
Eoalulavis may be incomplete. While the arrangement is similar, combined differences in
the overall wing structure such as the absence of remige papillae on the ulna (reportedly
present in the Kaiparowits avisaurid; Hutchison, 1993; Chiappe and Walker, 2002), a
fully-fused carpometacarpus, and dorsoventral expansion in the first phalanx of the major
digit in all known enantiornithines indicates that feather attachment differed not only
from that of Neornithes (Elzanowski, 2002) but also from more primitive taxa (Forster et
al., 1998; Turner et al., 2007b).

Wing Loading
Wing loading is an aerodynamic parameter that is highly correlated with flight
style. Wing loading is measured by taking the mass (in Newtons) over the wing area (in
303 
square-meters); it represents the weight that can be supported by a given wing area but
requires several measurements to be accurately measured (wing length, primary length,
and the femur to estimate body mass). As weight increases, so does wing loading, and a
bird must flap its wings faster. Different wing loading values reflect different flight
styles; for example, a hummingbird hovers, a flight style that already requires high wing
beat frequency and thus must have a low wing loading value (approximately 20 N/m
-2
;
Videler, 2005). Small passerines are efficient fliers with relatively large wings, and have
low wing loading values (25-40 N/m
-2
; Alerstam, 1993). Ducks can fly quickly and have
medium wing-loading values with higher values in diving ducks compared to wading
forms (56-130 N/m
-2
); the auk, whose wing shape is similar to that of a duck, can fly but
primarily uses its small wings for swimming underwater and thus has very high wing
loading values (approximately 320 N/m
-2
) and must maintain a high wing beat frequency
in flight.
Most fossil taxa are missing at least one data component and estimates would be
inaccurate from most known enantiornithine specimens. Nevertheless, published
estimates of wing-loading values have been provided for Iberomesornis, Concornis and
Eoalulavis (Sanz et al., 2001). The mass of each fossil taxon was based on estimated
masses derived from regression analyses of femora lengths in modern birds. The wing
area values were derived from a regression analysis of extant wing-loading values. The
values provided are therefore based on nothing other than femur length and comparable
modern birds, a circular derivation. Since the relationship between limb proportions and
wing area may differ in the enantiornithine clade, these estimates are extremely weak and
304 

Figure 10.1. Slab one of DNHM D2884 ½ with feather impressions; scale bar = 1 cm.
305 
baseless. For example, the primaries in Confuciusornis are relatively long compared to
other known birds, but since the Sanz et al. (2001) measurements did not include
anything beyond the femur length of Confuciusornis, this was not considered when
estimating the taxon’s wing loading. However, as mentioned, enantiornithines and
Mesozoic birds in which the wing area (including the area between the wings) can be
approximated are rare, thus providing no alternative for estimating wing loading.
The unpublished specimen, DNHM D2884½, is skeletally fairly complete,
although poorly preserved, and retains a faint albeit incomplete impression of the wing
(Fig. 10.1). The wing is not fully extended making it impossible to accurately measure
wing area, however it is estimated to fall somewhere between 0.045 and 0.095 m
2
. Based
on femur length, DNHM D2884½ is approximately the same size as Concornis; mass is
estimated to be 0.73 – 0.77 N (Alexander, 1983; Sanz et al., 2001). Estimated wing
loading values fall between 7.68 and 17.11 N/m
2
. Not surprising given the range of
estimated values, the wing loading value estimated for Concornis (13.18 N/m
2
), and thus
those of comparably sized neornithines, falls within this range. Unfortunately, the
preservation of the wing impression in DNHM D2884½ does not reveal wing shape and
thus the aspect ratio (wing length vs. width) of the wing cannot be inferred. More
accurate estimates will have to await the discovery of specimens with better preservation.

The Alula
While most known enantiornithine specimens do not preserve many details, the
presence of certain structures can be discerned. Eoalulavis hoyasi, from the Early
306 
Cretaceous of Spain, preserves at least one symmetrical feather that originates around the
alular metacarpal and is interpreted as a primitive alula (Sanz et al., 1996). From China,
several more specimens preserve a feathered alula: Protopteryx (Zhang and Zhou, 2000),
Eoenantiornis (Zhou et al., 2005), IVPP V13939 (Zhang and Zhou, 2004) and
‘Dalingheornis’ (Zhang Z-H. et al., 2006 - unfortunately the latter is in private hands and
thus cannot be used as evidence of enantiornithine diversity). In specimens where the
alular metacarpal is visible (Eoenantiornis, Protopteryx), the distal cranial surface lacks a
cranial projection for the attachment of feathers, the alular process (proc. alularis) of
modern birds. The alular digit of Protopteryx (Fig. 10.2) is unreduced so that the large
ungual phalanx lies distal to the distal margin of the major metacarpal; the alular digits of
Eoenantiornis and Eoalulavis (Fig. 10.3A, B) are short, level with the distal end of the
major metacarpal – a stage in the reduction of the avian hand. The absence of any real
modification to the enantiornithine manus prior to the acquisition of the feathered alula
shows that at least within Enantiornithes, the feathered structure preceded the evolution
of any osteological modification from the primitive morphology of more basal birds.
An alula is absent in more primitive taxa (Confuciusornis, Sapeornis, Jeholornis)
although the dromaeosaur, Microraptor gui (Xu et al., 2003) possesses short pennaceous
feathers on the alular digit (not metacarpal). The alular digit in this taxon is also reduced
relative to other dromaeosaurids suggesting these feathers may represent a structure
homologous to the alula in modern birds. The individual reduction of the manus in each
lineage suggests the structure may have evolved more than once within theropods. The
presence of an alula in basal enantiornithines and sympatric Jehol ornithuromorphs (Zhou
307 

Figure 10.2. Manus of Protopteryx IVPP V11665; A, photograph; B, camera lucida
drawing.
308 
and Zhang, 2005) suggests that the structure may be plesiomorphic for Ornithothoraces
(absent in Confuciusornithidae). The alula increases maneuverability by facilitating take-
off and landing, and aiding flight at low speeds, a structure that would be particularly
advantageous in an arboreal habitat (landing on branches). The alula responds to low
pressure on the dorsal surface of the wing, and when lifted allows the bird to increase its
angle of attack (the angle formed by the wing and the oncoming air) in flight beyond the
normal stall point and thus fly at lower speeds (Sanz et al., 1996). The presence of this
feature in enantiornithines, even without the presence of an alular process, suggests these
birds were quite advanced in their flight capabilities. The fact that an alula is present in
the basal enantiornithine Protopteryx (Zhang and Zhou, 2000) suggests that this trait may
be primitive and its apparent absence in most advanced enantiornithines may be
preservational.

iv. Tail
Enantiornithine tails preserve more diversity than their sympatric and more
advanced ornithuromorph relatives, or any other group of Mesozoic birds. The most
common morphology in the clade is for the pygostyle to bear short down-like tail coverts
and no elongate rectrices (i.e. Eoenantiornis, Longipteryx, Longirostravis; Fig. 10.4). In
such specimens, typically a fuzzy organic halo of feather impressions surrounds the body;
often preservation is best in the neck and tail region. These feathers are not
morphologically distinct from those that appear to cover most of the body (see below).

309 
Paired Rectrices
Display morphologies are the second most common, typically consisting of an
elongate pair of rectrices protruding from the mass of tail coverts, extending distally from
the pygostyle (Dapingfangornis, Protopteryx, DNHM D2884, CAGS-IG-07-CM-001).
The strange morphology of these feathers has led to their identification as elongate scales
and has been used to support alternative hypotheses for feather morphogenesis (Zhang
and Zhou, 2000; Zheng et al., 2007). Others argue that these represent modified
pennaceous feathers (Prum and Brush, 2002; Zhang F-C. et al., 2006). Information from
well-preserved specimens supports the latter hypothesis and hints at the particular
molecular modifications that may have produced such a morphology. Though not
originally interpreted as display features (Zhang and Zhou, 2000; Chuong et al., 2003),
new and more complete finds suggests this is the most likely interpretation for these
structures. The morphology of these feathers differs between taxa, suggesting a larger
hidden diversity of display morphologies and strong selection within the clade for sexual
display.

Known Diversity. The feathers in Protopteryx (IVPP V11665) are incomplete yielding
little information; they are preserved projecting straight and nearly parallel from the distal
end of the pygostyle for a length of 82 mm. The two feathers overlap proximally but
appear slightly splayed distally; Zhang and Zhou (2000) describe these feathers as scale-
like and primitive. The preserved portion of the feather appears to be a wide and flat
rachis, a morphology unrecognized in modern birds (Chuong et al., 2003).
310 

Figure 10.3. Enantiornithine alula, photograph with line drawing: A, Eoenantiornis; B,
Eoalulavis.
311 

Table 10.3. Enantiornithine specimens preserving elongate rectrices with Confuciusornis
and ornithuromorphs for comparison (measurements in mm).
312 

Figure 10.4. Typical enantiornithine caudal integument (elongate rectrices absent): A,
Longipteryx IVPP V12352; B, IVPP V13939; C, Eoenantiornis IVPP V11537.
313 
The paired rectrices in Dapingfangornis (Fig. 10.5) appear to be modified
pennaceous feathers that generally resemble the filoplumes of modern birds in that they
have an elongate rachis relative to the ‘vaned’ portion of the feather (simply branched in
filoplumes). Modern filoplumes are highly derived structures and not considered
homologous to the structures in enantiornithines. The rectrices in Dapingfangornis
appear in place and nearly complete with only the proximal third missing, not preserved
where the feathers overlapped skeletal elements. If this interpretation is correct, then
measured from the pygostyle to the distal end of the feather, the total length of these
feathers would have measured 131 mm. Measured from the proximal end of the
preserved portion (just distal to the left foot), the feathers measure 79 mm (Table 10.3).
The distal ends are complete in Dapingfangornis and show that these feathers were
narrow for most of their length (width 1.3 mm), proximally resembling the preserved
portion of the feathers in Protopteryx. A narrow dark region borders the lateral margins
of the rachis for most of its length; this is interpreted as undifferentiated vane (Zhang F-
C. et al., 2006). The vane rapidly elongates and differentiates into barbs over the distal
quarter of the feather, forming a bulb-like distal expansion (6.1 mm maximum distal
width) (15% of estimated feather length).
An undescribed specimen from the Xiagou Formation (~115 - 105 Ma; You et al.,
2006) of Gansu Province, northern China, also preserves paired elongate tail feathers
(CAGS-IG-07-CM-001). These are the best-preserved feathers of this morphology within
Enantiornithes with individual barbs clearly visible. The proximal ends of these feathers
are not preserved however their length is estimated based on the assumption they reached
314 

Figure 10. 5. Close-up of the right rectrice of Dapingfangornis LPM 00027 (formerly
LPM 00039): A, photograph; B, camera lucida drawing.
315 
the pygostyle (Table 10.3). The feathers end distally at more or less the same level,
supporting the interpretation they are preserved in place. The tail feathers in this Xiagou
enantiornithine are similar to those of Dapingfangornis in that they both possess the same
massive rachis, with a thin margin of undifferentiated vane for much of the total length.
However, the barbs in CAGS-IG-07-CM-001 begin to differentiate at the distal third, and
gradually elongate (lacking the rapid bulb-like expansion in Dapingfangornis). The
maximum distal width (measured 9 mm from the distal end) is 8.6 mm, nearly twice the
proximal width of 3.6 mm, which is measured 53.4 mm from the pygostyle. The thick
rachis stays approximately the same width (2.8 mm) the entire length of the feather,
tapering slightly at the distal end. The barbs form an acute angle (12˚) with the rachis
suggesting the barbs are brushed back (preserved distomedially displaced). The barbs are
nearly parallel to one and other. Proximally it is difficult to indentify individual barbs,
which supports Zhang et al.’s (2006) interpretation that the proximal vane is in fact
undifferentiated, but distally spaces clearly separate each barb. Although the feather is
not preserved well enough to say unequivocally, the pennaceous portion of these rectrices
may have been close vaned proximal on the barb and open vaned distally. If correct, this
implies the presence of differentiated barbules (into hooklets and cilia) that have spatially
arranged themselves only on the proximal half of the barb, a specialization known in
some modern feathers (Stettenheim, 2000).
Another undescribed specimen (DNHM D2884 ½) preserves a faint pair of tail
feathers that appear similar to those described above. The impressions are very faint and
thus difficult to interpret but two elongate structures clearly project from the pygostyle,
316 
extending distolaterally forming an acute angle. It is unlikely that these structures were
artificially added to the slabs given their association with the pygostyle and the
undisturbed coverts that cover most of the caudal region (Fig. 10.1,6A,B). The distal end
of the right, which measures 79 mm from the pygostyle, is clearly incomplete; the left
continues approximately 30 mm farther before fading so that the distal end cannot be
observed (Table 10.3). For their preserved lengths, the structures show minimal
expansion, the proximal width and distal widths are subequal (2.3-2.4 mm). These
structures are interpreted as poorly preserved feathers similar to those preserved in
CAGS-07-CM-001, with only the wide rachis discernible in DNHM D2884 and the vane,
along with the distal ends, is not preserved. Like Protopteryx, the width of the rachis and
size of the specimen indicate this feather was of the ‘rachis-dominated’ morphology
(Chuong et al., 2003). Interpretations based on Protopteryx were hindered by incomplete
preservation; the discovery of Dapingfangornis and CAGS-07-CM-001 reveals that these
feathers were pennaceous, possibly possessing barbules, in addition to barbs, that varied
in their distribution and morphology.
All these specimens described above appear to possess the same feather
phenotype, however, between specimens the feathers show a range of morphologies and
vary in length considerably, though in most they appear quite long (CAGS-05-CM-004,
DNHM D2884 ½). The feathers in Protopteryx and DNHM D2884 ½ are interpreted as
incomplete, and barbs may have been present distally, as in CAGS-05-CM-004 and
Dapingfangornis. The morphology of the pennaceous portion of the feather is unique in
317 

Figure 10.6. Close up of the pygostyle and proximal rectrices of DNHM D2884 ½ clearly
showing the elongate tail feathers emerging from the caudal coverts: A, photograph; B,
camera lucida drawing.
318 
each specimen where preserved, varying in extent relative to feather length and the length
of the individual barbs.

Feather or Scale. These feathers have been suggested to represent an intermediate
morphology in the evolution of the feather (Zhang and Zhou, 2000; Zheng et al., 2007).
The presence of modern flight feathers in the non-avian dinosaur Microraptor gui,
Archaeopteryx, and other basal birds and the absence of a specimen with elongate scale-
like integument largely covering the body makes this hypothesis weak. Instead,
protofeathers in the fossil record are known to be simple, hollow filament-like structures
(Chen et al., 1998; Xu et al., 1999; Xu et al., 2000); such structures with varying
branching morphologies (including pennaceous) are known throughout Theropoda in
varying combinations and distributions over the body (Ji et al., 1998; Ji et al., 2001; Xu et
al., 2001; Norell et al., 2002).
Current knowledge of feather morphogenesis also does not support this
hypothesis. Barbs are inferred to have evolved before the rachis, which is formed by barb
fusion (Chuong et al., 2003). Since the enantiornithine rectrices appear to be rachis
dominated and pennaceous, indicating barbules were also likely present, these feathers
are more likely to represent modified pennaceous feathers than primitive holdovers from
an early stage in feather evolution.

Molecular Inferences. The morphology of these feathers differs from that of any modern
feather; the wide rachis was at one time interpreted as an elongate scale and evidence that
319 
modified scales led to the evolution of feathers (Zhang and Zhou, 2000). The isolated
nature of this feather morphology on the skeleton (rather than distributed over the entire
body) suggested these feathers represent derived features (Prum and Brush, 2002;
Chuong et al., 2003). Novel experiments have expanded the current understanding of
feather morphogenesis (Yu et al., 2002; Prum and Brush, 2002; Yue et al., 2006), which
allows for speculation on the molecular pathways that may have produced the rectricial
morphology preserved in these specimens. Feather morphogenesis is the result of
complicated interactions between bone morphogenetic protein (BMP) 2 and BMP4,
noggin and sonic hedgehog (Shh) which results in a hierarchical pattern of branching in
the epithelial cells that produces the diversity of morphologies known within Aves
(Chuong and Widelitz, 1998; Yu et al., 2002; Harris et al., 2002; Chang et al., 2004;
Prum, 2005; Lin et al., 2006; Alibardi, 2006). Complex morphologies are produced by
the interactions and varying expression of important molecular signals such as wingless
int (Wnt3a), which has been shown recently to have an important role in producing the
asymmetrical morphology necessary for flight (Yue et al., 2006).
The following scenario is proposed for the morphogenesis of the avian feather: (1)
BMP4 exceeds the level of noggin at the proliferation zone causing epithelial cells to
form a cylinder; (2) epithelial cells form barb ridges as noggin expression exceeds BMP4
in the ramogenic zone; (3) a periodic arrangement of Shh and BMP2 positive and Shh
negative zones forms, the former representing where marginal plate cells die creating
barb ridge spaces and the latter representing the zone of growth of the barb ridge; (4) barb
ridge cells express BMP2 and BMP4, become ordered, and differentiate into barbules;
320 
and (5) noggin levels return to low levels, as in stage (1) and the calamus forms (Yu et
al., 2002). Experiments show that modifying the expression of these molecules can
produce primitive or novel morphologies; for example, the overproduction of BMP can
result in an enlarged shaft, such as those present in the elongate tail feathers of
enantiornithines (Yu et al., 2002).
The unique morphology of the elongate enantiornithine tail feathers could be
produced by a gradual reduction in noggin as the feather grows, resulting in the
decreasing length and absence of differentiation between barbs proximally, which would
be similar to the early onset of the last stage of feather morphogenesis. BMP2 over-
expression has been shown to result in feather phenotypes with an enlarged rachis and
barb fusion (Yu et al., 2002), both features present in these enantiornithine tail feathers.
This may suggest that the modulation of BMP2 and noggin may have played an
important roll in the evolution of this unique feather morphology. Within this feather
type, Dapingfangornis and CAGS-07-CM-001, though similar, possess morphological
differences suggesting diversity within the phenotype and the modification of a similar
molecular pathway; it is suggested that the main difference in appearance can be
produced by an earlier and more rapid return to stage (1) during the morphogenesis of the
tail feather of Dapingfangornis.

Function. Since Protopteryx, like many other enantiornithines, is inferred to be arboreal,
the elongate feathers in this taxon and others are inferred to have contributing to balance,
similar to the way a squirrel tail functions (Chuong et al., 2003). The subsequent
321 
discovery of several additional specimens preserving complete feathers questions this
interpretation. The length of these feathers suggests that despite the robust rachis, these
feathers would likely not have been functional for balance or defense, and thus may
represent display structures. The similar feathers preserved in some confuciusornithids
are also interpreted as display structures and their variable presence in specimens
suggests sexual dimorphism (Feduccia, 1996; Hou et al., 1996); recent studies have not
been able to support or reject this hypothesis (Chiappe et al., 2008).

Complex Tail Morphologies
The tail of modern birds is, in many taxa, highly specialized for aerodynamic
function, generating lift and increasing maneuverability (Gatesy and Dial, 1996). In these
taxa, the feathers are arranged to form an airfoil, which generates lift. Airfoils in birds are
formed by multiple slightly-overlapping feathers with special structural rigidity to
withstand the forces of flight (Gill, 1994). The long, thin, paired rectrices of
Confuciusornis, Protopteryx and other enantiornithines would not be capable of
generating substantial lift; since the only morphology known in the clade for sometime
was that of paired (Protopteryx, Dapingfangornis) or absent rectrices (i.e. Eoenantiornis),
it was suggested that enantiornithines did not evolve aerodynamic tail morphologies like
those of modern birds (Clarke et al., 2006). However, recent finds have started to reveal a
diversity of enantiornithines with multiple elongate tail rectrices suggesting that
enantiornithines may also have refined their flight abilities through rectricial
advancements.
322 

Paraprotopteryx. The first enantiornithine described with more than two elongate tail
feathers (Zheng et al., 2007), this taxon possesses four tail feathers very similar in
morphology to those of Dapingfangornis and CAGS-07-CM-001. The feathers are long
and distally expanded and form a loosely graded structure, with the lateral feathers
slightly shorter and smaller than the medial pair. Morphologically, like the paired
rectrices in other enantiornithines, these feathers appear to be rachis dominated and
distally pennaceous. Barbs are present on the distal fifth of the feather, elongating
distally; the feather appears to be close vaned and thus barbs and barbules are inferred to
be present in the distal portion.
The tail feathers in Paraprotopteryx are splayed in such a way that they do not
form a continuous surface that would have been capable of generating substantial lift.
Even if they are preserved displaced from their life posture, the length of the feathers
(Table 10.3) and their spoon-like morphology are also not consistent with an
aerodynamic function. These feathers, like those of Protopteryx and Dapingfangornis,
are therefore considered display structures. The main difference between these feathers
and those of Dapingfangornis is the number; the modified molecular pathway proposed
for the paired rectrices is also suggested for the feathers of Paraprotopteryx.

DNHM D1878 ½. Only one specimen suggests that enantiornithines may have achieved
tail modifications comparable to those of modern birds; the only known specimen of
Shanweiniao (DNHM D1878 ½) preserves several closely arranged elongate tail feathers
323 

Figure 10.7. The tail feathers of Shanweiniao DNHM D1878 ½ : A, photograph of slab
one; B, close up of photograph of boxed area preserving rectrices; C, camera lucida
drawing of rectrices.
324 
(Fig. 10.7). These feathers are largely incomplete, missing the proximal and distal ends,
as well as the lateral margins so that the exact number of feathers or the shape of the tail
cannot be determined. The published estimate of four is conservative (O’Connor et al.,
2009); six can be discerned (two are largely incomplete) and the total count may have
been even greater. What is preserved suggests the presence of an elongate, feathered tail
that formed a continuous surface that would have then been capable of generating lift and
increasing aerodynamic performance. The distal ends are not preserved so it cannot be
determined if the tail was graded, as in contemporaneous ornithuromorphs with similar
tail morphologies (Yixianornis and Hongshanornis; Clarke et al., 2006; Zhou and Zhang,
2005; pers. obs.).
The pygostyle morphology of Ornithuromorpha and Enantiornithes is very
different, suggesting functional differences (Clarke et al., 2006). The presence of an
aerodynamic tail within the enantiornithine clade suggests the presence of a bulb
rectricium, a feature that, in modern taxa, controls the movement of tail feathers,
allowing for fine-tuned flight capabilities. Prior to the discovery of Shanweiniao, tails of
this morphology were only known from two genera of ornithuromorph (Yixianornis and
Hongshanornis; Clarke et al., 2006; pers. obs.). This led to the suggestion that this
rectricial morphology and the associated bulb rectricium only evolved within
Ornithuromorpha. The differences in pygostyle morphology between ornithuromorphs
and more basal birds was used to corroborate this hypothesis, as even the pygostyles of
basal ornithuromorph where preserved (i.e. Yixianornis) are small, shorter than the
combined length of the free caudals, and plow-like, as in modern birds. More primitive
325 
pygostylians, enantiornithines and confuciusornithids, have a straight and robust
pygostyle that is equal to or longer than the combined length of the free caudals. While it
cannot be determined at this time if enantiornithines possessed a bulb rectricium or how
many times this feature evolved, we suggest that the presence of this feature cannot be
ruled out on the basis of pygostyle morphology alone.

CAGS-05-CM-004. An additional morphology is known for enantiornithines, preserved
in a single undescribed specimen (CAGS-05-CM-004) from the Xiagou Formation
(Lamanna et al., 2005). The specimen only preserves its caudal and distoventral
integument but it appears three or four feather morphologies were present in this region
alone. Down-like coverts approximately 7 mm long line the ventral margin of the pelvic
region, but elongate towards the tail region (approximately 12 mm). These feathers
continue over the tail region, but a large number of elongate feathers with different
morphologies are also present projecting caudally and dorsocaudally from the pygostyle.
The estimate of a minimum of twelve feathers is offered, however the quality of
preservation, degree of overlap and variation of the feather morphology hinders an
accurate assessment. Two types of pennaceous feather are present, differentiated by
length; the shorter feathers are approximately 18 mm while the longer feathers are
incomplete (approximate length 40-45 mm). Several rachis-dominated feathers like those
in Protopteryx, may be also be present, but also incomplete, so their distal ends are
unknown. Any conclusions about the number of feather morphotypes present in this
specimen and their function are premature until further study has been done.
326 
 
v. Body feathers
While modern feathers are present in enantiornithines (the remiges of the wing),
enantiornithine body feathers appear different from those of neornithines. In modern
birds, coverts are found on the unspecialized regions of the body surface (Stettenheim,
2000). Body coverts are modified pennaceous feathers; their barbs do not form
interlocking vanes but possess a stiffened base that maintains their alignment
(Stettenheim, 2000). In enantiornithines, poorly defined feathers are often preserved
associated with most of the skeleton, primarily the neck and caudal region
(Longirostravis, Eoenantiornis, Protopteryx, Dapingfangornis, Shanweiniao, Longipteryx
and DNHM D2884 ½). The feathers appear uniform with only some variation in length in
different regions of the body (Longipteryx) with the exception of those on the tibiotarsus,
which are separately discussed below. The body feathers in Longipteryx and Protopteryx
are non-shafted (Zhang F-C. et al., 2006), more similar to down feathers. Their
morphology is difficult to interpret because of the large overlap between feathers,
however Protopteryx preserves isolated feathers that show the absence of a shaft (Zhang
F-C. et al., 2006); the isolated feathers differ from down feathers in that they do not
radiate from a short rachis but rather seem to consist of undifferentiated vane that frays
into individual barbs distally (Fig. 10.8). No herringbone structure is apparent, as one
would expect if the coverts were pennaceous, as in modern birds. The exception is the
vaned pennaceous feathers on the tibiotarsus discussed below, interpreted as a specialized
feather tract. ‘Non-shafted’ feathers forming an organic halo of filaments radiating out
from the body contour are commonly preserved among Mesozoic birds and on parts of
327 

Figure 10.8. Close up of isolated body covert of Protopteryx IVPP V11665 showing
absence of vane.
328 
some non-avian theropods (Zhang F-C. et al., 2006). This morphology is unknown in
modern birds.

vi. Leg Feathers
Hindlimb feathers have received a great deal of attention since the discovery of
the dromaeosaur Microraptor gui, and the reinvigoration of the four-wing model of early
flight (Xu et al., 2003; Longrich, 2006; Chatterjee and Templin, 2007; Martin, 2008).
Recent studies have argued that Archaeopteryx possesses aerodynamically functional
‘hindlimb’ feathers, similar to M. gui, and that these feathers would have facilitated flight
in Archaeopteryx and other taxa known to possess them (Longrich, 2006). While the
evidence for hindlimb feathers in Archaeopteryx is poor (supposedly prepared away),
their documented presence in enantiornithines has led researchers to infer support for a
‘tetrapteryx’ stage in the evolution of flight in birds, in which hindlimb integument
allowed for flight at slower speeds and a tighter turning radius (Zhang and Zhou, 2004;
Longrich, 2006; Martin, 2008). There are many problems with this argument, and while
the feathers in M. gui are clearly aerodynamic, they show major differences between the
feathers in Archaeopteryx and enantiornithines suggesting a different origin and function.
‘Hindlimb’ feathers in M. gui are located on the tarsometatarsus (Fig. 10.9), as in
the basal maniraptoran Pedopenna daohugouensis (Xu and Zhang, 2005). In addition to
these feathers, M. gui preserves wing impressions comparable to Archaeopteryx in the
number and arrangement of remiges and their morphology (asymmetrical pennaceous
feathers). In face of such a clearly aerodynamic integumentary structure, researchers
329 

Figure 10.9. Hindlimb feathers of maniraptorans: A, Microraptor gui IVPP V3352; B,
Berlin Archaeopteryx (from Longrich, 2006); C, Golden Eagle Aquila chrysaetos; D,
Longipteryx IVPP V12325; E, DNHM D2884 ½; F, G, IVPP V139139.
330 
inferred that the elongate asymmetrical pennaceous feathers on the metatarsus must also
have been adapted for some function related to flight. Their length makes it difficult to
envision M. gui as cursorial, and many arguments have been made for an arboreal gliding
lifestyle, using its hindlimbs to supplement its forelimbs in generating lift (Xu et al.,
2003; Chatterjee and Templin, 2007; Martin, 2008). Pedopenna is represented by an
isolated hindlimb with feathers, which are recognizable but largely overlapping so that
little morphological information can be discerned. The feathers are clearly shorter than
those of M. gui and described as bilaterally symmetric and pennaceous (Xu and Zhang,
2005). These two taxa therefore suggest a great diversity of hindlimb feather patterns
expressed in a wide range of different taxonomic groups.
While the presence of hindlimb feathers in Archaeopteryx is accepted by some
researchers (Zhang F-C. et al., 2006; Martin, 2008) the ‘evidence’ is largely gone,
reportedly lost during preparation of the Berlin specimen over one hundred years ago
(Longrich, 2006). These feathers are reported on the femur and tibia (Christiansen and
Bonde, 2004; Longrich, 2006). The preservation of hindlimb feathers is in itself
equivocal, yet the morphology of the feathers on the tibia (crural feathers) has been
described as curved, asymmetrical and pennaceous, with overlap between individual
feathers to form an airfoil (Longrich, 2006). Given the current condition of these feathers,
such detailed morphological inferences are likely premature. However, crural feathers are
clearly documented within enantiornithines. The variable presence of hindlimb feathers
within the latter clade observed by previous researchers combined with their questionable
presence in Archaeopteryx produced two hypotheses very much at odds with each other:
331 
the avian common ancestor had hindlimb feathers or it didn’t (Longrich, 2006). New
specimens and a reevaluation of known material reveals the distribution of crural feathers
within enantiornithines is much more cosmopolitan than previously documented, lending
support to the former inference.
Most enantiornithines with well-preserved integument preserve crural feathers
(Longipteryx – Fig. 10.9A, contra Longrich, 2006, Dapingfangornis, Eoenantiornis,
Longirostravis, IVPP V13939, DNHM D2884 ½). The preservation is clearest in an
unnamed specimen, IVPP V13939 (Fig. 10.9F, G), preserving elongated pennaceous
feathers on the tibiotarsus (Zhang and Zhou, 2004). These feathers are nearly
symmetrical and slightly curved mediodistally and differ from abdominal coverts in their
greater length (per Zhang and Zhou, 2004) and breadth.
Crural feathers are not as clear in most other specimens (Longipteryx,
Eoenantiornis, Dapingfangornis, Longirostravis, DNHM D2884 ½ and possibly
Protopteryx). As in Pedopenna, the large overlap of these feathers makes it difficult to
unequivocally determine the morphology of these feathers. However, the feathers appear
to be pennaceous (parallel shafts are clearly preserved in Dapingfangornis) and slightly
longer than the non-shafted coverts of the body, as in IVPP 13939.
Following interpretations of ‘hindlimb’ feathers in Archaeopteryx and non-avian
theropods, Zhang and Zhou (2004) suggested the crural feathers in IVPP V13939 are the
vestiges of functional aerodynamic feathers present on the legs in basal taxa and kin
(Zhang and Zhou, 2004). However, as discussed above, the leg feathers in M. gui (Xu et
al., 2003) and Pedopenna are found on the tarsometatarsus, a condition currently
332 
unknown among the enantiornithines and other Mesozoic birds. The feathers preserved in
IVPP V13939 are on the tibiotarsus, not strongly asymmetrical and not greatly longer
than body coverts (feathers on the tarsometatarsus in M. gui are two to four times the
length of body coverts). This is similar to what has been described for Archaeopteryx,
though the preservation of the latter limits any comparison.
Crural feathers are present in modern birds (Fig. 10.9C) covering the proximal
portion of the tibiotarsus and contiguous with the coverts of the abdomen (Proctor and
Lynch, 1993). Some taxa have elongated these feathers for specialized functions (i.e.
Falconiformes, snow birds). In modern birds, crural feathers are reduced distally as the
scutellate scales of the podotheca appear and enlarge, a transition that typically occurs
around the intertarsal joint (Stettenheim, 2000).
Given the differences between the leg feathers in enantiornithines and M. gui,
inferences on function and homology are likely premature. The widespread distribution
of crural feathers within Enantiornithes and their purported presence in Archaeopteryx
suggests these feathers are plesiomorphic for Aves. The absence of metatarsal feathers
within Aves and the distribution and variation of this feature within Maniraptora suggests
metatarsal feathers evolved independently outside of Aves, though possibly convergently
adapting for a similar niche.
Enantiornithine crural feathers are symmetric and relatively short (IVPP 13939)
thus appearing to lack aerodynamic qualities, yet they are distinct from body feathers. It
is possible they are reduced from the ‘asymmetric pennaceous’ feathers reported for
Archaeopteryx, but such a hypothesis hinges on the feathers in Archaeopteryx being true
333 
features and indeed asymmetric, neither of which is known with any confidence.
Regardless, crural feathers are common in modern birds (especially among birds of prey;
Fig. 10.9C) and metatarsal feathers are absent (except in modified breeds such as fancy
chickens), as in Archaeopteryx and enantiornithines. This suggests that enantiornithine
crural feathers are common integumentary structures, not unusual within Aves, and that
mistaken comparison with the metatarsal feathers of M. gui caused unnecessary
inferences about hindlimb feather evolution in order to support preconceived notions
about the arboreal predecessor to birds. Considering the variety of tail morphologies in
enantiornithines interpreted for display, the slightly more prominent crural feathers of
IVPP V13939 may also represent such a feature.

vii. Conclusions
From the snapshots of enantiornithine integument that can be gleaned from the
fossil record, it is clear that even in the Early Cretaceous, enantiornithines were diverse
and specialized in their integument. The clade preserves a wider range of feather
variation than any other clade of Mesozoic bird. Some features of enantiornithine
integument resemble those of basal birds, however remiges appear to be of modern
aspect, and feathers are differentiated for different uses over the body (insulation, flight,
display). Like other basal birds, enantiornithines possess contour feathers different from
those of modern birds, and a unique rectrice feather type unknown in living taxa. This
supports hypotheses regarding the acquisition of feather types within Aves that suggest
coverts are the most derived feather type (Brush, 2000). Enantiornithines commonly
334 
preserve crural feathers, also purported to be present in Archaeopteryx, suggesting this
may be the plesiomorphic condition within Aves and that modern birds whose tibiotarsus
is primarily covered by scutellate scales possess a derived morphology. Enantiornithines
also possess advanced integumentary structures (alula, aerodynamic tail) similar to those
in modern birds but absent in Archaeopteryx.
The presence of an alula and ‘fan-shaped’ tail among Early Cretaceous
enantiornithines presents two possible interpretations of the current fossil record: either
these features are synapomorphies of Ornithothoraces, or they were independently
evolved by each group (see Chapter 12 for phylogenetic hypotheses). That
enantiornithines possessed these structures strongly supports hypotheses that they had
strong flight capabilities.
Details of enantiornithine integument still remain unknown. While the
identification of distinct pterylae is difficult, differentiation between feather lengths and
morphology in different regions of the body allows their presence to be inferred (IVPP
V13939) and some taxa are known to have possessed several disparate feather types
differentiated over the body (CAGS-05-CM-004).
Disparity between feather morphologies and distribution between taxa suggests a
great deal of hidden diversity. A large range of variation in this diverse group of early
birds is not surprising given the range of structures present within Theropoda (Ji et al.,
1998; Xu et al., 1999; Ji et al., 2001; Xu et al., 2001; Norell et al., 2002; Xu et al., 2003;
Ji et al., 2005) and Dinosauria as a whole (Mayr et al., 2002; Zheng et al., 2009). New
335 
taxa and exceptionally preserved specimens are sure to continue to change our perception
of enantiornithine integument.

336 
CHAPTER 11: PREVIOUS ENANTIORNITHINE SYSTEMATIC HYPOTHESES

i. Introduction
The systematic position of enantiornithines has been a subject of controversy
since the group’s conception. Not only has the validity of the group as a whole been
questioned, but also their relationship with more advanced taxa, although neither claim
has ever been well substantiated. While these issues have been resolved to a fair degree,
within the clade the relative systematic position of individual taxa remains poorly known,
an issue complicated by the size of the clade and differential preservation between taxa.
Previous issues within enantiornithine systematics are explored, including a review of
past phylogenies, a discussion necessary for the presentation of the new enantiornithine
matrix in the following chapter.

ii. Enantiornithes and Aves
The validity of the enantiornithines as a group was questioned early on due to
their unusual morphology, unsurprising given the disarticulated nature of the original
specimens (El Brete collection), but became accepted in light of new discoveries (i.e.
Neuquenornis) and systematic research (Chiappe, 1993; Chiappe, 2002). Despite the
persistence of alternate hypotheses, recent cladistic analyses targeted at Mesozoic birds as
a whole support a monophyletic Enantiornithes and consistently place these birds within
Aves, typically as the sister group to Ornithuromorpha (Chiappe, 2002; Senter, 2007; Cau
and Arduini, 2008; Gao et al., 2008; Zhang et al., 2008b; Zhou et al., 2008a; O’Connor et
337 
al., 2009). Neornithes is nested within Ornithuromorpha, and thus enantiornithines are
sister group to the clade that includes modern birds (Fig. 11.1).
Alternatively, one hypothesis regards enantiornithines as non-avian, unrelated to
modern birds beyond their shared archosaurian ancestry, and that all similarities between
Enantiornithes and modern birds are the result of convergence or ‘parallel evolution’
(Kurochkin, 2006). This hypothesis has not received strong cladistic support and also
incorporates a fossil that is here considered a chimera in agreement with a majority of
researchers (‘Protoavis’; Chatterjee, 1991; Witmer, 2001). Still, at risk of appearing an
unquestioning follower of the current cladistic orthodoxy, this hypothesis and
justification for disregarding it are reviewed. In this hypothesis, Enantiornithes is placed
with Archaeopteryx in a clade called Sauriurae, which is placed within Coelurosauria (but
not within the derived maniraptorans) while suggesting that Ornithuromorpha,
Confuciusornis and kin, and ‘Protoavis’ share a common (unknown) archosauromorph
ancestor in the Late Triassic (Fig. 11.2A; Kurochkin, 2006). Morphological similarities
between the relatively more basal ornithoracine enantiornithines and Archaeopteryx, the
presence of morphologies in Sauriurae that are allegedly more primitive than those of
some non-avian theropods (absence of fusion in hindlimb bones) and the absence of
derived neornithine features in both are postulated as evidence that these taxa could not
have had a single common ‘avian ancestor’ and that in fact, the currently widely accepted
“Aves (or Avialae)” is paraphyletic. This hypothesis appears to stem from a series of
misinterpretations of cladograms and cladistics itself, a narrow view of Mesozoic avian
diversity, and an attempt to accommodate the phalangeal formula of birds and dinosaurs
338 

Figure 11.1. Cladogram depicting the general placement of Mesozoic birds as resolved by
a majority of recent cladistic analyses (simplified from O’Connor et al., 2009).
339 
(by stating that the ‘ornithuran’ clade that includes Neornithes possesses 2-3-4 while the
Archaeopteryx clade possesses the theropod 1-2-3).
This hypothesis infers that ‘Protoavis’ is the oldest known bird, but not
necessarily a basal form. However, given the morphologies of the taxon, it is assumed
that certain derived features (i.e. elongate coracoid) had already evolved by the Late
Triassic, and thus that Archaeopteryx and enantiornithines of the Late Jurassic and
Cretaceous, respectively, cannot be related to ‘Protoavis,’ which only gave rise to more
advanced birds (the short coracoid of Confuciusornis is unexplained). According to this
hypothesis and despite the absence of “ornithurans” in the Jurassic, advanced birds are
inferred to have been present from the Late Triassic, with relic taxa giving rise to the
toothed Hesperornithiformes and Ichthyornis in the Cretaceous, while more advanced
taxa are finally preserved in the Early Cretaceous (i.e. Jehol ornithuromorphs and
Gansus).
This hypothesis receives only inferred support based on morphological
differences between enantiornithines and ornithuromorphs. However, all morphological
characters discussed (i.e. single vs. double-headed otic articulation of the quadrate;
convex scapular articular surface on the coracoid vs. concave; metatarsals proximally
aligned vs. metatarsal III plantarly displaced) are included in most cladistic analyses
(Chiappe, 2002; Clarke et al., 2006; O’Connor et al., 2009) that still reach the conclusion
that enantiornithines are sister group to Ornithuromorpha. These two groups do have a
great deal of morphological disparity in terms of development of their sterna or
tarsometatarsi. However, fossil taxa analyzed are contemporaneous or near so (primarily
340 
taxa come from the Early Cretaceous, ranging from 130-105 Ma) and thus based on the
suggested relationship, a deeper origination than known from the fossil record is inferred
(Hou et al., 2003; O’Connor et al., 2009). Though such inferences are frowned upon by
some (Dodson, 2000), the presence of more basal and derived characters in an Early
Cretaceous long-tailed bird (i.e. Jeholornis) relative to Archaeopteryx should be a clear
reminder that the observed diversity represents an obfuscated view of evolution.
Histological differences are also used to align Archaeopteryx with Enantiornithes,
forming a clade of taxa with prolonged growth, while Confuciusornis is inferred to have
had faster growth rates (evidenced from the fibrolamellar bone structure observed in
cross section) as in ornithuromorphs (Chinsamy et al., 1995; Kurochkin, 2006; de Ricqlès
et al., 2008). However, the diversity of growth patterns within troodontids (Erickson et
al., 2007) suggests that this may not be a strong indicator of phylogeny but simply reflect
avian developmental plasticity (Starck and Chinsamy, 2002). Furthermore, the histology
of enantiornithines is currently poorly understood given the differences in morphology
observed between studied specimens and therefore drawing conclusions about growth
patterns in the clade relative to other groups of birds is premature (see Chapter 9;
Chinsamy et al., 1995; Chinsamy and Elzanowski, 2001; Cambra-Moo et al., 2006).
The point is not to refute every supposed argument in favor of the hypothesis that
excludes Enantiornithes from Aves but to ensure that there is not valid evidence currently
being ignored. Arguments that Archaeopteryx, like Confuciusornis, possessed a proximal
foramen in the humerus are completely unsubstantiated given the excellent preservation
of the 10
th
“Thermopolis” specimen (Mayr et al., 2005; Mayr et al., 2007). Furthermore,
341 

Figure 11.2. Alternative hypotheses regarding the placement of Enantiornithes;
relationships not derived by the cladistic method. A, Kurochkin’s (2006) Sauriurae with a
paraphyletic Aves (from Kurochkin, 2006). B, Martin’s (1987) Sauriurae with a
monophyletic Aves (modified from Chiappe and Walker, 2002).
342 
removal of ‘Protoavis’ from this hypothesis significantly weakens it; given the highly
controversial status of this specimen (Witmer, 2001), even if one disagrees that
‘Protoavis’ is a chimera, evolutionary schematics involving this taxon should await new
specimens that support its validity as a taxonomic entity.
A similar and older hypothesis places Sauriurae and Ornithurae within Aves,
giving them a common origin, but considers the two ‘subclasses’ distantly related (Fig.
11.2B; Martin, 1987). In such a scenario, all the similarities between enantiornithines and
ornithuromorphs not present in Archaeopteryx are considered convergence (Chiappe,
1995). This hypothesis is unfounded by morphological data and knowledge of other basal
avians (i.e. Confuciusornis); as in the previous hypothesis, many of the characters used to
unify Archaeopteryx with enantiornithines are either distributed outside the clade or
present in enantiornithines but not Archaeopteryx.
A majority of phylogenetic hypotheses support a closer relationship between
enantiornithines and modern birds rather than with Archaeopteryx (Chiappe, 2002;
Clarke et al., 2006; You et al., 2006; Senter, 2007; Cau and Arduini, 2008; Gao et al.,
2008; Zhou et al., 2009). Two origination events for Aves have been suggested (Mayr et
al., 2005), separating Confuciusornis and Archaeopteryx, but this has been shown to be
no less parsimonious than a single origination event (Corfe and Butler, 2006). Since
Martin’s hypothesis (1983; 1987) also suggests a monophyletic Aves, but with
Enantiornithes closer to Archaeopteryx than to modern birds, it has been compared to the
current ‘cladistic orthodoxy’ that also resolves a monophyletic Aves, but with
Enantiornithes closer to Neornithes than Archaeopteryx (Chiappe, 2002). In this analysis,
343 
compared to the shortest tree (MPT) derived by parsimony, a tree that supports a
Sauriurae clade is more than 10% longer (39 steps longer than the MPT with a length of
304 steps). Admittedly this is not a huge disparity given that nature does not always
proceed parsimoniously (Dodson, 2000), however considering that even the inferred
morphological similarities do not hold up in light of our current knowledge of the
Mesozoic aviary (i.e. Sapeornithidae, Zhongornis), the absence of cladistic support
further weakens this hypothesis. Since cladistic analysis is the foundation for
phylogenetic hypotheses in this project, any hypothesis that cannot be supported through
such a method is considered invalid pending new evidence.

iii. Variance in Mesozoic Birds Phylogenies
Most recent phylogenetic hypotheses of Mesozoic birds place enantiornithines in
a dichotomy with Ornithuromorpha, thus forming the clade Ornithothoraces (and
supporting an enantiornithine + Neornithes clade rather than an Archaeopteryx +
enantiornithines clade) (Chiappe, 1995; Chiappe, 2002; Zhou and Zhang, 2002a; Clarke
et al., 2006; Cau and Arduini, 2008; Gao et al., 2008; O’Connor et al., 2009); resolved
relationships within these major clades vary widely between analyses, in particular within
the enantiornithines. As more clades of basal birds emerge, relationships have not
remained stable (You et al., 2006; Zhou and Zhang, 2006b; Zhou et al., 2009). There are
certain clades that currently vary in position between analyses, primarily
Confuciusornithidae, Sapeornithidae, and taxa such as Vorona, Rahonavis and
Zhongornis (Mayr et al., 2005; Zhou et al., 2008a; O’Connor et al., 2009; Zhou et al.,
344 
2009). Since these taxa, in particular Confuciusornis, vary in their position relative to
enantiornithines and in some cases the two groups are closely aligned, alternative
hypothetical phylogenetic relationships are discussed.
Confuciusornithidae and Sapeornithidae are commonly resolved as basal
pygostylians, falling outside Ornithothoraces (Fig. 11.3); some analyses find the latter
more advanced (Gao et al., 2008; O’Connor et al., 2009; Fig. 11.3A) while others suggest
the former is closer to Ornithothoraces (Zhou and Zhang, 2002a; Clarke et al., 2006; Cau
and Arduini, 2008; Zhou et al., 2008a). One analysis has suggested Confuciusornis and
enantiornithines form a clade, thus making Confuciusornis an ornithothoracine (Zhou and
Zhang, 2006b), while in another analysis the confuciusornithid clade is joined by
Zhongornis (pers. obs.; Fig. 11.3B), although neither result was strongly supported.
Sapeornis, considered a basal pygostylian in most analyses (Zhou and Zhang, 2006b; Cau
and Arduini, 2008; O’Connor et al., 2009), has recently found itself resolved in a more
basal position, less derived than Jeholornis (a taxon typically placed between
Archaeopteryx and Pygostylia), but more derived than Archaeopteryx (Zhou et al., 2009;
Fig. 11.3B). This would suggest two independent reductions in the long bony-tail and the
convergent evolution of the pygostyle (Zhou et al., 2009). These conclusions are unusual
but should not be disregarded given that there are many causal factors that result in
shifting hypothetical phylogenetic relationships between analyses (i.e. differential
taxonomic or character sampling, the addition of new morphological data for a given
taxon). The flexibility of basal bird relationships reflects the need for further cladistic
345 

Figure 11.3. The results of two recent cladistic analyses (A, modified from O’Connor et
al., 2009; B, modified from Zhou et al., 2009), which highlight the current plasticity of
certain basal bird relationships.
346 
research, as new discoveries shift our perception of past diversity (Zhou and Zhang,
2006b; Gao et al., 2008).
None of these analyses suggest enantiornithines are not a monophyletic group and
groups of varying phylogenetic relationships (i.e. Confuciusornis and kin) are included in
the analysis presented in the following chapter, thus the possibility of such relationships
as uncovered above, are explored. Furthermore, this discussion highlights some of the
reasons why some researchers oppose over zealous application of the cladistic method;
the dependence of results on taxonomic sample and other factors is a reminder that
cladistics produces only phylogenetic hypotheses subject to the specimens known at the
time and included in the analysis. Given the current rate of discovery, including the
recognition of new clades (i.e. Gao et al., 2008; Zhou et al., 2009), poor resolution is
unexpected, as character lists must be expanded to encapsulate the new diversity.

iv. A Review of Previous Enantiornithine Phylogenies
As mentioned, enantiornithine interrelationships are poorly known and fairly
unexplored. When discussing phylogenetic hypotheses, a focus is placed on
enantiornithine specific analyses, but since these are few, broader investigations that
include a large number of enantiornithine taxa are also reviewed. Attempts to reconstruct
enantiornithine relationships go back to the early 90’s, when a vast majority of the
current diversity was unknown (Chiappe, 1993; Sanz et al., 1995). The taxonomic and
character sampling varies, however analyses consistently place all included
enantiornithine taxa within a single clade (Chiappe, 2002; Cau and Arduini, 2008; Zhou
347 
et al., 2008; O’Connor et al., 2009). The morphology of the clade itself, however, when
resolved differs widely between analyses and the hypothetical relationships only receive
weak support (Cau and Arduini, 2008; O’Connor et al., 2009), or the results are a
polytomy (Clarke and Norell, 2002; Chiappe, 2002; Clarke et al., 2006; Zhang et al.,
2008b). Most of these analyses were aimed at Mesozoic birds as a whole, and thus the
scope of the analysis was broad, capable of recognizing Enantiornithes as a group but
incapable of deciphering their interrelationships, thus resulting in weak relationships or a
polytomy of taxa (Chiappe, 2002; Zhang et al., 2008b). These analyses contained
apomorphies of Enantiornithes but lacked sufficient characters to express the variation
within the diverse group.
The inability of Mesozoic bird matrices to resolve enantiornithine
interrelationships clearly indicated that more focused attention on the clade would be
required to break down the polytomy, given their diversity. The first enantiornithine
specific analysis was small, predating the discovery of a majority of the Liaoning birds
and thus extremely limited by the material known at the time (Fig. 11.4A; Chiappe,
1993). The analysis consisted of six Late Cretaceous enantiornithine taxa (Soroavisaurus,
Lectavis, Yungavolucris, Avisaurus archibaldi, A. gloriae and Neuquenornis), five of
which are almost known entirely from tarsometatarsi (at the time, Lectavis also had a
tibiotarsus referred to it and Neuquenornis is known from a partial skeleton; since, a
tibiotarsus has also been assigned to Soroavisaurus), scored for ten characters (Chiappe,
1993). The analysis produced three most parsimonious trees (MPTs), all of which
supported a monophyletic Enantiornithes with three unambiguous apomorphies: reduced
348 

Figure 11.4. A-F, Previous cladistic phylogenetic hypotheses regarding enantiornithines:
A, Chiappe, 1993 (modified from Chiappe and Walker, 2002); B, Sanz et al., 1995
(modified from Chiappe and Walker, 2002); C, from Chiappe, 2002; D, from Chiappe
and Walker, 2002; E, from Chiappe et al., 2006; F, from Cau and Arduini, 2008. G,
hypothetical enantiornithine phylogenetic relationships from Kurochkin, 1996.
349 

Figure 11.4., Continued.
350 
metatarsal IV, tubercle present on dorsal surface of metatarsal II, and metatarsal II
trochlea wider than that of metatarsal III (Chiappe, 1993).
Relationships within the clade differed between the three trees but all trees
supported a monophyletic Avisauridae formed by Neuquenornis, Soroavisaurus,
Avisaurus archibaldi and A. gloriae (Chiappe, 1993). A relationship between these taxa
had already been suggested (Chiappe, 1991), and here received phylogenetic support
from two synapomorphies: plantar projection of medial rim of metatarsal III trochlea and
a strong dorsal convexity on the midshaft of metatarsal III (Chiappe, 1993). Within this
clade the relationships were consistent between trees with the two Avisaurus species
forming a clade (supported by the presence of a medially concave metatarsal IV
trochlea), with Soroavisaurus and Neuquenornis forming successive outgroups. The
Soroavisaurus + Avisaurus clade is supported by one unambiguous synapomorphy
(metatarsal II with pronounced medial curvature of the distal end) and one ambiguous
(dorsally inclined proximal articular surface of tarsometatarsus). The three MPTs differed
in the relationships of Lectavis and Yungavolucris with Avisauridae, forming successive
outgroups in two analyses (differing in the position of Lectavis and Yungavolucris as
basal) or a polytomy (Chiappe, 1993). Considering the size of the analysis and limitations
in material, the results were considered tentative (Chiappe, 1993).
The Chiappe (1993) analysis was later expanded to 84 characters and included
Concornis lacustris, as well as ornithuromorph taxa Patagopteryx deferrariisi,
Ichthyornis and Hesperornis (Fig. 11.4B; Sanz et al., 1995). The analysis resulted in three
trees, differing only in the relative placement of advanced ornithuromorph taxa with all
351 
trees supporting a monophyletic Enantiornithes. The strict consensus tree placed
Concornis outside Avisauridae; the clade formed by Concornis + Avisauridae formed a
polytomy with Lectavis and Yungavolucris.
Enantiornithes received unambiguous support from 12 characters: laterally
excavated dorsal vertebrae; centrally located parapophyses on thoracic vertebrae;
supracoracoid nerve foramen opening in a medial groove and separated from the medial
margin by a bony bar; convex lateral margin of coracoid; furcula laterally excavated;
cranioventrally projecting bicipital crest; fossa for muscle attachment on lateral surface of
bicipital crest; ulna with convex dorsal cotyle separated from olecranon by groove;
caudal projection of lateral margin of distal femur; tibiotarsus with wide and bulbous
medial condyle; metatarsal IV thinner than II and III; and metatarsal II trochlea wider
than metatarsal III. Most of these characters are known to be absent in some if not a
current majority of more recently described specimens (i.e. hypertrophied bicipital crest
on the humerus absent in Rapaxavis; coracoid with convex margin, absent in Rapaxavis
and Longipteryx; lateral projection of the distal femur, absent in Cathayornis and
Longipteryx; tibiotarsus condyles approximately equal in Dapingfangornis; metatarsal IV
approximately same width as III in Longirostravis and Iberomesornis; metatarsal II
trochlea is not broad in Eoenantiornis and Longirostravis). Other characters, such as a
laterally excavated furcula and supracoracoid nerve foramen opening in medial groove,
are still considered enantiornithine synapomorphies, although the degree of excavation is
now known to vary considerably (i.e. Flat Rocks furcula vs. Elsornis) and information
regarding the medial surface of the coracoid in most Chinese slab specimens is equivocal.
352 
Other characters no longer accurately reflect the full range of diversity within the clade
(i.e. the fossa for muscle attachment on lateral surface of bicipital crest is known to vary
from ventrally located to cranially located). For these reasons, the results of older
analyses cannot be directly compared to current analyses that incorporate a greater
amount of fossil diversity.
One early enantiornithine phylogeny critiquing Sanz et al. (1995) was derived
without the cladistic method (Fig. 11.4G; Kurochkin, 1996) and includes several
extremely fragmentary taxa (i.e. Sazavis, Lenesornis, Zhyraornis) typically not analyzed
by other researchers (and here considered nomina dubia; see Chapter 3). Kurochkin
(1996) argued against some of the proposed synapomorphies presented by Sanz et al.
(1995), however these arguments often result from differential interpretation of the fossil
record. For example, Kurochkin (1996) considers the caudally projecting lateral margin
of the distal femur a Sauriurae synapomorphy based on its presence in Archaeopteryx;
however this feature is here considered not present in this taxon (Elzanowski, 2002).
Kurochkin’s (1996) study provides 34 enantiornithine synapomorphies, some of which
are consistent with those proposed by Sanz et al. (1995) (i.e. lateral margin of the
coracoid convex, dorsal cotyle of ulna convex). Some of the synapomorphies are
currently still regarded as true synapomorphies of the entire clade (i.e. V-shaped furcula,
cranially concave and caudally convex proximal humerus, transverse orientation of the
dorsal condyle of the humerus) or diagnose subclades (i.e. longitudinal groove on radius,
minor metacarpal exceeding major metacarpal in distal projection). However, several of
Kurochkin’s characters were only known in a few specimens, but still regarded as
353 
synapomorphic. Such assumptions are weak, especially given that features present in
only a single specimen were utilized. For example, despite the wealth of new
enantiornithine material, Gobipteryx is currently the only known taxon that possesses a
tubercle on the ascending process of the tibiotarsus (character 26, Kurochkin, 1996).
Given the taxonomic sample and the absence of cladistic support, the
relationships Kurochkin (1996) proposed between taxa without any comparable
preserved material can in no way be supported. For example, Kurochkin (1996) erected
the family Enantiornithidae for Enantiornis, Avisaurus and Soroavisaurus. However, the
last two taxa are known from tarsometatarsi, which is unknown in Enantiornis. Of the six
synapomorphies proposed for the clade, two characters refer to elements not preserved
for any of the included taxa (i.e. ilium, tibiotarsus), two refer to the scapula (known only
in Enantiornis), and two are tarsometatarsal characters (can only be scored for Avisaurus
and Soroavisaurus only). Since there are no valid arguments in favor of Kurochkin’s
proposed relationships (1996), and a lengthy discourse would be required to counter
every point, they will not be discussed further.
Euenantiornithes, the clade that includes most enantiornithines, was named in an
analysis aimed at the relationships of Mesozoic birds as a whole (Chiappe, 2002). The
analysis consisted of 169 characters scored for 18 taxa, seven of which were
enantiornithine (Concornis, Eoalulavis, Gobipteryx, Iberomesornis, Neuquenornis,
Noguerornis, and Sinornis). The strict consensus tree (drawn from 29 MPTs) from the
analysis placed Iberomesornis and Noguerornis together and the rest of the
enantiornithines in a polytomy (Fig. 11.4C), for which the name Euenantiornithes was
354 
erected, defined as all enantiornithines more closely related to Sinornis than
Iberomesornis (Chiappe, 2002). Iberomesornis and Noguerornis are considered basal
enantiornithines, and even though only five other enantiornithines are included, most
unscored taxa are envisioned to belong to the euenantiornithine clade (Chiappe, 2002;
Chiappe and Walker, 2002). Both the phylogenetic definition of Euenantiornithes and
the definition proposed for enantiornithines by Sereno (1998) reference Sinornis
(Chiappe, 2002). In this interpretation, most characters previously supporting the
enantiornithine clade are absent in Iberomesornis and Noguerornis and thus support the
more exclusive clade (i.e. centrally located parapophyses on thoracic vertebrae, convex
lateral margin of the coracoid, proximal humeral margin concave centrally rising dorsally
and ventrally, cranially projecting bicipital crest, presence of a longitudinal groove on the
radius, and metatarsal IV thinner than metatarsals II and III). An euenantiornithine clade
has since been supported in one analysis (Zhang et al., 2008b) while most subsequent
Mesozoic bird analyses have only included euenantiornithine taxa (and thus support for
this clade could not be tested; Ji et al., 2005; Clarke et al., 2006; You et al., 2006; Zhou et
al., 2008a). One recent analysis, however, has shown a collapse in this relationship
between Iberomesornis and other enantiornithines, placing the taxon in a polytomy with
‘euenantiornithines’ (O’Connor et al., 2009).
In 2002, Chiappe and Walker published an euenantiornithine specific analysis of
36 characters scored for 16 taxa (Fig. 11.4D; Chiappe, 2002). This increase in taxonomic
sampling reflected the greater number of largely complete specimens now known from
China and Spain (i.e. Sinornis, Eoalulavis). The results of the analysis when run with all
355 
16 euenantiornithines produced no resolution (Chiappe and Walker, 2002). When some
taxa (i.e. Nanantius, Otogornis, Alexornis) were excluded according to their degree of
completeness (in the matrix), no resolution was obtained until only taxa with a maximum
of 30% missing data were included. Only seven euenantiornithines at the time fit the
criteria given the characters sampled; the result was a polytomy between Eoenantiornis,
Sinornis, Eoalulavis, Gobipteryx and a ‘clade’ formed by Enantiornis, Concornis and
Neuquenornis (Chiappe and Walker, 2002). In Kurochkin (1996), the three taxa forming
the derived polytomy were separated into three distinct families and thus not closely
related. Given the diversity encapsulated by the euenantiornithines, the lack of resolution
in the final tree is interpreted as the result of inadequate character sampling rather than a
missing data problem (Kearny and Clark, 2003; Wiens, 2003). In the analysis presented
in the next chapter, no taxa fulfill Chiappe and Walker’s (2002) criterion of 30% or less
missing data.
The Chiappe and Walker (2002) euenantiornithine analysis was expanded and
revised to include 46 characters scored for 12 enantiornithine taxa (Chiappe et al. 2006).
The taxonomic sample included more of the nearly complete Chinese taxa not scored in
the Chiappe and Walker (2002) analysis and did not attempt to include largely
incomplete genera (i.e. Nanantius, Otogornis). The updated analysis produced three
MPTs, reflecting changes in the position of two taxa, Enantiornis and Eoalulavis. The
consensus tree (Fig. 11.4E) yielded greater resolution than previous analyses but still
placed more than half the included enantiornithine taxa in a large polytomy. The resultant
phylogenetic hypothesis found Protopteryx to be the most basal ‘euenantiornithine,’ a
356 
hypothesis suggested by Zhang and Zhou (2000) based on morphological observations.
Elsornis is part of a more exclusive clade, and falls outside a large dichotomy formed by
a Longipterygidae (Longipteryx and Longirostravis) + Eoenantiornis clade, and a
polytomy formed by Enantiornis, Concornis, Neuquenornis, Sinornis, Eoalulavis,
Gobipteryx, and Vescornis.
Following a trend of increased taxonomic and morphological sampling, the most
recent enantiornithine analysis consisting of 192 characters scored for 36 taxa, more than
half of which were enantiornithine (Cau and Arduini, 2008). The analysis included 19
enantiornithine genera and two unnamed specimens from the Early Cretaceous Xiagou
Formation of Northwestern China (CAGS-IG-04-CM-007, CAGS-IG-02-CM-0901)
regarded as enantiornithines (Harris et al., 2006; Lamanna et al., 2006). The analysis
drew its characters from a number of sources (Chiappe, 1993; Chiappe et al., 1999;
Chiappe, 2001; Clarke and Norell, 2002; Holtz et al., 2004) and does not seem to reflect
an enantiornithine specific analysis (from the character and taxonomic sampling) despite
the heavy inclusion of enantiornithine taxa. The analysis produced a single most
parsimonious tree of 629 steps (Figure 11.4F). The enantiornithine taxa form successive
relationships rather than a massive polytomy, but the results are only weakly supported
(CI = 0.5246, RI = 0.6215). The analysis concurred with Chiappe (1993) in the
placement of taxa within Avisauridae ([Avisaurus + Soroavisaurus] + Neuquenornis)
(contra Kurochkin, 1996), but expand the clade to include Concornis and place
Halimornis and Enantiophoenix as basal members (Cau and Arduini, 2008). Sinornis and
Eocathayornis form consecutive outgroups to ‘Avisauridae.’ This large group formed a
357 
dichotomy with a clade that includes ‘Longipterygidae’ (Chiappe et al., 2006),
Eoenantiornis and the two unnamed Xiagou specimens. Eoenantiornis formed a clade
with CAGS-IG-04-CM-007, which forms a dichotomy with Longipterygidae. CAGS-IG-
02-CM-0901 was resolved as basal to these taxa. A close relationship between
Eoenantiornis and Longipterygidae was also supported in Chiappe et al. (2006). A small
clade formed by Boluochia + Gobipteryx and Vescornis falls outside this dichotomy.
Eoalulavis, Dalingheornis (nomen dubium), Elsornis, Protopteryx and Iberomesornis
formed successive outgroups. Overall, this analysis was consistent with hypotheses that
placed Iberomesornis as a basal enantiornithine outside Euenantiornithes (Chiappe, 2002)
and that regarded Protopteryx and Elsornis as primitive euenantiornithines (Zhang and
Zhou, 2000; Chiappe et al., 2006). This analysis also supported the existence of a
longipterygid clade, and a close relationship between this clade and Eoenantiornis
(Chiappe et al., 2006).
Another recent Mesozoic bird analysis (O’Connor et al., 2009) included a
relatively large number of enantiornithines as well as enantiornithine specific characters
from Chiappe and Walker (2002). The analysis of 29 taxa (11 of which are
enantiornithine) scored for 242 characters produced 20 MPTs of 588 steps; the variation
between equal length trees occurred primarily in the ornithuromorph and enantiornithine
clades thus the strict consensus tree resulted in polytomies at both these nodes. Though
support for the tree was weak (CI = 0.48, RI = 0.68), the consensus tree does resolve a
longipterygid clade that includes two additional taxa (Morschhauser et al., 2009;
O’Connor et al., 2009) described since phylogenetic support for the clade was first
358 
proposed (Chiappe et al., 2006). The longipterygid clade is supported by the presence of
an elongate rostrum and dentition restricted to the premaxilla (O’Connor et al., 2009). In
this analysis, one of the new taxa, Rapaxavis, forms a more exclusive relationship with
Longirostravis based on two unambiguous apomorphies: sternal trabeculae that project
caudally beyond the xiphoid process and a radius to ulna shaft ratio that is larger than
0.70 (O’Connor et al., 2009). This analysis however, did not support a basal position for
Iberomesornis, placing this taxon in a polytomy with other non-longipterygid
enantiornithines (Euenantiornithes not resolved).

v. Problems With Previous Phylogenies
There are a number of factors that may be contributing to the overall lack of
resolution within enantiornithine phylogenies. Several may be intrinsic to the clade: given
its temporal breadth, taxa separated by 50 My have a long history of diversification,
specialization, and convergence with other members of the clade and with other clades of
birds. Phylogenetic analyses create hypotheses regarding homoplasy and homology
between character states in taxa (McKitrick, 1994), but with large amounts of
convergence observable between clades of birds and para-avians, combined with the
fragmentary nature of some of the material, it is difficult for an analysis (especially a
large one) to differentiate between homology and homoplasy. Increased character
sampling can help to overcome this problem, however the very fragmentary nature of one
third of all erected enantiornithine species makes it impossible to create a phylogenetic
hypothesis with cladistics that includes all taxa. With no comparable material preserved
359 
between a large number of OTUs, any resultant hypothesis (if the analysis could be
resolved) would likely be ambiguous and or weakly supported. A clade such as
Avisauridae, which includes three taxa known only from tarsometatarsi (and a tibiotarsus
in the case of Soroavisaurus), will likely not be resolved in most analyses simply because
these taxa are too fragmentary to run in an analysis that codes characters for the entire
skeleton (i.e. Chiappe and Walker, 2002; Chiappe et al., 2006). It is for this reason that it
is encouraged that future fragmentary specimens not be named (see Chapter 3).
The taxonomy of enantiornithines has long required revision, a fact that
unfortunately obfuscates phylogenetic attempts as some analyses inadvertently include
nomina dubia (Cau and Arduini, 2008). Removal of nomen dubium Dalingheornis liwei
in the Cau and Arduini (2008) analysis may affect the outcome because the results would
then be drawn from a different expression of ‘known’ morphological diversity. The
inclusion of this specimen suggests that this and other specimens were scored from
publications, since this specimen is in private hands and thus inaccessible (Zhang pers.
comm.). Unfortunately, the morphological information available from the publication of
this taxon is also extremely limited (Zhang Z-H. et al., 2006), which is true for several
named taxa (i.e. Paraprotopteryx, Alethoalaornis). This affects what information will be
scored by researchers depending on whether or not the specimen was studied or not (the
latter resulting in greater amounts of missing data). For this reason, publications should
include all relevant morphological information or provide high quality images that allow
for independent study and facilitate phylogenetic research.
360 
Even analyses in which each specimen has been studied personally and all taxa
are valid, the results are often unresolved suggesting that a main problem faced by past
enantiornithine specific analyses is inadequate character sampling largely as a
consequence of the incomplete nature of the fossils. This is supported by the trend
towards increasing resolution observed in recent analyses (Chiappe and Walker, 2002;
Chiappe et al., 2006), which sample a greater number of more complete specimens for
characters across the entire skeleton. However, with enantiornithines the issue cannot be
resolved by simply finding new morphological characters to score. This issue is directly
affected by the fossil material available, the preservation of which also determines what
morphological features can or cannot be scored for a given specimen (Fig. 11.5).
The early record of enantiornithine material in the 1980’s and 90’s, which today
still represents almost the entirety of the Late Cretaceous enantiornithine record,
consisted primarily of very incomplete three dimensionally preserved taxa (i.e. Alexornis,
Avisaurus, Enantiornis, Lectavis, Soroavisaurus). These specimens are free from matrix
and visible from all angles (Fig. 11.5B); furthermore, most of these taxa were large (i.e.
Lectavis, A. archibaldi), and thus morphological details are fairly easily discerned and
not as easily lost due to weathering. Most pre-existing enantiornithine characters are
derived from these specimens (Chiappe, 1993; Chiappe and Walker, 2002).
Unfortunately, because these Late Cretaceous specimens are so incomplete they often
cannot be compared to other taxa for lack of shared material (i.e. Alexornis and
Soroavisaurus). As discussed above, a majority of these specimens are only known from
or preserve a tarsometatarsus allowing for some comparison and a small phylogenetic
361 

Figure 11.5. Differential preservation within the enantiornithines: A, crushed coracoid
from the complete slab and counterslab specimen DNHM D2567/8; B, isolated three
dimensionally preserved coracoid (PVL 4035) from El Brete collection assigned to
Enantiornis leali.
362 
analysis (Chiappe, 1993). However, relating a group of birds based entirely on the
morphology of a single bone while ignoring additional morphological information (i.e.
Neuquenornis and later Concornis) is not likely to accurately reflect evolutionary
relationships (Chiappe, 1993; Sanz et al., 1996), especially give the subjectivity of the
tarsometatarsus to ecological adaptation (Zeffer et al., 2003).
More recently, far more complete enantiornithine material has become abundant,
largely due to the prolific Jehol deposits in northern China. Currently, the numerous
Chinese enantiornithines reveal important information about size, feather and
osteological diversity, and ecological specialization, more than they provide
morphological details. This is because the new wealth of largely complete specimens are
unfortunately more often than not poorly preserved (i.e. crushed, ripped between two
slabs, preserved as voids; Hou, 1997; Zheng et al., 2007; O’Connor et al., 2009). These
specimens can be scored for a number of superficial morphologies regarding limb
proportions or general morphology (i.e. shape of elements), but do not often preserve
morphological details such as the presence of small tubercles or fossae or the morphology
of articular surfaces (Fig. 11.6A). Since they are preserved in two dimensions or in a
single view, the presence of a dorsally excavated coracoid, for example, often remains
equivocal: is the coracoid simply flattened during preservation, or was it truly
unexcavated? Morphologies such as the plantar projection of the medial rim of metatarsal
III trochlea or the presence of an acrocoracoidal tubercle on the coracoid typically cannot
be discerned in even well preserved nearly complete taxa (i.e. Rapaxavis).
363 
The largely incomplete specimens from El Brete still provide most of the known
morphological details of the enantiornithine post-cranial skeleton, and thus despite their
incompleteness, can be scored for a number of characters and be resolved in analyses, a
fact that supports studies that have shown that incomplete taxa do not necessarily hinder
phylogenetic analysis (Wiens, 2003; Kearney and Clark, 2003). This is dependent on
whether a given incomplete fossil preserves key features that allow for its resolution
within a diversity of forms. A large number of fragmentary enantiornithines (i.e.
Bissetky enantiornithines ‘Abavornis’ and ‘Explorornis’) are morphological nomina
dubia because the few characteristics the specimens preserve are synapomorphies of
Enantiornithes, and thus in analysis these specimens do not represent unique taxonomic
units. Fragmentary taxa such as these do not contribute useful or unique data and
therefore can be safely excluded (i.e. Lenesornis; Wilkinson, 2001). Likewise, despite
many Chinese specimens being complete, the inability to score characters derived from
previously known enantiornithines (i.e. El Brete material) in these new specimens (i.e.
Shanweiniao; Chapter 7) means their completeness will not necessarily produce
resolution among enantiornithine relationships.
Past analyses have drawn heavily from characters that reflect enantiornithine
morphology as known from the El Brete and Spanish enantiornithines (Chiappe, 1993;
Sanz et al., 1995; Chiappe and Walker, 2002; Chiappe et al., 2006). It was hypothesized
therefore that increased character sampling from Chinese specimens then scored across
enantiornithines would result in greater resolution in the enantiornithine tree. This is
almost a cyclical challenge, however, given the preservation of most specimens prevents
364 
scoring existing characters. Even the relatively well-preserved specimens (i.e. Pengornis;
preserved embedded in a single slab) from Liaoning, China differ from three-dimensional
enantiornithine material (i.e. single surface visible, flattened) in such a way that finding
characters that can be scored for all enantiornithines is difficult.
Given some recent specimens are excellently preserved (i.e. Pengornis,
Rapaxavis) revealing a number of new morphologies, these subsequently cannot be
scored in other more poorly preserved Chinese specimens (i.e. Shanweiniao,
Paraprotopteryx) or fragmentary taxa (i.e. skull characters for Avisaurus) and thus a large
number of potential new characters prove to be uninformative. However, the increasing
number of well preserved specimens from China and improved quality of preservation
and preparation may help rectify this problem in the near future (Zhou et al., 2008a;
Morschhauser et al., 2009) especially with the discovery of new specimens of previously
known taxa (Zhang et al., in prep).

vi. Conclusions
The controversial relationships among enantiornithines pose a challenge to avian
systematists. Although the general placement of these taxa within the phylogeny of basal
birds is largely resolved by the fact that they collectively belong to a large clade,
Ornithothoraces, and are generally accepted to be the sister-group of Ornithuromorpha,
the inner relationships of Enantiornithes have remained fairly unexplored due to
difficulties associated with attempting to resolve the relationships of the known taxa. The
incomplete nature of a large number of important taxa (i.e. Nanantius, El Brete taxa,
365 
Alexornis) is a problem that is difficult to overcome without massive field efforts and a
good deal of luck. However, given the evolutionary importance of Enantiornithes,
previous efforts to resolve the clade are expanded and the results are presented in the
following chapter. The results are compared to previous hypotheses as discussed in
above.

366 
CHAPTER 12: ENANTIORNITHINE PHYLOGENY

i. Introduction
Given the current poor understanding of enantiornithine phylogeny, a new
enantiornithine matrix was created hoping to overcome some of the difficulties associated
with previous attempts. The large amount of morphological data acquired during this
study was translated into an expanded character matrix. This matrix is the largest ever
attempted for the clade and includes novel characters and new morphological
observations. However, even with highly fragmentary nomina dubia removed, the
missing data in the analysis exceeds 50%. The missing data problem is not one that can
be simply overcome by the cladist, and in the case of this analysis produced 15,268
MPTs with variation entirely isolated to the enantiornithine clade. Still the strict reduced
consensus tree is very resolved considering the nature of the included taxa (often
represented by incomplete non-overlapping material). The matrix and results are
presented below, and patterns and inferences are discussed.

ii. Character List
Mesozoic bird character lists modified from Chiappe, 2002 (Gao et al., 2008;
O’Connor et al., 2009, in prep.) and the Chiappe et al. (2006) enantiornithine specific
character list were used as starting points for this matrix. The former list is focused on
Mesozoic birds as a whole, while the latter is an enantiornithine specific list expanded
from previous efforts (Chiappe, 1993; Chiappe and Walker, 2002). Characters from the
367 
Mesozoic bird character list (O’Connor et al., in prep) meant to resolve
Confuciusornithidae or other specific clades were removed (i.e. character 38 of O’Connor
et al., 2009). Some of the characters from these lists were modified (i.e. 52, 73, 93-95,
122, 145, 160, 194, 214, 215, 233, 243, 244, 261, 266, 267, 279 of this list, see Appendix
B to reflect the expanded knowledge of enantiornithine and Mesozoic bird morphology
(additional character states). During the course of morphological research, new
characters were created to reflect observed enantiornithine variation (7-10, 38-40, 69-71,
100-102, 105, 117-121, 132, 143, 154, 187, 189, 199, 208-211, 235, 237, 245-248, 255,
263, 264, 268, 272, 280, 284).
The final compilation totals 286 skeletal and integumentary characters, 185 of
which are binary and 101 are multistate (Appendix B). Of these, 40 characters were
treated as ‘ordered’. This selection of characters is considered the final character list,
despite the fact that several characters were removed from the final analysis. These
characters are included in the appendix since they are considered helpful morphological
characters that may prove valuable in the near future upon the discovery of material with
better preservation, or restudy of existing specimens (i.e. Eoenantiornis) with finer
techniques (i.e. x-ray).
In order to resolve the clade, the matrix of 286 characters was further reduced.
When all OTU’s were included in the matrix, nine characters were found to be
uninformative (20, 34, 37, 72, 76, 105, 107, 216 and 251) and thus not optimized by the
analysis. In order to resolve this analysis with so much missing data (and retain
fragmentary taxa), characters that were largely uninformative, rather than taxa, were
368 
manually removed apriori (Jenner, 2004). Removal of characters was based on the
amount of missing information they contributed to the enantiornithine clade; if a
character could be scored for one or less taxa (but not originally considered
uninformative because they provide information for different clades of birds) it was
removed. Such characters contributed large amounts of missing information and no
resolution to enantiornithine relationships. Forty ‘fragmentary characters’ were removed;
pruned characters code almost entirely for the palatal region (15-21) and the quadrate
articulation of the skull (29-33), and can only be scored for a single enantiornithine
(Gobipteryx). New basicrania characters (largely derived from DNHM D2950/1), which
could only be scored for two or three taxa were also removed (38-40).
In the final analysis, 49 characters were excluded (15-21, 24-26, 29-40, 48, 51,
53, 54, 66-68, 72, 76, 105, 107, 118, 121, 135, 138, 174, 201-204, 216, 231-232, 247,
249-251) leaving a total of 237 characters (34 ordered).

iii. OTU's
The matrix was rooted using Archaeopteryx lithographica as the out-group. Basal
avians were represented by Jeholornis prima, Rahonavis ostromi, Sapeornis
chaoyangensis and Confuciusornis sanctus, and Ornithuromorpha was represented by
Archaeorhynchus spathula, Apsaravis ukhaana, Gansus yummenensis, Hesperornis
regalis, Ichthyornis dispar, Longicrusavis houi, Patagopteryx deferrariisi and
Yixianornis grabaui with Gallus gallus and Anas platyrhynchos representing Neornithes
(Appendix A).
369 
Table 12.1. A list of all enantiornithine OTU's scored for phylogenetic assessment. OTU's
highlighted in grey were not included in the final analysis. The material column lists what
is known for each OTU and the method column, if empty, indicates first hand study of
the holotype. The fraction on the right is the degree of incompleteness in terms of how
much missing data is scored for a given OTU.
370 

Table 12.1., Continued…
371 
Over 60 in-group enantiornithine operational taxonomic units were examined
(Table 12.1; Appendix A); every published species as well as isolated described material
(i.e. CAGS-02-CM-0901) was scored either from firsthand observations of known
material or publications and photos (see Chapter 1; Table 12.1). Additional undescribed
specimens were also scored (i.e. CAGS-06-CM-012).
With all possible OTU's considered, the most complete enantiornithine taxonomic
unit (Longipteryx, scored from two nearly complete specimens) is approximately 40%
incomplete (only this taxon and Rapaxavis are scored for less than 50% missing data),
compared to the most incomplete taxonomic units scored (PO 4604 and PO 3434,
formerly ‘Incolornis’ and ‘Lenesornis’), which are more than 99% missing data (Table
12.1). These two taxa, however, through an analysis of the dataset by Taxeq3 (Wilkinson,
2001) have been shown to be safely removable as they are taxonomic equivalents of Anas
and Hesperornis, respectively. The large number of incomplete nomina dubia cloud the
data matrix with potential ‘asymmetric both ways’ taxonomic equivalents (Wilkinson,
2001); this occurs when OTU's are identical for shared scored characters, however each
has missing data where the other is informative, and thus their unique taxonomic status is
ambiguous. Initially, despite their incompleteness, nomina dubia were retained in order to
test hypotheses regarding their invalidity.
However, because of the difficulty associated with resolving enantiornithine
relationships (fragmentary specimens and missing data), in the end it was considered
most parsimonious to remove all extremely fragmentary nomina dubia, undescribed
specimens, and most of the unnamed described material while retaining highly
372 
incomplete but important species (i.e. Noguerornis, Soroavisaurus, Nanantius,
Alexornis). The final analysis included 56 OTU's, 40 of which are enantiornithines (Table
12.1). Taxa that were inaccessible (but scored from published photographs and also
contribute large amounts missing information, i.e. C. chabuensis) were also removed.
The only unnamed specimens (not including those in review or press) run in the analysis
were two specimens (CAGS-02-CM-0901 and CAGS-IG-04-CM-023) from the Xiagou
Formation (You et al., 2005; Harris et al., 2006), in order to include at least some of the
diversity from this unit and thus sample a greater temporal and geographic range (one
distinct taxon currently under study from this formation was also included; CAGS-05-
CM-006 and CAGS-04-CM-006).

iv. Results
The data matrix (Appendix C) was analyzed with TNT (Goloboff et al., 2008);
optimal trees based on parsimony were obtained through a heuristic search implementing
1,000 replications of Tree Bisection Reconnection (TBR), retaining the single shortest
tree from every replicate. The shortest trees were then subjected to an additional round of
TBR. The analysis returned 15,268 most parsimonious trees (MPTs) of 902 steps. The
strict consensus tree (Fig. 12.1) is resolved in the basal and derived sections of the tree
(i.e. Pygostylia and Ornithuromorpha), however a majority of enantiornithines form a
large polytomy more derived than Pengornis with a few closer relationships nested
within.
373 

Figure 12.1. Strict consensus tree (length 902 steps) from 15,268 MPTs.
374 
Confuciusornis is resolved as the sister taxon to Ornithothoraces. Jeholornis +
Zhongornis, Sapeornis and Rahonavis form consecutive outgroups of the Confuciusornis
+ Ornithothoraces clade. Ornithothoraces is formed by a dichotomy between a resolved
Ornithuromorpha and a large enantiornithine clade with very little resolution. Despite the
removal of characters that lent support to the clade (i.e. palatine contacting premaxilla,
bi-condylar otic process of quadrate, reduced zygomatic process), relationships within
Ornithuromorpha are resolved (and remained stable during alternative enantiornithine
taxonomic samples). Lectavis is resolved as the most basal ornithuromorph (and not an
enantiornithine); Gansus + Yixianornis, Longicrusavis, Apsaravis, Patagopteryx and
Archaeorhynchus form consecutive outgroups of Ornithurae (Archaeorhynchus being the
furthest removed). Within Ornithurae, Hesperornis is resolved as more closely related to
modern birds (Neornithes) than Ichthyornis.
Pengornis is resolved as the most basal enantiornithine, falling outside a large
polytomy that includes all other enantiornithine taxa with a few more derived
relationships within. CAGS-04-CM-023 + Elsornis form a clade with CAGS-02-CM-
0901, Eocathayornis + Enantiophoenix form a clade with Gobipteryx, Longirostravis +
Noguerornis form a ‘longipterygid’ clade with Rapaxavis and Longipteryx, and
Shanweiniao + Eoenantiornis, DNHM D2950/1 and Dapingfangornis from a clade.
These subclades form a polytomy with remaining enantiornithines (Fig. 12.1).
After reviewing the large number of trees returned by TNT (15,268 MPTs), it is
clear that most enantiornithine relationships are stable, but cannot be resolved in the strict
375 

Figure 12.2. Enantiornithine clade in reduced strict consensus tree (with Gurilynia,
Nanantius, and Otogornis removed).
376 
consensus tree due to the instability of a few troublesome taxa (i.e. Otogornis, Nanantius,
Gurilynia); pruning these taxa from the strict consensus using TNT (but their data is still
optimized in the analysis), produces a fairly resolved strict reduced consensus tree,
although a large number of taxa still fall in a polytomy (Fig. 12.2). The reduced
consensus tree (Fig. 12.2) retains Pengornis in its basal position, now falling outside a
dichotomy between a clade formed by Elsornis + CAGS-04-CM-023 (Harris et al.,
2006), with CAGS-02-CM-0901 (You et al., 2005), LP 4450 (Sanz et al., 1997) and
Protopteryx forming consecutive outgroups, and more derived enantiornithines. The
‘Longipterygid’ clade is resolved as more derived than the Elsornis subclade, forming a
dichotomy with an Iberomesornis + ‘Euenantiornithes’ clade. Longirostravis +
Noguerornis are resolved as derived ‘longipterygids,’ with Rapaxavis and Longipteryx
forming successive outgroups.
Iberomesornis falls outside a clade that includes remaining enantiornithines and is
here referred to ‘Euenantiornithes’ (Chiappe, 2002). A clade formed by Eoenantiornis +
Shanweiniao, with DNHM D2950/1 and Dapingfangornis as consecutive outgroups,
holds the basal position within ‘Euenantiornithes.’ Cathayornis, Alethoalaornis, and an
Enantiophoenix + Eocathayornis and Gobipteryx clade form successive outgroups to a
dichotomy including the remaining taxa. This dichotomy consists of two polytomies,
which account for approximately one third the included enantiornithine OTU's. The
smaller polytomy consists of three taxa: Boluochia, Hebeiornis, and Yungavolucris. The
second polytomy consists of thirteen taxa: M. cruzyensis, M. vincei, A. archibaldi, A.
377 
gloriae, Neuquenornis, Soroavisaurus, Sinornis, Eoalulavis, Halimornis, Concornis,
Enantiornis, CAGS-04-CM-006/05-CM-006, and Alexornis.

v. Discussion
Early analyses of the data set which retained all characters and OTU's, regardless
of their degree of completeness, could not resolve ornithothoracines except for the most
derived ornithuromorphs that possess obvious modifications and consistent similarities.
The inability to resolve Enantiornithes even in light of an increased number of characters
highlights the incomparable nature of key enantiornithine collections rather than
inadequate sampling and scoring throughout the clade (Jenner, 2004). Increasing
character sampling is theoretically inferred to increase resolution (Hills, 1998; Jenner
2004). However, while this study created new characters to reflect increased knowledge
of enantiornithine morphology and included the most morphological data for an
enantiornithine matrix to date (286 characters when the whole basal bird phylogeny is
considered), it still failed to resolve the group. For reasons already detailed,
enantiornithines are a difficult group to compare between collections, and this inability to
compare taxa is translated into the matrix as missing data across most taxa for new
characters. This is unavoidable given the fragmentary nature of numerous holotypes (i.e.
Alexornis, A. gloriae, A. archibaldi, Gurilynia, Nanantius). No amount of extreme
pruning of taxa could resolve the enantiornithine clade and in any case, since the goal is
to understand the genealogical relationships of known enantiornithine diversity, creating
378 
a phylogeny based on a small sampling of complete taxa would not contribute to an
overall understanding of the clade’s evolution.
A large number of characters, though not uninformative in the strictest sense (i.e.
scored same for all taxa), could only be scored for a small amount of in-group taxa, or
reflect differences in morphology between more derived ornithothoracines but are
unknown in enantiornithines. These characters contribute large amounts of ambiguous or
missing data and do not lend resolution to enantiornithine relationships and thus were
removed in the final analysis. A majority of the excluded characters pertain to the skull,
in particular the palate, which is only known in a single enantiornithine (Gobipteryx).
Even after manual character and OTU pruning (even including taxa excluded in the
reduced strict consensus tree by TNT), the final analysis presented here represents the
largest of its kind, with 237 characters and 40 enantiornithine OTU's (37 in reduced
consensus), more than double the number of taxa included in any previous analysis
(Chiappe et al., 2006; Cau and Arduini, 2008).
Considering the amount of missing data associated with the enantiornithine clade,
and in light of the dim success of previous attempts to resolve the clade even with smaller
samplings (Chiappe and Walker, 2002; Chiappe et al., 2006), the fact that the
enantiornithines receive any resolution in the reduced strict consensus of 15,268 trees
with only three taxa removed is unexpected. The strict consensus tree is nearly
completely unresolved within the enantiornithine clade while ornithuromorphs are
resolved (Fig. 12.1) despite the removal of palatal and other characters. After reviewing a
large number of the MPTs, it became clear that despite the final polytomy, many
379 
enantiornithine relationships were stable in all trees. Only the extremely variable position
of a few incomplete taxa caused the strict consensus tree to collapse nearly all
relationships more derived than Pengornis.
There are three taxa that are particularly variable, Otogornis, Nanantius and
Gurilynia. Two of these three taxa represent the most incomplete OTU's in the analysis
(Gurilynia and Nanantius), scored for fewer characters than any other OTU. Incidentally,
the validity of Gurilynia was questioned for lack of material (see Chapter 3) and the only
known specimens of Nanantius have been lost (pers. obs.). Because other enantiornithine
relationships are stable, these three ‘problematic taxa’ were removed from the final tree,
creating a strict reduced consensus (Fig. 12.2). A strict reduced consensus tree retains all
relationships supported in all MPTs if the position of excluded taxa is ignored
(Wilkinson, 1994, 1995, 2003). The dataset is not rerun with ‘problematic taxa’ removed;
the reduced strict consensus tree is based on the same results so that the data from
selectively removed taxa is still optimized within the analysis. The removal of only three
fragmentary OTU's resulted in a substantially more resolved Enantiornithes. However,
due to the large number of equal length trees and difficulties in analyzing the data matrix,
the resultant relationships are interpreted with caution.

Basal Bird Relationships
Non-ornithothoracine birds form relationships consistent with the results from
some recent analyses (i.e. Zhou et al., 2009). The Late Cretaceous Rahonavis consistently
holds a more basal position than the Early Cretaceous non-ornithothoracines (Fig. 12.1;
380 
Chiappe, 2002; Zhang et al., 2008b). Confuciusornis is resolved as the most derived
pygostylian, consistent with most analyses (Clarke et al., 2006; Zhou et al., 2008a; Zhou
et al., 2009); the position of this taxon relative to Sapeornis and the ornithothoracine
clade changes between analyses, alternatively placing Sapeornis as the more derived
pygostylian (O’Connor et al., 2009). A traditional Pygostylia (Chiappe, 2002; Zhou et al.,
2008a; O’Connor et al., 2009) is not resolved due to the more basal position of Sapeornis
relative to Jeholornis, a result that has appeared in a recent analysis (Zhou et al., 2009).
Jeholornis and Zhongornis form a clade, whereas previous analyses have resolved the
shorter tailed taxon as more derived (Gao et al., 2008; O’Connor et al., 2009).
These results highlight two things: the susceptibility of the cladogram to the data
input (the total range of morphological variation), and the poorly known nature of the
basal section of the avian tree. Depending on the total morphology encapsulated,
character distributions will vary, which will result in differing parsimonious results,
especially if a particular node or clade is only weakly supported. In the case of taxa such
as Jeholornis and its kin, which clearly represent a distinct lineage, character or
morphological sampling for the node must be inadequate. This is not surprising given that
no thorough studies of Sapeornis and Jeholornis have ever been published despite the
numerous specimens and the morphological and evolutionary importance of these taxa.
Even Confuciusornithidae is known from hundreds more specimens and a new genus
since the publication of its monograph (Chiappe et al., 1999), suggesting more work on
the interrelationships and differences between these taxa can be done. New
morphological information on these specimens may translate into expanded characters
381 
that better encapsulate variation within these clades, as well as new characters which may
help to resolve relationships between basal Early Cretaceous birds from China; unlike the
enantiornithines, these species, with the exception of Zhongornis and Rahonavis, are well
known from multiple complete specimens and therefore it should be possible to increase
character sampling without the missing data problem of enantiornithines.

Ornithuromorph Relationships
Relationships within Ornithuromorpha are resolved relative to some other
analyses (i.e. Zhou and Zhang, 2006b; O’Connor et al., 2009; Zhou et al., 2009) and
remained stable throughout alternative analyses of the data matrix with varying
enantiornithine taxonomic samples. The resolution in this clade is interpreted as a result
of the small number of included taxa (ten) compared to recent analyses (18 in Zhou et al.,
2008a).
The most unusual result of this analysis is the placement of Lectavis outside
Enantiornithes (contra Chiappe, 1993; Sanz et al., 1995), reinterpreted as a basal
ornithuromorph. This taxon is very incomplete, represented by less than two complete
elements (a tibiotarsus and a partial tarsometatarsus). The bulb-like distal condyles of the
tibiotarsus, the absence of well-developed tibiotarsal cnemial crests, and the presence of a
reduced metatarsal IV (optimized in this analysis as plesiomorphic for all avians more
derived than Archaeopteryx because of its presence in Rahonavis; subsequently lost in all
ornithuromorphs more derived than Lectavis) suggest this taxon is an enantiornithine
(Chiappe, 1993). The presence of a well-fused tarsometatarsus compared to many
382 
enantiornithines, with a proximally located dorsal tubercle for the m. tibialis cranialis and
a process reminiscent to a ‘proto-hypotarsus’ on the proximal caudal surface suggest this
taxon may be more advanced. Additional material will clarify the phylogenetic affinity of
this taxon; pending new material, this taxon is regarded as Ornithothoraces indet.
The placement of Hesperornis as the most derived non-neornithine bird in the
analysis is unusual. Ichthyornis is typically resolved more advanced than
hesperornithiforms (Clarke, 2004; Clarke et al., 2006; You et al., 2006; Zhang et al.,
2008b; Zhou et al., 2009), supporting the existence of a Carinatae clade (Cracraft, 1986).
Ichthyornis has recently been redescribed in a large monograph (Clarke, 2004) while the
post-crania of Hesperornis has never been thoroughly reviewed since Marsh (1880). This
study, however, incorporates improved scorings on Hesperornis (Bell, pers. comm.)
derived from a comprehensive study of a large number of specimens (O’Connor et al., in
prep).
Gansus, from the Early Cretaceous of Gansu Province (China), is resolved outside
Ichthyornis (You et al., 2006) but in a sister-taxon relationship with Yixianornis. The
placement of Gansus relative to other taxa is difficult to compare to other analyses
because many recent analyses do not include this taxon (Zhou and Zhang, 2006b; Zhou et
al., 2008a, 2009). However, when included, the taxon appears as a close relative to
modern birds (Cau and Arduini, 2008), and in one case within the ornithurine clade, more
derived than hesperornithiforms (You et al., 2006). The more basal position of this taxon
obtained in the current analysis may reflect new information on Gansus (pers. obs.).
383 
The placement of Apsaravis in this analysis is far more basal than most analyses
that typically resolve the taxon as more derived than Yixianornis and hongshanornithids
(Norell and Clarke, 2001; Clarke et al., 2006; Zhou and Zhang, 2006b; Cau and Arduini,
2008; Zhou et al., 2008a; Zhou et al., 2009). This taxon does have several extremely
derived features of the carpometacarpus and pelvis, but also possesses features present in
enantiornithines such as a dorsally excavated coracoid. The position of Archaeorhynchus
as less derived than Patagopteryx is consistent with recent analyses that have included
both taxa (Zhou et al., 2008a, 2009).
While differences in scorings and new information could be producing the
differing relationships between ornithuromorphs resolved here, alternatively it could be
the result of poor character and taxonomic sampling within the clade, given that the
enantiornithines were the focus of this study.

Enantiornithine Relationships
In light of the weak support for proposed phylogenetic relationships and the large
number of equal length trees, the results obtained from the present analysis will be
interpreted lightly and in context of other analyses and observed morphology.
Comparisons are difficult given that the largest previous analysis contained only 20 valid
enantiornithine OTU's (Cau and Arduini, 2008) and Mesozoic bird analyses typically
contain only four to six enantiornithine taxa (Clarke et al., 2006; Zhou et al., 2008a).
Several important inferences, however, can be derived from the results. Relationships
within these results show some consistency with other analyses; for example, a
384 
‘longipterygid’ clade is still supported (Chiappe et al., 2007; Cau and Arduini, 2008;
O’Connor et al., 2009). The results also show substantial differences and new
relationships (likely a factor of differential taxonomic input as much as increased
character sampling); for example, a longipterygid clade has never before been suggested
to include Noguerornis (as resolved here). Only three enantiornithine clades have been
named and supported phylogenetically: Avisauridae (Chiappe, 1993), Longipterygidae
(O’Connor et al., 2009) and Euenantiornithes (Chiappe, 2002). The largest clade is
Euenantiornithes, which is defined as all taxa closer to Sinornis than Iberomesornis
(Chiappe, 2002). This clade has been inferred to include most enantiornithines, only
excluding the basal taxa Iberomesornis and Noguerornis (Chiappe, 2002; Chiappe and
Walker, 2002). This hypothesis, however, has not been strongly tested, and the validity of
this clade and others in the current phylogenetic hypothesis is discussed below.

Enantiornithine synapomorphies. The monophyly of Enantiornithes is supported by
nine synapomorphies: presence of premaxillary teeth throughout (reversal, character 4: 3
→ 0); dentary teeth present (a reversal, character 42: 1 → 0); lateral side of thoracic
vertebrae excavated by a groove (character 63: 0 → 1); present of an elongate
hypocleideum approximately 30% the length of clavicular rami (character 116: 0 → 2);
proximal margin of the humeral head concave in its central portion, rising ventrally and
dorsally (character 141: 0 → 1); well developed olecranon fossa on the caudal distal
humerus (character 157: 0 → 1); minor metacarpal projecting distally further than the
major metacarpal (character 188: 0 → 1); trochlea of metatarsal II broader than that of
385 
metatarsal III (character 273: 0 → 1); and J-shaped metatarsal I with both articular
surfaces forming parallel planes of articulation (character 279: 0 → 1).
Published diagnoses for Enantiornithes vary widely (Chiappe, 1993; Sanz et al.,
1995; Chiappe, 1996; Kurochkin, 1996; Sereno, 2000; Chiappe, 2002; Chiappe and
Walker, 2002). Throughout the years, characters originally considered synapomorphies of
Enantiornithes (i.e. dorsally excavated coracoid, reduced metatarsal IV) have been
reassigned in support of more derived clades (i.e. Euenantiornithes; Chiappe, 2002) or
become ambiguous in light of new discoveries with differing morphologies (i.e.
Pengornis, Rapaxavis). Given that synapomorphies are subject to change upon the
discovery of new material, comparison will focus on the results of the most recent major
attempt to diagnose the clade.
Chiappe (2002) provided four enantiornithine synapomorphies: elongate
hypocleideum, ulna shorter than humerus, minor metacarpal projecting distally beyond
the major metacarpal and round proximal surface of the tibiotarsus. Of these, the
presence of a long hypocleideum (character 116: 0→2) and minor metacarpal projecting
distally further than major metacarpal (character 188:0→1) are still resolved in support of
the clade. The presence of a concave proximal margin of the humerus (character
141:0→1) was considered an ‘euenantiornithine’ synapomorphy (Chiappe, 2002;
Chiappe and Walker, 2002), but is here resolved as the basal condition within
Enantiornithes. The presence of a metatarsal II trochlea wider than that of metatarsals III
and IV (273:0→1), and laterally excavated thoracic centra (character 63:0→1) have also
386 
previously been considered enantiornithine synapomorphies in older analyses (Chiappe,
1993; Sanz et al., 1995).
The extreme J-shaped (in medial view) metatarsal I (character 279: 1→2) has
been considered a synapomorphy of Avisauridae (Chiappe, 1993; Sanz et al., 1995). The
J-shaped morphology here resolved as a new enantiornithine synapomorphy (character
279: 0→1) refers to a different morphology in which the two articular surfaces are not
perpendicular as in avisaurids, but parallel or near parallel. This morphology is present in
most taxa, with the J-shape morphology of avisaurids considered a derived condition
within Enantiornithes (Chiappe, 1993; Sanz et al., 1995). This is a character that requires
further revision to better encapsulate enantiornithine morphological variation (for
example, the current lack of differentiation between DNHM D2950/1 and avisaurids
based on position of articular surfaces, despite the fact that in DNHM D2950/1 the caudal
ramus of metatarsal I is not elongated, thus lacking the extreme J-shape of the latter
clade). The phylogenetic placement of DNHM D2950/1 and avisaurids suggests
independent modification of this element in two lineages.
The presence of teeth has previously been resolved as plesiomorphic to
Ornithothoraces, but is here resolved as a reversal from the edentulous condition of
Confuciusornis and reduced dentition in Jeholornis (maxillary and premaxillary teeth
lost), Sapeornis (dentary teeth lost), and Zhongornis (possibly edentulous). The
widespread presence of teeth in ornithothoracines suggests the optimization of these
characters may reflect the small sampling of basal taxa and change in future analyses,
especially in light of the conflict with Dollo’s Law that consider traits such as teeth
387 
irreversibly lost (Farris, 1977). However, the fact still stands that all basal taxa more
derived than Archaeopteryx (Rahonavis skull material is currently unknown) are known
to have some degree of dental reduction compared to contemporaneous basal
ornithothoracines (i.e. Pengornis and Yanornis), a trend only strengthened by the recent
discovery of additional basal edentulous taxa (i.e. Zhongjianornis; Zhou et al., 2009). In
future analyses, it maybe possible to incorporate Dollo’s Law into the parsimony analysis
of this matrix (Farris, 1977) and thus change not only the optimization of this character,
but also the shape of the resultant tree. The results, however, may suggest that teeth were
regained in Aves and thus not all clades of organisms behave as predicted under Dollo’s
law.

Basal Enantiornithine Relationships. The basal region of the tree differs from other
analyses with far fewer taxa, however certain taxa (i.e. Pengornis, Protopteryx, Elsornis)
are consistently placed near the base of the enantiornithine tree. The relative positions of
Protopteryx and Elsornis are consistent with some previous results (Chiappe et al., 2006;
Cau and Arduini, 2008). Chiappe et al. (2006) suggested Protopteryx is the most basal
euenantiornithine, with Elsornis nested just within and all other euenantiornithines more
derived (most in a polytomy). These relationships are consistent with the results here; all
taxa in Chiappe et al. (2006) considered more derived than Elsornis + Protopteryx are
also here resolved as more derived. These taxa are also resolved as basal enantiornithines
by Cau and Arduini (2008); in their analysis, however, CAGS-02-CM-0901 is resolved as
more derived than Elsornis (less derived here). Other analyses (not including Elsornis)
388 
resolve Pengornis as more derived than Protopteryx, but with both taxa forming the most
basal members of Enantiornithes (Zhou et al., 2008a, 2009).
The clade that includes all enantiornithines more derived than Pengornis is
supported by nine synapomorphies: centrally located parapophyses on the cranial thoracic
vertebrae (character 64: 0 → 1, absent in Pengornis); lateral margin of the coracoid
convex distally or proximodistally (character 94: 0 → 12); coracoid with sternal margin
one half to one third the omalsterno length (character 100: 0 → 1); costolaterally wide
acromion (character 106: 0 → 1); hypocleidium hypertrophied, more than 50% the length
of the clavicular rami (character 116: 2 → 3); pneumatic fossa developed on the
caudoventral corner of the proximal end of the humerus (character 146: 0 → 1); reduction
in wing to hindlimb ratio (ImI) from greater than 1.1 to between 0.9 and 1.1 (reversal,
character 197: 3 → 2); a reversal in the degree of fusion in the tibiotarsus from fully
fused, to unfused or partially fused (character 233: 2 → 01); and medial rim of trochlea
of metatarsal III with strong plantar projection (character 278: 0 → 1).
Given the size of the clade, all these characters are ambiguous (none
unambiguously distributed through all taxa). The characters, centrally located
parapophyses on the cranial thoracic vertebrae, a costolaterally wide acromion, and a
convex lateral margin of the coracoid, have all previously been considered
synapomorphies of Euenantiornithes (Chiappe, 2002; Chiappe and Walker, 2002). The
presence of a strong plantar projection of the medial rim of the metatarsal trochlea III has
previously ambiguously supported the Avisauridae clade (Sanz et al., 1995).
389 
The character regarding the degree of fusion in the tibiotarsus is considered weak;
specimens scored as unfused may have to be re-examined to determine if growth was
indeed complete (see Chapter 9). Intermembral indices vary widely throughout the clade,
possibly indicating an ecological signal. The character regarding the presence of a well-
developed pneumatic fossa on the humerus should be re-examined. The character, which
only differentiates the presence of a well-developed fossa, could be expanded to better
encapsulate the morphology, including the moderate development of some Chinese
enantiornithines and the fully perforated canal of PVL 4043.
The fairly basal position of Longipteryx differs slightly from some analyses,
which have placed the clade in a more derived position (Chiappe et al., 2006; Cau and
Arduini, 2008) but this basal placement is consistent with more recent analyses which
have included more longipterygid taxa (O’Connor et al., 2009). Longipterygidae also
differs from previous analyses in the included taxa; one taxon previously not regarded as
a longipterygid (i.e., the Early Cretaceous Noguerornis from Spain; Lacasa-Ruiz, 1989)
has been resolved within the clade while another taxon (i.e., Shanweiniao; O’Connor et
al., 2009) previously interpreted as a longipterygid has been excluded. The placement of
Noguerornis within the longipterygid clade has never before been supported, however,
because the only known specimen is fairly incomplete, this taxon is not included in many
Mesozoic bird analyses (i.e. those that have previously resolved a longipterygid clade;
Chiappe et al., 2006; Cau and Arduini, 2008; O’Connor et al., 2009). Noguerornis has no
skull material preserved and thus, it is impossible to determine whether this taxon had the
most characteristic features of longipterygids (e.g., upper dentition restricted to
390 
premaxilla, ventrally concave dentary, rostrally restricted dentary teeth). The relationship
with Longirostravis is supported by a single synapomorphy (character 178: 0→1): the
presence of a round-shaped alular metacarpal, a condition also present in other
(apparently non-longipterygid) enantiornithines (Neuquenornis and Hebeiornis). The
discovery of additional material will surely help to confirm or reject this weakly
hypothesized relationship. The placement of Longipteryx as the most basal member of the
longipterygid clade is consistent with morphological inferences (i.e. basal morphology of
hand). Inferences that Boluochia may represent a longipterygid (see Chapter 3) are not
supported here. However given the highly fragmentary nature of the only known
specimen of Boluochia zhengi, new material will likely change the phylogenetic position
of this species.

The Validity of Euenantiornithes. Most enantiornithines, representing more derived
members, are envisioned to belong to a large clade named Euenantiornithes (Chiappe,
2002; Chiappe and Walker, 2002). It is the first major clade recognized after Chinese
material began to be included in cladistic analyses and is inferred to include most taxa
(Chiappe, 2002; Chiappe and Walker, 2002). Because of low taxonomic sampling in
recent analyses the validity of this clade was never well tested (i.e. You et al., 2006;
Clarke et al., 2006; Zhou et al., 2008a). In this analysis, Euenantiornithes precisely as
previously defined (Chiappe, 2002; Chiappe and Walker, 2002) is not resolved. However,
there is no contradiction between the placement of all taxa appearing in both analyses
(Chiappe, 2002; Zhang et al., 2008b), only with subsequent assumptions that some
391 
unanalyzed taxa belong within this clade (Chiappe and Walker, 2002; Chiappe et al.,
2006).
The first analysis to recognize Euenantiornithes (Chiappe, 2002) included only six
enantiornithines (Gobipteryx, Neuquenornis, Sinornis, Concornis, Eoalulavis,
Iberomesornis and Noguerornis). The Chiappe (2002) analysis resulted in a dichotomy
between Noguerornis + Iberomesornis and a polytomy of the remaining taxa, for which
the name Euenantiornithes was erected (also resolved in Zhang et al., 2008b). All
Chiappe’s (2002) ‘euenantiornithine’ taxa (the taxa that fell in the polytomy that
excluded Noguerornis and Iberomesornis) are resolved by this analysis in the clade more
derived than Iberomesornis. Noguerornis falls outside this clade and thus the results of
Chiappe (2002) and this analysis are not at odds except for the placement of Noguerornis
basal to Iberomesornis, rather than forming a clade. However, taxa such as Longipteryx,
assumed to belong to Euenantiornithes (Chiappe and Walker, 2002), are not resolved as
such in this analysis, a result that had been suggested by O’Connor et al. (2009;
Longipterygidae fell outside a polytomy which included Iberomesornis and
euenantiornithines and thus Iberomesornis was shown to be more closely related to
euenantiornithines than more primitive enantiornithines).
In the present analysis, the ‘euenantiornithine’ clade ends in a large polytomy.
However, less than half of these species are known from a decent amount of material (i.e.
Concornis, Hebeiornis, Eoalulavis) while the rest are extremely incomplete (i.e.
Alexornis, Avisaurus, Soroavisaurus, Martinavis) with no overlapping material.
Therefore, it is not surprising that this region of the tree cannot be resolved.
392 
‘Euenantiornithes,’ as defined here, shares some consistencies with previous analyses,
however most ‘Mesozoic bird’ phylogenetic analyses included only taxa from within this
clade and typically resolved them in a polytomy—thus comparison with other analyses
cannot be made (Clarke, 2004; Ji et al., 2005; Clarke et al., 2006; You et al., 2006).
Avisauridae—defined by Chiappe (1993) to include Avisaurus, Soroavisaurus,
and Neuquenornis—is not resolved in the consensus tree (although the clade is largely
stable in most trees of equal length). Instead, all ‘avisaurid’ taxa fall in the larger derived
‘euenantiornithine’ polytomy. All El Brete enantiornithines fall in the larger polytomy as
well, with the exception of Yungavolucris, a result consistent with previous hypotheses
that have resolved this taxon as the most basal member of the El Brete enantiornithine
assemblage (Chiappe, 1993; Sanz et al., 1995).

Taxa Removed in Reduced Consensus
Three taxa known by fragmentary remains were identified to be responsible for
creating the large numbers of equal length trees: Nanantius eos, Otogornis genghisi and
Gurilynia nessovi. These taxa appear in the strict consensus tree (Fig. 12.1), but because
variation within the placement of these OTU's produced most of the MPTs while other
relationships remained stable, a reduced consensus tree was drawn in order to show stable
relationships from the analysis (Fig. 12.2). The reduced strict consensus tree shows the
relationships that are resolved if the tree does not have to incorporate the position of the
excluded OTU’s.
393 
Otogornis zhengi is based on a partial thoracic girdle and wings; the slab was
imbedded in a resin plaque and prepared from both sides. The surface of imbedded in the
slab, however, is not clear. The taxon is fairly fragmentary only offering unequivocal
morphologies on one surface and is scored as 90% missing data. Nanantius eos and
Gurilynia nessovi are both known from less than a single complete element, the former
represented by a partial tibiotarsus (possibly lost along with referred material; pers. obs.)
and the latter known from a partial humerus (93% missing data).
Otogornis is most commonly resolved as either between CAGS-02-CM-0901 and
LP 4450 (outside ‘Euenantiornithes’) or as more derived than Iberomesornis, but less
derived than Cathayornis (within ‘Euenantiornithes’). Gurilynia sometimes places very
derived with Martinavis, Enantiornis and Alexornis (the taxon is consistent in
morphology and size with the former two taxa) while at other times holds a more basal
position in a clade with Boluochia, Yungavolucris and Hebeiornis. Nanantius commonly
places as the most basal ‘euenantiornithine’ (most basal taxon more derived than
Iberomesornis), or alternatively is placed more derived within this clade, grouping as a
basal ‘avisaurid’ (not resolved in final tree). Additional material of all three genera
should clarify the phylogenetic relationships of these taxa.
Reduced consensus methods allow a researcher to see stable relationships that
could be clouded by one or two incomplete OUT's. The OTU's excluded from the
reduced consensus tree (Gurilynia, Nanantius, Otogornis) are only known from very poor
specimens and short publications, and therefore there is very little information available
for these species. While it is preferred to find relationships between all known valid taxa,
394 
for this reason it may be more parsimonious to await more informative holotypic material
before erecting largely uninformative species such as these. Despite the large number of
such problematic but valid taxa within Enantiornithes (i.e. Alexornis, Soroavisaurus,
Yungavolucris), removing only three taxa, two of which are the most incomplete OTU’s
in the analysis, revealed stable relationships between more than half of the included taxa
(Fig. 12.2).

vi. Evolutionary Trends
Given the large number of trees and already highlighted characters that need
improvement, the results here are considered one attempt that provides a working
phylogenetic hypothesis and highlights where there needs to be additional work within
the clade. If new material is found for many of the fragmentary or otherwise problematic
specimens, relationships are not unexpected to change in light of the new information.
This analysis is the first attempt to resolve enantiornithine relationships at this scale and
thus the results are expected to be incomparable to past analyses. However, given that
there are large consistencies between the present study and the results of recent analyses,
these relationships will be interpreted, albeit loosely, for their evolutionary implications.
Further refinement as well as expansion of this analysis will surely lend support to some
hypotheses, while invalidating others.
395 

Figure 12.3. Reduced strict consensus tree of hypothetical enantiornithine relationships
indicating temporal placement of taxa within the Cretaceous.
396 

Figure 12.4. Reduced strict consensus tree of hypothetical enantiornithine relationships
with locality information illustrating the diversity present from each geologic unit. Mono-
specific localities are unlabelled.
397 
Implications of the basal position of Pengornis houi
The placement of this taxon as less derived than Protopteryx fengningensis and all
other enantiornithines is interesting for several reasons. The holotype of Pengornis houi
is fairly large (discussed below), but also preserves morphologies, such as a reduced
postorbital and a medially recessed wall of the maxilla, that vary within the clade and
thus possible evolutionary trends in the morphological changes of these bones can be
inferred. The excellent preservation, particularly in the skull, of the only known specimen
of Pengornis, however, makes it difficult to determine if characters are lost or simply not
preserved in more derived taxa.
A recessed medial wall of the maxilla appears lost in most enantiornithines
(alternatively not preserved due to the delicate nature of this bone), thus the presence of
this condition in Pengornis houi suggests that the existence of a medially recessed wall of
the maxilla may be ancestral for the clade (present in Archaeopteryx and paravians). The
medial wall is also largely imperforate, possessing only a small foramina that is not
inferred to be homologous to either the promaxillary or maxillary fenestra based on size
and position (see Chapter 4). Based on the well-preserved morphology of the holotype
specimen of Pengornis houi, it may be inferred that these features were lost outside
Enantiornithes (and their absence is plesiomorphic).
The small postorbital of Pengornis may also indicate that this is the ancestral
condition of the clade and that the elongate postorbital of DNHM D2950/1 (which in the
present analysis falls in a more derived position) is secondarily derived (see Chapter 6).
This is consistent with the reduced postorbital in Archaeopteryx (Elzanowski, 2002). If a
398 
reduced postorbital plesiomorphic is within Enantiornithes, then there is great potential
for the development of cranial kinesis during the long evolutionary history of the clade,
although currently it cannot be identified in any specimen due to preservation.

Geographic Dispersal
The results of the present cladistic analysis hint at what may prove to be a pattern
of geographic dispersal. While all ‘non-euenantiornithine’ enantiornithines (including
Late Cretaceous taxa) are from Eurasia (Spain, northeastern China and Mongolia), the
‘euenantiornithines’ cover Asia, Europe, Australia, North America and South America
(Fig. 12.3). This may represent a sampling bias, or it may suggest that enantiornithines
originated in Eurasia, and only the more advanced ‘euenantiornithines’ dispersed globally
(i.e. North America, South America). An Early Cretaceous dispersal would have been
facilitated by limited intercontinental distances at the time, a result of minimal
continental break up from an earlier Pangaea (Dietz and Holden, 1970). No pattern in
Late Cretaceous diversification associated with paleogeography can be gleaned from the
final polytomy; regardless, the Late Cretaceous Martinavis is known from three
continents (North and South America and Europe) suggesting it may have had advanced
migratory capabilities (Walker et al., 2007) and thus the break-up of the continents during
the middle Cretaceous may not have greatly hindered ‘euenantiornithine’ dispersal
(although if basal enantiornithines were not as capable fliers, this may explain their
restriction to Eurasia). Alternatively, this genus is known only from humeri and
additional material could separate the isolated specimens phylogenetically.
399 
All the Late Cretaceous enantiornithines (Fig. 12.3) with the exception of Elsornis
are members of ‘euenantiornithines.’ This may be either a sampling bias or the result of
the incomplete nature of nearly every Late Cretaceous specimen. However, these more
derived, younger taxa are grouped by synapomorphies such as the presence of a deeply
excavated dorsal coracoidal fossa. The placement of Elsornis basal within the clade may
be related to its flightlessness and the subsequent morphological transformations that may
be giving confusing phylogenetic signals. Alternatively, Elsornis may be shown to be
very primitive, despite morphologies (e.g., a derived sternum, a deeply excavated
coracoid, a fully fused carpometacarpus) to the contrary. Its derived placement within the
Protopteryx clade, however, is consistent with its Late Cretaceous age and thus temporal
separation from all other basal enantiornithines.
The Jehol Group of northeastern China samples the entire enantiornithine (and
Mesozoic bird) phylogenetic spectrum (basal and derived specimens reported from the
same formation; Fig. 12.4). All the small ‘cathayornithiform’ enantiornithines (i.e.
Cathayornis, Sinornis, Dapingfangornis, Alethoalaornis) fall within the
‘euenantiornithine’ clade while basal enantiornithines are represented by Protopteryx and
the longipterygids. As in extant passerines, which are diverse and small with very similar
morphology, the ‘cathayornithiforms’ (Zhou and Zhang, 2006a) are a difficult group to
resolve phylogenetically (similar to modern passerines; Barker et al., 2002). These highly
similar taxa are dispersed through the ‘euenantiornithine’ clade and it is expected that
only a detailed morphological investigation of this ‘group’ will clarify their relationships.
400 
The Jehol samples the entire phylogenetic spectrum of enantiornithines however,
unlike the Spanish or Xiagou enantiornithines which come from isolated well known
localities that represent a very limited period of deposition, the Jehol spans over ten My
with localities dispersed across three provinces in northeastern China (Liaoning, Hebei,
Inner Mongolia). Locality information for individual specimens (and thus age) is
typically poorly known (and published date is ambiguous) preventing detailed
phylogenetic patterns within the evolution of this fauna. Protopteryx has been recently
argued to be older than the Yixian Formation, now reportedly from the Lower Dabeigou
Formation (131 Ma; Zhou, 2006). The age of other taxa reported from the same or nearby
localities is now ambiguous (i.e. Hebeiornis and Paraprotopteryx; Zhang et al., 2004;
Zheng et al., 2007) and thus currently only basal enantiornithines are definitively
recorded in the lower Jehol unit. The distribution of Chinese enantiornithines within the
cladogram suggests that the ‘euenantiornithines’ evolved prior to the deposition of the
Yixian Formation (128-125 Ma), given that a diversity of both basal enantiornithines and
‘euenantiornithines’ are present in this geologic unit. The oldest enantiornithine,
Protopteryx fengningensis, is also one of the most basal taxa, but the Dabeigou
Formation of Hebei Province from which it is known is only a few million years older
than the Yixian Formation. Although no ‘euenantiornithines’ are known from the
Dabeigou Formation, an earlier origination is suggested by the incredible diversity of
enantiornithines and ‘euenantiornithines’ in the Yixian Formation. With only a single
enantiornithine reported from the Dabeigou Formation (Protopteryx fengningensis),
401 
conclusions must await new discoveries, however it is interesting to note that the only
enantiornithine purported to be older (DNHM D2950/1), falls outside ‘Euenantiornithes.’
The Xiagou Member of the Xinmingpu Group shows the same diverse
phylogenetic sampling as the Jehol (Fig. 12.4), however the temporal-geographic data
from this unit is much more constrained (Harris et al., 2006; Lamanna et al., 2006). The
Xiagou enantiornithines that are known from wing elements (CAGS-02-CM-0901 and
CAGS-04-CM-023) are placed in the more basal section of the tree (outside
‘euenantiornithines’), while CAGS-05-CM-006/CAGS-04-CM-006, known from
hindlimb elements, is resolved within ‘euenantiornithines.’ Given the incomplete nature
of these specimens, further material could easily change the interpretation of their
phylogenetic placement. However, CAGS-05-CM-006/CAGS-04-CM-006 does show
several derived morphologies (i.e. fusion of the pelvis, well developed cnemial crest,
fully fused tibiotarsus, very small size) that do lend support to its interpretation as a fairly
derived enantiornithine.
Unlike the Xiagou locality, Spanish localities sample different regions of the tree;
all Spanish taxa from Las Hoyas are members of the Iberomesornis clade, while all
Montsec specimens (also from Spain) are resolved outside this clade (Noguerornis + LP
4450; Fig. 12.4). The basal position of the Montsec enantiornithines may be interpreted
as a result of the early ontogenetic stage of LP 4450 and the incompleteness of
Noguerornis, or this phylogenetic pattern may have an interesting implication for
radiation events within enantiornithines. The age of the Montsec locality, 350 km from
Las Hoyas, is poorly known, estimates ranging from Upper Berriasian – Lower
402 
Barremian (Chiappe and Lacasa-Ruiz, 2002). The Las Hoyas locality has a Late
Barremian age (Sanz et al., 2002; Buscalioni et al., 2008), making it younger than the
Montsec locality, even if one considers the younger extreme of the bracketed age (Lower
Barremian). This correlation between age and phylogenetic placement can be interpreted
several ways alone, but given data from China which records the first appearance of
Euenantiornithes at approximately 128 Ma (Late Hauterivian), the distribution of taxa
and localities may suggest that Euenantiornithes originated in Asia and dispersed across
Europe by the Late Barremian. Alternatively, the two Spanish localities could be
interpreted as recording a faunal shift from basal enantiornithine to ‘euenantiornithine’
dominant in at least this region of Spain (rather than a first appearance). With data based
on a few isolated localities, is far too premature to infer further or place weight on these
hypotheses, which can only be clarified through the discovery of new localities.

Size
Size can be used as one measure of niche diversification: a greater size range
reflects the utilization of more ecomorphospace. The increase in size associated with
known Late Cretaceous taxa (i.e. Enantiornis, Martinavis, A. archibaldi) has been
inferred to represent the result of more advanced flight capabilities later in the evolution
of the enantiornithine clade (Chiappe and Walker, 2002; Walker et al., 2007), which
accommodated a wider range of ecomorphological specialization.
403 

Figure 12.5. Reduced strict consensus tree of hypothetical enantiornithine relationships
showing size distributions. Note the fairly large size of basal taxon Pengornis houi, but
that the largest specimens are found in the most derived clade.
404 

All the largest enantiornithines (i.e. Enantiornis, Martinavis; also all Late Cretaceous) are
members of the ‘euenantiornithine’ clade, however all Jehol ‘euenantiornithines’ are
small. The two largest Jehol taxa (still smaller than the largest Late Cretaceous
‘euenantiornithines’), Pengornis and Longipteryx, are basal enantiornithines falling
outside the ‘euenantiornithine’ clade. The basal position of Pengornis suggests two size
trends, one within Enantiornithes and the other within ‘euenantiornithes.’
Pengornis houi is not only the most basal enantiornithine but also the largest
known from the Early Cretaceous (Fig. 12.5). This suggests that the plesiomorphic size
may not have been the small one that characterizes most of the Early Cretaceous
enantiornithines (Sanz et al., 2002; Zhou and Hou, 2002; Zhou and Zhang, 2006a) -
instead, basal enantiornithines may have radiated from a relatively large size into a range
of large to small sizes, but never achieving the size range of ‘euenantiornithines’ (Fig.
12.5). The more advanced ‘euenantiornithines’ can be interpreted as experiencing a
second size radiation into an even greater size range that includes the largest members of
the clade (i.e. Enantiornis). In particular, the enantiornithines from the Jehol show a trend
towards reduced size and arboreal capabilities in ‘euenantiornithine’ taxa and also within
Longipterygidae (i.e. Rapaxavis). It is also interesting to note that the smallest
enantiornithine (Iberomesornis) is the out-group to ‘Euenantiornithes’ suggesting a trend
towards reduced size in the evolution of this advanced clade. However, given the current
instability of ontogenetic inferences without histological analysis (Starck and Chinsamy,
2002; Cambra-Moo et al., 2006), the tiny Iberomesornis may prove to be a subadult
405 
(though not an early juvenile) and thus its size (and possibly some morphologies) could
be an artifact of ontogeny.
The relatively large size of basal enantiornithines highlights an important trend.
Basal birds are all fairly large, with the exception of the juvenile Zhongornis (adult size
unknown), exemplified by Sapeornithidae. Basal ornithuromorphs (i.e. Archaeorhynchus,
Lectavis, Patagopteryx) are also fairly large compared to more derived non-ornithurine
ornithuromorphs (i.e. Hongshanornis, Yixianornis). The fairly large size of basal
ornithothoracines suggests that the large size of more primitive birds was retained in the
common ornithothoracine ancestor. The small size of many ornithuromorphs and
enantiornithines was likely independently developed, perhaps representing ecological
specialization into smaller niches.

Feathers
As suggested by the already basal position inferred for Protopteryx (Zhang and
Zhou, 2000), the alula is optimized as plesiomorphic to Enantiornithes but not
Ornithothoraces (Fig. 12.6). No basal ornithuromorphs were scored for this character
(although Longicrusavis is ambiguously regarded to have possessed an alula given the
presence of this structure in the closely related Hongshanornis; O’Connor et al., in press).
The most distinct and diverse integumentary structure preserved among
enantiornithines is the tail. The presence of a wide range of tail morphologies outside
‘euenantiornithines’ suggests that this diversity evolved early in enantiornithine
evolution. All preserved tail feather morphologies (i.e. paired streamers, four streamers,
406 

Figure 12.6. Reduced strict consensus tree of hypothetical avian relationships mapped
with integumentary structures. Grey taxa preserve no integument; black taxa with no
information preserve no integumentary structures. Grey symbols indicate ambiguous data
(i.e. crural feathers in Archaeopteryx).
407 
‘fan-shaped,’ rectrices absent) are known from the Early Cretaceous (and from China)
while there is no information on Late Cretaceous enantiornithine integument. The fan-
shaped tail appears in the basal ‘euenantiornithine’ (Shanweiniao) and in Early
Cretaceous ornithuromorphs suggesting that this condition arose independently in each
ornithothoracine clade. Eoenantiornis, which forms a sister relationship with
Shanweiniao, clearly preserves the absence of any elongate rectrices, suggesting this
feature arose independently within the Shanweiniao lineage (Fig. 12.6).
Within Ornithuromorpha, the fan-tail character is optimized for the Yixianornis +
Gansus node and more derived taxa. As with the alula, the presence of a fan-shaped tail
in Hongshanornis (pers. obs.), closely related to Longicrusavis (O’Connor et al, in press)
exemplifies how the hypotheses derived from a cladistic analysis are subject to the
selection of taxa. The analysis has no knowledge of this relationship (since
Hongshanornis was not included) nor can it recognize the presence of this morphology in
taxa less basal to Yixianornis and Gansus. The paired tail feather morphology that is
found throughout the enantiornithine clade including the basal Protopteryx and more
derived taxa (i.e. Dapingfangornis) is possibly ancestral for the entire clade (present in
Confuciusornis, here and commonly resolved as the ornithothoracine sister taxon). The
absence of preserved feathers in the holotype of Pengornis houi is unfortunate.

Skeletal Fusion
Fusion is typically associated with the ontogenetic age of a specimen, with an
absence of complete fusion inferred to be indicative of subadult status (Elzanowski,
408 
1981; Sereno, 2000; Morschhauser et al., 2009). Recent discoveries of enantiornithines
with no other juvenile features (i.e. DNHM D2950/1) and histological analysis of the
holotype of Concornis lacustris have made the correlation between lack of fusion among
compound bones and immaturity less clear. Pengornis, the most basal enantiornithine
resolved here, has a fully fused tibiotarsus and tarsometatarsus; due to the absence of
fusion in specimens such as the holotype of Rapaxavis pani and DNHM D2950/1 and
missing data due to preservation in other specimens, the clade more derived than
Pengornis is optimized for a reversal in the degree of fusion of the tibiotarsus (character
233: 2→01).
This highlights a problem: taxa such as Zhongornis that are only known from
obvious juvenile specimens (Gao et al., 2008) are treated as missing data for characters
interpreted as subject to ontogenetic change (i.e. fusion of compound bones). However,
DNHM D2950/1 appears adult and was thus scored based on the condition visible in the
fossil. In the future, given the general lack of understanding regarding enantiornithine
ontogeny, it is recommended these specimens and others with incomplete fusion be
treated as missing information until the degree of growth can be estimated through
histological analysis. Despite potential subadults clouding patterns in degrees of fusion
throughout the clade, Late Cretaceous ‘euenantiornithines,’ at least those from North and
South America, still show a relative increase in fusion within compound bones (i.e.
Avisaurus, Enantiornis).
Complete fusion of the proximal carpometacarpus is optimized here as
plesiomorphic for Ornithothoraces, suggesting that the absence of fusion in the
409 
enantiornithines Hebeiornis, DNHM D2950/1, Longipteryx, and the basal
ornithuromorph Archaeorhynchus are reversals. However, further investigation into the
ontogenetic stage of these specimens should be conducted before inferences about their
ontogenetic status are made (for example, the holotype of Archaeorhynchus being
described as a possible subadult – Zhou and Zhang, 2006b). The absence of distal fusion
in the carpometacarpus is consistent throughout enantiornithines, and a feature that
presumably was not affected by ontogeny.

vii. Conclusions
This analysis of enantiornithine taxa is the largest ever conducted and represents
the first attempt to analyze all taxa within this clade, as well as to place several new taxa
in a phylogenetic context (i.e. DNHM D2950/1, Martinavis). Because of the amount of
‘missing data baggage’ that comes with the enantiornithine clade, useful new characters
were difficult to identify and the final strict consensus cladogram including all taxa is not
well resolved within the clade. Problems associated with resolving this data matrix reflect
the incomplete nature of man known enantiornithine fossils. An example of this problem
is illustrated by palatal characters, which can currently only be scored for one
enantiornithine taxon and no amount of additional studies will reveal more information
on this region of the skeleton; it is simply not preserved in most specimens. The same is
true for many characters, especially detailed characters regarding scars for muscle
attachment, which require excellent preservation. The anatomy of many named species
has been only superficially described and only more detailed studies will provide more
410 
morphological information (i.e. Pengornis, Alethoalaornis, Dapingfangornis). However
the largest problem continues to be the fragmentary nature of most specimens that form
the large polytomies (i.e. Martinavis, Enantiornis, Lectavis, Boluochia). Given that new
specimens of fragmentary species such as Nanantius and Alexornis will not appear
overnight (and indeed no new material has appeared in the past two and three decades
respectively), analyses including these taxa will continue to be challenged by missing
data and ambiguous optimizations. Regardless, this matrix will continue to be updated
and expanded with characters and taxa (not only within Enantiornithes) in hopes that
continuous refinement of the character matrix will return phylogenetic hypotheses of
increasing accuracy. This study represents a starting point in truly understanding
enantiornithines as a whole. The results highlight problems within the clade (i.e.
differences within Longipterygidae, placement of Lectavis, inadequacy of metatarsal I
character) and areas that do require further research (i.e. scorings related to fusion, or the
optimization of certain ornithoracine characters in light of missing taxa within
Ornithuromorpha such as Hongshanornis).
The hypothesis currently presented (reduced strict consensus) resolves Pengornis
as the most basal taxon, and supports a basal position for Protopteryx. An
‘euenantiornithine’ clade is resolved and it includes the majority but not most
enantiornithines. Despite success in resolving some areas of the tree (i.e. basal
enantiornithines), 13 taxa remain unresolved in two derived polytomies of primarily Late
Cretaceous taxa (these taxa are highly incomplete) with some Early Cretaceous Chinese
enantiornithines. The distribution of taxa on the resultant reduced consensus cladogram
411 
suggests a Eurasian origin for enantiornithines, which disperse globally with the
divergence of ‘euenantiornithines.’

412 
CHAPTER 13: DISCUSSION AND CONCLUSIONS

i. Introduction
This extensive study has significantly refined the taxonomy of Enantiornithes and
permitted the formulation of improved diagnoses for several ambiguous species. This
study has also provided a series of morphological descriptions of recently discovered
species from the Early Cretaceous of northwestern China (anatomical case studies of
enantiornithines) and greatly increased our knowledge of the spectrum of skeletal
variation among Enantiornithes, especially in the skull which has been previously poorly
known. This new morphological information has been translated into a series of new
characters with phylogenetic signal, which together with those from previous phylogenies
have been used to create the first comprehensive phylogenetic hypothesis of the clade.
The resultant pattern of relationships—albeit not fully resolved—has been used to put
forward tentative hypotheses regarding the biogeographic and evolutionary history of the
group. Further cladistic research and new fossils will be required to fully understand the
clade, however this study facilitates research efforts by clarifying taxonomy and
expanding current morphological information. Given the growth rate of the
enantiornithine fossil record, the current summary of morphological information may
quickly become outdated, however given the trend in recent publications towards more
thorough descriptions and figures with valid diagnoses, the taxonomy may not again need
revision in the near future, with the exception of the ‘cathayornithiform’ functional
nomina dubia (i.e. Cathayornis aberransis).
413 

ii. Taxonomic Revision of the Enantiornithes
Fifty-eight named species existed to varying degrees of validity upon the start of
this project, with Nanantius valifanovi and Lingyuanornis parvus widely accepted as
invalid prior to this study (60 species total named; Table 13.1). Twenty-one of these taxa
are here considered nomina dubia, almost all of which can be attributed as the result of
either inadequate holotype material or ambiguous diagnosis and description.
Eleven fragmentary taxa named primarily from Uzbekistan and Mongolia
(Abavornis bonaparti, Catenoleimus anachoretus, Explorornis nessovi, Enantiornis
walkeri, Enantiornis martini, Incolornis silvae, Lenesornis maltshevskyi, Sazavis prisca,
Zhyraornis kashkarovi, and Z. logunovi) are considered invalid species based on the
highly fragmentary nature of the holotype (less than half a single bone in most cases).
Those recognized from synsacral elements (Lenesornis maltshevskyi, Zhyraornis
kashkarovi, Z. logunovi) appear to be more derived ornithothoracines (not
enantiornithines; Kurochkin, 2006), however the specimens are still extremely
fragmentary and the species are here considered nomina dubia.
Ten Chinese taxa are considered invalid (the invalidity of several of which has
been previously proposed; Chiappe et al., 2007; Zhou et al., 2008b). Of the invalidated
taxa, five are unfortunately considered nomina dubia on the basis of the poor preservation
and lack of adequate preparation of the holotype combined with the absence of a rigorous
diagnosis and comprehensive documentation (figures and text; Cathayornis aberransis,
C. caudatus, Cuspirostrisornis houi, Largirostrornis sexdentornis, Longchengornis
414 
Table 13.1. List of published enantiornithine species and their current taxonomic status as
of this study. 
415 
sanyanensis). While some species are known from well-preserved specimens and their
validity is supported (i.e. Dapingfangornis sentisorhinus), many other specimens are
poorly preserved and required further preparation that went beyond time constraints of
this project (i.e. Longchengornis sanyanensis). Other specimens were inaccessible and
therefore their validity could only be assessed from the literature (i.e. Cathayornis
aberransis, C. caudatus). These specimens, after further preparation and study might
prove to be valid taxa. However, given the current published data, these specimens
behave as functional nomina dubia and are thus regarded as invalid. The holotype of
‘Vescornis hebeiensis’ (Zhang et al., 2004) has been published twice and the senior
synonym is Hebeiornis fengningensis (Xu et al., 1999). The holotypes of Dalingheornis
liwei and Jibeinia luanhera are unavailable making these taxa also invalid. Support for
the invalidity of Liaoxiornis delicatus and Aberratiodontus wui (Chiappe et al., 2007;
Cau and Arduini, 2008; Zhou et al., 2008) is discussed, reducing the total number of valid
taxa to 37 (Table 13.1). Two valid taxa are identified as requiring further study to clarify
their diagnoses (Alethoalaornis agitornis and Paraprotopteryx gracilis).

iii. Morphological Diversity among Enantiornithes
The large number of enantiornithine specimens and taxa currently known greatly
expands our knowledge of the osteology, characters states, and morphological
combinations in and throughout the clade. Many descriptions of enantiornithine
morphology were primarily based on what now appears to be a very derived portion of
the enantiornithine clade (the El Brete enantiornithines all falling in the most derived
416 
polytomies in this phylogenetic analysis; Chiappe, 1995; Chiappe and Walker, 2002).
The Early Cretaceous enantiornithines from China reveal more basal morphologies and
elucidate the plesiomorphic condition within the clade, however the diversity of these
birds already present in the oldest geologic unit to record their presence hints towards
unknown, more basal morphologies in older taxa.
This comprehensive review of enantiornithine skeletal morphology has also
resulted in an expansion of enantiornithine characters for cladistic analysis, creating a
larger and more accurate matrix (states reflecting enantiornithine morphology) from
which to derive phylogenetic hypotheses. Sampling all enantiornithines has revealed the
basal position of some taxa and derived position of others, suggesting trajectories in the
evolution of some enantiornithine characters (i.e. deep dorsal fossa of Late Cretaceous
enantiornithines).

Case Studies
Three species from the Early Cretaceous Jehol Group are fully described, which
illustrates the morphological diversity present within a single biota. Each taxon is known
from a single complete or nearly complete specimen. Two specimens are new species
(DNHM D2950/1 and DNHM D1878 ½), which reveal important previously unknown
morphologies: DNHM D950/1 preserves the first elongate postorbital within
Enantiornithes (and Ornithothoraces) suggesting a possibly akinetic skull, and DNHM
D1878 ½ preserves the first enantiornithine tail with aerodynamic potential. The third
species has been previously described but from the unprepared holotype (DNHM D2522;
417 
Morschhauser et al., 2009); this morphological review provides a more accurate
description of the specimen based on studies before and after preparation. Without this
necessary redescription of the specimen, character scorings would vary widely between
studies depending on whether the researcher had studied the specimen or relied on the
original publication.
The variable preservation between unique specimens obfuscates comparison and
phylogenetic analysis, as in the case of DNHM D1878 ½ (Shanweiniao cooperorum).
This specimen shares some morphological similarities with the longipterygid
enantiornithines (i.e. Rapaxavis pani) that suggested this species maybe a member of this
diverse clade (O’Connor et al., 2009), a relationship not supported here. Each
morphological description varies in content, a result of preservation (i.e. absence or
presence of integument), which is an important consideration when interpreting the
results of cladistic analyses.

Skull
The morphology of certain regions of the skull remain poorly known, in particular
the palatal region and braincase. Like the post-cranial skeleton, some regions of the skull
vary more than others, one extreme in morphological specialization being the
longipterygids. Relative to modern birds, the enantiornithine skull is conservative,
mesorostrine with skull units aligned in a single plane (extended), a condition that
appears to be plesiomorphic of ornithothoracines. The jaws are typically toothed, the
premaxilla is small, bones are unfused, a postorbital is present and the quadrate lacks
418 
modifications present in more advanced birds (i.e. long pointed orbital ramus, double-
headed otic articulation). The nasals show a high degree of variation; holorhinal nares
appear plesiomorphic to the clade but schizorhinal nostrils are known in at least one
taxon (Rapaxavis, possibly Longirostravis). The latter morphology is correlated with
specific form of cranial kinesis, of which there is no other evidence other than a reduced
postorbital (and consequent absence of a postorbital – jugal bar) in basal taxa. The
dentary is typically unforked, unfused and imperforate.

Post-crania
The pectoral girdle shows the most obvious morphological diversity. The
morphology of the coracoid varies widely throughout the clade, from wide and spatulate
in basal taxa (i.e. Pengornis, Longipteryx) to very narrow and deeply excavated in more
derived taxa. The degree of convexity of the lateral margin, once defining the clade,
ranges from absent (i.e. Rapaxavis) to strongly convex (i.e. Concornis). The sternum
displays a diversity of morphologies, but the basic common structure has a quadrangular
proximal imperforate region with elongate outer trabeculae and short inner trabeculae
(relative to ornithuromorphs), medially ending in a xiphoid process. Within this basic
morphology, there is a great deal of diversity exemplified by the longipterygids, while
Eoalulavis and Elsornis testify to the diversity of overall shapes.
The wing also shows a diversity of shapes and proportions. The humerus ranges
from short and sigmoidal (i.e. Longirostravis) to long and straight (i.e. Concornis). All
taxa share a cranially concave and caudally convex proximal humeral head, although this
419 
becomes markedly more pronounced in more derived taxa (e.g., El Brete specimens). In
profile, the humeral head is concave on the midline, rising dorsally and ventrally,
consistently throughout the clade. Distally, the humerus is transversely and distally
expanded to varying degrees, absent in some (i.e. Longipteryx) to strongly expanded
distally (i.e. Alexornis) and transversely (i.e. Martinavis). Morphologies of the ulna are
poorly known in basal enantiornithines and the presence of a convex dorsal cotyle with
cotyla separated by a groove are currently resolved as synapomorphies of more derived
enantiornithines. The manus shows a great deal of diversity in degree of reduction and
the relative proportions of the major and minor metacarpals and the intermetacarpal
space.
The hindlimb seems more conservative, although the femur shows some features
unique to enantiornithines (i.e. the presence of a caudally projected lateral flange on the
distal femur of some derived enantiornithines). The tibiotarsus bears a single low cnemial
crest in most taxa, preservation permitting. Distally the tibiotarsus is typically fused, the
condyles bulbous and contacting or only separated by a narrow incisure. The condyles
range from the plesiomorphic condition, with the medial condyle greatly exceeding the
lateral in mediolateral width, to subequal.
The tarsometatarsus is fairly unmodified among basal enantiornithines, with a
greater diversity of morphologies in more derived taxa (epitomized by Yungavolucris).
Typically, the metatarsals are proximally fused, without forming an intercotylar
eminence, and coplanar, varying in relative lengths. The metatarsal IV is not as reduced
in some basal enantiornithines, in which metatarsals II and IV are nearly subequal. The
420 
hallux may not have been reversed in basal enantiornithines, given the diversity of
reversed metatarsal I morphologies (i.e. DNHM D2950/1, Soroavisaurus).

Feathers
Preserved integument is limited to the Early Cretaceous and thus any evolutionary
trends would be difficult to assess, however the dispersal of morphologies throughout the
cladogram suggests a few patterns. The plesiomorphic condition in enantiornithine
integument appears to be already fairly advanced, with an alula present. The fan-shaped
tail evolved convergently between at least one lineage of enantiornithines and
Ornithuromorpha. The paired streamer morphology evolved early in the clade and is
retained in advanced enantiornithines; whether this morphology represents the
plesiomorphic condition is unknown. The integument of enantiornithines retains a unique
combination of derived (alula) and basal (un-vaned body coverts) morphologies, as well
as unique features such as the paired pennaceous tail feathers with proximally
undifferentiated vane.

Morphological Comparisons with Ornithuromorpha
Enantiornithines, while possessing all the same key components of the skeleton
present in ornithuromorphs (i.e. large sternum, strut-like coracoid, narrow furcula), differ
in detailed morphologies and lack important specializations (i.e. procoracoid process on
the coracoid). The furcula of enantiornithines almost always possesses a long, straight
hypocleideum that is nearly in the same plane as the clavicular rami; ornithuromorphs
421 
have a furcula with omal tips directed caudodorsally, so that the furcula is much more
effective in acting as a spring between the coracoids. One enantiornithine (Shanweiniao)
appears to have dorsally curved rami as well as expanded omal extremities, as in more
derived birds. Notable modifications of the coracoid are found only in Ornithuromorpha,
such as a true procoracoid process, sternolateral process and expanded sternal margin.
The basal Protopteryx possesses a modification of the coracoid that may have functioned
similar to the procoracoid process in ornithuromorphs but this feature appears to be an
autapomorphy of this taxon. The sternum of ornithuromorphs is consistently different
from that of enantiornithines; the imperforate region is much longer rostrocaudally.
Distally, what is interpreted as elongated medial trabeculae curve medially and fuse to the
caudal midline demarcating a pair of caudal fenestrae, while enantiornithine medial
trabeculae are comparatively poorly developed.
The ornithuromorph pygostyle is different from that of enantiornithines, much
smaller and tapering throughout its length (plough-shaped). This morphology appears to
have been independently evolved by the basal sapeornithids; considering the shortened
long bony-tail lacking a pygostyle of Zhongornis, there appears to be a certain degree of
homoplasy in the caudal morphology of birds (possibly multiple reduction events). The
pygostyle varies considerably within enantiornithines in terms of relative size (i.e.
Longipterygidae) and shape (i.e. Hebeiornis); this element is rarely preserved (or poorly
preserved) among ornithuromorphs, possibly due to its relatively smaller size.
The manus of basal ornithothoracines in both lineages retains a claw on the alular
and major digits and therefore these were independently reduced in each clade, possibly
422 
multiple times within enantiornithines (i.e. Rapaxavis and Longirostravis, and
Shanweiniao).
In the hindlimb, a single cnemial crest in the tibiotarsus is plesiomorphic to Aves
and apparently for Ornithothoraces; in no enantiornithine is there clear evidence for two
cnemial crests although one taxon appears to have independently cranially expanded the
single cnemial crest, similar to the large dorsally expanded cranial cnemial crest of more
advanced birds (i.e. Gansus) however in the latter, the crest is also typically expanded
proximally as well (absent in CAGS-04-CM-006/05-CM-006). The enantiornithine
tarsometatarsus is fairly primitive, and compared to even basal ornithuromorphs (i.e.
Patagopteryx, Yanornis), remains relatively unmodified throughout the evolution of the
clade. Even the derived Late Cretaceous ‘euenantiornithines’ do not have a fully fused
tarsometatarsus, or features such as fully formed vascular foramen and a hypotarsus.
Ornithothoracines share the presence of a dorsal tubercle for the attachment of the m.
tibialis cranialis however in ornithuromorphs it is consistently smaller and more
proximally located. The morphology of this feature in Lectavis is very similar to what is
observed in ornithuromorphs, unlike the more distally located and globose tubercle of
sympatric enantiornithines (Yungavolucris and Soroavisaurus).
Within Maniraptora there is a great deal of convergence that is difficult to
differentiate from homology given the poorly understood nature of the relationships
between clades (Clark et al., 2002; Senter, 2007; James and Pourtless IV, 2009). This is
also true within Aves, where typical ‘bird’ features such as a beak appear in some fossils
but not others. The two ornithothoracine clades experience at least 65 My of parallel
423 
evolution, in which features such as the loss of teeth, enlarged premaxilla, and
dorsoventrally bowed furcula were independently evolved by enantiornithines and
Ornithuromorpha. Many of these features may represent similar modifications related to
the refinement of flight or ecological specialization (i.e. medial process on the proximal
coracoid; enlarged cnemial crest).

iv. Current Review of Enantiornithine Life History
No new material is contributed towards the understanding of enantiornithine life
history, however when all data is reviewed new conclusions are apparent.
Enantiornithine eggshell is only ambiguously known. Specimens from Argentina
strongly suggest they are enantiornithine, however their incomplete nature and early
ontogenetic stage make any determinations equivocal (Schweitzer et al., 2002).
Evidence, primarily the numerous juveniles with rectrices, regarding the developmental
mode of enantiornithines hints towards a precocial development, however the restriction
of the oviduct due to the distally contacting pubes suggests that this mode of development
might have been highly constrained. Phylogenies of parental care suggest that the bi-
parental care required by modern altricial birds did not evolve outside Neornithes
(McKitrick, 1992), and clutch sizes of closely related non-avian dinosaurs suggest
paternal care (Varricchio et al., 2008).
Histological analyses hint at a unique growth trajectory relative to modern birds
and non-avian dinosaurs. Studies are few and given the diversity of enantiornithines and
the plasticity of growth strategies (Starck and Chinsamy, 2002; Erickson et al., 2007),
424 
interpretations must be taken lightly. At least some enantiornithines grew quickly early
during their ontogeny, but where rapid growth ceased in the growth curve is unclear.
One study suggests rapid growth ceased when terminal size was nearly achieved
(Cambra-Moo et al., 2006). The large number of known juveniles (Chiappe et al., 2007)
and the fibrolamellar bone and ossified epiphyses in late stage embryos of Gobipteryx
(Elzanowski, 1981; Chinsamy and Elzanowski, 2001) suggest that not all enantiornithines
grew to full size rapidly, but that growth may have slowed very early in some lineages,
related to the energetic demands of precocial flight. At least some enantiornithines also
experienced prolonged periods of slow growth interrupted by LAG’s for part of their
ontogeny (Chinsamy et al., 1994, 1995; Cambra-Moo et al., 2006). Therefore, many
specimens that appear to be adult may actually be expected to increase in size
substantially and ontogenetic features subject to change (i.e. the unfused tarsals of
DNHM D2950/1).
Multiple specimens of a single species are few, yet the differences between
known specimens of Longipteryx suggest that ontogenetic changes such as fusion of
compound bones may form very late in ontogeny. These few studies suggest that
enantiornithine ontogeny is unique from other known groups, with periods of rapid
growth but also prolonged periods of slow, interrupted growth. The unanswered
questions regarding enantiornithine ontogeny suggests that many assumptions regarding
the ontogenetic stage of a specimen based on features present in modern birds (i.e. size of
orbit relative to skull, periosteal ossification), may be premature.

425 
v. Phylogenetic Systematics
Cladistics is the primary methodology employed here for seeking hypotheses
regarding the potential relationships of extinct taxa. For this reason, this research is
conducted in the context of the ‘birds are maniraptoran theropod dinosaurs’ hypothesis,
which has been well supported by the cladistic method (Gauthier, 1986; Senter, 2007;
Turner et al., 2007a). There are, of course, anthropogenic problems with this method,
however, when data is collected carefully and results are interpreted cautiously, cladistics
can be an excellent method for inferring potential phylogenetic relationships. This
method relies on the constant refinement of the character lists and data matrices from
which hypotheses of relationships are generated so that results are based on the most
accurate assessment of the current morphological range of a given clade. Previous
attempts to resolve the phylogeny of enantiornithines were expanded and the results of a
new morphological matrix, although derived from a large number of MPT's, do support
some previous inferences and hypotheses. Previous cladistic attempts have had limited
taxonomic sampling (Chiappe and Walker, 2002; Chiappe et al., 2006), and proposed
relationships have never been rigorously tested. Therefore, the fact that there is
consistency between previous analyses and the results of the new analysis, the largest
enantiornithine matrix ever analyzed, lends support to these relationships as well as
expands our interpretations of existing clades.
Pengornis is resolved as the most basal enantiornithine, with Protopteryx more
derived. A clade similar to Euenantiornithes of Chiappe (2002) is supported, with
Iberomesornis as the sister taxon and Noguerornis falling more basal in the tree (Chiappe
426 
and Walker, 2002). A longipterygid clade is resolved, however one taxon previously
included within this clade (Shanweiniao; O’Connor et al., 2009) is placed more derived
(within ‘Euenantiornithes’), which may suggest that the elongate rostrum evolved more
than once within Enantiornithes. Avisauridae (Chiappe, 1993) is not resolved in the
reduced strict consensus tree; all avisaurids fall within the large derived polytomy
together with other Early and Late Cretaceous taxa. Lectavis (Chiappe, 1993) is no longer
resolved as an enantiornithine, a hypothesis that cannot be unambiguously tested without
further material.
Beyond Enantiornithes, basal bird relationships no longer resolve a pygostylian
clade and other traditional relationships, consistent with trends in most recent Mesozoic
bird analyses (Zhou et al., 2009). Ornithuromorpha is resolved; differences in proposed
relationships between taxa (i.e. positions of Hesperornis and Apsaravis) compared to
other analyses may reflect new information for several taxa as well as the restricted
taxonomic sample.

vi. Evolutionary Trends
Size
Enantiornithes exhibits a wide spectrum of sizes – in the Late Cretaceous, the
largest specimen is ten times the size of the smallest specimen from the Early Cretaceous.
Traditionally, the very small size of the first known Early Cretaceous enantiornithines
(Iberomesornis, Sinornis; Sanz et al., 1988; Sereno and Rao, 1992) compared to the large
size of many Late Cretaceous specimens (i.e. the El Brete specimens; Walker, 1981;
427 
Chiappe, 1993) was interpreted as evidence for an overall increase in size throughout the
evolution of the clade. The small size of most Early Cretaceous enantiornithines
suggested that early in the clade’s evolutionary history, taxa may have been restricted to
smaller sizes due to their flight capabilities, and thus as the enantiornithine flight
apparatus refined, body size increased as the group expanded into new ecological
morphospace. This interpretation however, was based on the fossil record from ten years
ago. The recent discovery of a large enantiornithine from the Early Cretaceous indicates
that enantiornithines did not only achieve large size late in their evolution. The
phylogenetic placement of this specimen (the holotype of Pengornis houi) as the basal
most enantiornithine also suggests that size and flight capabilities appear not to be
correlated within the clade. Given the current size range in the Early Cretaceous and the
suggested phylogenetic relationships between taxa (basal Early Cretaceous taxa are larger
on average than more derived Early Cretaceous taxa), it appears that the plesiomorphic
condition was a bird near the middle of the current size spectrum. Given the large size of
most basal birds (i.e. Sapeornis, Confuciusornis), and the size of basal ornithuromorphs
(Archaeorhynchus, Lectavis, Patagopteryx) this is also interpreted as true for
ornithothoracines as a whole. Within Enantiornithes, as the clade diversified they
achieved greater and smaller sizes. The largest Late Cretaceous enantiornithines
(Gurilynia, Enantiornis) are bigger than the largest Early Cretaceous taxa (Pengornis,
Longipteryx) indicating that the original statement, that the advancement of
enantiornithine flight capabilities may have resulted in larger size in some taxa, may be
true to some degree. Late Cretaceous taxa certainly show some advancements relative to
428 
Early Cretaceous forms, namely the increase in fusion (i.e. pelvic girdle, tarsometatarsus)
and pneumaticity (i.e. deep dorsal coracoidal fossa, pneumotricipital fossa of humerus).
Though enantiornithines appear to have achieved larger size in the Late Cretaceous, the
existence of small-bodied taxa (Alexornis) indicates that a wide range of sizes was
maintained throughout their evolution

Biogeographical Patterns
Given the weakness of the phylogenetic hypothesis resolved here, strong caution
is used in inferring biogeographical patterns, however an interesting pattern of dispersal
is apparent. This pattern is considered a hypothesis to be tested with future cladistic
analyses and new material. Basal enantiornithines (those outside the ‘euenantiornithine’
clade) have only been collected from Eurasia (Spain, northeastern China and Mongolia),
while the more derived ‘euenantiornithines’ cover Asia, Europe, Australia, North
America and South America, suggesting a Eurasian origin for enantiornithines. This also
suggests that only the more advanced ‘euenantiornithines’ dispersed globally (i.e. North
America, South America). With the exception of extremely fragmentary specimens from
Australia, Early Cretaceous enantiornithines are unknown outside Eurasia.
The two Spanish localities differ in that the older locality (Montsec, lower
Barremian; Chiappe and Lacasa-Ruiz, 2002) is entirely composed of basal
enantiornithines while the younger (Los Hoyas, Upper Barremian; Sanz et al., 2002;
Buscalioni et al., 2008) is dominated by ‘euenantiornithines.’ Additional sampling of this
fauna will elucidate whether this is a biased interpretation due to the fragmentary and
429 
juvenile nature of the Montsec basal enantiornithines, or a true pattern. If a genuine
signal, the ages of these localities may further constrain the faunal shift (at least in this
region of Spain) to the Barremian. Unlike Spanish localities, Chinese localities preserve
specimens across the entire phylogenetic spectrum (basal enantiornithines and
‘euenantiornithines’ coexisting). The dispersal of Chinese taxa within the cladogram
suggests that the ‘euenantiornithines’ evolved prior to the Yixian Formation (128-125
Ma), given that members of both basal enantiornithines and ‘euenantiornithines’ are
present in this geologic unit. The origin of Enantiornithes is likely nested in the
Valanginian, Berriasian or older; the discovery of older material will certainly affect
inferences regarding the origination of features and trends in size.

Diversity and Ecological Specialization
Early in the history of enantiornithine studies, the clade seemed very diverse
relative to ornithuromorphs, especially in the Early Cretaceous. As new specimens of
both clades are uncovered, this disparity is no longer as apparent. The Jehol has revealed
specialized basal ornithuromorphs such as the hongshanornithids and the edentulous
Archaeorhynchus that occupy a decent size range. Beyond the elongated rostrum of the
diverse longipterygids, very few skeletal modifications associated with ecological
specializations are evident among Jehol enantiornithines. DNHM D2950/1, however, has
a modified skull with a secondarily derived elongate postorbital process; this would have
prevented cranial kinesis in this specimen. The teeth are also highly modified, larger than
the typical enantiornithine suggesting that the rigidity of the skull and robust teeth may
430 
have been dietary specializations for hard food items (i.e. durophagy). The teeth of
enantiornithines vary widely suggesting that these features were still under heavy
selection for different dietary niches (i.e. Pengornis, DNHM D2950/1, Longipteryx). This
is primarily evident among less derived enantiornithines although this could be a result of
the heavier sampling of skull material in the basal part of the clade. Limb proportions
vary between species, however few enantiornithines show the extreme proportions of a
wading (possibly Lectavis if considered an enantiornithine, however the only known
specimen is incomplete and intermembral indices cannot be measured) or primarily
cursorial bird, with the exception of the Late Cretaceous Elsornis, which may have been
flightless (Chiappe et al., 2006). The diversity of tarsometatarsal morphologies in the
Late Cretaceous hints towards a wide range of specializations and ecological adaptations
(although not as diverse as previously interpreted given that Lectavis may not be an
enantiornithine).

Enantiornithes and the K-T
Enantiornithines were obviously a successful clade, given the known taxonomic
diversity, spectrum of lifestyles, and extensive biochronology. The extinction of the
clade at the very end of the Mesozoic is poorly understood. There are obvious differences
in the morphology of the flight apparatus between enantiornithines and ornithuromorphs,
yet there is little to indicate that enantiornithines were not capable fliers (Walker et al.,
2007). A drop in oxygen levels has been associated with the end-Cretaceous mass
extinctions (Berner, 2002), which may have affected the survival of enantiornithines and
431 
other non-avian dinosaurs (Ward, 2006). Late Cretaceous taxa however, show high
degrees of pneumatization (i.e. PVL 4022) indicating they possessed a sophisticated and
efficient respiratory mechanism (Chiappe and Walker, 2002; O’Connor, 2004; O’Connor
and Claessens, 2005). Available material however, is not adequate for measuring
pneumaticity indices or making intra clade comparisons. Perhaps other key biological
differences between enantiornithines and other birds contributed not only in their
extinction, but also the extinction of all other basal birds as well. Histological studies
(Chinsamy et al., 1995; Chinsamy and Elzanowski, 2001; Cambra-Moo et al., 2006)
indicate that even small enantiornithines took long periods of time to reach adulthood
(although the timing of reproductive maturity is unknown). The slow postnatal growth in
at least some taxa, small egg size and inferred precocial developmental mode (Chinsamy
et al., 1995; Chinsamy and Elzanowski, 2001), suggest that the differences in these
aspects of enantiornithine life history (with respect to modern birds) may have made the
clade more susceptible to extinction than their modern analogues.

vii. Status of Enantiornithine Research
Currently, two thirds of all enantiornithine species are considered valid, although
the clade is still the most diverse in the Mesozoic. A handful of named taxa need further
research in order to assess their validity, and thus unfortunately the clade still requires
some taxonomic review. Other valid taxa are very fragmentary and will continue to
obfuscate phylogenetic analysis until new material is uncovered, an unavoidable problem.
Recent material and quality of publications show a trend towards better holotype material
432 
and more thorough descriptions, which will surely help to minimize the amount of
ambiguous data being added to future character matrices, although problems such as
differential interpretation will always continue to affect phylogenetic systematic research.
The phylogenetic hypothesis presented here represents a working hypothesis
subject to change. Creating a character matrix for enantiornithines at this scale is the first
step; the continual refinement and expansion of this matrix is most important. The results
of this revisionary study highlight the increasing instability of other regions of the basal
avian tree (i.e. varying phylogenetic positions of basal pygostylians and ornithurines)
apparently correlated with increasing taxonomic diversity, a trend also observed within
the enantiornithine clade (Chiappe, 1993; Chiappe and Walker, 2002). Expanding
character sampling and accuracy, and taxonomic diversity for basal and derived birds
may also affect relationships within enantiornithines.
By the end of this decade, another handful of enantiornithine taxa will be known
and therefore patterns, here inferred on the basis of information from a handful of
localities, will likely be subject to change. Consider, for example, if this research had
been conducted a year prior, before the description of Pengornis houi, how greatly
different trends in size would be interpreted. It is the sincere goal that this compilation of
data and new character matrix will help those whose research concerns avian evolution to
better understand Enantiornithes, a clade that given its phylogenetic importance and
biological success is integral to the understanding of this subject.

433 
REFERENCES

Alerstam, T. 1993. Bird Migration. 420 pp. Springer, Heidelberg.

Alibardi, L. 2006. Cell structure of barb ridges in down feathers and juvenile wing
feathers of the developing chick embryo: Barb ridge modification in relation to
feather evolution. Annals of Anatomy 188: 303-318.

Alvarenga, H. and Nava, W.R. 2005. Aves Enantiornithes do Cretáceo Superior da
Formação Adamantina do Estado de São Paulo, Brasil. II Congresso Latino-
Americano de Paleontologia de Vertebrados: 20.

Amadon, D. 1963. Comparison of Fossil and Recent Species: Some Difficulties. The
Condor 65 (5): 407-409.

Assis, L.C.S. 2009. Coherence, correspondence, and the renaissance of morphology in
phylogenetic systematics Cladistics 25: 1-17.

Barker, F.K., Barrowclough, G.F., and Groth, J.G. 2002. A phylogenetic hypothesis for
passerine birds: taxonomic and biogeographic implications of an analysis of
nuclear NDNA sequence data. Proceedings of the Royal Society of London B 269
(1488): 295-308.

Barsbold, R., Currie, P.J., Myhrvold, N.P., Osmólska, H., Tsogtbaatar, K., and Watabe,
M. 2000. A pygostyle from a non-avian theropod. Nature 403: 155-156.

Baumel, J.J. and Witmer, L.M. 1993. Osteologia. In: J.J. Baumel, A.S. King, J.E.
Breazile, H.E. Evans, and J.C. Vanden Berge (eds.), Handbook of Avian
Anatomy: Nomina Anatomica Avium, Second Edition, 45-132. Nuttall
Ornithological Club, Cambridge.

Benton, M.J. 1998. Diversity in European and African Cretaceous dinosaurs. Newsletter
of the European Palaeontological Association 13: 12.

Benton, M.J. 2004. Origin and relationships of Dinosauria. In: D.B. Weishampel, P.
Dodson, and H. Osmólska (eds.), The Dinosauria, Second Edition, 7-19.
University of California Press, Berkeley.

Benton, M.J. 2008. Fossil quality and naming dinosaurs. Biology Letters.

Berner, R.A. 2002. Examination of Hypotheses for the Permo-Triassic Boundary
Extinction by Carbon Cycle Modeling. Proceedings of the National Academy of
Sciences of the United States of America 99 (7): 4172-4177.
434 

Bonaparte, J.F., Salfity, J.A., Bossi, G., and Powell, J.E. 1977. Hallazgo de dinosaurios y
aves Cretacicas en la Formacion Lecho de El Brete (Salta), proximo al limite con
Tucuman. Acta Geologica Lilloana 14: 5-17.

Bourdon, E., Castanet, J., de Ricqles, A.J., Scofield, P., Tennyson, A., Lamrous, H., and
Cubo, J. 2009. Bone growth marks reveal protracted growth in New Zealand kiwi
(Aves, Apterygidae). Biology Letters doi:10.1098/rsbl.2009.0310.

Brett-Surman, M.K. and Paul, G.S. 1985. A new family of bird-like dinosaurs linking
Laurasia and Gondwanaland. Journal of Vertebrate Paleontology 5 (2): 133-138.

Bray, E.S. 2002. Eggshell from the Upper Campanian Kaiparowits Formation. The
Geological Society of America - Rocky Mountain.

Brodkorb, P. 1976. Discovery of a Cretaceous bird, apparently ancestral to the Orders
Coraciiformes and Piciformes (Aves: Carinatae). In: S.L. Olson (ed.), Collected
Papers in Avian Paleontology Honoring the 90th Birthday of Alexander Wetmore,
67-73.

Brush, A.H. 2000. Evolving a protofeather and feather diversity. American Zoologist 40
(4): 631-639.

Buffetaut, E. 1998. First evidence of enantiornithine birds from the Upper Cretaceous of
Europe: postcranial bones from Cruzy (Herault, southern France). Oryctos 1: 131-
136.

Buffetaut, E. 2002. Giant ground birds at the Cretaceous-Tertiary boundary: extinction or
survival? In: C. Koeberl, and K.G. MacLeod (eds.), Catastrophic Events and
Mass Extinction: Impacts and Beyond, 303-306. Geological Society of America,
Boulder.

Buffetaut, E. and Le Loeuff, J. 1998. A new giant ground bird from the Upper Cretaceous
of southern France. Journal of the Geological Society of London 155: 1-4.

Buffetaut, E., Grellet-Tinner, G., Suteethorn, V., Cuny, G., Tong, H., Kosir, A., Cavin,
L., Chitsing, S., Griffiths, P.J., Tabouelle, J., and Le Loeuff, J. 2005. Minute
theropod eggs and embryo from the Lower Cretaceous of Thailand and the
dinosaur-bird transition. Naturwissenschaften 92: 477-482.

Bühler, P., Martin, L.D., and Witmer, L.M. 1988. Cranial kinesis in the Late Cretaceous
birds Hesperornis and Parahesperornis. Auk 105: 111-122.

435 
Burke, A.C. and Feduccia, A. 1997. Developmental patterns and the identification of
homologies in the avian hand. Science 278: 666-668.

Busbey, A.B. 1995. The structural consequences of skull flattening in crocodilians. In: J.
Thomason (ed.), Functional morphology in vertebrate paleontology, 173-193.
Cambridge University Press, Cambridge, Massachusetts.

Buscalioni, A.D., Frenegal, M.A., Bravo, A., Poyato-Ariza, F.J., Sanchíz, B., Báez, A.M.,
Cambra-Moo, O., Martín Closas, C., Evans, S.E., and Marugán Lobón, J. 2008.
The vertebrate assemblage of Buenache de la Sierra (Upper Barremian of Serrania
de Cuenca, Spain) with insights into its taphonomy and palaeoecology.
Cretaceous Research 29 (4): 687-710.

Cai, Z. and Zhao, L. 1999. A long tailed bird from the Late Cretaceous of Zhejiang.
Science in China (Series D) 42 (4): 434-441.

Cambra-Moo, O., Buscalioni, A.D., Cubo, J., Castanet, J., Loth, M.-M., de Margerie, E.,
and de Ricqlès, A. 2006. Histological observations of enantiornithine bone
(Saurischia, Aves) from the Lower Cretaceous of Las Hoyas (Spain). Comptes
Rendus Palevol 5 (3): 685-691.

Case, J.A., Martin, J.E., and Reguero, M. 2007. A dromaeosaur from the Maastrichtian of
James Ross Island and the Late Cretaceous Antarctic dinosaur fauna. In: A.
Cooper, C. Raymond, and I.E. Team (eds.), Antarctica: a Keystone in a Changing
World -- Online Proceedings for the Tenth International Symposium on Antarctic
Earth Sciences, 1-4. U.S. Geological Survey, Washington, D.C.

Cau, A. and Arduini, P. 2008. Enantiophoenix electrophyla gen. et sp. nov. (Aves,
Enantiornithes) from the Upper Cretaceous (Cenomanian) of Lebanon and its
phylogenetic relationships. Atti della Società Italiana di Scienze Naturali e del
Museo Civico di Storia Naturale di Milano 149 (2): 293-324.

Chang, C.-H., Yu, M.-K., Wu, P., Jiang, T.-X., Yu, H.-S., Widelitz, R.B., and Chuong,
C.-M. 2004. Sculpting Skin Appendages Out of Epidermal Layers Via
Temporally and Spatially Regulated Apoptotic Events. Journal of Investigative
Dermatology 122: 1348-1355.

Chatterjee, S. 1991. Cranial anatomy and relationships of a new Triassic bird from Texas.
Philosophical Transactions of the Royal Society of London B 332 (1265): 277-
346.

Chatterjee, S. and Templin, R.J. 2007. Biplane wing planform and flight performance of
the feathered dinosaur Microraptor gui. Proceedings of the National Academy of
Sciences 104 (5): 1576-1580.
436 

Chen, P. 1988. Distribution and migration of Jehol fauna with reference to nonmarine
Jurassic-Cretaceous boundary in China. Acta Palaeontologica Sinica 27: 659-683.

Chen, P.-J., Dong, Z., and Zhen, S. 1998. An exceptionally well-preserved theropod
dinosaur from the Yixian Formation of China. Nature 391: 147-152.

Chiappe, L.M. 1991. Cretaceous avian remains from Patagonia shed new light on the
early radiation of birds. Alcheringa 15: 333-338.

Chiappe, L.M. 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho
Formation of northwestern Argentina. American Museum Novitates 3083: 1-27.

Chiappe, L.M. 1995. The phylogenetic position of the Cretaceous birds of Argentina:
Enantiornithes and Patagopteryx deferrariisi. In: D.S. Peters (ed.), Acta
Palaeornithologica, 55-63.

Chiappe, L.M. 1996. Late Cretaceous birds of southern South America: anatomy and
systematics of Enantiornithes and Patagopteryx deferrariisi. Münchner
Geowissenschaften Abhandlungen 30: 203-244.

Chiappe, L.M. 2001. Rise of birds. In: D.E.G. Briggs, and P. Crowther (eds.),
Palaeobiology II, 102-106. Blackwell Science.

Chiappe, L.M. 2002. Basal bird phylogeny: problems and solutions. In: L.M. Chiappe,
and L.M. Witmer (eds.), Mesozoic Birds: Above the Heads of Dinosaurs, 448-
472. University of California Press, Berkeley.

Chiappe, L.M. 2004. The closest relatives of birds. Ornitologia Neotropical 15 suppl.: 1-
16.

Chiappe, L.M. 2007. Glorified Dinosaurs: the Origin and Early Evolution of Birds. 263
pp. John Wiley & Sons, Inc., Hoboken.

Chiappe, L.M. 2009. Downsized Dinosaurs: The Evolutionary Transition to Modern
Birds. Evolution: Education and Outreach 2: 248-256.

Chiappe, L.M. and Calvo, J.O. 1994. Neuquenornis volans, a new Late Cretaceous bird
(Enantiornithes: Avisauridae) from Patagonia, Argentina. Journal of Vertebrate
Paleontology 14 (2): 230-246.

437 
Chiappe, L.M. and Walker, C.A. 2002. Skeletal morphology and systematics of the
Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In: L.M. Chiappe,
and L.M. Witmer (eds.), Mesozoic Birds: Above the Heads of Dinosaurs, 240-
267. University of California Press, Berkeley.

Chiappe, L.M. and Dyke, G.J. 2002. The Mesozoic radiation of birds. Annual Review of
Ecology and Systematics 33: 91-124.

Chiappe, L.M. and Lacasa-Ruiz, A. 2002. Noguerornis gonzalezi (Aves:
Ornithothoraces) from the Early Cretaceous of Spain. In: L.M. Chiappe, and L.M.
Witmer (eds.), Mesozoic Birds: Above the Heads of Dinosaurs, 230-239.
University of California Press, Berkeley.

Chiappe, L.M. and Dyke, G.J. 2006. The early evolutionary history of birds. In: Y.-N.
Lee (ed.), Proceedings of the 2006 Goseong International Dinosaur Symposium,
133-151.

Chiappe, L.M. and Dyke, G.J. 2007. The beginnings of birds: recent discoveries, ongoing
arguments, and new directions. In: H.-D. Sues, and J.S. Anderson (eds.), Major
Transitions in Vertebrate Evolution, 303-336. Indiana University Press,
Bloomington.

Chiappe, L.M., Norell, M.A., and Clark, J.M. 1998. The skull of a relative of the stem-
group bird Mononykus. Nature 392: 275-278.

Chiappe, L.M., Ji, S., Ji, Q., and Norell, M.A. 1999. Anatomy and systematics of the
Confuciusornithidae (Theropoda: Aves) from the Late Mesozoic of northeastern
China. Bulletin of the American Museum of Natural History 242: 1-89.

Chiappe, L.M., Norell, M., and Clark, J. 2001. A new skull of Gobipteryx minuta (Aves:
Enantiornithes) from the Cretaceous of the Gobi Desert. American Museum
Novitates 3346: 1-15.

Chiappe, L.M., Lamb, J.P., Jr., and Ericson, P.G.P. 2002a. New enantiornithine bird from
the marine Upper Cretaceous of Alabama. Journal of Vertebrate Paleontology 22
(1): 170-174.

Chiappe, L.M., Norell, M.A., and Clark, J.M. 2002b. The Cretaceous, short-armed
Alvarezsauridae. In: L.M. Chiappe, and L.M. Witmer (eds.), Mesozoic Birds:
Above the Heads of Dinosaurs, 87-120. University of California Press, Berkeley.

Chiappe, L.M., Suzuki, S., Dyke, G.J., Watabe, M., Tsogtbaatar, K., and Barsbold, R.
2006. A new enantiornithine bird from the Late Cretaceous of the Gobi Desert.
Journal of Systematic Palaeontology.
438 

Chiappe, L.M., Ji, S., and Ji, Q. 2007. Juvenile birds from the Early Cretaceous of China:
implications for enantiornithine ontogeny. American Museum Novitates 3594: 1-
46.

Chiappe, L.M., Marugán-Lobón, J., Ji, S., and Zhou, Z. 2008. Life history of a basal bird:
morphometrics of the Early Cretaceous Confuciusornis. Biology Letters.

Chinsamy, A. and Elzanowski, A. 2001. Evolution of growth pattern in birds. Nature
412: 402-403.

Chinsamy, A., Chiappe, L.M., and Dodson, P. 1994. Growth rings in Mesozoic birds.
Nature 368: 196-197.

Chinsamy, A., Chiappe, L.M., and Dodson, P. 1995. Mesozoic avian bone
microstructure: physiological implications. Paleobiology 21 (4): 561-574.

Chinsamy-Turan, A. 2005. The Microstructure of Dinosaur Bone: Deciphering Biology
with Fine-scale Techniques. 216 pp. The Johns Hopkins University Press,
Baltimore.

Christiansen, P. and Bonde, N. 2004. Body plumage in Archaeopteryx: a review, and new
evidence from the Berlin specimen. Comptes Rendus Palevol 3 (2): 99-118.

Chuong, C.-M. and Widelitz, R.B. 1998. Feather morphogenesis: A model of the
formation of epithelial appendage. In: C.-M. Chuong (ed.), Molecular Basis of
Epithelial Appendage Morphogenesis, 57-74. Landes Bioscience, Austin.

Chuong, C.-M., Wu, P., Zhang, F.-C., Xu, X., Yu, M., Widelitz, R.B., Jiang, T.-X., and
Hou, L. 2003. Adaptation to the sky: defining the feather with integument fossils
from Mesozoic China and experimental evidence from molecular laboratories.
Journal of Experimental Zoology 298B (1): 42-56.

Clark, J.M., Norell, M.A., and Barsbold, R. 2001. Two new oviraptorids (Theropoda:
Oviraptorosauria), Upper Cretaceous Djadokhta Formation, Ukhaa Tolgod,
Mongolia. Journal of Vertebrate Paleontology 21 (2): 209-213.

Clark, J.M., Norell, M.A., and Rowe, T. 2002. Cranial anatomy of Citipati osmolskae
(Theropoda, Oviraptorosauria), and a reinterpretation of the holotype of Oviraptor
philoceratops. American Museum Novitates 3364: 1-24.

Clarke, J.A. 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis
and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural
History 286: 1-179.
439 

Clarke, J.A. and Norell, M.A. 2002. The morphology and phylogenetic position of
Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum
Novitates 3387: 1-46.

Clarke, J.A., Tambussi, C.P., Noriega, J.I., Erickson, G.M., and Ketcham, R.A. 2005.
Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature
433: 305-309.

Clarke, J.A., Zhou, Z., and Zhang, F. 2006. Insight into the evolution of avian flight from
a new clade of Early Cretaceous ornithurines from China and the morphology of
Yixianornis grabaui. Journal of Anatomy 208 (3): 287-308.

Close, R.A., Vickers-Rich, P., Chiappe, L.M., O’Connor, J.K., Rich, T.H., and Kool, L.
2009. Earliest Gondwanan bird from the Cretaceous of southeastern Australia.
Journal of Vertebrate Paleontology 29 (2): 616-619.

Cobbett, A., Wilkinson, M., and Wills, M.A. 2007. Fossils impact as hard as living taxa
in parsimony analyses of morphology. Systematic Biology 56 (5): 753-766.

Corfe, I.J. and Butler, R.J. 2006. Comment on 'A well-preserved Archaeopteryx specimen
with theropod features'. Science 313: 1238b.

Cracraft, J. 1986. The origin and early diversification of birds. Paleobiology 12 (4): 383-
399.

Cracraft, J. 1988. The major clades of birds. In: M.J. Benton (ed.), The Phylogeny and
Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds, 339-361.
Clarendon Press, Oxford.

Cracraft, J. and Eldredge, N. 1979. Phylogenetic analysis and paleontology. pp.
Columbia University Press, New York.

Currie, P.J. and Dong, Z. 2001. New information on Shanshanosaurus huoyanshanensis,
a juvenile tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of
China. Canadian Journal of Earth Sciences 38 (12): 1729-1737.

Currie, P.J., Trexler, D., Koppelhus, E.B., Wicks, K., and Murphy, N. 2005. An unusual
multi-individual tyrannosaurid bonebed in the Two Medicine Formation (Late
Cretaceous, Campanian) of Montana (USA). In: K. Carpenter (ed.), Carnivorous
Dinosaurs, 313-324. Indiana University Press, Bloomington.

Dalla Vecchia, F.M. and Chiappe, L.M. 2002. First avian skeleton from the Mesozoic of
northern Gondwana. Journal of Vertebrate Paleontology 22 (4): 856-860.
440 

Dalsätt, J., Zhou, Z., Zhang, F., and Ericson, P.G.P. 2006. Food remains in
Confuciusornis sanctus suggest a fish diet. Naturwissenschaften 93 (9): 444-446.

Davies, S. 2002. Ratites and Tinamous. 310 pp. Oxford University Press, Oxford.

Davis, P.G. and Briggs, D.E.G. 1998. The impact of decay and disarticulation on the
preservation of fossil birds. Palaios 13: 3-13.

de Ricqlès, A.J. 1976. On bone histology of fossil and living reptiles, with comments on
its functional and evolutionary significance. In: A.d.A. Bellairs, and C.B. Cox
(eds.), Morphology and Biology of Reptiles, 123-150. Linnean Society of London,
London.

de Ricqlès, A.J. 1980. Tissue structure of dinosaur bone: Functional significance and
possible relation to dinosaur physiology. In: R.D.K. Thomas, and E.C. Olson
(eds.), A Cold-blooded Look at the Warm-blooded Dinosaurs, 103-139. Westview
Press, Boulder.

de Ricqles, A.J. 1991. Les fossiles sont en forme: quelques aspects du problème des
relations entre formes et fonctions en Paléontologie. Geobios 13: 127-134.

de Ricqlès, A.J. 2008. Fifty years after Enlow and Brown's Comparative histological
study of fossil and recent bone tissues (1956–1958): A review of Professor
Donald H. Enlow's contribution to palaeohistology and comparative histology of
bone. Comptes Rendus Palevol 6 (8): 591-601.

de Ricqlès, A.J., Padian, K., Horner, J.R., Lamm, E.-T., and Myhrvold, N. 2003.
Osteohistology of Confuciusornis sanctus (Theropoda: Aves). Journal of
Vertebrate Paleontology 23 (2): 373-386.

Dietz, R.S. and Holden, J.C. 1970. Reconstruction of Pangaea: breakup and dispersion of
continents, Permian to present. Journal of Geophysical Research 75 (26): 4939-
4956.

Dingus, L., Clarke, J., Scott, G.R., Swisher, C.C.I., Chiappe, L.M., and Coria, R.A. 2000.
Stratigraphy and magnetostratigraphic/faunal constraints for the age of sauropod
embryo-bearing rocks in the Neuquén Group (Late Cretaceous, Neuquén
Province, Argentina). American Museum Novitates 3290: 1-11.

Dodson, P. 1990. Counting dinosaurs: how many kinds were there? Proceedings of the
National Academy of Sciences 87: 7608-7612.

Dodson, P. 2000. Origin of birds: the final solution? American Zoologist 40: 504-512.
441 

Dong, Z. 1993. A Lower Cretaceous enantiornithine bird from the Ordos Basin of Inner
Mongolia, People's Republic of China. Canadian Journal of Earth Sciences 30:
2177-2129.

Dupuis, C. 1984. Willi Hennig's impact on taxonomic thought. Annual Review of
Ecological Systems 15: 1-24.

Dyke, G.D. and Kaiser, G. 2008. Unrestricted egg size and the evolution of the obligatory
parental care in birds. Proceedings of the Society of Avian Paleontology and
Evolution.

Dyke, G.D. and Nudds, R.L. 2009. The fossil record and limb disparity of
enantiornithines, the dominant flying birds of the Cretaceous. Lethaia 42 (2): 248-
254.

Dyke, G.J., Malakhov, D.V., and Chiappe, L.M. 2006. A re-analysis of the marine bird
Asiahesperornis from northern Kazakhstan. Cretaceous Research 27 (6): 947-953.

Elzanowski, A. 1974. Preliminary note on the palaeognathous bird from the Upper
Cretaceous of Mongolia. Palaeontologica Polonica 30: 103-109.

Elzanowski, A. 1976. Paleognathous bird from the Cretaceous of central Asia. Nature
264: 51-53.

Elzanowski, A. 1977. Skulls of Gobipteryx (Aves) from the Upper Cretaceous of
Mongolia. Palaeontologica Polonica 37: 153-165.

Elzanowski, A. 1981. Embryonic bird skeletons from the Late Cretaceous of Mongolia.
Palaeontologica Polonica 42: 147-179.

Elzanowski, A. 2001. A novel reconstruction of the skull of Archaeopteryx. Netherlands
Journal of Zoology 51 (2): 207-215.

Elzanowski, A. 2002. Archaeopterygidae (Upper Jurassic of Germany). In: L.M.
Chiappe, and L.M. Witmer (eds.), Mesozoic Birds: Above the Heads of
Dinosaurs, 129-159. University of California Press, Berkeley.

Elzanowski, A. and Brett-Surman, M.K. 1995. Avian premaxilla and tarsometatarsus
from the uppermost Cretaceous of Montana. Auk 112 (3): 762-767.

Erickson, G.M. 2005. Assessing dinosaur growth patterns: a microscopic revolution.
Trends in Ecology and Evolution 20 (12): 677-684.

442 
Erickson, G.M., Curry, K.C., and Yerby, S.A. 2001. Dinosaurian growth patterns and
rapid avian growth rates. Nature 412: 429-433.

Erickson, G.M., Makovicky, P.J., Currie, P.J., Norell, M.A., Yerby, S.A., and Brochu,
C.A. 2004. Gigantism and comparative life-history parameters of tyrannosaurid
dinosaurs. Nature 43-: 772-775.

Erickson, G.M., Currie, P.J., Inouye, B.D., and Winn, A.A. 2006. Tyrannosaur life tables:
an example of nonavian dinosaur population biology. Science 313: 213-217.

Erickson, G.M., Rogers, K.C., Varricchio, D.J., Norell, M.A., and Xu, X. 2007. Growth
patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian
dinosaurs and genesis of the avian condition. Biology Letters.

Estrella, S.M. and Masero, J.A. 2007. The use of distal rhynchokinesis by birds feeding
in water. Journal of Experimental Biology 210 (21): 3757-3762.

Farris, J.S. 1977. Phylogenetic analysis under Dollo's Law. Systematic Zoology 26 (1):
77-88.

Farris, J.S. 2008. Parsimony and explanatory power. Cladistics 24: 825-847.

Feduccia, A. 1996. The Origin and Evolution of Birds. 420 pp. Yale University Press,
New Haven.

Feduccia, A. 2001. Digit homology of birds and dinosaurs: accomdating the cladogram.
Trends in Ecology and Evolution 16 (6): 285-6.

Feduccia, A. 2003. 'Big bang' for Tertiary birds? Trends in Ecology and Evolution 18 (4):
172-176.

Feduccia, A. and Nowicki, J. 2002. The hand of birds revealed by early ostrich embryos.
Naturwissenschaften 89 (9): 391-393.Foote, M. and Sepkoski, J.J., Jr. 1999.
Absolute measures of the completeness of the fossil record. Nature 398: 415-417.

Feduccia, A., Lingham-Soliar, T., and Hinchliffe, J.R. 2005. Do feathered dinosaurs
exist? Testing the hypothesis on neontological and paleontological evidence.
Journal of Morphology 266 (2): 125-166.

Forster, C.A., Chiappe, L.M., Krause, D.W., and Sampson, S.D. 1996. The first
Cretaceous bird from Madagascar. Nature 382: 532-534.

443 
Forster, C.A., Sampson, S.D., Chiappe, L.M., and Krause, D.W. 1998. The theropod
ancestry of birds: new evidence from the Late Cretaceous of Madagascar. Science
279: 1915-1919.

Fountaine, T.M.R., Benton, M.J., Dyke, G.J., and Nudds, R.L. 2005. The quality of the
fossil record of Mesozoic birds. Proceedings of the Royal Society of London B
272 (1560): 289-294.

Francillon-Viellot, H., De Buffrénil, V., Castanet, J., Géraudie, J., Meunier, F.J., Sire,
J.Y., Zylberberg, L., and De Ricqlès, A.J. 1990. Microstructure and
mineralization of vertebrate skeletal tissues. In: J.G. Carter (ed.), Skeletal
Biomineralization: Patterns, Processes and Evolutionary Trends, Volume I, 471-
530. Van Nostrand Reinhold, New York.

Galis, F., Kundrát, M., and Sinervo, B. 2003. An old controversy solved: bird embryos
have five fingers. Trends in Ecology and Evolution 18 (1): 7-9.

Galton, P.M. and Martin, L.D. 2002. Postcranial anatomy and systematics of Enaliornis
SEELEY, 1876, a foot-propelled diving bird (Aves: Ornithurae:
Hesperornithiformes) from the Early Cretaceous of England. Revue de
Paléobiologie, Genève 21 (2): 489-538. Gao, C-L. and Liu, J-Y. 2005. A new
avian taxon from Lower Cretaceous Jiufotang Formation of western Liaoning.
Global Geology 24 (4): 313-318.

Gao, C., Chiappe, L.M., Meng, Q., O'Connor, J., Wang, X., Cheng, X., and Liu, J. 2008.
A new basal lineage of Early Cretaceous birds from China and its implications on
the evolution of the avian tail. Palaeontology 51 (4): 775-791.

Gatesy, S.M. and Dial, K.P. 1996. From frond to fan: Archaeopteryx and the evolution of
short-tailed birds. Evolution 50 (5): 2037-2048.

Gauthier, J. 1986. Saurischian monophyly and the origin of birds. In: K. Padian (ed.), The
Origin of Birds and the Evolution of Flight, 1-55. California Academy of
Sciences, San Francisco.

Geist, N.R. and Jones, T.D. 1996. Dinosaurs and their youth. Science 273 (5272): 167-
168.

Gill, F.B. 1994. Ornithology, 2nd Edition. 766 pp. W.H. Freeman and Company, New
York.

Göhlich, U.B. and Chiappe, L.M. 2006. A new carnivorous dinosaur from the Late
Jurassic Solnhofen archipelago. Nature 440: 329-332.

444 
Göhlich, U.B., Chiappe, L.M., Clark, J.M., and Sues, H.-D. 2005. The systematic
position of the Late Jurassic alleged dinosaur Macelognathus (Crocodylomorpha:
Sphenosuchia). Canadian Journal of Earth Sciences 42 (3): 307-321.

Goloboff, P.A. 2003. Parsimony, likelihood, and simplicity. Cladistics 19: 91-103.

Goloboff, P.A., Farris, J.S., and Nixon, K.C. 2008. TNT, a free program for phylogenetic
analysis. Cladistics 24 (5): 774-786.

Goloboff, P.A., Catalano, S.A., Mirande, J.M., Szumik, C.A., Salvador Arias, J.,
Kallersjo, M., and Farris, J.S. 2009. Phylogenetic analysis of 73 060 taxa
corroborates major eukaryotic groups. Cladistics 25: 211-230.

Gong, E., Hou, L., and Wang, L. 2004. Enantiornithine bird with diapsidian skull and its
dental development in the Early Cretaceous in Liaoning, China. Acta Geologica
Sinica 78 (1): 1-7.

Gregory, J.T. 1952. The jaws of the Cretaceous toothed birds, Ichthyornis and
Hesperornis. Condor 54 (2): 73-88.

Grellet-Tinner, G. 2005. A phylogenetic analysis of oological characters: a case study of
saurischian dinosaur relationships and avian evolution. 221 pp., University of
Southern California, Los Angeles.

Grellet-Tinner, G. and Norell, M. 2002. An avian egg from the Campanian of Bayn Dzak,
Mongolia. Journal of Vertebrate Paleontology 22 (3): 719-721.

Grellet-Tinner, G., Chiappe, L.M., Norell, M., and Bottjer, D. 2006. Dinosaur eggs and
nesting behaviors: a paleobiological investigation. Palaeogeography,
Palaeoclimatology, Palaeoecology 232 (2-4): 294-321.

Hackett, S.J., Kimball, R.T., Reddy, S., Bowie, R.C.K., Braun, E.L., Braun, M.J.,
Chojnowski, J.L., Cox, W.A., Han, K.-L., Harshman, J., Huddleston, C.J., Marks,
B.D., Miglia, K.J., Moore, W.S., Sheldon, F.H., Steadman, D.W., Witt, C.C., and
Yuri, T. 2008. A phylogenomic study of birds reveals their evolutionary history.
Science 320: 1763-1768.

Harris, M.P., Fallon, J.F., and Prum, R.O. 2002. Shh-Bmp2 signaling module and the
evolutionary origin and diversification of feathers. Journal of Experimental
Zoology 294: 160-176.

445 
Harris, J.D., Lamanna, M.C., You, H.-L., Ji, S.-A., and Ji, Q. 2006. A second
enantiornithean (Aves: Ornithothoraces) wing from the Early Cretaceous Xiagou
Formation near Changma, Gansu Province, People's Republic of China. Canadian
Journal of Earth Sciences 43 (5): 547-554.

Hauser, D.L. and Presch, W. 1991. The effect of ordered characters on phylogenetic
reconstruction. Cladistics 7: 243-265.

Hayward, J.L., Zelenitsky, D.A., Smith, D.L., Zaft, D.M., and Clayburn, J.K. 2000.
Eggshell taphonomy at modern gull colonies and a dinosaur clutch site. Palaios
15: 343-355.

He, H.-Y., Wang, X.-L., Jin, F., Zhou, Z.-H., Wang, F., Yang, L.-K., Ding, X., Boven,
A., and Zhu, R.-X. 2006. The 40Ar/39Ar dating of the early Jehol Biota from
Fengning, Hebei Province, northern China. Geochemistry, Geophysics,
Geosystems 7 (4): 1-8.

He, Z., ed. 2007. The Fossils of China. Chinese University of Geosciences Press, Beijing.

Heilmann, G. 1926. The Origin of Birds. 210 pp. D. Appleton and Company, London.

Hennig, W. 1966. Phylogenetic Systematics. 263 pp. University of Illinois, Urbana.

Hicks, J.A. 2002. Magnetostratigraphy and geochronology of the Hell Creek and basal
Fort Union Formations of southwestern North Dakota and a recalibration of the
age of the Cretaceous-Tertiary boundary. In: J.H. Hartman, K.R. Johnson, and
D.J. Nichols (eds.), The Hell Creek Formation and the Cretaceous-Tertiary
boundary in the northern Great Plains. Geological Society of America.

Hills, D.M. 1998. Taxonomic sampling, phylogenetic accuracy, and investigator bias.
Systematic Biology 47: 3-8.

Hinchliffe, J.R. 1985. 'One, two, three' or 'two, three, four': an embryologist's view of the
homologies of the digits and carpus of modern birds. In: M.K. Hecht, J.H.
Ostrom, G. Viohl, and P. Wellnhofer (eds.), The Beginnings of Birds, 141-147.
Freunds des Jura-Museums Eichstatt, Willibaldsburg.

Holtz, T.R., Jr. 1994. The phylogenetic position of the Tyrannosauridae: implications for
theropod systematics. Journal of Paleontology 68 (5): 1100-1117.

Holtz, T.R., Jr. 1998. A new phylogeny of the carnivorous dinosaurs. In: B.P. Pérez-
Moreno, T. Holtz, J.L. Sanz, and J.J. Moratalla (eds.), Aspects of Theropod
Paleobiology, 5-61. Museu Nacional de História Natural, Lisbon.

446 
Holtz, T.R., Jr. 2001. Arctometatarsalia, revisited: the problem of homoplasy in
reconstructing theropod phylogenetics. In: J. Gauthier, and L.F. Gall (eds.), New
Perspectives on the Origin and Early Evolution of Birds, 99-122. Peabody
Museum of Natural History, New Haven.

Holtz, T.R., Jr., Molnar, R.E., and Currie, P.J. 2004. Basal Tetanurae. In: D.B.
Weishampel, P. Dodson, and H. Osmólska (eds.), The Dinosauria, Second
Edition, 71-110. University of California Press, Berkeley.

Hope, S. 2002. The Mesozoic radiation of Neornithes. In: L.M. Chiappe, and L.M.
Witmer (eds.), Mesozoic Birds: Above the Heads of Dinosaurs, 339-388.
University of California Press, Berkeley.

Hopson, J.A. 2001. Ecomorphology of avian and nonavian theropod phalangeal
proportions: implications for the arboreal versus terrestrial origin of bird flight. In:
J. Gauthier, and L.F. Gall (eds.), New Perspectives on the Origin and Early
Evolution of Birds, 211-235. Peabody Museum of Natural History, New Haven.

Hou, L. 1994. A late Mesozoic bird from Inner Mongolia. Vertebrata PalAsiatica 32 (4):
258-266.

Hou, L. 1997a. Mesozoic Birds of China. 221 pp. Feng-huang-ku Bird Park, Taiwan.

Hou, L. 1997b. A carinate bird from the Upper Jurassic of western Liaoning, China.
Chinese Science Bulletin 42 (5): 413-416.

Hou, L. 2000. Picture Book of Chinese Fossil Birds. 89 pp. Yunnan Science and
Technology Press, Kunming.

Hou, L. 2002. Fossil Birds of China. 234 pp. Yunnan Science and Technology Press,
Kunming.

Hou, L. and Liu, Z. 1984. A new fossil bird from Lower Cretaceous of Gansu and early
evolution of birds. Scientia Sinica, Series B 27 (12): 1296-1301.

Hou, L. and Zhang, J. 1993. A new fossil bird from Lower Cretaceous of Liaoning.
Vertebrata PalAsiatica 31 (3): 217-224.

Hou, L. and Chen, P. 1999. Liaoxiornis delicatus gen. et sp. nov., the smallest Mesozoic
bird. Chinese Science Bulletin 44 (9): 834-838.

Hou, L., Zhonghe, Z., Martin, L.D., and Feduccia, A. 1995. A beaked bird from the
Jurassic of China. Nature 377: 616-618.

447 
Hou, L., Martin, L.D., Zhou, Z., and Feduccia, A. 1996. Early adaptive radiation of birds:
evidence from fossils from northeastern China. Science 274: 1164-1167.

Hou, L., Martin, L.D., Zhou, Z., and Feduccia, A. 1999. Archaeopteryx to opposite birds
-- missing link from the Mesozoic of China. Vertebrata PalAsiatica 37 (2): 88-95.

Hou, L., Zhou, Z., Zhang, F., and Gu, Y. 2002. Mesozoic Birds from Western Liaoning in
China. 120 pp. Liaoning Science and Technology Publishing House.

Hou, L., Chiappe, L.M., Zhang, F., and Chuong, C.-M. 2004. New Early Cretaceous
fossil from China documents a novel trophic specialization for Mesozoic birds.
Naturwissenschaften 91: 22-25.

Houck, M.A., Gauthier, J.A., and Strauss, R.E. 1990. Allometric scaling in the earliest
fossil bird, Archaeopteryx lithographica. Science 247: 195-198.

Howard, H. 1929. The avifauna of Emeryville shellmound. University of California
Publications in Zoology 32 (2): 301-394.

Huang, S.H., Norell, M.A., Ji, Q., and Gao, K. 2002. New specimens of Microraptor
zhaoianus (Theropoda: Dromaeosauridae) from northeastern China. American
Museum Novitates 3381: 1-44.

Hutchison, J. 1993. Avisaurus: a 'dinosaur' grows wings. Journal of Vertebrate
Paleontology 13 (suppl. 3): 43A.

Huxley, T.H. 1868. Remarks upon Archaeopteryx lithographica. Proceedings of the
Royal Society of London 16: 243-248.

James, F.C. and Pourtless IV, J.A. 2009. Cladistics and the Origin of Birds: A Review
and Two New Analyses Ornithological Monographs: 1-84.

Jenner, R.A. 2004. The scientific status of metazoan cla-distics: why current research
practice must change. Zoologica Scripta 33: 293–310.

Ji, Q. 2004. Mesozoic Jehol Biota of Western Liaoning, China. 375 pp. Geological
Publishing House, Beijing.

Ji, Q. and Ji, S. 1999. A new genus of the Mesozoic birds from Lingyuan, Liaoning,
China. Chinese Geology 262 (3): 45-48.

Ji, Q., Currie, P.J., Norell, M.A., and Ji, S.-A. 1998. Two feathered dinosaurs from
northeastern China. Nature 393 (6687): 753-761.

448 
Ji, Q., Chiappe, L.M., and Ji, S. 1999. A new late Mesozoic confuciusornithid bird from
China. Journal of Vertebrate Paleontology 19 (1): 1-7.

Ji, Q., Norell, M.A., Gao, K.-Q., Ji, S.-A., and Ren, D. 2001. The distribution of
integumentary structures in a feathered dinosaur. Nature 410: 1084-1088.

Ji, Q., Ji, S., You, H., Zhang, J., Yuan, C., Ji, X., Li, J., and Li, Y. 2002a. Discovery of an
avialae bird - Shenzhouraptor sinensis gen. et sp. nov. - from China. Geological
Bulletin of China 21 (7): 363-369.

Ji, Q., Ji, S., Zhang, H., You, H., Zhang, J., Wang, L., Yuan, C., and Ji, X. 2002b. A new
avialian bird - Jixiangornis orientalis gen. et sp. nov. - from the Lower
Cretaceous of western Liaoning, NE China. Journal of Nanjing University
(Natural Sciences) 38 (6): 723-735.

Ji, Q., Ji, S., Lü, J., You, H., Chen, W., Liu, Y., and Liu, Y. 2005. First avialian bird from
China (Jinfengopteryx elegans gen. et sp. nov.). Geological Bulletin of China 24
(3): 197-205.

Kearney, M. and Clark, J.M. 2003. Problems due to missing data in phylogenetic
analyses including fossils: a critical review. 23 2 (263-274).

Kitching, I., Forey, P., Humphries, C., and Williams, D. 1992. Cladistics: Theory and
practice of parsimony analysis. 248 pp. Oxford University Press.

Kurochkin, E.N. 1995. The assemblage of the Cretaceous birds in Asia. In: S. Ailing, and
W. Yuanqing (eds.), Sixth Symposium on Mesozoic Terrestrial Ecosystems and
Biota, Short Papers, 203-208. China Ocean Press, Beijing.

Kurochkin, E.N. 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a
general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of
Sciences, Palaeontological Institute, Special Issue: 1-50.

Kurochkin, E.N. 1999. A new large enantiornithid from the Upper Cretaceous of
Mongolia (Aves, Enantiornithes). Russian Academy of Sciences, Proceedings of
the Zoological Institute 277: 130-141.

Kurochkin, E.N. 2003. Mesozoic birds of Mongolia and the former USSR. In: M.J.
Benton, M.A. Shishkin, D.M. Unwin, and E.N. Kurochkin (eds.), The Age of
Dinosaurs in Russia and Mongolia, 533-559. Cambridge University Press,
Cambridge.

Kurochkin, E. 2004. The truth about Gobipteryx. 4th Meeting of the Society of Avian
Paleontology and Evolution. Université de Bourgogne, Quillan, France.
449 

Kurochkin, E.N. 2006. Parallel evolution of theropod dinosaurs and birds. Entomological
Review 86 (suppl. 1): 283-297.

Kurochkin, E.N. and Molnar, R.E. 1997. New material of enantiornithine birds from the
Early Cretaceous of Australia. Alcheringa 21: 291-297.

Lacasa-Ruiz, A. 1989. Nuevo genero de ave fosil del Yacimiento Neocomiense del
Montsec (Provincia de Lerida, España). Estudios Geologia 45: 417-425.

Lamanna, M.C., You, H.-L., Ji, S.-A., Lü, J., Ji, Q., and Chiappe, L.M. 2005. A new
enantiornithine partial skeleton from the Early Cretaceous of northwestern China.
Journal of Vertebrate Paleontology 25 (suppl. 3): 81A-82A.

Lamanna, M.C., You, H.-L., Harris, J.D., Chiappe, L.M., Ji, S.-A., Lü, J.-C., and Ji, Q.
2006. An enantiornithine (Aves: Ornithothoraces) partial skeleton from the Early
Cretaceous of northwestern China. Acta Palaeontologica Polonica 51 (3): 423-
434.

Larsson, H.C.E. and Wagner, G.P. 2002. Pentadactyl ground state of the avian wing.
Journal of Experimental Zoology 294: 146-151.

Legendre, P. and Legendre, L. 1998. Numerical ecology. 853 pp. Elsevier, Amsterdam.

Leidy, J. 1856. Notices of remains of extinct Reptilia and fishes, discovered by Dr. F.V.
Hayden in the bad lands of the Judith River, Nebraska Territory. Proceedings of
the Academy of Natural Sciences of Philadelphia 8: 72-73.

Li, J.-J., Z-H. Li, Y-G. Zhang, Z-H. Zhou, Z-Q. Bai, L-F. Zhang, T-Y. Ba. 2008. A new
species of Cathayornis from the Lower Cretaceous of Inner Mongolia, China and
its stratigraphic significance. Acta Geologica Sinica 82 (6): 1115-1123.

Li, L., Duan, Y., Hu, D., Wang, L., Cheng, S., and Hou, L. 2006. New eoentantiornithid
bird from the Early Cretaceous Jiufotang Formation of western Liaoning, China.
Acta Geologica Sinica (English edition) 80 (1): 38-41.

Li, L., Hu, D.-Y., Duan, Y., Gong, E.-P., and Hou, L.-H. 2007. Alethoalaornithidae fam.
nov.: a new family of enantiornithine bird from the Lower Cretaceous of western
Liaoning. Acta Palaeontologica Sinica 46 (3): 365-372.

Lin, C.-M., Jiang, T.-X., Widelitz, R.B., and Chuong, C.-M. 2006. Molecular signaling in
feather morphogenesis. Current Opinion in Cell Biology 18: 730-741.

450 
Linnaeus, C. 1758. Systema naturae per regna tria naturae, secundum classes, ordines,
genera, species, cum characteribus, differentiis, synonymis, locis. Vol. 1: Regnum
animale. Editio decima, reformata. 824 pp. Laurentii Salvii, Stockholm.

Lipscomb, D.L. 1992. Parsimony, homology and the analysis of multistate characters.
Cladistics 8: 45-65.

Lo, C.-H., Chen, P.-J., Tsou, T.-Y., Sun, S.-S., and Lee, C.-Y. 1999. Age of
Sinosauropteryx and Confuciusornis -
40
Ar/
39
Ar laser single-grain and K-Ar dting
of the Yixian Formation, NE China. Geochimica 28 (4): 405-410.

Longrich, N. 2006. Structure and function of hindlimb feathers in Archaeopteryx
lithographica. Paleobiology 32 (3): 417-431.

Lü, J. and Hou, L. 2005. A possible long-tailed bird with a pygostyle from the Late
Mesozoic Yixian Formation, western Liaoning, China. Acta Geologica Sinica
(English edition) 79 (1): 7-10.

Makovicky, P.J. and Sues, H.-D. 1998. Anatomy and phylogenetic relationships of the
theropod dinosaur Microvenator celer from the Lower Cretaceous of Montana.
American Museum Novitates 3240: 1-27.

Makovicky, P.J. and Norell, M.A. 2004. Troodontidae. In: D.B. Weishampel, P. Dodson,
and H. Osmólska (eds.), The Dinosauria, Second Edition, 184-195. University of
California Press, Berkeley.

Makovicky, P.J., Apesteguía, S., and Agnolin, F. 2005. The earliest dromaeosaurid
theropod from South America. Nature 437: 1007-1011.

Marinelli, W. 1928. U¨ber den Scha¨del der Schnepfe. Paleobiologica 1: 135-160.

Marsh, O.C. 1872a. Notice of a new and remarkable fossil bird. American Journal of
Science (Third Series) 6: 344.

Marsh, O.C. 1872b. Preliminary description of Hesperornis regalis, with notice of four
other species of Cretaceous birds. American Journal of Science (Third Series) 3:
360-365.

Marsh, O.C. 1880. Odontornithes: a monograph on the extinct toothed birds of North
America. Professional Papers of the Engineer Department, U.S. Army 18 (7): 1-
201.

Marsh, O.C. 1892. Notice of new reptiles from the Laramie Formation. American Journal
of Science 43: 449-453.
451 

Martin, L.D. 1983. The origin of birds and of avian flight. In: R.F. Johnston (ed.),
Current Ornithology, 105-129. Plenum Press, New York.

Martin, L.D. 1987. The beginning of the modern avian radiation. In: C. Mourer-Chauviré
(ed.), L'Evolution des Oiseaux d'Apres le Temoignage des Fossiles, 9-19.
Département des Sciences de la Terre, Université Claude-Bernard, Lyon.

Martin, L.D. 1995. The Enantiornithes: terrestrial birds of the Cretaceous. In: D.S. Peters
(ed.), Acta Palaeornithologica, 23-36.

Martin, L.D. 2004. A basal archosaurian origin for birds. Acta Zoologica Sinica 50 (6):
978-990.

Martin, L.D. 2008. Origins of avian flight -- a new perspective. Oryctos 7: 45-54.

Martin, L.D. and Zhou, Z. 1997. Archaeopteryx-like skull in enantiornithine bird. Nature
389: 556.

Martin, L.D. and Stewart, J.D. 1999. Implantation and replacement of bird teeth. In: S.L.
Olson, P. Wellnhofer, C. Mourer-Chauviré, D.W. Steadman, and L.D. Martin
(eds.), Avian Paleontology at the Close of the 20th Century: Proceedings of the
4th International Meeting of the Society of Avian Paleontology and Evolution,
Washington, D.C., 4-7 June 1996, 295-300.

Martin, J.E. and Cordes-Person, A. 2007. A new species of the diving bird Baptornis
(Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper
Cretaceous) of southwestern South Dakota. In: J.E. Martin, and D.C. Parris (eds.),
The Geology and Paleontology of the Late Cretaceous Marine Deposits of the
Dakotas, 227-237.

Martinez, R.N. and Alcober, O.A. 2009. A Basal Sauropodomorph (Dinosauria:
Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the Early
Evolution of Sauropodomorpha. PLoS ONE 4 (2): e4397.

Marugán-Lobón, J. and Buscalioni, A.D. 2003. Disparity and geometry of the skull in
Archosauria (Reptilia: Diapsida). Biological Journal of the Linnean Society 80:
67-88.

Marugán-Lobón, J. and Buscalioni, A.D. 2006. Avian skull morphological evolution:
exploring exo- and endocranial covariation with two-block partial least squares.
Zoology 109: 217-230.

452 
Maryanska, T., Osmólska, H., and Wolsan, M. 2002. Avialan status for Oviraptorosauria.
Acta Palaeontologica Polonica 47 (1): 97-116.

Matsuoka, H., Kusuhashi, N., Takada, T., and Setoguchi, T. 2002. A clue to the
Neocomian vertebrate fauna: initial results from the Kuwajima 'Kaseki-kabe'
(Tetori Group) in Shiramine, Ishikawa, central Japan. Memoirs of the Faculty of
Science, Kyoto University, Series of Geology and Mineralogy 59 (1): 33-45.

Mayr, E. 1982. The growth of biological thought: diversity, evolution and inheritance.
221 pp. Havard University Press, Cambridge, MA.

Mayr, G., Peters, D.S., Plowdowski, G., and Vogel, O. 2002. Bristle-like integumentary
structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften
89 (8): 361-365.

Mayr, G., Pohl, B., and Peters, D.S. 2005. A well-preserved Archaeopteryx specimen
with theropod features. Science 310: 1483-1486.

Mayr, G., Pohl, B., Hartman, S., and Peters, D.S. 2007. The tenth skeletal specimen of
Archaeopteryx. Zoological Journal of the Linnean Society 149 (1): 97-116.

McKitrick, M.C. 1992. Phylogenetic analysis of avian parental care. the Auk 109 (4):
828-846

McKitrick, M.C. 1994. On Homology and the Ontological Relationship of Parts
Systematic Biology 43 (1): 1-10.

Metcalf, S.J., Vaughan, R.F., Benton, M.J., Cole, J., Simms, M.J., and Dartnall, D.L.
1992. A new Bathonian (Middle Jurassic) mircovertebrate site, within the
Chipping Norton Limestone Formation at Hornsleasow Quarry, Gloucestershire.
Proceedings of the Geologists’ Association 103: 321-342.

Mikhailov, K.E. 1991. Classification of fossil eggshells of amniotic vertebrates. Acta
Palaeontologica Polonica 36 (2): 193-238.

Mikhailov, K.E. 1996. Bird eggs in the Upper Cretaceous of Mongolia. Paleontological
Journal 30 (1): 114-116.

Mikhailov, K.E. 1997. Fossil and recent eggshell in amniotic vertebrates: fine structure,
comparative morphology and classification. 1-80 pp. Palaeontological
Association, London.

453 
Mikhailov, K., Sabath, K., and Kurzanov, S. 1994. Eggs and nests from the Cretaceous of
Mongolia. In: K. Carpenter, K.F. Hirsch, and J.R. Horner (eds.), Dinosaur Eggs
and Babies, 88-115. Cambridge University Press, Cambridge.

Molnar, R.E. 1986. An enantiornithine bird from the Lower Cretaceous of Queensland,
Australia. Nature 322: 736-738.

Molnar, R.E. 1999. Avian tibiotarsi from the Early Cretaceous of Lightning Ridge, New
South Wales. In: Y. Tomida, T.H. Rich, and P. Vickers-Rich (eds.), Proceedings
of the Second Gondwana Dinosaur Symposium, 197-209. National Science
Museum of Tokyo, Tokyo.

Morrison, D.A. 2007. Increasing the Efficiency of Searches for the Maximum Likelihood
Tree in a Phylogenetic Analysis of up to 150 Nucleotide Sequences. Systematic
Biology 56 (6): 988-1010.

Morschhauser, E., Liu, J., Meng, Q., and Varricchio, D.J. 2006. Anatomical details from
a well preserved specimen of Longirostravis (Aves, Enantiornithes) from the
Jiufotang Formation, Liaoning Province, China. Journal of Vertebrate
Paleontology 26 (suppl. 3): 103A.

Morschhauser, E., Varricchio, D.J., Gao, C.-H., Liu, J.-Y., Wang, X.-R., Cheng, X.-D.,
and Meng, Q.-J. 2009. Anatomy of the Early Cretaceous bird Rapaxavis pani, a
new species from Liaoning Province, China. Journal of Vertebrate Paleontology
29 (2): 545-554.

Naish, D., Martill, D.M., and Merrick, I. 2007. Birds of the Crato Formation. In: D.M.
Martill, G. Bechly, and R.F. Loveridge (eds.), The Crato fossil beds of Brazil:
window into an ancient world, 525-533. Cambridge University Press.

Nessov, L.A. 1984. Upper Cretaceous pterosaurs and birds from central Asia.
Paleontological Journal 18 (1): 38-49.

Nessov, L.A. 1986. The first finding of Late Cretaceous bird Ichthyornis in Old World
and some other bird bones from Cretaceous and Paleogene of Soviet Middle Asia.
Proceedings of the Zoological Institute of Leningrad 147: 31-38.

Nessov, L.A. 1992. Mesozoic and Paleogene birds of the USSR and their
paleoenvironments. In: K.E. Campbell, Jr. (ed.), Papers in Avian Paleontology
Honoring Pierce Brodkorb, 465-478.

Nessov, L.A. and Jarkov, A.A. 1989. New Cretaceous-Paleogene birds of the USSR and
some remarks on the origin and evolution of the Class Aves. Trudy
Zoologicheskogo Instituta Akademii Nauk SSSR 197: 79-97.
454 

Nessov, L.A. and Panteleyev, A.B. 1993. About similarities of the Late Cretaceous
ornithofaunas of South America and western Asia. In: R.L. Potapov (ed.), Russian
Academy of Sciences, Proceedings of the Zoological Institute, 84-94. Moscow.

Nixon, K.C. 1999. The parsimony ratchet, a new method for rapid parsimony analysis.
Cladistics 15 (4): 407-414.

Nomenclature, I.C.o.Z. 2000. International Code of Zoological Nomenclature, Fourth
Edition. 306 pp. International Trust for Zoological Nomenclature, London.

Norell, M.A. and Clarke, J.A. 2001. Fossil that fills a critical gap in avian evolution.
Nature 409: 181-184.

Norell, M.A. and Makovicky, P.J. 2004. Dromaeosauridae. In: D.B. Weishampel, P.
Dodson, and H. Osmólska (eds.), The Dinosauria, Second Edition, 196-209.
University of California Press, Berkeley.

Norell, M.A. and Xu, X. 2005. Feathered dinosaurs. Annual Review of Earth and
Planetary Science 33: 277-299.

Norell, M.A., Clark, J.M., Chiappe, L.M., and Demberelyin, D. 1995. A nesting dinosaur.
Nature 378: 774-776.

Norell, M.A., Clark, J.M., and Makovicky, P.J. 2001. Phylogenetic relationships among
coelurosaurian theropods. In: J. Gauthier, and L.F. Gall (eds.), New Perspectives
on the Origin and Early Evolution of Birds, 49-67. Peabody Museum of Natural
History, New Haven.

Norell, M., Ji, Q., Gao, K., Yuan, C., Zhao, Y., and Wang, L. 2002. 'Modern' feathers on
a non-avian dinosaur. Nature 416: 36-37.

Norell, M.A., Clark, J.M., Turner, A.H., Makovicky, P.J., Barsbold, R., and Rowe, T.
2006. A new dromaeosaurid theropod from Ukhaa Tolgod (Ömnögov, Mongolia).
American Museum Novitates 3545: 1-51.

Noriega, J.J. and Tambussi, C.P. 1995. A Late Cretaceous Presbyornithidae (Aves:
Anseriformes) from Vega Island, Antarctic Peninsula: paleobiogeographic
implications. Ameghiniana 32 (1): 57-61.

Novas, F.E. and Pol, D. 2005. New evidence on deinonychosaurian dinosaurs from the
Late Cretaceous of Patagonia. Nature 433: 858-861.

455 
O'Connor, J.K., Wang, X.-R., Chiappe, L.M., Gao, C.-H., Meng, Q.-J., Cheng, X.-D., and
Liu, J.-Y. 2009. Phylogenetic support for a specialized clade of Cretaceous
enantiornithine birds with information from a new species. Journal of Vertebrate
Paleontology 29 (1): 188-204.

O'Connor, J.K., Gao, K.-Q., and Chiappe, L.M. in press. A new ornithuromorph (Aves:
Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity.
Journal of Vertebrate Paleontology in press.

O'Connor, J.K., Bell, A., and Chiappe, L.M. in prep. Mesozoic Birds: the great
evolutionary transition. In: G.D. Dyke, and G. Kaiser (eds.), the Complete Bird.

O’Connor, P.M. 2004. Pulmonary pneumaticity in the postcranial skeleton of extant
Aves: a case study examining Anseriformes. Journal of Morphology 261: 141-
161.

O'Connor, P.M. and Claessens, L.P. 2005. Basic avian pulmonary design and flow-
through ventilation in non-avian theropod dinosaurs. Nature 436: 253-256.

Organ, C.L., Shedlock, A.M., Meade, A., Pagel, M., and Edwards, S.V. 2007. Origin of
avian genome size and structure in non-avian dinosaurs. Nature 446: 180-184.

Ösi, A. 2008. Enantiornithine bird remains from the Late Cretaceous of Hungary. Oryctos
7: 55-60.

Ostrom, J.H. 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the
Lower Cretaceous of Montana. Bulletin of the Peabody Museum of Natural
History 30: 1-165.

Ostrom, J.H. 1973. The ancestry of birds. Nature 242: 136.

Padian, K. 1997. Avialae. In: P.J. Currie, and K. Padian (eds.), Encyclopedia of
Dinosaurs. Academic Press, San Diego.

Padian, K. and Chiappe, L.M. 1998. The origin and early evolution of birds. Biological
Reviews 73: 1-42.

Padian, K., Hutchinson, J.R., and Holtz, T.R., Jr. 1999. Phylogenetic definitions and
nomenclature of the major taxonomic categories of the carnivorous Dinosauria
(Theropoda). Journal of Vertebrate Paleontology 19 (1): 69-80.

Padian, K., de Ricqlès, A., and Horner, J.R. 2001. Dinosaurian growth rates and bird
origins. Nature 412: 405-408.

456 
Panteleyev, A.V. 1998. New species of enantiornithines (Aves: Enantiornithes) from
Upper Cretaceous of central Kyzylkum. Russkii Ornithologicheskii Zhurnal
Ekspress-Vy.Pvsk 35: 3-15.

Paul, G. 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and
Birds. pp. John Hopkins University Press, Baltimore.Pleijel, F. 1995. On
character coding for phylogeny reconstruction. Cladistics (11): 309-315.

Ponton, F., Elzanowski, A., Castanet, J., Chinsamy, A., de Margerie, E., de Ricqles, A.J.,
and Cubo, J. 2004. Variation of the outer circumferential layer in the limb bones
of birds. Acta Ornithologica 39 (2): 21-24.

Proctor, N.S. and Lynch, P.J. 1993. Manual of Ornithology: Avian Structure and
Function. 340 pp. Yale University Press, New Haven.

Provini, P., Zhou, Z.-H., and Zhang, F.-C. in press. A new species of the basal bird
Sapeornis from the Early Cretaceous of Liaoning, China. Canadian Journal of
Earth Sciences.

Prum, R.O. 2005. Evolution of the morphological innovations of feathers. Journal of
Experimental Zoology B 304: 570-579.

Prum, R.O. and Brush, A.H. 2002. The evolutionary origin and diversification of
feathers. Quarterly Review of Biology 77 (3): 261-295.

Reig, O.A. 1963. La presencia de dinosaurios saurisquios en los 'Estratos de
Ischigualasto' (Mesotriásico Superior) de Las Provincias de San Juan y La Rioja
(República Argentina). Ameghiniana 3 (1): 3-20.

Ricklefs, R. 2007. Tyrannosaur ageing. Biology Letters 3 (2): 214-217.

Ricklefs, R.E. and Starck, J.M. 1998. Embryonic growth and development. In: J.M.
Starck, and R.E. Ricklefs (eds.), Avian Growth and Development. Evolution
Within the Altricial-Precocial Spectrum, 31-58. Oxford University Press, New
York.

Ricklefs, R.E., White, S., and Cullen, J. 1980. Post-natal development of Leach's storm-
petrel. the Auk 97: 768-781.

Sabath, K. 1991. Upper Cretaceous amniotic eggs from the Gobi Desert. Acta
Palaeontologica Polonica 36 (2): 151-192.

Sanz, J.L., Bonaparte, J.F., and Lacasa, A. 1988. Unusual Early Cretaceous birds from
Spain. Nature 331: 433-435.
457 

Sanz, J.L. and Bonaparte, J.F. 1992. A new order of birds (Class Aves) from the Lower
Cretaceous of Spain. In: K.C. Campbell, Jr. (ed.), Papers in Avian Paleontology
Honoring Pierce Brodkorb, 39-49.

Sanz, J.L. and Buscalioni, A.D. 1992. A new bird from the Early Cretaceous of Las
Hoyas, Spain, and the early radiation of birds. Palaeontology 35 (4): 829-845.

Sanz, J.L., Chiappe, L.M., and Buscalioni, A.D. 1995. The osteology of Concornis
lacustris (Aves: Enantiornithes) from the Lower Cretaceous of Spain and a
reexamination of its phylogenetic relationships. American Museum Novitates
3133: 1-23.

Sanz, J.L., Chiappe, L.M., Pérez-Moreno, B.P., Buscalioni, A.D., Moratalla, J.J., Ortega,
F., and Poyato-Ariza, F.J. 1996. An Early Cretaceous bird from Spain and its
implications for the evolution of avian flight. Nature 382: 442-445.

Sanz, J.L., Chiappe, L.M., Pérez-Moreno, B., Moratalla, J.J., Hernández-Carrasquilla, F.,
Buscalioni, A.D., Ortega, F., Poyato-Ariza, F.J., Rasskin-Gutman, D., and
Martinez-Delclòs, X. 1997. A nestling bird from the Lower Cretaceous of Spain:
implications for avian skull and neck evolution. Science 276: 1543-1546.

Sanz, J.L., Chiappe, L.M., Fernández-Jalvo, Y., Ortega, F., Sánchez-Chillon, B., Poyato-
Ariza, F.J., and Pérez-Moreno, B.P. 2001. An Early Cretaceous pellet. Nature
409: 998-999.

Sanz, J.L., Pérez-Moreno, B.P., Chiappe, L.M., and Buscalioni, A.D. 2002. The birds
from the Lower Cretaceous of Las Hoyas (province of Cuenca, Spain). In: L.M.
Chiappe, and L.M. Witmer (eds.), Mesozoic Birds: Above the Heads of
Dinosaurs, 209-229. University of California Press, Berkeley.

Sanz, J.L., Álvarez, J.C., Soriano, C., Hernández-Carrasquilla, F., Pérez-Moreno, B.P.,
and Meseguer, J. 2002. Wing loading in primitive birds. In: Z. Zhou, and F.
Zhang (eds.), Proceedings of the 5th Symposium of the Society of Avian
Paleontology and Evolution, Beijing, 1-4 June 2000, 253-258. Science Press,
Beijing.

Schweitzer, M.H., Jackson, F.D., Chiappe, L.M., Schmitt, J.G., Calvo, J.O., and Rubilar,
D.E. 2002. Late Cretaceous avian eggs with embryos from Argentina. Journal of
Vertebrate Paleontology 22 (1): 191-195.

Schweitzer, M.H., Wittmeyer, J.L., and Horner, J.R. 2005. Gender-specific reproductive
tissue in ratites and Tyrannosaurus rex. Science 308: 1456-1460.

458 
Schweitzer, M.H., Suo, Z., Avci, R., Asara, J.M., Allen, M.A., Arce, F.T., and Horner,
J.R. 2007. Analyses of soft tissue from Tyrannosaurus rex suggest the presence of
protein. Science 316: 277-280.

Senter, P. 2007. A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda).
Journal of Systematic Palaeontology 5 (4): 429-463.

Senter, P. and Robins, J.H. 2003. Taxonomic status of the specimens of Archaeopteryx.
Journal of Vertebrate Paleontology 23 (4): 961–965.

Sereno, P.C. 1993. The pectoral girdle and forelimb of the basal theropod Herrerasaurus
ischigualastensis. Journal of Vertebrate Paleontology 13 (4): 425-450.

Sereno, P.C. 1997. The origin and evolution of dinosaurs. Annual Review of Earth and
Planetary Sciences 25: 435-489.

Sereno, P.C. 1998. A rationale for phylogenetic definitions, with application to the
higher-level taxonomy of Dinosauria. Neues Jahrbuch für Geologie und
Paläontologie Abhandlungen 210 (1): 41-83.

Sereno, P.C. 1999. The evolution of dinosaurs. Science 284: 2137-2147.

Sereno, P.C. 2000. Iberomesornis romerali (Aves, Ornithothoraces) reevaluated as an
Early Cretaceous enantiornithine. Neues Jahrbuch für Geologie und
Paläontologie Abhandlungen 215 (3): 365-395.

Sereno, P.C. and Arcucci, A.B. 1990. The monophyly of crurotarsal archosaurs and the
origin of bird and crocodile ankle joints. Neues Jahrbuch für Geologie und
Paläontologie Abhandlungen 180 (1): 21-52.

Sereno, P.C. and Rao, C. 1992. Early evolution of avian flight and perching: new
evidence from the Lower Cretaceous of China. Science 255: 845-848.

Sereno, P.C., Rao, C., and Li, J. 2002. Sinornis santensis (Aves: Enantiornithes) from the
Early Cretaceous of northeastern China. In: L.M. Chiappe, and L.M. Witmer
(eds.), Mesozoic Birds: Above the Heads of Dinosaurs, 184-208. University of
California Press, Berkeley.

Sharov, A.G. 1970. An unusual reptile from the Lower Triassic of Fergana.
Paleontological Journal 1970 (1): 112-116.

Sibley, C.G. and Ahlquist, J.E. 1990. Phylogeny and Classification of Birds: A Study in
Molecular Evolution. 976 pp. Yale University Press, New Haven.

459 
Slowinski, J.B. 1993. Unordered versus ordered characters. Systematic Biology 42: 155-
165.

Sneath, R.R. and Sokal, H.A. 1963. The Principles of Numerical Taxonomy. W.H.
Freeman.

Starck, J.M. and Ricklefs, R.E. 1998. Patterns of development: the altricial-precocial
spectrum. In: J.M. Starck, and R.E. Ricklefs (eds.), Avian Growth and
Development, 3-30. Oxford University Press, New York City.

Starck, J.M. and Chinsamy, A. 2002. Bone microstructure and developmental plasticity
in birds and other dinosaurs. Journal of Morphology 254 (3): 232-246.

Steadman, D.W. 1983. Commentary. In: A.H. Brush, and G.A. Clark, Jr. (eds.),
Perspectives in Ornithology: Essays presented for the Centennial of the American
Ornithological Union, 338-344. Cambridge University Press, Cambridge.

Stettenheim, P.R. 2000. The integumentary morphology of modern birds - an overview.
American Zoologist 40 (4): 461-477.

Swisher, C.C., III, Wang, Y., Wang, X.-L., Xu, X., and Wang, Y. 1999. Cretaceous age
for the feathered dinosaurs of Liaoning, China. Nature 400: 58-61.

Swisher, C.C., III, Wang, X., Zhou, Z., Wang, Y., Jin, F., Zhang, J., Xu, X., Zhang, F.,
and Wang, Y. 2002. Further support for a Cretaceous age for the feathered-
dinosaur beds of Liaoning, China: new
40
Ar/
39
Ar dating of the Yixian and
Tuchengzi formations. Chinese Science Bulletin 47 (2): 135-138.

Taylor, M.P. 2006. Dinosaur diversity analysed by clade, age, place and year of
description. In: P.M. Barrett, and S.E. Evans (eds.), 9th International Symposium
on Mesozoic Terrestrial Ecosystems and Biota, 134-138.

Turner, A.H., Pol, D., Clarke, J.A., Erickson, G.M., and Norell, M.A. 2007a. A basal
dromaeosaurid and size evolution preceding avian flight. Science 317: 1378-1381.

Turner, A.H., Makovicky, P.J., and Norell, M.A. 2007b. Feather quill knobs in the
dinosaur Velociraptor. Science 317: 1721.

Turner, A.H., Hwang, S.H., and Norell, M.A. 2007c. A small derived theropod from
Öösh, Early Cretaceous, Baykhangor Mongolia. American Museum Novitates
3557: 1-27.

460 
Upchurch, P., Barrett, P.M., McIntosh, J.S., and Dodson, P. 2004. Sauropoda. In: D.B.
Weishampel, P. Dodson, and H. Osmólska (eds.), The Dinosauria, Second
Edition, 259-322. University of California Press, Berkeley.

van Tuinen, M. and Hedges, S.B. 2001. Avian molecular clocks and neornithine
divergence times. In, North American Paleontological Conference 2001
Abstracts. University of California, Berkeley.

Van der Klaauw, C.J. 1948. Size and position of the functional components of the skull.
A contribution to the knowledge of the architecture of the skull, based on data in
the literature. Archives Néerlandaises de Zoology 9: 1–558.

Vanden Berge, J.C. and Zweers, G.A. 1993. Myologia. In: J.J. Baumel, A.S. King, J.E.
Breazile, H.E. Evans, and J.C. Vanden Berge (eds.), Handbook of Avian
Anatomy: Nomina Anatomica Avium, Second Edition, 189-250. Nuttall
Ornithological Club, Cambridge.

Varricchio, D.J. 1993. Bone microstructure of the Upper Cretaceous theropod dinosaur
Troodon formosus. Journal of Vertebrate Paleontology 13 (1): 99-104.

Varricchio, D.J. 2002. A new bird from the Upper Cretaceous Two Medicine Formation
of Montana. Canadian Journal of Earth Sciences 39: 19-26.

Varricchio, D.J. and Chiappe, L.M. 1995. A new enantiornithine bird from the Upper
Cretaceous Two Medicine Formation of Montana. Journal of Vertebrate
Paleontology 15 (1): 201-204.

Varricchio, D.J. and Jackson, F.D. 2004. A phylogenetic assessment of prismatic
dinosaur eggs from the Cretaceous Two Medicine Formation of Montana. Journal
of Vertebrate Paleontology 24 (4): 931-937.

Varricchio, D.J., Horner, J.R., and Jackson, F.D. 2002. Embryos and eggs for the
Cretaceous theropod dinosaur Troodon formosus. Journal of Vertebrate
Paleontology 22 (3): 564-576.

Varricchio, D.J., Moore, J.R., Erickson, G.M., Norell, M.A., Jackson, F.D., and
Borkowski, J.J. 2008. Avian paternal care had dinosaur origin. Science 322: 1826-
1828.

Videler, J.J. 2005. Avian Flight. 280 pp. Oxford University Press.

Wagner, G.P. and Gauthier, J.A. 1999. 1,2,3 = 2,3,4: a solution to the problem of the
homology of the digits in the avian hand. Proceedings of the National Academy of
Sciences, USA 96 (9): 5111-5116.
461 

Walker, A.D. 1972. New light on the origin of birds and crocodiles. Nature 237: 257-263.

Walker, C.A. 1981. New subclass of birds from the Cretaceous of South America. Nature
292: 51-53.

Walker, C.A., Buffetaut, E., and Dyke, G.J. 2007. Large euenantiornithine birds from the
Cretaceous of southern France, North America and Argentina. Geological
Magazine 144 (6): 977-986.

Wiens, J.J. 2003. Incomplete taxa, incomplete characters, and phylogenetic accuracy: is
there a missing data problem? Journal of Vertebrate Paleontology 23 (2): 297-
310.

Wellnhofer, P. 1974. Das funfte skelettexemplar von Archaeopteryx. Palaeontographica
Abteilung A 147: 169-215.

Wellnhofer, P. 1993. Das siebte exemplar von Archaeopteryx aus den Solnhofer
Schichten. Archaeopteryx 11: 1-47.

Wellnhofer, P. 2008. Archaeopteryx. Der Urvogel von Solnhofen. pp. Friedrich Pfeil.,
München.

Welman, J. 1995. Euparkeria and the origin of birds. South African Journal of Science
91: 533-537.

Wesolowski, T. 1994. On the Origin of Parental Care and the Early Evolution of Male
and Female Parental Roles in Birds. The American Naturalist 143 (1): 39-58.

Wilkinson, M.T. 1992. Ordered versus unordered characters. Cladistics 8: 375-385.

Wilkinson, M.T. 1994. Common cladistic information and its consensus representation:
reduced Adams and reduced cladistic consensus trees and profiles. Systematic
Biology 43: 343–368.

Wilkinson, M.T. 1995. More on reduced consensus methods. Systematic Biology 44 (435-
439).

Wilkinson, M.T. 2001. TAXEQ3: software and documentation. Department of Zoology,
The Natural History Museum, London.

Wilkinson, M. 2003. Missing entries and multiple trees: instability, relationships, and
support in parsimony analysis. Journal of Vertebrate Paleontology 23 (2): 311-
323.
462 

Witmer, L.M. 1991. Perspectives on avian origins. In: H.-D. Schultze, and L. Trueb
(eds.), Origins of the Higher Groups of Tetrapods, 427-466. Comstock Publishing
Associates, Ithaca.

Witmer, L.M. 1997. The evolution of the antorbital cavity of archosaurs: a study in soft-
tissue reconstruction in the fossil record with an analysis of the function of
pneumaticity. Society of Vertebrate Paleontology Memoir 3: 1-73.

Xu, G.-L., Yang, Y.-S., and Deng, S.-Y. 1999. First discovery of Mesozoic bird fossils
in Hebei Province and its significance. Regional Geology of China 18 (4): 444-
448.

Xu, X. and Zhang, F. 2005. A new maniraptoran dinosaur from China with long feathers
on the metatarsus. Naturwissenschaften 92 (4): 173-177.

Xu, X. 2006. Feathered dinosaurs from China and the evolution of major avian
characters. Integrative Zoology 1 (1): 4-11.

Xu, X. and Norell, M.A. 2004. A new troodontid dinosaur from China with avian-like
sleeping posture. Nature 431: 838-841.

Xu, X. and Norell, M.A. 2006. Non-avian dinosaur fossils from the Lower Cretaceous
Jehol Group of western Liaoning, China. Geological Journal 41 (3-4): 419-437.

Xu, X., Wang, X.-L., and Wu, X.-C. 1999. A dromaeosaurid dinosaur with a filamentous
integument from the Yixian Formation of China. Nature 401: 262-266.

Xu, X., Zhou, Z., and Wang, X. 2000. The smallest known non-avian theropod dinosaur.
Nature 408: 705-708.

Xu, X., Zhou, Z., and Prum, R.O. 2001. Branched integumental structures in
Sinornithosaurus and the origin of feathers. Nature 410: 200-204.

Xu, X., Norell, M.A., Wang, X.-L., Makovicky, P.J., and Wu, X.-C. 2002. A basal
troodontid from the Early Cretaceous of China. Nature 415: 780-784.

Xu, X., Zhou, Z., Wang, X., Kuang, X., and Du, X. 2003. Four-winged dinosaurs from
China. Nature 421: 335-340.

Xu, X., Clark, J.M., Mo, J.-Y., Choiniere, J., Forster, C.A., Erickson, G.M., Hone, D.W.,
Sullivan, C., Eberth, D.A., Nesbitt, S.J., Zhao, Q., Hernandez, R., Jia, C.-K., Han,
F.-L., and Guo, Y. 2009a. A Jurassic ceratosaur from China helps clarify avian
digital homologies. Nature 459: 941-944.
463 

Xu, X., Zhao, Q., Norell, M.A., Sullivan, C., Hone, D.W., Erickson, G.M., Wang, X.-L.,
Han, F.-L., and Guo, Y. 2009b. A new feathered maniraptoran dinosaur fossil that
fills a morphological gap in avian origin Chinese Science Bulletin 54 (3): 430-
435.

Yalden, D.W. 1984. What size was Archaeopteryx? Zoological Journal of the Linnean
Society 82: 177-188.

Yang, W., Li, S., and Jiang, B. 2007. New evidence for Cretaceous age of the feathered
dinosaurs of Liaoning: zircon U-Pb SHRIMP dating of the Yixian Formation in
Sihetun, northeast China. In: J. Sha (ed.), Current Research on Cretaceous Lake
Systems in Northeast China, 177-182.

You, H., O'Connor, J., Chiappe, L.M., and Ji, Q. 2005. A new fossil bird from the Early
Cretaceous of Gansu Province, northwestern China. Historical Biology 17 (1-4):
7-14.

You, H.-L., Lamanna, M.C., Harris, J.D., Chiappe, L.M., O'Connor, J., Ji, S.-A., Lü, J.-
C., Yuan, C.-X., Li, D.-Q., Zhang, X., Lacovara, K.J., Dodson, P., and Ji, Q.
2006. A nearly modern amphibious bird from the Early Cretaceous of
northwestern China. Science 312: 1640-1643.

Yu, M., Wu, P., Widelitz, R.B., and Chuong, C.-M. 2002. The morphogenesis of feathers.
Nature 420: 308-312.

Yuan, C. 2008. A new genus and species of Sapeornithidae from Lower Cretaceous in
western Liaoning, China. Acta Geologica Sinica 82 (1): 48-55.

Yue, Z., Jiang, T.-X., Widelitz, R.B., and Chuong, C.-M. 2006. Wnt3a gradient converts
radial to bilateral feather symmetry via topological arrangement of epithelia.
Proceedings of the National Academy of Sciences 103: 951-955.

Zeffer, A., Johansson, L.C., and Marmebro, A. 2003. Functional correlation between
habitat use and leg morphology in birds (Aves). Biological Journal of the Linnean
Society 79 (3): 461-484.

Zhang, F. and Zhou, Z. 2000. A primitive enantiornithine bird and the origin of feathers.
Science 290: 1955-1960.

Zhang, F. and Zhou, Z. 2004. Leg feathers in an Early Cretaceous bird. Nature 431: 925.

Zhang, F., Hou, L., and Ouyang, L. 1998. Osteological microstructure of Confuciusornis:
preliminary report. Vertebrata PalAsiatica 36 (2): 126-135.
464 

Zhang, F., Zhou, Z., Hou, L., and Gu, G. 2000. Early diversification of birds: evidence
from a new opposite bird. Kexue Tongbao 45 (24): 2650-2657.

Zhang, F., Zhou, Z., Xu, X., and Wang, X. 2002. A juvenile coelurosaurian theropod
from China indicates arboreal habits. Naturwissenschaften 89 (9): 394-398.

Zhang, F. and Zhou, Z. 2003. Birds. In: M. Chang, P. Chen, Y. Wang, Y. Wang, and D.
Miao (eds.), The Jehol Biota: the Emergence of Feathered Dinosaurs, Beaked
Birds and Flowering Plant, 129-150. Shanghai Scientific and Technical
Publishers, Shanghai.

Zhang, F., Ericson, P.G., and Zhou, Z. 2004. Description of a new enantiornithine bird
from the Early Cretaceous of Hebei, northern China. Canadian Journal of Earth
Sciences 41 (9): 1097-1107.

Zhang, F., Zhou, Z., and Dyke, G.J. 2006. Feathers and 'feather-like' integumentary
structures in Liaoning birds and dinosaurs. Geological Journal 41 (3-4): 395-404.

Zhang, F.-C., Zhou, Z.-H., Xu, X., Wang, X.-L., and Sullivan, C. 2008a. A bizarre
Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455:
1105-1108.

Zhang, F., Zhou, Z., and Benton, M.J. 2008b. A primitive confuciusornithid bird from
China and its implications for early avian flight. Science in China, Series D:
Earth Sciences 51 (5): 625-639.

Zhang, F.-C., Chiappe, L.M., and Zhou, Z.-H. in prep. Anatomy of the Early Cretaceous
enantiornithine bird Longipteryx chaoyangensis from the Jiufotang Formation of
Northeastern China.

Zhang, Z., Hou, L., Hasegawa, Y., O'Connor, J., Martin, L.D., and Chiappe, L.M. 2006.
The first Mesozoic heterodactyl bird from China. Acta Geologica Sinica (English
edition) 80 (5): 631-635.

Zheng, X., Zhang, Z., and Hou, L. 2007. A new enantiornitine bird with four long
rectrices from the Early Cretaceous of northern Hebei, CHina. Acta Geologica
Sinica (English edition) 81 (5): 703-708.

Zheng, X.-T., You, H.-L., Xu, X., and Dong, Z.-M. 2009. An Early Cretaceous
heterodontosaurid dinosaur with filamentous integumentary structures. Nature
458: 333-337.

465 
Zhou, Z. 1995. Discovery of a new enantiornithine bird from the Early Cretaceous of
Liaoning, China. Vertebrata PalAsiatica 33 (2): 99-113.

Zhou, Z. 2002. A new and primitive enantiornithine bird from the Early Cretaceous of
China. Journal of Vertebrate Paleontology 22 (1): 49-57.

Zhou, Z. 2006. Evolutionary radiation of the Jehol Biota: chronological and ecological
perspectives. Geological Journal 41 (3-4): 377-393.

Zhou, Z. and Hou, L. 2002. The discovery and study of Mesozoic birds in China. In:
L.M. Chiappe, and L.M. Witmer (eds.), Mesozoic Birds: Above the Heads of
Dinosaurs, 160-183. University of California Press, Berkeley.

Zhou, Z. and Zhang, F. 2001. Two new ornithurine birds from the Early Cretaceous of
western Liaoning, China. Kexue Tongbao 46 (5): 371-377.

Zhou, Z. and Zhang, F. 2002a. A long-tailed, seed-eating bird from the Early Cretaceous
of China. Nature 418: 405-409.

Zhou, Z. and Zhang, F. 2002b. Largest bird from the Early Cretaceous and its
implications for the earliest avian ecological diversification. Naturwissenschaften
89 (1): 34-38.

Zhou, Z. and Zhang, F. 2003. Anatomy of the primitive bird Sapeornis chaoyangensis
from the Early Cretaceous of Liaoning, China. Canadian Journal of Earth
Sciences 40 (5): 731-747.

Zhou, Z. and Zhang, F. 2004. A precocial avian embryo from the Lower Cretaceous of
China. Science 306: 653.

Zhou, Z. and Zhang, F. 2005. Discovery of an ornithurine bird and its implication for
Early Cretaceous avian radiation. Proceedings of the National Academy of
Sciences 102 (52): 18998-19002.

Zhou, Z-H. and Zhang, F-C. 2006a. Mesozoic birds of China - a synoptic review.
Vertebrata PalAsiatica 44 (1): 74-98.

Zhou, Z-H. and Zhang, F-C. 2006b. A beaked basal ornithurine bird (Aves, Ornithurae)
from the Lower Cretaceous of China. Zoologica Scripta 35 (4): 363-373.

Zhou, Z., Jin, F., and Zhang, J. 1992. Preliminary report on a Mesozoic bird from
Liaoning, China. Chinese Science Bulletin 37 (16): 1365-1368.

Zhou, Z., Clarke, J.A., and Zhang, F. 2002. Archaeoraptor's better half. Nature 420: 285.
466 

Zhou, Z., Clarke, J., Zhang, F., and Wings, O. 2004. Gastroliths in Yanornis: an
indication of the earliest radical diet-switching and gizzard plasticity in the
lineage leading to living birds. Naturwissenschaften 91 (12): 571-574.

Zhou, Z., Chiappe, L.M., and Zhang, F. 2005. Anatomy of the Early Cretaceous bird
Eoenantiornis buhleri (Aves: Enantiornithes) from China. Canadian Journal of
Earth Sciences 42 (7): 1331-1338.

Zhou, Z., Clarke, J., and Zhang, F. 2008a. Insight into diversity, body size and
morphological evolution from the largest Early Cretaceous enantiornithine bird.
Journal of Anatomy 212 (5): 565-577.

Zhou, Z., Zhang, F., and Hou, L.-H. 2008b. Aves. In: J. Li, G. Wu, and F. Zhang (eds.),
The Chinese Fossil Reptiles and Their Kin, 337-378. Science Press, Beijing.

Zhou, Z.-H., Zhang, F.-C., and Li, Z.-H. 2009. A new lower cretaceous bird from China
and tooth reduction in early avian evolution. Proceedings of the Royal Society of
London B doi: 10.1098/rspb.2009.0885.

Zhu, R., Pan, Y., Shi, R., Liu, Q., and LI, D. 2007. Palaeomagnetic and 40Ar/39Ar dating
constraints on the age of the Jehol Biota and the duration of depostion of the
Sihetun fossil-bearing lake sediments, northeast China. Cretaceous Research 28:
171-176.

Zusi, R.L. 1984. A functional and evolutionary analysis of rhynchokinesis in birds.
Smithsonian Contributions to Zoology 395: 1-40.

Zusi, R.L. 1993. Patterns of diversity in the Avian skull. In: J. Hanken, and B.K. Hall
(eds.), The Skull: patterns of structural and systematic diversity, 391-437.
University of Chigago Press.

467 
APPENDIX A: LIST OF OUTGROUP AND INGROUP TAXA
The following alphabetically lists the in-group and out-group operational taxonomic units
and the information used to score them.

Out-group
Archaeopteryx lithographica (Meyer, 1861) – Information on this taxon comes from
publications and casts of the 10 skeletal specimens. Following Senter and Robins (2003),
the six most complete specimens are all considered a single species. The relatively more
recently described “Thermopolis specimen” (WDC-CSG-100) was assigned to A.
bavarica (Mayr et al., 2007). Since this species is considered a junior synonym to A.
lithographica by Senter and Robins (2003), this specimen is also considered to belong to
the latter genus and information from publications on this specimen contribute to the
scorings of this taxon.

In-group
Abavornis bonaparti (Panteyelev, 1998) – Data on this taxon is derived from published
data on the holotype and only known specimen (PO 4605; Panteyelev, 1998) a partial
coracoid from the Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum
Desert of Uzbekistan.

Alethoalaornis agitornis (Li et al., 2008) – Data for this taxon derives from one specimen
(LPM-B00017, published as LPM 00040), from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China. The holotype and three other specimens were unavailable
and studied from the publication but based on equivocal differences they are not
incorporated into the scorings for this species (Li et al., 2008). See Chapter 3 for a
discussion of the validity of this taxon.

Anas platyrhynchos – Data on this taxon comes from firsthand observations from LACM
103277.

Apsaravis ukhaana (Norell and Clarke, 2001) – Date on this taxon comes from
publications (Clarke and Norell, 2002) on the only known specimen (IGM 100/1017)
from Late Cretaceous (Campanian?) deposits in Ukhaa Tolgod, Mongolia.

Archaeorhynchus spathula (Zhou and Zhang, 2006) – Data on this taxon comes from
firsthand study of the holotype (IVPP V14287), a nearly complete specimen in a single
slab from the Early Cretaceous (Hauterivian – Barremian) Yixian Formation, Liaoning,
China.

Alexornis antecedens (Brodkorb, 1976) – Data comes from the publication and casts of
the holotype specimen (LACM 33212), a very fragmentary partial skeleton from the Late
Cretaceous (Campanian) Bocana Roja Formation, Baja California, Mexico.

468 
Avisaurus archibaldi (Brett-Surman and Paul, 1985) – Data is based on observations
from the holotype, a tarsometatarsus (UCMP 117600), from the Late Cretaceous
(Maastrichtian) Hell Creek Formation, Montana, USA.

Avisaurus gloriae (Varricchio and Chiappe, 1995) – Data is based on observations from a
cast of the holotype (MOR 553 e/6.199164), an isolated tarsometatarsus from the Late
Cretaceous (Campanian) Two Medicine Formation, Montana, USA.

Boluochia zhengi (Zhou, 1995) – Data comes from observations of the only known
specimen of this taxon (IVPP 9770), an articulated partial skeleton preserving the rostral
portion of the skull and the caudal half of the skeleton. The specimen is reported from the
Early Cretaceous (Aptian) Jiufotang Formation, Liaoning, China. Bones are preserved as
voids and no integument is preserved.

Catenoleimus anachoretus (Panteyelev, 1998) – The only known specimen of this taxon
(PO 4606), a partial coracoid, comes from the Late Cretaceous (Conacian) Bissekty
Formation in the Kyzyl kum Desert of Uzbekistan was studied from published figures
(Panteyelev, 1998).

Cathayornis aberransis (Hou et al., 2000) – The specimen was studied only from
published photographs and data of the holotype (Hou et al., 2000; Hou, 2002), a single
nearly complete specimen preserved in slab and counterslab (IVPP V12352) from the
Early Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Cathayornis caudatus (Hou, 1997a) – Data on this taxon comes from published
photographs and data on the single known specimen (Hou, 1997, 2002), a nearly
complete individual preserved in slab and counterslab (IVPP V10917) from the Early
Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Cathayornis chabuensis (Li et al., 2008) – Data on this taxon comes from published
photographs and data on the single known specimen, a partial skeleton preserved in slab
and counterslab (BMNH Ph000110 a/b) from the Early Cretaceous (120 Ma?) Jingchuan
Formation, Liaoning, China.

Cathayornis yandica (Zhou et al., 1992) – Data for this species was taken only from the
holotype (IVPP V9769), which comes from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China. This species is known from several specimens, however the
certainty to which some referred specimens actually belong to this taxon is unclear. The
holotype specimen is a partial skeleton preserved in two slabs. Bones are preserved as
voids so casts were studied as well as the specimens. This taxon is considered a junior
synonym of Sinornis santensis (Sereno and Rao, 1992; Sereno et al., 2002) by some,
however morphological support for the validity of this species is provided in Chapter 3,
and the species are here considered distinct and valid.

469 
Concornis lacustris (Sanz and Buscalioni, 1992) – Data on this taxon comes from study
of the only known specimen of this taxon (LH-2814), a partial skeleton of a subadult
individual, missing the skull, from the Early Cretaceous (Upper Hauteverian) Calizas de
la Huerguina Formation, Spain.

Confuciusornis sanctus (Hou, 1995) – Data on this taxon, known from hundreds of
specimens from the Early Cretaceous (Upper Hauterivian – Lower Barremian) Yixian
Formation and numerous publications, comes primarily from the Chiappe et al. (1999)
monograph, as well as firsthand study of IVPP V10921 and V13156.

Cuspirostrisornis houi (Hou, 1997a) – This species is known from a single nearly
complete specimen preserved in slab and counterslab (IVPP V10897) from the Early
Cretaceous (Aptian) Jiufotang Formation, Liaoning, China. The specimen was studied
only from published photographs and data, which provide little information (Hou, 1997,
2002).

Dalingheornis liwei (Zhang et al., 2006) – Data on this taxon comes from published
photographs and data on the only known specimen, a nearly complete subadult individual
preserved in slab and counterslab (CNU VB2005001) from the Early Cretaceous (Upper
Hauterivian – Lower Barremian) Yixian Formation, Liaoning, China.

Dapingfangornis sentisorhinus (Li et al., 2006) – Data on this taxon comes from
firsthand observations of the holotype and only known specimen (LPM 00039, published
as LPM B00027) from the Early Cretaceous (Aptian) Jiufotang Formation, Liaoning,
China.

Elsornis keni (Chiappe et al., 2006) – Data on this taxon comes from casts of the
holotype, a partial skeleton from the Late Cretaceous (Campanian) Djadokhta Formation,
Mongolia.

Enantiophoenix electrophyla (Dalla Vecchia and Chiappe, 1995; Cau and Arduini, 2008)
– Data on this taxon comes from publications on the holotype, a partial skeleton from the
Late Cretaceous (Cenomanian) Ouadi al Gabour locality, Nammoura, Lebanon.

Enantiornis leali (Walker, 1981) – Data on this taxon comes from first hand observations
of the holotype (PVL 4035) and assigned material (PVL 4020), both partial skeletons
from the Late Cretaceous (Maastrichtian) Lecho Formation, Argentina.

Enantiornis martini (Panteyelev, 1998) – Data on this taxon comes from published
photos of the only known specimen of this taxon (PO 4609), a partial coracoid from the
Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum Desert of Uzbekistan.

470 
Enantiornis walkeri (Panteyelev, 1998) – Data on this taxon comes from published
photos of the only known specimen of this taxon (PO 4819), a partial coracoid from the
Late Cretaceous (Conacian) Bissekty Formation, Kyzyl kum, Uzbekistan.

Enantiornithes indet. (Sanz et al., 1997) – Data on this taxon comes from publications on
the holotype (LP 4450), an articulated partial skeleton from the Early Cretaceous (Lower
Hauteverian?) La Pedrera de Rubies Lithographic Limestones, Spain.

Enantiornithes indet. (Harris et al., 2006) – Data on this taxon comes from published
photos of the only known specimen of this taxon (CAGS-04-CM-023), an isolated wing
from the Early Cretaceous (Albian?) Xiagou Formation, Gansu, China.

Enantiornithes indet. (You et al., 2005) – Data on this taxon comes from observations of
the only known specimen of this taxon (CAGS-02-CM-0901), a partial thoracic girdle
and limb from the Early Cretaceous (Albian?) Xiagou Formation, Gansu, China.

Enantiornithes n sp. (unpublished) – Data on this taxon comes from observations of the
only known specimens of this taxon (CAGS-04-CM-006, CAGS-05-CM-006), a partial
pelvic girdle and hindlimbs from the Early Cretaceous (Albian?) Xiagou Formation,
Gansu, China.

Enantiornithes n sp. (unpublished) – Data on this taxon comes from observations of the
only known specimen of this taxon (DNHM D2950/1), a nearly complete specimen in
slab and counter slab from the Mesozoic (Late Jurassic – Early Cretaceous) Qiaotou
Formation, Hebei, China.

Enantiornithes indet. CAGS-05-CM-004 (unpublished) – Data on this taxon comes from
observations of the only known specimens of this taxon (CAGS-05-CM-004), a fully
articulated partial skeleton with feathers from the Early Cretaceous (Albian?) Xiagou
Formation, Gansu, China.

Enantiornithes indet. CAGS-06-CM-012 (unpublished) – Data on this taxon comes from
observations of the only known specimens of this taxon (CAGS-06-CM-012), a partial
skeleton from the Early Cretaceous (Albian?) Xiagou Formation, Gansu, China.

Enantiornithes indet. CAGS-07-CM-001 (unpublished) – Data on this taxon comes from
observations of the only known specimens of this taxon (CAGS-07-CM-001), a fully
articulated pelvic girdle and hindlimbs with rectrices from the Early Cretaceous (Albian?)
Xiagou Formation, Gansu, China.

Enantiornithes indet. CAGS−04−CM−007 (Lamanna et al., 2006) – Data on this taxon
comes from observations of the only known specimens of this taxon (CAGS-04-CM-
007), a partial pelvic girdle and hindlimbs from the Early Cretaceous (Albian?) Xiagou
Formation, Gansu, China.
471 

Enantiornithes indet. DNHM D2130 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2130), a poorly
preserved nearly complete specimen in a single slab from the Early Cretaceous (Aptian)
Jiufotang Formation, Liaoning, China.

Enantiornithes indet. DNHM D2510/1 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2510, 2511), a poorly
preserved nearly complete specimen in slab and counter slab from the Early Cretaceous
(Aptian) Jiufotang Formation, Liaoning, China.

Enantiornithes indet. DNHM D2567/8 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2567, 2568), a nearly
complete specimen in slab and counter slab from the Early Cretaceous (Aptian) Jiufotang
Formation?, Liaoning, China.

Enantiornithes indet. DNHM D2836 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2836), a nearly
complete specimen in a single slab from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China.

Enantiornithes indet. DNHM D2884 1/2 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2510, 2511), a nearly
complete poorly preserved specimen in slab and counter slab from the Early Cretaceous
(Aptian) Jiufotang Formation, Liaoning, China.

Enantiornithes indet. DNHM D2952/3 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2952, D2953), a nearly
complete poorly preserved specimen in slab and counter slab from the Early Cretaceous
(Aptian) Jiufotang Formation, Liaoning, China.

Eoalulavis hoyasi (Sanz et al., 1996) – Data on this taxon comes from firsthand study of
the only known specimen of this taxon (LH 13000), a partial skeleton from the Early
Cretaceous (Upper Barremian) Calizas de la Huerguina Formation, Spain.

Eocathayornis walkeri (Zhou, 2002) – Data on this taxon comes from firsthand study of
the only known specimen of this taxon (IVPP 10916), a partial skeleton from the Early
Cretaceous (Albian – Aptian) Jiufotang Formation, Liaoning, China.

Eoenantiornis buhleri (Hou et al., 1999) – Data on this taxon comes from firsthand study
of the only known specimen of this taxon (IVPP 11537), a nearly complete skeleton from
the Early Cretaceous (Aptian) Yixian Formation, Liaoning, China.

472 
Explorornis nessovi (Panteyelev, 1998) – Data on this taxon comes from published
photos of the only known specimen of this taxon (PO 4605), a partial coracoid Late
Cretaceous (Conacian) Bissekty Formation, Kyzyl kum, Uzbekistan.

Gallus gallus – Data on this taxon comes from firsthand observations from LACM
87011.

Gansus yummenensis (Hou and Liu, 1984) – Data on this taxon comes from observations
of several specimens (CAGS-04-CM-001, 04-CM-002, 04-CM-003, 04-CM-004, 04-
CM-012, 04-CM-017, 04-CM-020, 05-CM-005, and 06-CM-011), all partial skeletons
from the Early Cretaceous (Albian?) Xiagou Formation, Gansu, China.

Gobipteryx minuta (Elzanowski, 1974) – Data on this taxon comes from publications and
includes data from ‘Nanantius valifanovi’ (Elzanowski, 1974; Elzanowski, 1981;
Kurochkin, 1996; Chiappe et al., 2001). This taxon is known from several partial
skeletons from the Late Cretaceous (Coniacian - Campanian) Barun Goyot and
Djadokhta Formations, Mongolia.

Gurilynia nessovi (Kurochkin, 1999) – Data on this taxon, a partial humerus, comes from
published data and photographs of the holotype (PIN-4492), from the Late Cretaceous
(Late Campanian – Early Maastrichtian) Nemegt Formation, Mongolia.

Halimornis thompsoni (Chiappe et al., 2002) – Data on this taxon comes from casts and
publications of the holotype (UAMNH D2K-025/UANMH-PV966.1.1), a fragmentary
partial skeleton, from the Late Cretaceous (Campanian) Mooreville Chalk Formation,
Alabama, USA.

Hebeiornis fengningensis (Xu et al., 1999) – Data on this taxon comes from study of a
peel of the only known specimen of this taxon (NIGP CAS 130722), a nearly complete
skeleton from the Early Cretaceous (Hauterivian - Barremian) Yixian Formation, Hebei,
China.

Hesperornis regalis (Marsh, 1872) – Data on this taxon, known from several partial
skeletons and isolated elements from the Late Cretaceous Niobrara Chalk Formation of
North America, comes from published material (Marsh, 1880; Buhler et al., 1988), as
well as casts (YPM 1200) and photographs (AMNH 2181, YPM 1476, YPM 1200, YPM
1207, FHSM VP 2293).

Iberomesornis romerali (Sanz et al., 1989) – Data on this taxon comes from firsthand
study of the holotype (LH-22), a nearly complete skeleton from the Early Cretaceous
(Upper Barremian) Calizas de la Huerguina Formation, Spain.

473 
Ichthyornis dispar (Marsh, 1880) – Data on this taxon, known from several partial
skeletons and isolated elements from the Late Cretaceous of Kansas, North America,
comes from the published data, photographs (Clarke, 2004) and casts (YPM 1450).

Incolornis silvae (Panteyelev, 1998) – Data on this taxon comes from published figures
of the only known specimen of this taxon (PO 4604), a partial coracoid from the Late
Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum Desert of Uzbekistan. This
specimen was studied from published figures (Panteyelev, 1998).

Jeholornis prima (Zhou and Zhang, 2002a) – Data on this taxon comes from published
data on four partial skeletons (V13274 – holotype, V13550, V13353, V13553), as well as
personal observations of the holotype (Zhou and Zhang, 2002a, 2003b). All specimens
are from the Early Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Jibeinia luanhera (Hou, 1997a) – Data on this species comes from published photos of
the only known specimen, a nearly complete skeleton (GH-001) that has reportedly been
lost (Zhang et al., 2004). This species is only known from the Early Cretaceous
(Hauterivian – Barremian) Yixian Formation, Hebei, China.

Kizylkumavis cretacea (Nessov, 1984) – Data on this taxon comes from published photos
of the only known specimen of this taxon (TsNIGRI 51/11915), a distal humerus from
the Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum Desert of
Uzbekistan. This specimen was studied from published figures (Panteyelev, 1998).

Largirostrornis sexdentornis (Hou, 1997a) – Data on this species comes from published
photos of the only known specimen, a partial skeleton (IVPP V10531) from the Early
Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Lectavis bretincola (Chiappe, 1993) – Data on this taxon comes from first hand
observations of the holotype (PVL 4021), an isolated tibiotarsus and partial
tarsometatarsus from the Late Cretaceous (Maastrichtian) Lecho Formation, Argentina.

Lenesornis maltshevskyi (Nessov, 1986; Kurochkin, 1996) – Data on this taxon comes
from published photos of the only known specimen of this taxon (PO 3434), a partial
synsacrum from the Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum
Desert of Uzbekistan.

Longchengornis sanyanensis (Hou, 1997a) – Data on this species comes from firsthand
study of the only known specimen, a partial skeleton (IVPP V10530) from the Early
Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Longicrusavis houi (O’Connor et al., in press) – Data on this species comes from casts as
well as firsthand study of the holotype, a nearly complete skeleton preserved as voids in a
474 
slab and counterslab (PKUP V1069) from the Early Cretaceous (Hauterivian –
Barremian, 128 Ma) Yixan Formation, Liaoning, China.

Longipteryx chaoyangensis (Zhang et al., 2000) – Data on this species comes from
firsthand study of the holotype, a nearly complete skeleton (IVPP V12325), and a nearly
complete referred specimen (IVPP V12552), both from the Early Cretaceous (Aptian)
Jiufotang Formation, Liaoning, China.

Longipteryx sp. DNHM D2566 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2566), a nearly
complete specimen in a single slab from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China.

Longipteryx sp. DNHM D2889 (unpublished) – Data on this taxon comes from
observations of the only known specimen of this taxon (DNHM D2889), a nearly
complete specimen in a single slab from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China.

Longirostravis hani (Hou et al., 2003) – Data on this species comes from firsthand study
of the holotype, a nearly complete skeleton (IVPP V11309) from the Early Cretaceous
(Hauterivian – Barremian, 128 Ma) Yixan Formation, Liaoning, China.

Martinavis cruzyensis (Walker et al., 2007) – Data on this taxon comes from published
photos and data of the holotype (ACAP-M-1957), a humerus from Late Cretaceous (Late
Campanian – Early Maastrichtian) deposits in Massecaps, Cruzy, France.

Martinavis vincei (Walker et al., 2007) – Data on this taxon comes from published photos
and data of the only known specimen of the holotype (PVL 4054), a humerus from the
Late Cretaceous (Maastrichtian) Lecho Formation, Argentina.

Nanantius eos (Molnar, 1986) – Data on this taxon, a partial tibiotarsus from the Early
Cretaceous (Albian) Toolebuc Formation in Australia, comes from a partial cast of the
holotype and published data. The holotype is lost and has not resurfaced at the time of
this publication.

Neuquenornis volans (Chiappe, 1992) – Data on this taxon, a partial skeleton (MUCPv
142) from the argentine Late Cretaceous (Campanian) Rio Colorado Formation, comes
from casts and published data (Chiappe and Calvo, 1994).

Noguerornis gonzalezi (Lacasa-Ruiz, 1989) – Data on this taxon comes from publications
on the holotype (LP 1702), a partial skeleton from the Early Cretaceous (Lower
Hauteverian?) La Pedrera de Rubies Lithographic Limestones, Spain (Chiappe and
Lacasa-Ruiz, 2002).

475 
Otogornis genghisi (Dong, 1993) – Data on this species comes from firsthand study of
the holotype (IVPP V9607), a partial skeleton from the Early Cretaceous Yijinhuoluo
Formation, Inner Mongolia, China.

Patagopteryx deferrarisii (Alvarenga and Bonaparte, 1992) – Data on this taxon comes
from publications (Chiappe and Alvarenga, 2002) and casts of the holotype (MACN-N 3,
11), a partial specimen from the Late Cretaceous (Campanian) Rio Colorado Formation,
Neuquen, Argentina.

Paraprotopteryx gracilis (Zheng et al., 2007) – Data on this taxon comes from
publications on the holotype (STM V001), a partial skeleton from the Early Cretaceous
(Hauterivian – Barremian) Yixian Formation, Hebei, China.

Pengornis houi (Zhou et al., 2008) – Data on this species comes from firsthand study of
the holotype (IVPP V15336), a nearly complete skeleton from the Early Cretaceous
(Aptian) Jiufotang Formation, Liaoning, China.

Protopteryx fengningensis (Zhang et al., 2001) – Data on this species comes from
firsthand study of the holotype (IVPP V11665), a nearly complete skeleton from the
Early Cretaceous (Hauterivian) Dabeigou Formation, Hebei, China.

Rahonavis ostromi (Forster et al., 1998) – Data on this taxon, known only from a
disarticulated partial skeleton (UA 8656) from the Late Cretaceous (Maastrichtian)
Maevarano Formation in Madagascar, was studied from casts and publications.

Rapaxavis pani (Morschhauser et al., 2009) – Data on this taxon comes from
observations of the only known specimens of this taxon (DNHM D2522), a nearly
complete and fully articulated specimen from the Early Cretaceous (Aptian) Jiufotang
Formation, Liaoning, China.

Sapeornis chaoyangensis (Zhou and Zhang, 2002b) – Data on this taxon comes from
published data on the holotype (IVPP V12698) and two later referred species (IVPP
V13275, V13276), all from the Early Cretaceous (Aptian) Jiufotang Formation of
Liaoning, China. Two additional unpublished specimens were used to supplement this
information (DNHM D1197, D2523).

Sazavis prisca (Nessov and Jarkov, 1989) – Data on this taxon comes from published
photos of the only known specimen of this taxon (PO 3472), a distal tibiotarsus from the
Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum Desert of Uzbekistan.

Shanweiniao cooperorum (O’Connor et al., 2009) – Data on this taxon comes from
firsthand study of the only known specimen of this taxon (DNHM D1878 ½), a nearly
complete skeleton preserved in slab and counterslab from the Early Cretaceous
(Hauterivian – Barremian) Yixian Formation, Liaoning, China.
476 

Sinornis santensis (Sereno and Rao, 1992) – Data on this taxon comes from publications
(Sereno et al., 2002) and casts of the holotype (BNHM BPV 538a), a nearly complete
skeleton from the Early Cretaceous (Aptian) Jiufotang Formation, Liaoning, China.

Soroavisaurus australis (Chiappe, 1993) – Data on this taxon comes from firsthand study
of the holotype (PVL 4690), a tarsometatarsus, and the assigned tibiotarsus (PVL 4048)
from the Late Cretaceous (Maastrichtian) Lecho Formation, Argentina.

Yixianornis grabaui (Zhou and Zhang, 2001) – Data on this taxon comes from firsthand
study of the holotype (IVPP V12631), a nearly complete specimen in a single slab from
the Early Cretaceous (Hauterivian – Barremian) Yixian Formation, Liaoning, China.

Yungavolucris brevipedalis (Chiappe, 1993) – Data on this taxon comes from firsthand
study of the holotype (PVL 4653), a complete tarsometatarsus, and the referred material
(PVL 4040, 4052, 4692, and 4268), all from the Late Cretaceous (Maastrichtian) Lecho
Formation, Argentina.

Zhongornis haoae (Gao et al., 2008) – Data on this taxon comes from firsthand study of
the only known specimen (DNHM D2455/6), a nearly complete juvenile specimen
preserved in slab and counterslab from the Early Cretaceous Yixian (Hauterivian –
Barremian) Formation, Liaoning, China.

Zhyraornis kashkarovi (Nessov, 1984) – Data on this taxon comes from published photos
of the only known specimen of this taxon (TsNIGRI 42/11915), a partial synsacrum from
the Late Cretaceous (Conacian) Bissekty Formation in the Kyzyl kum Desert of
Uzbekistan. Given that no differences could be discerned from photographs, Zhyraornis
logunovi (PO 4600; Nessov, 1984), another partial synsacrum from the Late Cretaceous
(Conacian) Bissekty Formation in the Kyzyl kum Desert of Uzbekistan, information from
this specimen was also scored for Z. kashkarovi.

477 
APPENDIX B: LIST OF CHARACTERS AND CHARACTER STATES

Skull

1. Premaxillae in adults: unfused (0); fused only rostrally (1); completely fused (2).
(ORDERED)

2. Maxillary process of the premaxilla: restricted to its rostral portion (0); subequal or
longer than the facial contribution of the maxilla (1).

3. Frontal process of the premaxilla: short (0); relatively long, approaching the rostral
border of the antorbital fenestra (1); very long, extending caudally near the level of
lacrimals (2). (ORDERED)

4. Premaxillary teeth: present throughout (0); present but rostral tip edentulous (1); teeth
restricted to rostral half of bone (2); absent (3).

5. Caudal margin of naris: far rostral than the rostral border of the antorbital fossa (0);
nearly reaching or overlapping the rostral border of the antorbital fossa (1).

6. Naris longitudinal axis: considerably shorter than the long axis of the antorbital fossa
(0); subequal or longer (1). We are using the longitudinal axis of these structures as a
proxy for their relative size. The longitudinal axis is often easier to measure than the
actual area enclosed by either the naris or the antorbital fossa.

7. Nasals, degree of fusion: unfused (0); caudally fused (1); nearly or fully fused (2).

8. Nasal caudally expanded into a broad sheet: absent (0); present (1).

9. Nasal, maxillary process (descending ramus): present (0); absent (1).

10. Position of maxillary process on nasal: rostral third (0); midpoint (1); caudal third
(2).

11. Nasal and nasal process of premaxilla, articulation: restricted to rostral portion of
nasal (0); extends for at least 50% of the nasal length (1).

12. Maxillary teeth: present (0); absent (1).

13. Premaxillary process of maxilla: considerably shorter than the jugal process (0);
subequal (1); longer (2).

478 
14. Dorsal (ascending) ramus of the maxilla: present with two fenestra (the promaxilllary
and maxillary fenestra) (0); present with one fenestra (1); unfenestrated (2); absent (3).
(ORDERED)

15. Caudal margin of choana: located rostrally, not overlapping the region of the orbit
(0); displaced caudally, at the same level or overlapping the rostral margin of the orbit
(1).

16. Rostral margin of the jugal: away from the caudal margin of the naris (0); or very
close to (leveled with) the caudal margin of the naris (1).

17. Contact between palatine and maxilla/premaxilla: palatine contact maxilla only (0);
contacts premaxilla and maxilla (1).

18. Vomer and pterygoid articulation: present, well developed (0); reduced, narrow
process of pterygoid passes dorsally over palatine to contact vomer (1); absent, pterygoid
and vomer do not contact (2).

19. Contact between palatine and pterygoid: long, craniocaudally overlapping contact
(0); short, primarily dorsoventral contact (1).

20. Contact between vomer and premaxilla: present (0); absent (1).

21. Ectopterygoid: present (0); absent (1).

22. Postorbital: present (0); absent (1).

23. Contact between postorbital and jugal: present (0); absent (1).

24. Lateral, round cotyla on the mandibular process of the quadrate (quadratojugal
articulation): absent (0); present (1).

25. Squamosal incorporated into the braincase, forming a zygomatic process: absent (0);
present (1).

26. Squamosal, ventral or “zygomatic” process: variably elongate, dorsally enclosing
otic process of the quadrate and extending cranioventrally along shaft of this bone, dorsal
head of quadrate not visible in lateral view (0); short, head of quadrate exposed in lateral
view (1).

27. Frontal/parietal suture in adults: open (0); fused (1).

28. Quadrate, lateral view: straight (0); caudally concave, bowed (1).

479 
29. Quadrate orbital process (pterygoid ramus): broad (0); sharp and pointed (1).

30. Quadrate pneumaticity: absent (0); present (1).

31. Quadrate: articulating only with the squamosal (0); articulating with both prootic and
squamosal (1).

32. Otic articulation of the quadrate: articulates with a single facet (squamosal) (0);
articulates with two distinct facets (prootic and squamosal) (1); articulates with two
distinct facets and quadrate differentiated into two heads (2). (ORDERED)

33. Quadrate distal end: with two transversely aligned condyles (0); with a triangular,
condylar pattern, usually composed of three distinct condyles (1).

34. Basipterygoid processes: long (0); short (articulation with pterygoid subequal to, or
longer than, amount projected from the basisphenoid rostrum) (1).

35. Pterygoid, articular surface for basipterygoid process: concave “socket”, or short
groove enclosed by dorsal and ventral flanges (0); flat to convex (1); flat to convex facet,
stalked, variably projected (2). (ORDERED)

36. Eustachian tubes: paired, lateral, and well-separated from each other (0); paired,
close to each other and to cranial midline or forming a single cranial opening (1).

37. Osseous interorbital septum (mesethmoid): absent (0); present (1).

38. Deep excavations that shallow laterally on either side of the foramen magnum:
absent (0); present (1).

39. Shape of foramen magnum: circular (0); pentagonal (1).

40. Size of occipital condyle relative to the foramen magnum: greater than 15% (0); less
than 15% (1).

41. Dentary, caudal half ventrally concave: absent (0); present (1).

42. Dentary teeth: present (0); absent (1).

43. Dentary tooth implantation: teeth in individual sockets (0); teeth in a communal
groove (1).

44. Symphysial portion of dentaries: unfused (0); fused (1).

480 
45. Small ossification present at the rostral tip of the mandibular symphysis
(intersymphysial ossification): absent (0); present (1). Martin (1987:13) refers to this
ossification as the “predentary.” This term is inappropriate as it implies a homology
between this ossification and the predentary bone of ornithischian dinosaurs-a hypothesis
that is not supported by parsimony.

46. Caudal margin of dentary strongly forked: unforked, or with a weakly developed
dorsal ramus (0); strongly forked with the dorsal and ventral rami approximately equal in
caudal extent (1).

47. Cranial extent of splenial: stops well caudal to mandibular symphysis (0); extending
to mandibular symphysis, though noncontacting (1); extending to proximal tip of
mandible, contacting on midline (2). (ORDERED)

48. Meckel's groove (medial side of mandible): not completely covered by splenial, deep
and conspicuous medially (0); covered by splenial, not exposed medially (1).

49. Rostral mandibular fenestra: absent (0); present (1).

50. Caudal mandibular fenestra: present (0); absent (1). We regard the caudal mandibular
fenestra of neornithines as homologous to the surangular fenestra of non-avian dinosaurs
(Chiappe, 2002).

51. Articular pneumaticity: absent (0); present (1).

52. Tooth morphology: peg-like (0); recurved so that the apex of the tooth is slightly
caudal to the midpoint of the tooth's base (1); strongly recurved so that the apex of the
tooth is close to level with the caudal margin of the base of the tooth (2).

Axial Skeleton

53. Atlantal hemiarches in adults: unfused (0); fused, forming a single arch (1).

54. One or more pneumatic foramina piercing the centra of mid-cranial cervicals, caudal
to the level of the parapophysis-diapophysis: present (0); absent (1).

55. Cervical vertebrae: variably dorsoventrally compressed, amphicoelous (“biconcave”:
flat to concave articular surfaces) (0); cranial surface heterocoelous (i.e., mediolaterally
concave, dorsoventrally convex), caudal surface flat or slightly concave (1);
heterocoelous cranial (i.e., mediolaterally concave, dorsoventrally convex) and caudal
(i.e., mediolaterally convex, dorsoventrally concave) surfaces (2). (ORDERED)

56. Prominent carotid processes in the intermediate cervicals: absent (0); present (1).

481 
57. Postaxial cervical epipophyses: prominent, projecting further back from the
postzygapophysis (0); weak, not projecting further back from the postzygapophysis, or
absent (1).

58. Keel-like ventral surface of cervical centra: absent (0); present (1).

59. Prominent (50% or more the height of the centrum's cranial articular surface) ventral
processes of the cervicothoracic vertebrae: absent (0); present (1).

60. Thoracic vertebral count: 13-14 (0); 11-12 (1); fewer than 11 (2). The transition
between cervical and thoracic vertebrae is often difficult to identify, which makes
counting these vertebrae problematic. Here, thoracic vertebrae are defined as possessing
free, ventrally projecting ribs. When inarticulated, vertebral morphology should be used.
(ORDERED)

61. Thoracic vertebrae: at least part of series with subround, central articular surfaces
(e.g., amphicoelous/opisthocoelous) that lack the dorsoventral compression seen in
heterocoelous vertebrae (0); series completely heterocoelous (1).

62. Caudal thoracic vertebrae, centra, length and midpoint width: approximately equal in
length and midpoint width (0); length markedly greater than midpoint width (1).

63. Lateral side of the thoracic centra: weakly or not excavated (0); deeply excavated by
a groove (1); excavated by a broad fossa (2).

64. Cranial thoracic vertebrae, parapophyses: located in the cranial part of the centra of
the thoracic vertebrae (0); located in the central part of the centra of the thoracic
vertebrae (1).

65. Sacral vertebrae, number ankylosed (synsacrum): less than 7 (0); 7 (1); 8 (2); 9 (3);
10 (4); 11 or more (5); 15 or more (6). (ORDERED)

66. Synsacrum, procoelous articulation with last thoracic centrum (deeply concave facet
of synsacrum receives convex articulation of last thoracic centrum): absent (0); present
(1).

67. Cranial vertebral articulation of first sacral vertebra: approximately equal in height
and width (0); wider than high (1).

68. Series of short sacral vertebrae with dorsally directed parapophyses just cranial to the
acetabulum: absent (0); present, three such vertebrae (1); present, four such vertebrae (2).
(ORDERED)

482 
69. Synsacrum, axial groove running along ventral surface: absent (0); present for entire
length (1); present, restricted to the central sacrals, absent proximally and caudally (2).

70. Synsacrum, spinal crest (crista spinosa synsacri): absent (0); present, low and
subequal for entire length (1); present, prominent cranially, diminishing caudally (2).

71. Caudal synsacrum, transverse processes of vertebrae distally expanded: absent (0);
present, expanded but no contact (1); present, expanded so that the transverse processes
contact, 1-2 such vertebrae (2); present, 3 or more vertebrae with contacting transverse
processes (3). (ORDERED)

72. Convex caudal articular surface of the synsacrum: absent (0); present (1).

73. Degree of fusion of distal caudal vertebrae: fusion absent (0); few vertebrae partially
ankylosed (intervening elements are well discernable) (1); vertebrae completely fused
into a pygostyle (2). (ORDERED)

74. Proximal pygostyle: elements discernable and retaining processes (0); vertebrae
completely fused into a single element, individual elements cannot be discerned (1).

75. Free caudal vertebral count: more than 35 (0); 35-26 (1); 25 - 20 (2); 19-9 (3); 8 or
less (4). (ORDERED)

76. Procoelous caudals: absent (0); present (1).

77. Distal caudal vertebra prezygapophyses: elongate, exceeding the length of the
centrum by more than 25% (0); shorter (1); absent (2). (ORDERED)

78. Free caudals, length of transverse processes: approximately equal to, or greater than,
centrum width (0); significantly shorter than centrum width (1).

79. Proximal haemal arches: elongate, at least 3 times longer than wider (0); shorter (1);
absent (2). (ORDERED)

80. Pygostyle: longer than or equal to the combined length of the free caudals (0);
shorter (1).

81. Cranial end of pygostyle dorsally forked: absent (0); present (1).

82. Cranial end of pygostyle with a pair of laminar, ventrally projected processes: absent
(0); present (1).

483 
83. Distal constriction of pygostyle: absent (0); present (1). In the pygostyles of some
enantiornithine taxa, the distal-most mediolateral width is reduced so that the midline of
the pygostyle projects distally farther than the lateral margins (Chiappe et al. 2002).

84. Ossified uncinate processes in adults: absent (0); present and free (1); present and
fused (2).

85. Gastralia: present (0); absent (1).

Thoracic Girdle

86. Coracoid shape: rectangular to trapezoidal in profile (0); strutlike (1).

87. Coracoid and scapula articulation: through a wide, sutured articulation (0); through
more localized facets (1).

88. Scapula: articulated at the shoulder (proximal) end of the coracoid (0); well below it
(1).

89. Humeral articular facets of the coracoid and the scapula: placed in the same plane
(0); forming a sharp angle (1).

90. Coracoid, acrocoracoid: straight (0); hooked medially (1).

91. Proximal end of coracoid with peg-like process (acrocoracoidal tubercle): absent (0);
present (1).

92. Laterally compressed shoulder end of coracoid, with nearly aligned acrocoracoid
process, humeral articular surface, and scapular facet, in dorsal view: absent (0); present
(1).

93. Proximal coracoid, medial margin: flat (0); slight medially directed bump (1); well-
developed (procoracoid) process (2). (ORDERED)

94. Coracoid, lateral margin: straight or concave (0); slightly convex (1); straight
proximally but convex distally (as it approaches the sternal margin) (2); straight
proximally and distally with a strongly convex area in between (3); strongly convex (4).

95. Coracoid, dorsal surface: excavation absent (0); shallow excavation (1); strongly
excavated so that the proximal end of the fossa is deep (2). (ORDERED)

96. Supracoracoidal nerve foramen of coracoid: centrally located (0); displaced toward
(often as an incisure) the medial margin of the coracoid (1); displaced so that it nerve no
longer passes through the coracoid (absent) (2). (ORDERED) In some taxa the n.
484 
supracoracoideus does not pierce the coracoid, but is assumed to pass medially at the
level between the bone's midpoint and its glenoid (humeral articular facet).

97. Coracoid, medial surface, strongly depressed elongate furrow at the level of the
passage of n. supracoracoideus: absent (0); present (1).

98. Supracoracoid nerve foramen, location relative to dorsal coracoidal fossa: above
fossa (0); inside fossa (1).

99. Coracoid, lateral process (sternocoracoidal process): absent (0); weakly developed,
lateral corner of coracoid slightly expanded (1); present as a well-developed, squared-off
process (2); present and with a distinct omal projection (hooked) (3). (ORDERED)

100. Coracoid, relative width to length: width approximately half the length or greater
(0); width between half to a third the length (1); width less than one third the length (2).
(ORDERED?)

101. Sternal margin of coracoid: convex (0); straight (1); slightly concave (2); strongly
concave (3).

102. Coracoid, lateral margin distinctly longer than medial margin so that the sternal
margin is strongly angled: absent (0); present (1).

103. Scapular shaft: straight (0); sagittally curved (1).

104. Scapula, length: shorter than humerus (0); as long as or longer than humerus (1).

105. Scapula, shaft kinked distal to the glenoid: absent (0); present (1).

106. Scapular acromion costolaterally wider than deeper: absent (0); present (1).

107. Scapula, acromion process: projected cranially surpassing the articular surface for
coracoid (facies articularis coracoidea; Baumel and Witmer, 1993) (0); projected less
cranially than the articular surface for coracoid (1).

108. Scapula, acromion process: straight (0); laterally hooked tip (1).

109. Scapula, acromion proximal margin: blunt (0); tapered (1).

110. Proximal end of scapula, pit between acromion and humeral articular facet: absent
(0); present (1).

111. Costal surface of scapular blade with prominent longitudinal furrow: absent (0);
present (1).
485 

112. Scapular caudal end: blunt (may or may not be expanded) (0); sharply tapered (1).

113. Furcula, shape: boomerang-shaped (0); V to Y-shaped (1); U-shaped (2).

114. Furcula, interclavicular angle: 90˚ - 70˚ (0); 70˚ - 50˚ (1); 50˚ - 30˚ (2).
(ORDERED?) The interclavicular angle is measured as the angle formed between three
points, one at the omal end of each rami and the apex located at the clavicular symphysis.

115. Dorsal and ventral margins of the furcula: subequal in width (0); ventral margin
distinctly wider than the dorsal margin so that the furcular ramus appears concave
laterally (1).

116. Hypocleideum: absent (0); present as a tubercle or short process (1); present as an
elongate process approximately 30% rami length (2); hypertrophied, exceeding 50% rami
length (3). ORDERED

117. Furcula, small ridge present on the ventral surface of hypocleideum: absent (0);
present (1).

118. furcula, hypocleideum and symphysial region, keeled dorsal surface: absent (0);
present (1)

119. Furcula rami, omal tips: straight (0); curved dorsally (1).

120. Furcula omal tips expanded in lateral view :absent (0); present (1).

121. Paired triangular ossifications present dorsolateral to the sternocoracoidal
articulation: absent (0); present (1). (UPO - Unidentified Pectoral Ossifications)

122. Sternum: unossified (0); partially ossified, coracoidal facets cartilaginous (1); fully
ossified (2). (ORDERED)

123. Ossified sternum: two flat plates (0); single flat element (1); single element, with
slightly raised midline ridge (2); single element, with projected carina (3). (ORDERED)

124. Ossified sternal carina: absent (0); present, restricted to caudal half of sternum (1);
caudally restricted but bifurcated proximally, converging on the midline to form a single
carina distally (2); present, reaching or nearly reaching the cranial margin of the sternum
(3).

125. Sternum, caudal margin, number of paired caudal trabecula: none (0); one (1); two
(2). The use of “lateral” and “medial” to identify the specific sternal processes is
abandoned here due to the difficulty of identifying trabecula when only one is present.
486 
Eoenantiornis is scored as a “?” due to the uncertain status of the sternal processes; it is
possible that the identified “lateral process” (Zhou et al. 2005) is actually the distal
humerus.

126. Sternum, outermost trabecula, shape: tips terminate cranial to caudal end of sternum
(0); tips terminate at or approaching caudal end of sternum (1); tips extend caudally past
the termination of the sternal midline (2).

127. Outer trabecula of sternum, distal end: tapered, expansions absent (0); simple bulb
or fan-like expansion (1); branched (2); complex, branching expansions (3).

128. Outer sternal trabecula: parallel or nearly parallel to the long axis of the sternum
(0); directed laterodistally so that the distal ends are located laterodistal to the rostral half
of the sternum (1).

129. Innermost trabecula of sternum: developed as a visible bump (0); present as a
straight process (1); curved medially (2).

130. Rostral margin of the sternum broad and rounded: absent (0); present (1).

131. Sternum, rostrolateral margin: smooth, continuous with parabolic rostral margin (0);
rostral and lateral margins meet to form a distinct corner that does not project laterally
relative to the lateral margin (1); sternocoracoidal processes well-developed with
prominent lateral or craniolateral projection (2). (ORDERED?)

132. Sternum lateral margin, medial constriction and caudolaterally projecting process
just proximal to the beginning of the outer trabecula: absent (0); present (1).

133. Sternum, coracoidal sulci spacing on cranial edge: widely separated mediolaterally
(0); adjacent (1); crossed on midline (2). (ORDERED?) In taxa such as Eoalulavis in
which the preserved sternum does not bear actual sulci, the placement of the coracoids
can be used to infer their position relative to the sternum.

134. Costal facets of the sternum: absent (0); present (1).

135. Sternal costal processes: three (0); four (1); five (2); six (3); seven (4); eight (5).
(ORDERED)

136. Sternal midline, caudal end: blunt W-shape (0); V-shape (1); elongate straight
projection (xiphoid process) (2); flat (3); rounded (4).

137. Sternum, caudal half, paired enclosed fenestra: absent (0); present (1).

138. Sternum, dorsal surface, pneumatic foramen (or foramina): absent (0); present (1).
487 

Thoracic Limb

139. Proximal and distal humeral ends: twisted (0); expanded nearly in the same plane
(1).

140. Humeral head: concave cranially and convex caudally (0); globe shaped,
craniocaudally convex (1).

141. Proximal margin of the humeral head concave in its central portion, rising ventrally
and dorsally: absent (0); present (1).

142. Humerus, proximocranial surface, well-developed circular fossa on midline: absent
(0); present (1).

143. Humerus, insertion of the m. coracobrachialis cranialis: absent (0); circular scar on
cranial surface (1).

144. Humerus with distinct transverse ligamental groove: absent (0); present (1).

145. Humerus, caudal surface: capital incision absent (0); present but shallows distally
and is delimited by a margin of the ventral tubercle (1); deep, extends through end of
ventral tubercle (2). (ORDER?)

146. Pneumatic fossa in the caudoventral corner of the proximal end of the humerus:
absent or rudimentary (0); well developed (1).

147. Humerus, deltopectoral crest: projected dorsally coplanar with humeral head) (0);
projected cranially (1).

148. Humerus, deltopectoral crest: less than shaft width (0); approximately same width
(1); prominent and subquadrangular (i.e., subequal length and width) (2).

149. Humerus, deltopectoral crest, perforated by a large fenestra: absent (0); present (1).

150. Humerus, deltopectoral crest: quadrangular, dorsal margin nearly parallel to the
humeral shaft, distally ending abruptly (0); rounded and tapered into the shaft distally
(1).

151. Humerus, bicipital crest: little or no cranial projection (0); developed as a cranial
projection relative to shaft surface in ventral view (1); hypertrophied, rounded
tumescence (2).

488 
152. Humerus, distal end of bicipital crest, pit-shaped fossa for muscular attachment:
absent (0); craniodistal on bicipital crest (1); directly ventrodistal at tip of bicipital crest
(2); caudodistal, variably developed as a fossa (3).

153. Distal end of the humerus very compressed craniocaudally: absent (0); present (1).

154. Distal humerus expanded: absent (0); dorsally (1); transversely (2).

155. Humerus, demarcation of muscle origins (e.g., m. extensor metacarpi radialis in
Aves) on the dorsal edge of the distal humerus: no indication (0); indication as a pit-
shaped scar or facet (1); developed into variably projecting tubercle (dorsal
supracondylar process) (2).

156. Well-developed brachial depression on the cranial face of the distal end of the
humerus: absent (0); present (1). We interpret the brachial fossa not as a depression on
the craniodistal end of the humerus but as a distinct scar for muscle attachment.

157. Well-developed olecranon fossa on the caudal face of the distal end of the humerus:
absent (0); present (1).

158. Humerus, distal end, caudal surface, groove for passage of m. scapulotriceps:
absent (0); present (1).

159. Humerus, m. humerotricipitalis groove: absent (0); present as a well-developed
ventral depression contiguous with the olecranon fossa (1).

160. Humerus, distal margin: approximately perpendicular to long axis of humeral shaft
(0); ventrodistal margin projected significantly distal to dorsodistal margin, distal margin
angling ventrally (1); ventrodistal margin projected strongly distal to dorsodistal margin,
distal margin (distally expanded ventral epicondyle or well-developed flexor process) (2).

161. Humeral distal condyles: mainly located on distal aspect (0); on cranial aspect (1).

162. Humerus, long axis of dorsal condyle: at low angle to humeral axis, proximodistally
oriented (0); at high angle to humeral axis, almost transversely oriented (1).

163. Humerus, distal condyles: subround, bulbous (0); weakly defined, “strap-like” (1).

164. Humerus, ventral condyle: length of long axis of condyle less than the same
measure of the dorsal condyle (0); same or greater (1).

165. Ulna: shorter than humerus (0); nearly equivalent to or longer than humerus (1).

166. Ulnar shaft, radial-shaft/ulnar-shaft ratio: larger than 0.70 (0); smaller than 0.70 (1).
489 

167. Ulna, cotylae: dorsoventrally adjacent (0); widely separated by a deep groove (1).

168. Ulna, dorsal cotyla strongly convex: absent (0); present (1).

169. Ulna, bicipital scar: absent (0); developed as a slightly raised scar (1); developed as
a conspicuous tubercle (2).

170. Proximal end of the ulna with a well-defined area for the insertion of m. brachialis
anticus: absent (0); present (1).

171. Semilunate ridge on the dorsal condyle of the ulna: absent (0); present (1).

172. Shaft of radius with a long longitudinal groove on its ventrocaudal surface: absent
(0); present (1).

173. Ulnare: heart-shaped with little differentiation into short rami (0); U-shaped to V-
shaped, well-developed rami (1).

174. Ulnare, ventral ramus (crus longus, Baumel and Witmer, 1993): shorter than dorsal
ramus (crus brevis) (0); same length as dorsal ramus (1); longer than dorsal ramus (2).

175. Semilunate carpal and proximal ends of metacarpals in adults: unfused (0);
semilunate fused to the alular (I) metacarpal (1); semilunate fused to the major (II) and
minor (III) metacarpals (2); fusion of semilunate and all metacarpals (3). Any specimen
that is inferred to be a juvenile should be scored as a “?” in order to account for the
possibility of ontogenetic change.

176. Carpometacarpus, proximoventral surface: flat (0); raised ventral projection
contiguous with minor metacarpal (1); pisiform process as distinct peg-like projection
(2).

177. Carpometacarpus, ventral surface, supratrochlear fossa deeply excavating proximal
surface of pisiform process: absent (0); present (1).

178. Round-shaped alular metacarpal (I): absent (0); present (1).

179. Alular metacarpal (I), extensor process: absent, no cranioproximally projected
muscular process (0); present, tip of extensor process just surpassed the distal articular
facet for phalanx 1 in cranial extent (1); tip of extensor process conspicuously surpasses
articular facet by approximately half the width of facet, producing a pronounced knob
(2); tip of extensor process conspicuously surpasses articular facet by approximately the
width of facet, producing a pronounced knob (3). (ORDERED)

490 
180. Alular metacarpal (I), distal articulation with phalanx I: ginglymoid (0); shelf (1);
ball-like (2).

181. Metacarpal III, craniocaudal diameter as a percentage of same dimension of
metacarpal II: approximately equal or greater than 50% (0); less than 50% (1).

182. Proximal extension of metacarpal III: level with metacarpal II (0); ending distal to
proximal surface of metacarpal II (1).

183. Intermetacarpal process or tubercle on metacarpal II: absent (0); present as scar (1);
present as tubercle or flange (2).

184. Intermetacarpal space: absent or very narrow (0); at least as wide as the maximum
width of minor metacarpal (III) shaft (1).

185. Intermetacarpal space: reaches proximally as far as the distal end of metacarpal I
(0); terminates distal to end of metacarpal I (1).

186. Distal end of metacarpals: unfused (0); partially or completely fused (1).

187. Carpometacarpus, distal contact between major and minor metacarpals: short,
contact for less than 1/4 length of major metacarpal (0); long, abutting or fused for nearly
a third or more of the major metacarpal length (1); intermetacarpal space absent,
metacarpals abut along entire length (2).

188. Minor metacarpal (III) projecting distally more than the major metacarpal (II):
absent (0); present (1).

189. Distal end of metacarpal III, ventral surface with small tubercle: absent (0); present
(1).

190. Alular digit (I): long, exceeding the distal end of the major metacarpal (0); subequal
(1); short, not surpassing this metacarpal (2). (ORDERED)

191. Proximal phalanx of major digit (II): of normal shape (0); flat and craniocaudally
expanded (1).

192. Intermediate phalanx of major digit (II): longer than proximal phalanx (0); shorter
than or equivalent to proximal phalanx (1).

193. Ungual phalanx of major digit (II): present (0); absent (1).

491 
194. Ungual phalanx of major digit (II): larger or subequal to other manual claws (0);
smaller than the alular ungual but larger than that of the minor (which may or may not be
present) (1); much smaller than the unguals of the alular (I) and minor (III) digits (2).

195. Ungual phalanx of minor digit (III): present (0); absent (1).

196. Length of manus (semilunate carpal + major metacarpal and digit) relative to
humerus: longer (0); subequal (1); shorter (2). (ORDERED)

Pelvic Girdle

197. Intermembral index = (length of humerus + ulna)/(length of femur + tibiotarsus):
less than 0.7, flightless (0); between 0.7 and 0.9 (1); between 0.9 and 1.1 (2); greater than
1.1 (3).

198. Pelvic elements in adults, at the level of the acetabulum: unfused or partial fusion
(0); completely fused (1).

199. Ilium, dorsal crest (iliac crista dorsalis) contacting on midline: absent (0); present
(1).

200. Preacetabular process of ilium twice as long as postacetabular process: absent (0);
present (1).

201. Preacetabular ilium: approach on midline, open, or cartilaginous connection (0); co-
ossified, dorsal closure of “iliosynsacral canals” (1).

202. Ilium, m. cuppedicus fossa as broad, mediolaterally oriented surface directly
cranioventral to acetabulum: present (0); surface absent, insertion variably marked by a
small entirely lateral fossa cranial to acetabulum (1).

203. Preacetabular pectineal process (Baumel and Witmer, 1993): absent (0); present as
a small flange (1); present as a well projected flange (2). (ORDERED)

204. Small acetabulum, acetabulum/ilium length ratio equal to or smaller than 0.11:
absent (0); present (1).

205. Prominent antitrochanter: caudally directed (0); caudodorsally directed (1). (typical
enantiornithine condition is with the AT above the acetabulum dorsal margin and
caudodorsally oriented)

206. Postacetabular process shallow, less than 50% of the depth of the preacetabular
wing at the acetabulum: absent (0); present (1).

492 
207. Iliac brevis fossa: present (0); absent (1).

208. Ischium, in lateral view: strap-like (0); curved, scimitar-shaped (1).

209. Ischium, lateral crest: absent (0); located along dorsal margin (1); centered on the
corpus (2).

210. Ischium: projects caudally (0); curved medially (1).

211. Ischium: approximately equal width entire length, distal end blunt (0); tapered
distally (1); expanded distally (2).

212. Obturator process of ischium: prominent (0); reduced or absent (1). The ischium of
Archaeopteryx is forked distally; the thicker cranioventrally oriented fork is here
interpreted to be the obturator process.

213. Ischium, caudal demarcation of the obturator foramen: absent (0); present,
developed as a small flange or raised scar contacting/fused with pubis and demarcating
the obturator foramen distally (1).

214. Ischium, dorsal process: absent (0); located proximally (1); located at, or more
distal, to the midpoint (2).

215. Ischium, dorsal process: does not contact postacetabular ilium (0); contacts and
completely demarcates a fenestra but unfused (1); fused to ilium (ilioschiadic fenestra)
(2) .

216. Ischiadic terminal processes forming a symphysis: present (0); absent (1).

217. Ischium: two-thirds or less the length of the pubis (0); more than two-thirds the
length of the pubis (1).

218. Orientation of proximal portion of pubis: cranially to subvertically oriented (0);
retroverted, separated from the main synsacral axis by an angle ranging between 65º and
45º (1); more or less parallel to the ilium and ischium (2). (ORDERED)

219. Pubic pedicel of ilium very compressed laterally and hook-like: absent (0), present
(1).

220. Pubic shaft laterally compressed throughout its length: absent (0); present (1).

221. Pubic apron: one-third or more the length of the pubis (0); shorter (1); absent
(absence of symphysis) (2). (ORDERED)

493 
222. Pubic foot: present (0); absent (1).

Pelvic Limb

223. Femur with distinct fossa for the capital ligament: absent (0); present (1).

224. Femoral neck: present (0); absent (1).

225. Femoral anterior trochanter: separated from the greater trochanter (0); fused to it,
forming a trochanteric crest with a convex lateral surface (1); fused to it, forming a
trochanteric crest with a flattened lateral surface (2).

226. Femoral trochanteric crest: projects proximally beyond femoral head (0); equal in
proximal projection (1); does not project beyond femoral head (2).

227. Femoral posterior trochanter: present, developed as a slightly projected tubercle or
flange (0); hypertrophied, “shelf-like” conformation (1) (in combination with
development of the trochanteric shelf; see Hutchinson, 2001); absent (2).

228. Femur with prominent patellar groove: absent (0); present as a continuous extension
onto the distal shaft (1); present and separated from the shaft by a slight ridge, giving it a
pocketed appearance (2).

229. Femur: ectocondylar tubercle and lateral condyle separated by deep notch (0);
ectocondylar tubercle and lateral condyle contiguous but without developing a
tibiofibular crest (1); tibiofibular crest present, defining laterally a fibular trochlea (2).
Proximal to the lateral condyle in theropod dinosaurs there is a caudal projection known
as the ectocondylar tubercle (Welles, 1984). It is hypothesized that this tubercle is
homologous to the precursor to the tibiofibular crest, formed through the connection of
the ectocondylar tubercle and the lateral condyle (Chiappe 1996). (ORDERED)

230. Caudal projection of the lateral border of the distal end of the femur, proximal and
contiguous to the ectocondylar tubercle, lateral condyle or tibiofibular crest: absent (0);
present (1).

231. Femoral popliteal fossa distally bounded by a complete transverse ridge: absent (0);
present (1).

232. Fossa for the femoral origin of m. tibialis cranialis: absent (0); present (1).

233. Tibia, calcaneum, and astragalus: unfused or poorly co-ossified (sutures still
visible) (0); tightly co-ossified but ascending process of the astragalus forms a raised
surface (1); completely incorporated into tibiotarsus (2).

494 
234. Round proximal articular surface of tibiotarsus: absent (0); present (1).

235. Tibiotarsus, proximal articular surface: flat (0); angled so that the medial margin is
elevated with respect to the lateral margin (1).

236. Tibiotarsus, cnemial crests: absent (0); present, one (1); present, two (2).
(ORDERED)

237. Tibiotarsus, single cnemial crest: low, poorly developed (0); prominent, well
developed (1).

238. Tibia, caudal extension of articular surface for distal tarsals/tarsometatarsus: absent,
articular restricted to distalmost edge of caudal surface (0); well-developed caudal
extension, sulcus cartilaginis tibialis of Aves (Baumel and Witmer, 1993), distinct
surface extending up the caudal surface of the tibiotarsus (1); with well-developed,
caudally projecting medial and lateral crests (2). (ORDERED)

239. Extensor canal on tibiotarsus: absent (0); present as an emarginate groove (1);
groove bridged by an ossified supratendinal bridge (2). (ORDERED)

240. Tibia/tarsal-formed condyles: medial condyle projecting farther cranially than
lateral condyle (0); equal in cranial projection (1).

241. Tibia/tarsal-formed condyles, mediolateral widths: medial condyle wider (0);
approximately equal (1); lateral condyle wider (2). (ORDERED)

242. Tibia/tarsal-formed condyles: gradual sloping of condyles towards midline of
tibiotarsus (0); no tapering of either condyle (1). Circular condyles that contact medially
and thus "taper" towards each other are here considered (1). This character refers to the
morphology in which one or both (typically the lateral) condyles are slightly triangular
medially, thus tapering towards the midline (i.e. Lectavis). This character is used
differently by Clarke et al. (2002); characters that would be scored as a (1) by Clarke are
also here considered (1), however the only distinctly asymmetrical condyles narrowing
towards the midline are scored as (0).

243. Tibiotarsus, proximal margin of condyles at contact with tibiotarsus: gentle, smooth
margin (0); sharp, incised (1).

244. Tibiotarsus, distal condyles: contacting (0); non-contacting, separated by a narrow
intercondylar incisure (1); incisure wide, approximately 1/3 the width of the distal
tibiotarsus (2).

495 
245. Tibiotarsus, projection of distal condyles: medial and lateral approximately equal in
distal projection (0); medial condyle projects further than lateral (1); lateral projects
further than medial (2).

246. Tibiotarsus, lateral epicondylar depression (depressio epicondylaris lateralis):
absent (0); present (1)

247. Tibiotarsus, distal end, lateral margin, tubercle dorsally closing the epicondylar
depression: absent (0); present (1)

248. Distal tibiotarsus, medial surface of medial condyle deeply excavated by a pit-like
epicondylar depression (depressio epicondylaris medialis): absent (0); present (1).

249. Proximal end of the fibula: prominently excavated by a medial fossa (0); nearly flat
(1).

250. Fibula, tubercle for m. iliofibularis: craniolaterally directed (0); laterally directed
(1); caudolaterally or caudally directed (2). (ORDERED)

251. Fibula, distal end reaching the proximal tarsals: present (0); absent (1).

252. Distal tarsals in adults: free (0); completely fused to the metatarsals (1). Any
specimen that is inferred to be a juvenile should be scored as a “?” in order to account for
the possibility of ontogenetic change.

253. Metatarsals II-IV, intermetatarsal fusion: absent or minimal co-ossification (0);
partial fusion (sutural contacts easily discernable) (1); completely (or nearly completely)
fused (sutural contacts absent or poorly demarcated) (2). (ORDERED)

254. Proximal end of metatarsus: plane of articular surface perpendicular to longitudinal
axis of metatarsus (0); strongly inclined dorsally (1).

255. Tarsometatarsus. proximal articular surface with cranially convex and caudally
concave margins (kidney shaped): absent (0); present (1).

256. Metatarsal V: present (0); absent (1).

257. Well-developed tarsometatarsal intercotylar eminence: absent (0); present, low and
rounded (1); present, high and peaked (2).

258. Metatarsals, relative mediolateral width: metatarsal IV approximately the same
width as metatarsals II and III (0); metatarsal IV narrower than metatarsals II and III (1);
metatarsal IV greater in width than either metatarsal II or III (2).

496 
259. Proximal end of metatarsal III: in the same plane as metatarsals II and IV (0);
plantarly displaced with respect to metatarsals II and IV (1).

260. Strong transverse convexity of dorsal surface of mid-shaft of metatarsal III: absent
(0); present (1).

261. Proximal plantar surface of tarsometatarsus: flat (0); plantarly projecting tubercle
present (1); well developed, smooth plantarly projected surface (2); well-developed
surface with projected grooves and ridges (3). (ORDERED)

262. Plantar surface of tarsometatarsus excavated: absent (0); present (1). (Excavation
can result from a # of morphs - keeled II and IV included)

263. Metatarsal II, plantar surface: flat or rounded (0); proximal half keeled (1); mid-
shaft keeled (2).

264. Metatarsal IV mediolaterally compressed so that the plantolateral margin is keeled
mid-shaft: absent (0); present (1).

265. Tarsometatarsal proximal vascular foramen/foramina: absent (0); one between
metatarsals III and IV (1); two (2).

266. Tarsometatarsus, distal vascular foramen between metatarsals III and IV: absent (0);
demarcated but open distal contact between metatarsals III and IV (1); fully developed,
completely closed distally by fusion of metatarsals III and IV (2).

267. Metatarsal II tubercle (associated with the insertion of the tendon of the m. tibialis
cranialis in Aves): absent (0); present, developed on the craniomedial margin of
metatarsal II (1); present, on approximately the center of the proximodorsal surface of
metatarsal II (2); present, developed on lateral surface of metatarsal II, at contact with
metatarsal III or on lateral edge of metatarsal III (3).

268. Tarsometatarsus, dorsal tubercle for the m. tibialis cranialis (on metatarsal II or III):
located just distal to the proximal articular surface (0); located approximately 1/3 down
the shaft of metatarsal II (1); located approximately at the midpoint (2).

269. Relative position of metatarsal trochlea: trochlea III more distal than trochlea II and
IV (0); trochlea III at same level as trochlea IV, both more distal than trochlea II (1);
trochlea III at same level as trochlea II and IV (2); distal extent of trochlea III
intermediate to trochlea IV and II where trochlea IV projects furthest distally (3).

270. Metatarsal II, distal extent of metatarsal II relative to metatarsal IV: approximately
equal in distal extent (0); metatarsal II shorter than metatarsal IV but reaching distally
497 
farther than base of metatarsal IV trochlea (1); metatarsal II shorter than metatarsal IV,
reaching distally only as far as base of metatarsal IV trochlea (2).

271. Metatarsal II, distal end: trochlea in same plane as III and IV (0); plantarly
displaced with respect to metatarsal III and IV (1); metatarsal II strongly displaced
plantarly with respect to III and IV, such that there is little or no overlap in medial view
(2). (ORDERED)

272. Metatarsal IV trochlea: in same plane as II and III (0); plantarly displaced with
respect to metatarsal III (1).

273. Trochlea of metatarsal II broader than the trochlea of metatarsal III: absent (0);
present (1).

274. Distal end of metatarsal II strongly curved medially: absent (0); present (1).

275. Metatarsal IV, distal end deflected laterally: absent (0); present (1).

276. Metatarsal III, trochlea in plantar view, proximal extent of lateral and medial edges
of trochlea: trochlear edges approximately equal in proximal extent (0); medial edge
extends farther (1).

277. Metatarsal III, lateral trochlea: equal to medial trochlea in distal projection (0);
projects distally farther (1); projects less distally than medial (2).

278. Medial rim of trochlea of metatarsal III with strong plantar projection: absent (0);
present (1).

279. Metatarsal I: straight (0); J-shaped, the articulation of the hallux is located on the
same plane as the attachment surface of the metatarsal I (1); J-shaped; the articulation of
the hallux is perpendicular to the attachment surface (2); the distal half of the metatarsal I
is laterally deflected so that the laterodistal surface is concave (3).

280. Metatarsal I articular surface: flat (0); concave (1).

281. Completely reversed hallux (arch of ungual phalanx of digit I opposing the arch of
the unguals of digits II-IV): absent (0); present (1).

282. Size of claw of hallux relative to other pedal claws: shorter, weaker, and smaller
(0); similar in size (1); longer, more robust, and larger (2).

283. Unguals lateral surface with laterally projecting ridge: absent (0); limited to central
portion of claw (1); extends for most of claw length, not including horny sheath but
shallows distally (2).
498 

284. Digit IV ungual, considerably smaller than the other pedal claws: absent (0); present
(1).

285. Alula: absent (0); present (1).

286. Fan-shaped feathered tail composed of more than two elongate rectrices: absent (0);
present (1).

APPENDIX C: CHARACTER MATRIX
The following lists the entire matrix coded for this project. The first column
indicates whether or not the operational taxonomic unit was included in the final analysis
(Y, yes; N, no). The numbers in the first row indicate the character for which the scorings
correspond. Characters highlighted in grey indicate the data from this character was not
optimized in the final analysis due to missing data.
 
499
Appendix C: Character Matrix Continued.
run Taxa\characters 1 2 3 4 5 6 7 8 9 10
Y Archaeopteryx (all ten) 0 0 0 0 0 0 0 1 0 0
Y Jeholornis prima [01] ? 2 3 1 1 ? ? ? ?
Y Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Y Zhongornis haoae ? ? ? 3 ? ? ? ? ? ?
Y Confuciusornis sanctus 1 0 2 3 1 1 0 0 ? ?
Y Sapeornis chaoyangensis 1 0 1 0 0 1 0 ? ? ?
Y Apsaravis ukhaana ? ? ? ? ? ? ? ? ? ?
Y Patagopteryx deferrariisi ? ? ? ? ? ? ? ? ? ?
Y Longicrusavis houi 1 0 [12] 0 1 ? [01] ? ? ?
Y Gansus yumenensis ? ? ? ? ? ? ? ? ? ?
Y Archaeorhynchus spathula 1 0 1 3 1 1 1 1 0 1
Y Yixianornis grabaui 1 1 2 1 ? ? ? ? ? ?
Y Ichthyornis dispar 2 1 [12] ? ? ? 0 0 ? ?
Y Hesperornis regalis 1 1 2 3 1 1 0 ? 0 1
Y Anas 2 1 2 3 0 1 0 0 ? ?
Y Gallus 1 1 2 3 1 1 0 1 0 1
Y Longipteryx chaoyangia ? 1 2 2 1 1 [01] 0 1 -
Y Rapaxavis pani [01] 0 2 2 ? ? 0 0 1 ?
Y Cathyaornis yandica [12] 0 [12] 0 ? ? [01] 1 0 0
Y Enan. n. sp. DNHM D2950/1 [01] 0 1 0 1 1 0 0 1 -
Y Dapingfangornis sentisorhinus [01] ? [12] 0 1 ? ? ? ? ?
Y Pengornis houi 0 0 [01] 0 1 1 [12] ? ? ?
Y Hebeiornis fengningensis ? 0 ? ? ? ? ? ? ? ?
Y Longirostravis hani [01] 0 2 2 ? ? 0 0 1 -
Y Longipteryx DNHM D2566 ? 0 2 2 1 ? [01] 1 0 [01]
Y Gobipteryx minuta 1 0 [12] 3 1 0 [01] ? 0 ?
Y Alethoalaornis agitornis ? ? ? 0 ? ? ? ? ? ?
N Longipteryx DNHM D2889 ? 0 2 2 1 1 [01] 0 1 -
Y Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Y Eoenantiornis buhleri [01] 0 1 0 ? ? 0 1 0 [01]
Y Protopteryx fengningensis [01] ? [12] [02] 1 ? ? 1 ? ?
N Enan. indet. DNHM D2952/3 [01] ? 1 ? ? ? ? ? ? ?
500
Appendix C: Character Matrix Continued.
run Taxa\characters 1 2 3 4 5 6 7 8 9 10
N Enan. indet. DNHM D2130 ? 0 1 0 1 ? [12] 0 1 -
Y Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Y Shanweiniao cooperorum [01] ? [12] [23] ? ? 0 ? ? ?
N Enan. indet. DNHM D2884 1/2 ? ? [12] 0 1 ? ? ? ? ?
Y Elsornis keni ? ? ? ? ? ? ? ? ? ?
Y Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Y Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
N Enan. indet. DNHM D2567/8 ? 0 2 0 ? ? [01] 1 ? ?
Y El Montsec Hatchling ? 0 1 0 1 1 ? 1 0 1
Y Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Y Eocathayornis walkeri ? ? ? 0 ? ? ? ? ? ?
N Enan. indet. DNHM D2836 ? 0 [12] 0 ? ? ? 1 ? ?
N Enan. indet. DNHM D2510/1 ? ? [12] [02] ? ? ? ? ? ?
Y Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
N Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
N Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
N Jibeinia luanhera ? ? ? [02] ? ? ? ? ? ?
N Cathayornis caudatus [12] 0 2 0 ? ? ? ? ? ?
N Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Y Enantiornis leali ? ? ? ? ? ? ? ? ? ?
N Cathayornis aberransis ? ? ? ? ? ? 0 1 0 [01]
Y Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
N Largirostrornis sexdentornis [12] 0 [12] 0 ? ? ? ? ? ?
N Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
N Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
N Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
N Cuspirostrisornis houi 2 0 [12] [02] ? ? ? ? ? ?
Y Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
N Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Y Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Y Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Y Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
501
Appendix C: Character Matrix Continued.
run Taxa\characters 1 2 3 4 5 6 7 8 9 10
Y Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Y Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Y Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Y Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Y Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Y Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Y Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Y Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Y Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Y Nanantius eos ? ? ? ? ? ? ? ? ? ?
N Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
N Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
N Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
N Sazavis prisca ? ? ? ? ? ? ? ? ? ?
N Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
N Enantiornis martini ? ? ? ? ? ? ? ? ? ?
N Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
N Incolornis silvae ? ? ? ? ? ? ? ? ? ?
N Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
502
Appendix C: Character Matrix Continued.
Taxa\characters 11 12 13 14 15 16 17 18 19 20
Archaeopteryx (all ten) 0 0 1 0 0 0 0 0 0 ?
Jeholornis prima ? 1 ? ? ? ? ? ? ? ?
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? 1 ? ? ? ? ? ? ? ?
Confuciusornis sanctus 1 1 ? 1 ? 0 ? ? ? ?
Sapeornis chaoyangensis ? 0 ? [01] ? 0 ? ? ? ?
Apsaravis ukhaana ? ? ? ? ? ? ? ? ? ?
Patagopteryx deferrariisi ? ? ? ? ? ? ? ? ? ?
Longicrusavis houi 1 0 ? ? ? ? ? ? ? ?
Gansus yumenensis ? ? ? ? ? ? ? ? ? ?
Archaeorhynchus spathula ? 1 [01] [12] ? ? ? ? ? ?
Yixianornis grabaui ? ? ? ? ? ? ? ? ? ?
Ichthyornis dispar 1 0 ? ? ? ? ? ? ? ?
Hesperornis regalis 1 0 1 3 1 1 0 2 0 1
Anas 1 1 2 3 1 0 1 1 1 1
Gallus 1 1 ? 3 1 1 1 2 1 1
Longipteryx chaoyangia 1 1 2 ? ? ? ? ? ? ?
Rapaxavis pani 1 1 2 [012] ? ? ? ? ? ?
Cathyaornis yandica 1 0 ? [012] ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 1 0 1 2 ? ? ? ? ? ?
Dapingfangornis sentisorhinus ? ? 1 [012] ? ? ? ? ? ?
Pengornis houi 0 0 1 1 ? 0 ? ? ? ?
Hebeiornis fengningensis ? ? [01] [12] ? ? ? ? ? ?
Longirostravis hani 1 1 2 ? ? ? ? ? ? ?
Longipteryx DNHM D2566 1 1 ? 2 ? ? ? ? ? ?
Gobipteryx minuta 1 1 1 3 0 0 0 2 ? 1
Alethoalaornis agitornis ? 0 [01] [012] ? ? ? ? ? ?
Longipteryx DNHM D2889 1 1 2 [012] ? ? ? ? ? ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri 1 0 ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
503
Appendix C: Character Matrix Continued.
Taxa\characters 11 12 13 14 15 16 17 18 19 20
Enan. indet. DNHM D2130 0 ? ? [012] ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? 1 ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 1 0 ? ? ? ? ? ? ? ?
El Montsec Hatchling ? 0 0 [012] ? 0 ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? 0 ? [012] ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? [012] ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
504
Appendix C: Character Matrix Continued.
Taxa\characters 11 12 13 14 15 16 17 18 19 20
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
505
Appendix C: Character Matrix Continued.
Taxa\characters 21 22 23 24 25 26 27 28 29 30
Archaeopteryx (all ten) 0 0 1 0 0 ? 0 ? 0 ?
Jeholornis prima ? ? ? 0 ? ? ? ? ? ?
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? ? ? ? ? ? ? ? 0 ?
Confuciusornis sanctus 0 0 0 0 1 0 0 0 0 0
Sapeornis chaoyangensis ? 0 0 0 1 ? 0 ? ? ?
Apsaravis ukhaana ? ? ? ? ? ? ? ? ? ?
Patagopteryx deferrariisi ? 1 - 1 1 0 0 1 0 1
Longicrusavis houi ? ? ? ? ? ? ? ? ? ?
Gansus yumenensis ? ? ? ? ? ? ? ? ? ?
Archaeorhynchus spathula ? ? ? ? ? ? ? 0 ? ?
Yixianornis grabaui ? ? ? ? ? ? 0 ? ? ?
Ichthyornis dispar ? 1 - 1 1 ? ? 0 1 1
Hesperornis regalis 1 1 - 1 1 1 0 0 1 0
Anas 1 1 - 1 1 1 1 1 1 1
Gallus 1 1 - 1 1 1 1 1 1 1
Longipteryx chaoyangia ? ? ? ? ? ? ? ? ? ?
Rapaxavis pani ? ? ? ? ? ? ? 1 ? ?
Cathyaornis yandica ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 ? 0 ? ? ? ? 0 0 ? 1
Dapingfangornis sentisorhinus ? ? ? ? ? ? 0 ? ? ?
Pengornis houi ? 0 1 ? ? ? 0 1 ? 1
Hebeiornis fengningensis ? ? ? ? ? ? ? ? ? ?
Longirostravis hani ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2566 ? ? ? ? ? ? ? ? ? ?
Gobipteryx minuta 0 ? ? ? ? ? ? ? 0 ?
Alethoalaornis agitornis ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2889 ? ? ? ? ? ? 0 0 ? ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? ? ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? 0 0 ? ?
506
Appendix C: Character Matrix Continued.
Taxa\characters 21 22 23 24 25 26 27 28 29 30
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? 0 1 ? 0 1 ? 0 0 ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? ? ? ? ? ? 0 0 ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? 0 ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? 0 ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? 0 ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
507
Appendix C: Character Matrix Continued.
Taxa\characters 21 22 23 24 25 26 27 28 29 30
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
508
Appendix C: Character Matrix Continued.
Taxa\characters 31 32 33 34 35 36 37 38 39 40
Archaeopteryx (all ten) 0 0 0 ? ? 0 ? ? ? ?
Jeholornis prima ? ? ? ? ? ? ? ? ? ?
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? ? ? ? ? ? ? ? ? ?
Confuciusornis sanctus 1 2 0 ? ? ? 1 ? ? 0
Sapeornis chaoyangensis ? ? ? ? ? ? ? ? ? ?
Apsaravis ukhaana 1 [01] ? ? ? ? ? ? ? ?
Patagopteryx deferrariisi 1 1 1 ? ? ? ? 0 ? ?
Longicrusavis houi ? ? ? ? ? ? ? ? ? ?
Gansus yumenensis ? ? ? ? ? ? ? ? ? ?
Archaeorhynchus spathula ? ? ? ? ? ? ? ? ? ?
Yixianornis grabaui ? 1 ? 1 ? ? ? ? ? ?
Ichthyornis dispar 1 1 ? ? ? 0 1 ? ? 0
Hesperornis regalis 1 1 1 ? 1 ? 1 0 0 0
Anas 1 2 1 1 2 1 1 0 1 1
Gallus 1 2 1 1 2 1 1 0 0 1
Longipteryx chaoyangia ? ? ? ? ? ? ? ? ? ?
Rapaxavis pani ? ? ? ? ? ? ? ? ? ?
Cathyaornis yandica ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 ? ? ? ? ? ? ? 1 1 0
Dapingfangornis sentisorhinus ? ? ? ? ? ? ? ? ? ?
Pengornis houi ? ? ? ? ? ? ? ? ? ?
Hebeiornis fengningensis ? ? ? ? ? ? ? ? ? ?
Longirostravis hani ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2566 ? ? ? ? ? ? ? ? ? ?
Gobipteryx minuta ? ? 0 ? 1 ? ? ? ? ?
Alethoalaornis agitornis ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2889 ? ? ? ? ? ? ? ? ? ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? ? ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
509
Appendix C: Character Matrix Continued.
Taxa\characters 31 32 33 34 35 36 37 38 39 40
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? ? ? 0 0 1
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? 0 ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? 0 ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
510
Appendix C: Character Matrix Continued.
Taxa\characters 31 32 33 34 35 36 37 38 39 40
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
511
Appendix C: Character Matrix Continued.
Taxa\characters 41 42 43 44 45 46 47 48 49 50
Archaeopteryx (all ten) 0 0 0 0 0 0 0 0 0 0
Jeholornis prima 0 0 0 ? ? 0 0 ? 0 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? 1 - ? ? ? ? ? ? ?
Confuciusornis sanctus 0 1 - 1 0 1 ? 1 1 0
Sapeornis chaoyangensis 0 1 - 0 ? 0 ? ? 0 ?
Apsaravis ukhaana ? 1 - 1 ? 1 ? ? ? ?
Patagopteryx deferrariisi 0 ? ? ? ? ? ? ? 0 0
Longicrusavis houi 1 ? 0 0 1 0 ? ? 0 1
Gansus yumenensis ? ? ? ? ? ? ? ? ? ?
Archaeorhynchus spathula ? 1 - 0 ? 0 0 0 ? ?
Yixianornis grabaui ? 0 ? 0 1 1 ? ? ? ?
Ichthyornis dispar 0 0 0 1 ? 0 2 1 0 1
Hesperornis regalis 0 0 1 1 1 0 ? 1 0 1
Anas 0 1 - 1 - 0 0 1 0 1
Gallus 0 1 - 1 - 0 0 1 0 1
Longipteryx chaoyangia 1 0 0 0 ? 0 ? ? 0 1
Rapaxavis pani 0 0 0 0 0 ? ? ? ? 1
Cathyaornis yandica 0 0 0 0 ? 0 ? ? ? ?
Enan. n. sp. DNHM D2950/1 0 0 0 0 0 0 ? ? ? 1
Dapingfangornis sentisorhinus 1 0 0 0 ? 0 ? ? 0 1
Pengornis houi 0 0 0 0 0 ? ? ? ? ?
Hebeiornis fengningensis ? 0 0 0 ? 0 [12] 0 0 1
Longirostravis hani 1 0 0 ? ? 0 ? ? 0 1
Longipteryx DNHM D2566 1 0 0 ? ? 0 ? ? 0 ?
Gobipteryx minuta 0 1 - 0&1 ? 1 ? ? ? 1
Alethoalaornis agitornis 0 0 0 ? ? 0 ? ? ? 1
Longipteryx DNHM D2889 1 0 0 0 ? 0 ? ? 0 1
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? 0 0 ? ? ? ? ? ? ?
Protopteryx fengningensis 0 0 0 ? ? ? 0 ? ? ?
Enan. indet. DNHM D2952/3 1 0 0 ? ? 0 ? ? ? ?
512
Appendix C: Character Matrix Continued.
Taxa\characters 41 42 43 44 45 46 47 48 49 50
Enan. indet. DNHM D2130 0 0 0 ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum 0 ? ? 0 ? 0 ? ? 0 1
Enan. indet. DNHM D2884 1/2 0 0 0 ? ? 0 ? ? 0 ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? 0 0 0 ? ? ? ? 0 1
El Montsec Hatchling 0 0 0 ? ? 0 ? ? 1 0
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? 0 0 0 ? 0 ? ? ? ?
Enan. indet. DNHM D2836 0 0 0 ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? 0 0 ? ? 0 ? ? 0 1
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? 0 ? ? ? ? ? ? ? ?
Cathayornis caudatus ? 0 0 ? ? 0 ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? 0 0 0 ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? 0 ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? 0 0 0 ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
513
Appendix C: Character Matrix Continued.
Taxa\characters 41 42 43 44 45 46 47 48 49 50
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
514
Appendix C: Character Matrix Continued.
Taxa\characters 51 52 53 54 55 56 57 58 59 60
Archaeopteryx (all ten) ? 0 0 0 0 ? 1 0 0 0
Jeholornis prima ? 0 ? ? 0 ? ? ? ? 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? - ? ? ? ? ? ? ? 0
Confuciusornis sanctus 0 - 1 0 1 ? 1 0 1 [01]
Sapeornis chaoyangensis ? 0 ? ? ? ? 1 0 0 [01]
Apsaravis ukhaana ? ? ? 0 2 1 ? 1 ? 2
Patagopteryx deferrariisi 0 ? 1 1 2 1 1 0 1 1
Longicrusavis houi ? ? ? ? 1 1 ? 1 1 ?
Gansus yumenensis ? ? ? 1 2 1 ? 1 ? 2
Archaeorhynchus spathula 1 - ? ? 0 ? ? ? ? ?
Yixianornis grabaui ? [01] ? ? 1 ? 1 ? ? 2
Ichthyornis dispar 1 1 1 1 [01] 1 1 0 1 2
Hesperornis regalis 0 1 ? 1 2 1 0 0 1 2
Anas 1 - 1 0 2 1 1 0 1 2
Gallus 1 - 1 0 2 1 1 0 1 2
Longipteryx chaoyangia ? 2 ? ? 1 0 1 1 ? ?
Rapaxavis pani ? 0 ? ? ? ? ? 1 ? ?
Cathyaornis yandica ? [01] ? ? 1 ? ? 1 ? ?
Enan. n. sp. DNHM D2950/1 ? 1 ? ? ? 1 1 ? 0 ?
Dapingfangornis sentisorhinus ? 0 ? ? [01] ? ? 1 ? ?
Pengornis houi ? 1 1 ? 2 ? ? 1 ? ?
Hebeiornis fengningensis ? [01] ? ? 2 1 ? 1 ? ?
Longirostravis hani ? [12] ? ? 1 ? ? ? ? ?
Longipteryx DNHM D2566 ? 2 ? ? [12] 1 ? 1 ? ?
Gobipteryx minuta 0 - ? ? ? ? ? 1 ? ?
Alethoalaornis agitornis ? [01] ? ? ? ? 1 ? ? ?
Longipteryx DNHM D2889 ? 2 ? ? ? ? ? ? ? ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? 1 ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? [01] ? ? ? ? ? ? ? 1
Enan. indet. DNHM D2952/3 ? 0 ? ? [01] ? ? ? ? [12]
515
Appendix C: Character Matrix Continued.
Taxa\characters 51 52 53 54 55 56 57 58 59 60
Enan. indet. DNHM D2130 ? 0 1 ? [01] ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? 0 0 1 1 1 2
Shanweiniao cooperorum ? ? ? ? ? ? 1 ? ? ?
Enan. indet. DNHM D2884 1/2 ? 0 ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? [01] ? ? 1 0 ?
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? 1 ? ? 0 ? ? ? ? ?
El Montsec Hatchling ? 0 0 0 1 1 0 1 ? ?
Iberomesornis romerali ? ? ? ? 0 ? ? 1 1 1
Eocathayornis walkeri ? 0 ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? [01] ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? [01] ? ? ? ? ? ? ? [12]
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? [01] ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? 0 ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? 1 ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
516
Appendix C: Character Matrix Continued.
Taxa\characters 51 52 53 54 55 56 57 58 59 60
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
517
Appendix C: Character Matrix Continued.
Taxa\characters 61 62 63 64 65 66 67 68 69 70
Archaeopteryx (all ten) 0 0 0 0 0 0 ? 0 ? ?
Jeholornis prima 0 ? 0 0 0 ? ? ? ? 1
Rahonavis ostromi 0 ? 2 0 0 1 0 ? 0 2
Zhongornis haoae 0 1 0 ? [01] ? ? ? ? ?
Confuciusornis sanctus 0 1 2 0 1 0 0 0 ? 1
Sapeornis chaoyangensis 0 0 1 0 1 0 ? 0 1 1
Apsaravis ukhaana 0 1 0 0 4 ? ? 0 [12] ?
Patagopteryx deferrariisi 0 0 0 0 3 1 1 0 1 1
Longicrusavis houi 0 ? 2 0 ? ? ? ? ? ?
Gansus yumenensis 0 1 1 0 4 0 0 1 [02] 2
Archaeorhynchus spathula 0 ? ? ? 2 0 0 0 1 ?
Yixianornis grabaui 0 1 1 0 3 ? ? 0 ? ?
Ichthyornis dispar 0 1 2 0 [34] ? 0 1 [02] 2
Hesperornis regalis 1 1 2 0 4 0 1 0 1 1
Anas 1 1 0 0 6 0 1 2 2 2
Gallus 1 1 0 0 6 0 1 2 2 2
Longipteryx chaoyangia ? ? ? ? 2 ? ? ? ? ?
Rapaxavis pani 0 1 1 1 1 ? ? ? 1 ?
Cathyaornis yandica 0 ? 1 1 2 ? ? ? 1 [12]
Enan. n. sp. DNHM D2950/1 0 1 1 1 ? ? ? ? ? 1
Dapingfangornis sentisorhinus ? ? ? ? [01234] ? ? ? ? ?
Pengornis houi 0 ? 1 0 1 ? ? ? ? 1
Hebeiornis fengningensis 0 ? 1 ? 2 ? ? ? 1 ?
Longirostravis hani 0 ? ? ? 1 ? ? ? ? 1
Longipteryx DNHM D2566 ? ? ? ? [123] ? ? ? 0 ?
Gobipteryx minuta ? ? ? ? [012] 1 0 ? 1 1
Alethoalaornis agitornis ? ? ? ? [0123] ? ? ? ? 1
Longipteryx DNHM D2889 0 ? 1 ? [12] ? ? ? [01] ?
Concornis lacustris 0 1 1 1 ? ? ? ? 1 ?
Eoenantiornis buhleri ? ? ? ? [012] ? ? ? ? 1
Protopteryx fengningensis 0 ? ? ? 1 ? ? ? ? ?
Enan. indet. DNHM D2952/3 0 0 ? ? [12] ? ? ? 1 ?
518
Appendix C: Character Matrix Continued.
Taxa\characters 61 62 63 64 65 66 67 68 69 70
Enan. indet. DNHM D2130 ? ? 1 ? [12] ? ? ? ? ?
Eoalulavis hoyasi 0 0 2 ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? ? ? 1 ?
Enan. indet. DNHM D2884 1/2 0 0 ? ? ? ? ? ? ? 1
Elsornis keni 0 ? 1 0 ? ? ? ? ? ?
Sinornis santensis 0 ? 1 ? ? ? ? ? ? ?
Neuquenornis volans 0 ? 1 1 ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali 0 ? 0 0 0 0 1 ? ? ?
Eocathayornis walkeri 0 0 ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 0 0 1 ? 1 ? ? ? 0 ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis 0 ? 1 ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 0 1 [01] 1 ? 0 ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? [0123] ? ? ? ? 1
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? 1
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 0 ? ? ? [1234] ? ? ? ? 1
Enan. indet. CAGS-IG-06-CM-012 0 ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? [12345] ? ? ? 1 ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi 0 ? ? ? ? ? ? ? ? [12]
Halimornis thompsoni 0 ? 1 1 ? ? ? ? ? ?
519
Appendix C: Character Matrix Continued.
Taxa\characters 61 62 63 64 65 66 67 68 69 70
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? [123456] ? 1 ? 0 2
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? 1 ? 1 ?
520
Appendix C: Character Matrix Continued.
Taxa\characters 71 72 73 74 75 76 77 78 79 80
Archaeopteryx (all ten) ? 0 0 - 2 0 0 0 1 -
Jeholornis prima [12] ? 0 - 1 0 0 0 0 -
Rahonavis ostromi ? ? 0 - [0123] 0 0 0 1 -
Zhongornis haoae ? ? [01] - 3 0 ? 1 ? -
Confuciusornis sanctus [12] 0 2 1 4 0 0 0 ? 0
Sapeornis chaoyangensis 3 0 2 0 4 0 0 0 0 0
Apsaravis ukhaana [01] ? 2 1 4 ? 1 0 ? ?
Patagopteryx deferrariisi ? 1 ? ? ? 1 2 0 ? ?
Longicrusavis houi ? ? ? ? ? ? ? ? ? ?
Gansus yumenensis 2 0 2 1 4 ? 2 0 2 1
Archaeorhynchus spathula 1 ? ? ? [34] 0 1 1 1 ?
Yixianornis grabaui ? ? 2 1 4 ? ? ? ? 1
Ichthyornis dispar ? 0 2 1 4 0 1 0 2 1
Hesperornis regalis 0 ? 2 1 3 0 2 0 2 1
Anas 3 0 2 1 4 0 2 0 2 1
Gallus [12] 0 2 1 4 0 2 0 2 1
Longipteryx chaoyangia [12] ? 2 ? 4 ? ? 0 ? 0
Rapaxavis pani [12] 0 2 1 4 ? ? 0 ? 0
Cathyaornis yandica 1 ? 2 1 4 0 ? 0 ? 0
Enan. n. sp. DNHM D2950/1 [12] ? ? ? ? ? ? 0 ? ?
Dapingfangornis sentisorhinus ? 0 2 1 4 ? ? 0 ? ?
Pengornis houi 2 ? 2 ? 4 0 ? 0 [12] ?
Hebeiornis fengningensis 0 ? 2 1 ? ? ? ? ? ?
Longirostravis hani [123] ? 2 1 4 ? ? 0 ? 0
Longipteryx DNHM D2566 [123] ? [12] ? 4 ? ? 0 ? 0
Gobipteryx minuta ? ? [12] 0 4 0 1 ? ? ?
Alethoalaornis agitornis [01] ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2889 ? ? 2 1 4 ? ? 0 ? 0
Concornis lacustris ? ? ? ? ? 0 ? 0 1 ?
Eoenantiornis buhleri ? ? 2 ? 4 0 2 0 ? ?
Protopteryx fengningensis [12] ? 2 ? 4 ? ? ? ? 0
Enan. indet. DNHM D2952/3 [12] ? 2 1 4 ? ? 0 ? 0
521
Appendix C: Character Matrix Continued.
Taxa\characters 71 72 73 74 75 76 77 78 79 80
Enan. indet. DNHM D2130 1 ? 2 ? 4 ? ? 0 ? 0
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? 2 ? 4 ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? 2 1 4 ? ? ? ? 0
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? 2 1 4 0 ? 0 ? 0
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? [12] ? 4 0 ? 0 ? 0
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? 0 [12] 0 4 0 1 0 1 0
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? [12] ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 1 ? 2 ? 4 ? ? 0 ? 0
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? 2 1 4 ? ? ? 1 0
Jibeinia luanhera ? ? 2 ? ? ? ? 0 ? 0
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? [12] ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis [01] ? [12] ? ? ? ? 0 ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 [12] ? 2 ? 4 ? 0 0 ? 0
Enan. indet. CAGS-IG-06-CM-012 ? ? 2 1 ? ? ? ? ? ?
Cuspirostrisornis houi ? 0 2 1 [34] ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? [12] 0 ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? 2 1 ? 0 0 ? 2 ?
522
Appendix C: Character Matrix Continued.
Taxa\characters 71 72 73 74 75 76 77 78 79 80
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
523
Appendix C: Character Matrix Continued.
Taxa\characters 81 82 83 84 85 86 87 88 89 90
Archaeopteryx (all ten) - - - 0 0 0 0 0 0 0
Jeholornis prima - - - ? 0 1 1 0 ? 0
Rahonavis ostromi - - - ? ? ? 1 ? ? ?
Zhongornis haoae - - - ? 0 1 ? ? ? 0
Confuciusornis sanctus 0 0 0 1 0 1 0 0 0 0
Sapeornis chaoyangensis 0 ? 0 0 0 0 1 0 1 0
Apsaravis ukhaana ? ? ? ? ? 1 1 1 1 0
Patagopteryx deferrariisi ? ? ? ? ? 1 1 1 1 0
Longicrusavis houi ? ? ? ? ? 1 1 1 1 0
Gansus yumenensis 0 0 0 0 1 1 1 1 1 0
Archaeorhynchus spathula ? ? ? ? 0 1 1 1 ? 0
Yixianornis grabaui 0 0 0 [12] 0 1 1 1 1 0
Ichthyornis dispar 0 0 0 ? ? 1 1 1 1 1
Hesperornis regalis 0 0 0 1 ? 0 1 0 0 ?
Anas 0 0 0 2 1 1 1 1 1 1
Gallus 0 0 0 2 1 1 1 1 1 1
Longipteryx chaoyangia 1 ? 1 1 0 1 1 1 1 0
Rapaxavis pani ? ? 1 0 0 1 1 ? ? 0
Cathyaornis yandica 1 1 1 ? ? 1 1 1 ? 0
Enan. n. sp. DNHM D2950/1 ? ? ? ? 0 1 1 1 ? 0
Dapingfangornis sentisorhinus ? 1 1 ? 0 1 1 1 ? ?
Pengornis houi ? ? ? ? 0 1 1 1 ? ?
Hebeiornis fengningensis ? 0 0 ? 0 1 1 1 ? 0
Longirostravis hani 1 ? 1 0 0 1 1 1 ? ?
Longipteryx DNHM D2566 ? 1 1 ? ? 1 1 1 ? 0
Gobipteryx minuta ? ? ? ? ? 1 1 1 ? 0
Alethoalaornis agitornis ? ? ? ? ? 1 1 1 1 0
Longipteryx DNHM D2889 1 1 1 ? 0 1 1 1 1 ?
Concornis lacustris ? ? ? ? ? 1 1 1 1 0
Eoenantiornis buhleri ? ? ? 1 0 1 1 1 1 0
Protopteryx fengningensis ? ? 1 ? ? 1 1 1 ? 0
Enan. indet. DNHM D2952/3 ? 1 1 0 ? 1 1 ? ? ?
524
Appendix C: Character Matrix Continued.
Taxa\characters 81 82 83 84 85 86 87 88 89 90
Enan. indet. DNHM D2130 ? ? ? ? 0 1 1 ? ? 0
Eoalulavis hoyasi ? ? ? 0 ? 1 1 1 1 0
Shanweiniao cooperorum ? ? 1 ? 0 1 1 1 ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? 0 0 1 1 ? ? 0
Elsornis keni ? ? ? ? ? 1 1 1 1 0
Sinornis santensis 1 1 1 ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? 1 1 1 ? ?
Enan. indet. DNHM D2567/8 1 ? 1 ? 0 1 1 1 1 0
El Montsec Hatchling ? ? ? ? ? 1 1 ? ? 0
Iberomesornis romerali ? ? ? 0 ? 1 1 ? ? 0
Eocathayornis walkeri ? ? ? ? ? 1 1 ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? 0 1 1 ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? 0 0 1 1 ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? 1 1 1 1 0
Enan. indet. CAGS-IG-05-CM-004 ? 1 ? ? 0 ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? 1 1 ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? 1 1 1 ? ?
Enantiornis leali ? ? ? ? ? 1 1 1 1 0
Cathayornis aberransis ? ? ? ? ? 1 1 ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? 1 1 ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 1 1 ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? 1 ? ? 1 ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? 1 1 1 ? 0
Longchengornis sanyanesis 1 ? 1 ? ? 1 1 ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? 1 1 ? 1 ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni 1 1 1 ? ? ? 1 ? ? ?
525
Appendix C: Character Matrix Continued.
Taxa\characters 81 82 83 84 85 86 87 88 89 90
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? 1 1 ? 0
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? 1 1 1 1 ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? 1 ? ? ? ?
Enantiornis walkeri ? ? ? ? ? 1 1 1 ? 0
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? 1 1 ? 0
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? 1 ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
526
Appendix C: Character Matrix Continued.
Taxa\characters 91 92 93 94 95 96 97 98 99 100
Archaeopteryx (all ten) ? 0 0 0 0 0 0 - 0 0
Jeholornis prima ? 0 ? 0 0 1 ? - 1 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? 0 ? 0 0 ? ? - 0 0
Confuciusornis sanctus ? 0 0 0 0 ? ? - 0 ?
Sapeornis chaoyangensis ? 0 0 0 0 0 ? - 0 0
Apsaravis ukhaana 0 0 1 0 2 1 1 1 1 1
Patagopteryx deferrariisi 0 0 0 0 0 ? 0 - 1 ?
Longicrusavis houi 0 0 ? 0 [01] ? ? ? [12] 0
Gansus yumenensis 0 0 2 0 1 2 0 - 3 0
Archaeorhynchus spathula ? 0 [01] [01] ? 2 0 - [01] 0
Yixianornis grabaui 0 0 2 0 0 1 0 - 2 0
Ichthyornis dispar 0 0 2 0 1 1 0 - 2 0
Hesperornis regalis 0 0 2 0 1 1 0 - 0 0
Anas 0 0 2 0 0 2 0 - 2 1
Gallus 0 0 2 0 1 2 0 - 2 1
Longipteryx chaoyangia ? 1 0 0 ? ? ? ? 0 ?
Rapaxavis pani ? ? 0 0 ? [12] ? ? 0 0
Cathyaornis yandica ? ? ? [01] [01] ? ? ? 0 1
Enan. n. sp. DNHM D2950/1 ? ? 0 2 ? [12] ? ? 0 0
Dapingfangornis sentisorhinus ? ? [01] ? ? ? ? ? 0 ?
Pengornis houi ? ? 0 0 ? ? ? ? ? 0
Hebeiornis fengningensis ? ? 0 1 ? [12] ? ? 0 1
Longirostravis hani ? ? [01] 0 ? 2 ? ? 0 1
Longipteryx DNHM D2566 ? ? [01] 0 ? [12] ? ? 0 0
Gobipteryx minuta 0 1 ? 1 [12] ? ? ? 0 2
Alethoalaornis agitornis ? 1 ? 1 [01] ? ? - 0 1
Longipteryx DNHM D2889 ? ? [01] 2 ? ? ? ? 0 0
Concornis lacustris ? ? 0 2 ? 1 1 ? 0 1
Eoenantiornis buhleri ? 1 ? [01] ? 1 1 0 0 1
Protopteryx fengningensis 0 ? 2 2 [01] [12] ? ? 2 0
Enan. indet. DNHM D2952/3 ? ? ? 1 1 ? ? ? 0 1
527
Appendix C: Character Matrix Continued.
Taxa\characters 91 92 93 94 95 96 97 98 99 100
Enan. indet. DNHM D2130 ? ? ? [01] ? ? ? ? 0 1
Eoalulavis hoyasi ? 1 0 2 ? 1 1 0 0 1
Shanweiniao cooperorum ? ? 0 0 [01] [12] ? - 0 1
Enan. indet. DNHM D2884 1/2 ? ? ? 2 1 ? ? ? 0 [01]
Elsornis keni 0 0 1 2 2 2 1 ? 0 1
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? 0 1 2 1 1 1 0 2
Enan. indet. DNHM D2567/8 1 1 ? [01] 1 [12] ? ? 0 1
El Montsec Hatchling ? ? [01] 2 1 2 ? ? 0 0
Iberomesornis romerali ? ? [01] 0 ? 2 ? ? 0 1
Eocathayornis walkeri ? ? [01] [01] ? ? ? ? 0 1
Enan. indet. DNHM D2836 ? ? ? ? [12] ? ? ? 0 ?
Enan. indet. DNHM D2510/1 ? ? [01] 1 [01] [12] ? ? 0 [01]
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? 0 [24] 1 ? ? ? 0 1
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? 0 ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? [01] 1 ? ? ? ? ?
Paraprotopteryx ? ? [01] ? ? ? ? ? 0 ?
Enantiornis leali 1 1 0 1 2 1 1 0 ? [12]
Cathayornis aberransis ? ? [01] 1 1 [12] ? ? 0 1
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? 1 ? ? ? 0 ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla 1 ? 0 [12] [12] 1 ? ? 0 [12]
Longchengornis sanyanesis ? ? ? 0 [01] ? ? ? 0 ?
Enan. indet. CAGS-02-CM-0901 ? ? ? 2 ? ? ? ? 0 ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
528
Appendix C: Character Matrix Continued.
Taxa\characters 91 92 93 94 95 96 97 98 99 100
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens 0 1 ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? [01] ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? 0 [02] 2 1 1 0 ? ?
Enantiornis walkeri ? 1 0 ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? 0 ? 2 1 1 0 ? ?
Enantiornis martini ? 1 ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? 2 ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
529
Appendix C: Character Matrix Continued.
Taxa\characters 101 102 103 104 105 106 107 108 109 110
Archaeopteryx (all ten) 0 0 0 0 0 0 ? 0 0 ?
Jeholornis prima 1 0 1 0 0 ? ? ? ? ?
Rahonavis ostromi ? ? 0 ? 0 0 0 0 0 0
Zhongornis haoae [01] 0 0 0 0 ? ? ? ? ?
Confuciusornis sanctus 0 ? 0 0 0 0 0 0 0 0
Sapeornis chaoyangensis 0 0 0 0 0 0 0 0 ? ?
Apsaravis ukhaana 2 1 1 1 0 0 0 1 0 0
Patagopteryx deferrariisi 1 ? 1 1 0 0 0 ? ? 0
Longicrusavis houi 1 0 1 1 0 0 0 ? ? ?
Gansus yumenensis 1 0 1 0 0 0 ? ? ? 0
Archaeorhynchus spathula 1 1 1 0 0 0 0 0 ? ?
Yixianornis grabaui 1 0 1 0 0 0 0 0 ? 0
Ichthyornis dispar 1 0 1 1 0 0 1 0 ? 0
Hesperornis regalis 1 0 1 0 0 ? ? ? - 0
Anas 2 1 1 0 0 0 0 0 1 0
Gallus 2 0 1 1 0 0 0 0 1 0
Longipteryx chaoyangia ? ? 0 0 0 ? 0 0 ? 0
Rapaxavis pani 1 0 ? ? ? 1 0 ? 0 ?
Cathyaornis yandica [12] ? 0 0 0 1 0 0 0 ?
Enan. n. sp. DNHM D2950/1 1 0 0 0 0 ? 0 ? ? ?
Dapingfangornis sentisorhinus 1 0 0 0 0 ? ? ? ? ?
Pengornis houi 1 0 0 ? 0 0 0 1 0 ?
Hebeiornis fengningensis 1 ? 0 0 0 ? 0 0 0 ?
Longirostravis hani 1 0 0 0 ? ? 0 0 0 ?
Longipteryx DNHM D2566 [12] 0 0 0 0 ? 0 ? 0 ?
Gobipteryx minuta 2 0 ? ? ? 0 0 0 0 0
Alethoalaornis agitornis 2 1 0 0 0 ? 0 0 0 ?
Longipteryx DNHM D2889 [12] 0 0 0 0 ? 0 0 0 ?
Concornis lacustris [12] 1 0 ? 0 1 ? ? 0 ?
Eoenantiornis buhleri ? ? 0 ? ? ? 0 0 0 ?
Protopteryx fengningensis 1 0 0 0 0 ? 0 0 0 ?
Enan. indet. DNHM D2952/3 2 0 0 0 0 ? 0 0 0 ?
530
Appendix C: Character Matrix Continued.
Taxa\characters 101 102 103 104 105 106 107 108 109 110
Enan. indet. DNHM D2130 [12] 0 0 0 0 ? 0 0 0 ?
Eoalulavis hoyasi 1 1 0 0 0 0 0 0 0 0
Shanweiniao cooperorum [12] 0 0 0 0 ? 0 0 0 ?
Enan. indet. DNHM D2884 1/2 1 1 0 0 0 ? 0 0 ? ?
Elsornis keni 2 1 0 0 1 1 0 0 0 0
Sinornis santensis ? ? 0 ? 0 ? 0 0 ? ?
Neuquenornis volans [12] ? 0 0 0 ? ? ? ? ?
Enan. indet. DNHM D2567/8 2 0 0 ? 0 ? 0 0 ? ?
El Montsec Hatchling [12] 0 0 0 0 ? 0 0 0 ?
Iberomesornis romerali 1 0 ? ? ? ? ? ? ? ?
Eocathayornis walkeri 2 0 0 0 0 0 0 0 1 ?
Enan. indet. DNHM D2836 ? ? 0 ? 0 ? 0 ? 0 ?
Enan. indet. DNHM D2510/1 2 0 0 0 0 ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? 0 0 0 ? 0 0 ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? 0 0 0 ? 0 ? 0 ?
Cathayornis caudatus [12] ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? 0 0 0 ? 0 ? 0 ?
Enantiornis leali ? ? 0 0 0 1 0 0 0 1
Cathayornis aberransis 2 1 ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis [12] ? 0 ? 0 ? 0 ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? 0 ? ? ? ? ?
Enantiophoenix electrophyla [123] ? 0 ? 0 0 0 0 1 ?
Longchengornis sanyanesis 2 0 0 0 0 ? 0 ? ? ?
Enan. indet. CAGS-02-CM-0901 2 ? ? ? 0 1 0 0 0 ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? 0 ? 0 1 0 0 0 0
531
Appendix C: Character Matrix Continued.
Taxa\characters 101 102 103 104 105 106 107 108 109 110
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? 0 1 0 1
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? 0 ? 0 ? 0 0 0 ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
532
Appendix C: Character Matrix Continued.
Taxa\characters 111 112 113 114 115 116 117 118 119 120
Archaeopteryx (all ten) 0 0 0 0 0 0 - 0 0 0
Jeholornis prima ? 1 ? ? 0 0 - ? 0 ?
Rahonavis ostromi 0 0 ? ? ? ? ? ? ? ?
Zhongornis haoae 0 0 ? 0 ? [01] ? ? 0 ?
Confuciusornis sanctus 0 0 0 0 0 0 - 0 0 0
Sapeornis chaoyangensis ? 1 0 0 0 2 0 0 0 0
Apsaravis ukhaana 0 1 ? ? ? ? ? ? ? ?
Patagopteryx deferrariisi ? ? ? ? ? ? ? ? ? ?
Longicrusavis houi 0 1 2 2 0 ? 0 0 1 ?
Gansus yumenensis 0 1 2 2 0 0 - 0 1 0
Archaeorhynchus spathula 0 ? 2 2 0 0 - ? ? 0
Yixianornis grabaui 0 1 2 2 0 ? ? ? ? 0
Ichthyornis dispar 0 1 2 2 0 0 - 0 1 0
Hesperornis regalis 0 0 2 0 0 ? ? 0 1 1
Anas 0 1 2 2 0 1 0 0 1 0
Gallus 0 1 2 2 0 1 1 0 1 1
Longipteryx chaoyangia ? 1 1 1 1 3 ? ? 0 0
Rapaxavis pani ? ? 1 2 ? 3 0 ? 0 0
Cathyaornis yandica 0 ? 1 2 ? 3 1 ? 0 ?
Enan. n. sp. DNHM D2950/1 ? 0 1 2 ? [23] 1 ? 1 1
Dapingfangornis sentisorhinus ? ? 1 [12] 1 3 1 ? 0 1
Pengornis houi ? ? 1 [12] ? 2 ? ? ? 0
Hebeiornis fengningensis ? 0 1 2 ? 3 1 ? 0 0
Longirostravis hani ? 0 1 1 1 [123] ? ? 0 ?
Longipteryx DNHM D2566 ? ? 1 1 1 [123] ? ? 0 ?
Gobipteryx minuta ? ? 1 [12] 1 [23] 1 1 ? ?
Alethoalaornis agitornis ? ? 1 2 1 ? ? ? ? ?
Longipteryx DNHM D2889 ? ? 1 1 ? 3 ? ? 0 ?
Concornis lacustris ? ? 1 [12] 1 2 ? ? 0 ?
Eoenantiornis buhleri ? ? 1 2 1 2 ? 1 ? ?
Protopteryx fengningensis ? 0 1 2 1 3 ? ? 0 ?
Enan. indet. DNHM D2952/3 1 0 1 1 1 [23] ? ? 0 ?
533
Appendix C: Character Matrix Continued.
Taxa\characters 111 112 113 114 115 116 117 118 119 120
Enan. indet. DNHM D2130 ? ? [12] 1 1 ? ? ? 0 ?
Eoalulavis hoyasi ? 1 1 2 ? 3 1 ? 0 0
Shanweiniao cooperorum ? 0 1 2 ? 2 ? ? 1 1
Enan. indet. DNHM D2884 1/2 ? ? 1 1 1 [123] ? ? 0 ?
Elsornis keni 1 0 1 1 1 [23] 0 0 0 ?
Sinornis santensis 0 ? 1 ? ? 2 ? ? ? ?
Neuquenornis volans 1 ? 1 2 1 1 ? ? ? ?
Enan. indet. DNHM D2567/8 1 ? 1 [12] 1 [23] ? 1 ? ?
El Montsec Hatchling ? ? 1 2 ? [23] 0 ? ? ?
Iberomesornis romerali ? ? 1 2 ? [23] 0 ? ? ?
Eocathayornis walkeri ? 0 ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? 1 2 1 [123] ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? 0 ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? 0 1 ? ? ? ? ? 0 ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? 0 ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? 1 1 ? 3 1 ? 0 ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla 0 0 [12] 1 ? [23] ? ? ? ?
Longchengornis sanyanesis ? 0 1 2 ? 3 ? ? 0 ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? 1 2 ? 2 ? ? 0 ?
Halimornis thompsoni 1 ? ? ? ? ? ? ? ? ?
534
Appendix C: Character Matrix Continued.
Taxa\characters 111 112 113 114 115 116 117 118 119 120
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
535
Appendix C: Character Matrix Continued.
Taxa\characters 121 122 123 124 125 126 127 128 129 130
Archaeopteryx (all ten) 0 0 - - - - - - - -
Jeholornis prima 0 [12] ? ? ? ? ? ? ? ?
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? ? ? ? ? ? ? ? ? ?
Confuciusornis sanctus 0 2 [12] [01] 1 1 0 ? - 0
Sapeornis chaoyangensis ? ? ? ? ? ? ? ? ? ?
Apsaravis ukhaana ? 2 3 3 ? ? ? ? ? 1
Patagopteryx deferrariisi ? 2 [12] ? ? ? ? ? ? 1
Longicrusavis houi ? 2 3 ? 1 2 [01] 0 - 1
Gansus yumenensis 0 2 3 3 1 1 0 0 - 1
Archaeorhynchus spathula ? 2 [23] 3 [12] ? ? 0 ? 1
Yixianornis grabaui ? 2 3 3 1 1 [01] 0 - 1
Ichthyornis dispar ? 2 3 3 0 ? - - - 1
Hesperornis regalis ? 2 1 0 0 - - - - 1
Anas 0 2 3 1 1 1 0 1 - 1
Gallus 0 2 3 1 2 0 1 1 1 1
Longipteryx chaoyangia ? 2 [23] ? 2 1 1 1 0 1
Rapaxavis pani 1 2 2 [12] 2 2 2 0 0 1
Cathyaornis yandica ? 2 2 2 2 2 1 0 [01] 1
Enan. n. sp. DNHM D2950/1 ? 2 [123] 1 [12] [12] 1 ? ? ?
Dapingfangornis sentisorhinus ? 2 2 1 2 1 [12] 0 2 1
Pengornis houi ? ? ? ? ? ? ? ? ? ?
Hebeiornis fengningensis ? 2 2 [12] [12] ? ? 0 0 1
Longirostravis hani ? 2 [123] ? 2 2 3 0 2 1
Longipteryx DNHM D2566 ? 2 [123] ? 2 ? 1 1 0 1
Gobipteryx minuta ? ? ? ? ? ? ? ? ? ?
Alethoalaornis agitornis ? 2 [23] ? 2 [01] 1 0 0 1
Longipteryx DNHM D2889 ? 2 [123] ? ? ? ? ? ? 1
Concornis lacustris 1 2 2 [12] 2 2 1 1 0 1
Eoenantiornis buhleri ? 2 [123] ? 1 - - - 2 1
Protopteryx fengningensis ? 2 2 [12] 1 1 [01] 0 - ?
Enan. indet. DNHM D2952/3 0 2 [123] ? 2 1 1 0 1 1
536
Appendix C: Character Matrix Continued.
Taxa\characters 121 122 123 124 125 126 127 128 129 130
Enan. indet. DNHM D2130 ? 2 [123] ? [12] ? 1 ? ? 1
Eoalulavis hoyasi 0 1 2 0 0 - - - - 0
Shanweiniao cooperorum ? 2 [123] ? 2 1 1 0 1 ?
Enan. indet. DNHM D2884 1/2 ? 2 [123] ? [12] 1 1 0 [01] 1
Elsornis keni ? 2 2 2 1 0 ? 1 - 1
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? 2 3 3 [12] ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? 2 [23] ? 2 ? 1 0 ? 1
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? [12] [123] ? ? ? ? ? ? ?
Eocathayornis walkeri ? 2 2 [12] 2 [12] 1 0 ? 1
Enan. indet. DNHM D2836 ? 2 [23] ? 2 ? [12] ? [12] 1
Enan. indet. DNHM D2510/1 ? [12] [123] ? ? ? ? ? ? 1
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? 2 2 1 2 0 1 0 0 1
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? 2 [12] ? 2 ? ? 1 2 1
Cathayornis caudatus ? 2 [12] 1 2 ? 1 0 ? 1
Paraprotopteryx ? 2 [12] ? [12] 1 ? 0 ? 1
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? 2 2 1 [12] ? ? ? ? 1
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? 2 2 ? [12] [12] 1 0 ? 1
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? 2 [123] ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
537
Appendix C: Character Matrix Continued.
Taxa\characters 121 122 123 124 125 126 127 128 129 130
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
538
Appendix C: Character Matrix Continued.
Taxa\characters 131 132 133 134 135 136 137 138 139 140
Archaeopteryx (all ten) - - - - - - - - 0 0
Jeholornis prima ? ? ? ? ? ? ? ? 0 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae ? ? ? ? ? ? ? ? ? ?
Confuciusornis sanctus 0 ? 1 1 2 1 0 0 0 0
Sapeornis chaoyangensis ? ? ? ? ? ? ? ? ? 0
Apsaravis ukhaana ? ? 1 ? ? ? ? ? 1 1
Patagopteryx deferrariisi ? ? 0 ? ? ? ? ? 1 0
Longicrusavis houi 1 ? 1 ? ? 1 0 ? 1 1
Gansus yumenensis 2 0 1 1 2 4 1 ? 1 1
Archaeorhynchus spathula 0 ? ? ? ? ? ? ? ? ?
Yixianornis grabaui 2 ? ? ? ? 4 1 ? ? 1
Ichthyornis dispar 2 0 ? 1 2 ? 0 1 1 1
Hesperornis regalis 1 0 1 1 1 0 0 0 ? 1
Anas 2 0 1 1 3 3 0 1 1 1
Gallus 2 0 1 1 2 2 0 1 1 1
Longipteryx chaoyangia 0 0 1 ? ? 2 0 ? ? 0
Rapaxavis pani 0 0 1 ? ? 2 0 ? ? 0
Cathyaornis yandica 0 1 1 ? ? 2 0 ? 0 0
Enan. n. sp. DNHM D2950/1 ? ? 1 ? ? 2 0 ? ? 0
Dapingfangornis sentisorhinus 0 ? 1 ? ? 2 0 ? 0 ?
Pengornis houi ? ? ? ? ? ? ? ? 0 0
Hebeiornis fengningensis 0 0 1 ? ? 2 0 ? 0 0
Longirostravis hani 0 0 1 0 - 2 0 ? ? 0
Longipteryx DNHM D2566 0 1 1 ? ? ? 0 ? 0 0
Gobipteryx minuta ? ? ? ? ? ? ? ? 0 ?
Alethoalaornis agitornis 0 1 1 ? ? 2 0 ? 0 0
Longipteryx DNHM D2889 0 ? 1 ? ? ? ? ? ? ?
Concornis lacustris 0 ? 1 0 - 2 0 ? 0 0
Eoenantiornis buhleri 0 ? 1 0 - 2 0 0 0 ?
Protopteryx fengningensis 1 1 1 ? ? 1 0 ? ? ?
Enan. indet. DNHM D2952/3 0 ? 1 ? ? 2 0 ? 0 0
539
Appendix C: Character Matrix Continued.
Taxa\characters 131 132 133 134 135 136 137 138 139 140
Enan. indet. DNHM D2130 [01] ? [01] ? ? ? ? ? ? ?
Eoalulavis hoyasi 0 ? 1 0 - 3 0 ? 0 0
Shanweiniao cooperorum 1 0 [01] ? ? 2 0 ? ? ?
Enan. indet. DNHM D2884 1/2 0 ? 1 ? ? 2 0 ? 1 ?
Elsornis keni 0 0 1 ? ? [12] 0 ? 0 0
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? 1 ? ? ? ? ? 0 ?
Enan. indet. DNHM D2567/8 1 1 1 ? ? ? 0 ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? 0 0
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri 0 ? 1 ? ? 2 0 ? ? 0
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? 0 0
Enan. indet. DNHM D2510/1 ? ? 1 ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis 0 ? 1 ? ? 2 0 ? 0 0
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? 1 ? ? 2 0 ? ? ?
Cathayornis caudatus 1 1 1 ? ? 2 0 ? ? ?
Paraprotopteryx 0 ? 1 ? ? 2 0 ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? 0 0
Cathayornis aberransis ? ? 1 ? ? 2 ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis [01] ? 1 ? ? 2 0 ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? 0
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? 0
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? 0
Halimornis thompsoni ? ? ? ? ? ? ? ? ? 0
540
Appendix C: Character Matrix Continued.
Taxa\characters 131 132 133 134 135 136 137 138 139 140
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? 0 ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? 0 0
Martinavis vincei ? ? ? ? ? ? ? ? 0 0
Gurilynia nessovi ? ? ? ? ? ? ? ? ? 0
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
541
Appendix C: Character Matrix Continued.
Taxa\characters 141 142 143 144 145 146 147 148 149 150
Archaeopteryx (all ten) 0 ? 0 0 0 0 0 1 0 0
Jeholornis prima 0 0 0 0 0 0 0 1 0 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae 0 0 0 0 0 ? 0 1 0 0
Confuciusornis sanctus 0 0 0 1 0 0 0 2 1 0
Sapeornis chaoyangensis 0 ? ? ? 0 0 0 1 1 0
Apsaravis ukhaana 0 0 ? 1 [01] 0 0 1 0 1
Patagopteryx deferrariisi 0 1 ? ? ? ? 1 0 0 1
Longicrusavis houi 0 ? 1 0 1 ? 1 1 0 1
Gansus yumenensis 0 0 0 1 ? ? 0 1 0 1
Archaeorhynchus spathula 0 0 ? 0 ? ? 0 1 0 1
Yixianornis grabaui 0 ? ? ? 1 1 ? ? 0 1
Ichthyornis dispar 0 0 1 1 1 0 0 1 0 0
Hesperornis regalis 0 0 0 0 0 0 - 0 0 -
Anas 0 0 1 1 2 1 1 0 0 1
Gallus 0 0 1 1 2 1 1 0 0 1
Longipteryx chaoyangia 1 1 ? 0 ? ? 0 0 0 1
Rapaxavis pani 1 0 0 0 ? ? 0 0 0 ?
Cathyaornis yandica 1 1 1 ? 1 1 0 1 0 1
Enan. n. sp. DNHM D2950/1 1 1 ? 0 [12] ? 0 0 0 0
Dapingfangornis sentisorhinus 1 0 0 0 ? ? 0 0 0 0
Pengornis houi 1 ? ? 1 1 0 0 1 0 1
Hebeiornis fengningensis 1 1 1 0 ? ? 0 1 0 1
Longirostravis hani 1 ? ? ? ? ? ? 0 0 0
Longipteryx DNHM D2566 1 ? ? ? ? ? 0 0 0 ?
Gobipteryx minuta ? ? ? ? ? ? 0 ? ? ?
Alethoalaornis agitornis 1 ? ? ? 1 0 0 1 0 1
Longipteryx DNHM D2889 ? ? ? ? ? ? ? 0 0 ?
Concornis lacustris 1 1 ? 1 ? ? 0 [01] 0 0
Eoenantiornis buhleri 1 ? ? ? [12] ? 0 0 0 1
Protopteryx fengningensis 1 ? ? ? ? ? 0 1 0 0
Enan. indet. DNHM D2952/3 1 ? ? ? [12] ? 0 0 0 1
542
Appendix C: Character Matrix Continued.
Taxa\characters 141 142 143 144 145 146 147 148 149 150
Enan. indet. DNHM D2130 1 ? ? ? [12] ? 0 0 0 1
Eoalulavis hoyasi 1 1 ? 1 2 0 0 1 0 0
Shanweiniao cooperorum 1 ? ? ? ? ? ? 0 0 1
Enan. indet. DNHM D2884 1/2 1 1 ? ? ? ? 0 0 0 1
Elsornis keni 1 1 1 0 1 0 0 0 0 1
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? [12] 1 ? ? ? ?
Enan. indet. DNHM D2567/8 1 ? ? ? ? ? ? 0 0 ?
El Montsec Hatchling 1 ? ? ? 1 ? 0 1 0 1
Iberomesornis romerali ? ? ? 0 ? ? ? ? ? ?
Eocathayornis walkeri 1 ? ? ? [12] ? 0 0 0 1
Enan. indet. DNHM D2836 1 ? ? ? 1 ? ? 0 0 1
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis 1 ? ? ? [12] ? 0 0 0 1
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera 1 ? ? ? ? ? 0 0 0 1
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? 0 0 ?
Enantiornis leali 1 1 1 1 2 1 0 0 0 0
Cathayornis aberransis ? ? ? ? ? ? 0 0 0 ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? 0 ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi 1 ? ? ? [12] ? 0 [01] 0 1
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis 1 ? ? ? [12] ? ? [01] 0 ?
Enan. indet. CAGS-02-CM-0901 1 ? ? ? [12] ? 0 0 0 1
Noguerornis gonzalezi 0 1 ? ? ? ? ? 0 0 1
Halimornis thompsoni 1 1 ? 1 2 1 ? ? ? ?
543
Appendix C: Character Matrix Continued.
Taxa\characters 141 142 143 144 145 146 147 148 149 150
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi 1 ? ? ? 1 0 0 1 0 1
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis 1 1 1 1 2 1 0 0 0 0
Martinavis vincei 1 1 1 1 2 1 0 1 0 1
Gurilynia nessovi 1 1 1 ? [12] 1 0 ? 0 ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
544
Appendix C: Character Matrix Continued.
Taxa\characters 151 152 153 154 155 156 157 158 159 160
Archaeopteryx (all ten) 0 0 0 ? 0 0 0 0 0 0
Jeholornis prima 0 ? 0 [01] [01] 0 0 ? ? 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae 0 ? ? 0 ? ? 0 0 0 0
Confuciusornis sanctus 0 ? 0 1 0 0 0 0 1 0
Sapeornis chaoyangensis 0 0 0 [01] 0 0 ? ? ? 0
Apsaravis ukhaana [12] 1 1 1 0 0 0 0 1 2
Patagopteryx deferrariisi 0 ? 0 [12] ? 0 0 0 0 0
Longicrusavis houi 1 2 0 ? 2 1 1 0 0 0
Gansus yumenensis 1 3 0 2 ? 1 ? ? ? 0
Archaeorhynchus spathula ? ? ? 0 ? 0 ? ? ? 0
Yixianornis grabaui ? 0 ? 1 0 ? 1 1 0 0
Ichthyornis dispar 1 2 0 0 2 1 0 ? 1 0
Hesperornis regalis 0 0 0 0 0 0 0 0 0 0
Anas 0 3 0 0 1 1 1 1 1 0
Gallus 0 3 0 0 1 1 1 1 1 0
Longipteryx chaoyangia 2 ? ? 0 [01] ? 0 ? 0 [12]
Rapaxavis pani 0 ? ? 0 [01] 0 ? ? ? 1
Cathyaornis yandica 2 1 1 1 [01] 0 1 0 0 1
Enan. n. sp. DNHM D2950/1 ? ? ? 0 ? ? ? ? ? 0
Dapingfangornis sentisorhinus [12] 1 ? [01] ? ? ? ? ? 1
Pengornis houi 1 ? ? 0 [01] ? 1 0 0 [01]
Hebeiornis fengningensis 1 ? 1 1 [01] 0 ? ? ? 1
Longirostravis hani ? ? ? 0 [01] ? ? ? ? 1
Longipteryx DNHM D2566 ? ? ? 0 ? ? ? ? 0 0
Gobipteryx minuta ? ? ? ? ? 0 ? ? ? ?
Alethoalaornis agitornis ? ? ? [12] ? ? ? 0 0 ?
Longipteryx DNHM D2889 ? ? ? ? ? ? ? ? ? 1
Concornis lacustris 2 1 1 ? ? ? ? ? ? ?
Eoenantiornis buhleri ? ? ? ? ? ? ? ? ? [01]
Protopteryx fengningensis ? ? ? 0 ? ? ? ? ? [01]
Enan. indet. DNHM D2952/3 [12] ? ? ? ? ? ? ? ? 0
545
Appendix C: Character Matrix Continued.
Taxa\characters 151 152 153 154 155 156 157 158 159 160
Enan. indet. DNHM D2130 ? ? ? 1 ? ? ? ? ? 1
Eoalulavis hoyasi 2 1 1 1 0 0 1 0 0 2
Shanweiniao cooperorum ? ? ? 0 ? ? ? ? ? 1
Enan. indet. DNHM D2884 1/2 2 ? ? ? ? ? ? ? ? ?
Elsornis keni 0 2 0 2 1 0 0 0 0 1
Sinornis santensis ? ? ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? 1 [01] ? 0 1 ? 0 [12]
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? 1 1 ? ? ? ? ? 1
Iberomesornis romerali [01] ? 1 ? ? 0 ? ? ? 1
Eocathayornis walkeri ? ? ? 1 ? ? ? ? ? 1
Enan. indet. DNHM D2836 ? ? ? 1 ? ? ? ? ? [01]
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis [12] ? ? [12] ? ? ? ? ? 1
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali 2 1 1 2 ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? 1 ? ? ? ? ? 1
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? [01]
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? 1 ? ? ? ? ? 0
Noguerornis gonzalezi [01] ? ? 2 ? ? 0 ? ? 1
Halimornis thompsoni 2 1 ? ? ? ? ? ? ? ?
546
Appendix C: Character Matrix Continued.
Taxa\characters 151 152 153 154 155 156 157 158 159 160
Enan. indet. CAGS-IG-04-CM-023 ? ? ? 2 ? 0 ? ? ? [12]
Alexornis antecedens ? ? 1 2 1 0 1 0 0 2
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? 1 [01] ? 0 0 0 1
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis 2 2 1 2 0 0 1 0 0 2
Martinavis vincei 2 2 1 2 0 0 1 0 0 2
Gurilynia nessovi 1 1 ? [12] [12] 0 ? 0 0 ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? 1 2 2 ? ? ? ? [12]
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
547
Appendix C: Character Matrix Continued.
Taxa\characters 161 162 163 164 165 166 167 168 169 170
Archaeopteryx (all ten) 0 ? ? ? 0 0 0 0 0 0
Jeholornis prima 0 0 1 1 1 1 0 ? 0 0
Rahonavis ostromi ? ? ? ? ? 1 0 ? 0 0
Zhongornis haoae ? ? ? ? 0 0 ? ? ? ?
Confuciusornis sanctus 1 0 0 0 0 1 0 0 2 1
Sapeornis chaoyangensis 0 0 0 1 1 1 ? ? ? ?
Apsaravis ukhaana 1 1 1 1 1 1 0 1 2 1
Patagopteryx deferrariisi 1 0 0 ? 0 0 0 0 ? 0
Longicrusavis houi 1 0 0 0 1 1 0 0 ? ?
Gansus yumenensis 1 0 0 1 1 1 0 0 1 1
Archaeorhynchus spathula 1 1 0 ? 1 0 ? ? ? ?
Yixianornis grabaui 1 ? 0 ? 1 0 0 0 2 1
Ichthyornis dispar 1 0 0 0 1 1 0 0 2 1
Hesperornis regalis - - - - ? ? ? ? ? ?
Anas 1 0 0 0 0 1 0 0 1 1
Gallus 1 0 0 0 1 1 0 0 1 1
Longipteryx chaoyangia 1 ? 1 ? 1 1 ? ? ? ?
Rapaxavis pani 1 1 1 ? 1 0 ? ? ? 1
Cathyaornis yandica 1 1 1 0 1 1 ? ? ? ?
Enan. n. sp. DNHM D2950/1 1 ? ? ? 1 1 ? ? ? ?
Dapingfangornis sentisorhinus 1 ? ? 1 1 1 ? ? ? ?
Pengornis houi 1 ? ? ? 1 1 ? ? ? ?
Hebeiornis fengningensis 1 1 1 1 1 1 ? ? ? ?
Longirostravis hani ? ? ? ? 1 0 ? ? ? ?
Longipteryx DNHM D2566 ? ? ? ? 1 1 ? ? ? ?
Gobipteryx minuta ? ? ? ? 1 1 ? ? ? 1
Alethoalaornis agitornis ? ? ? ? 1 0 ? ? ? ?
Longipteryx DNHM D2889 1 ? ? ? 1 0 ? ? ? ?
Concornis lacustris 1 ? ? ? ? 1 1 1 2 ?
Eoenantiornis buhleri ? ? ? ? 1 1 ? ? ? ?
Protopteryx fengningensis ? ? ? ? 1 1 ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? 1 1 ? ? ? ?
548
Appendix C: Character Matrix Continued.
Taxa\characters 161 162 163 164 165 166 167 168 169 170
Enan. indet. DNHM D2130 1 ? ? ? 1 1 ? ? ? ?
Eoalulavis hoyasi 1 1 1 1 1 1 1 ? 2 1
Shanweiniao cooperorum 1 ? ? ? 1 1 ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? 1 1 ? ? ? ?
Elsornis keni 1 1 ? ? 0 1 0 0 [12] 1
Sinornis santensis 1 ? ? ? ? 1 ? ? ? ?
Neuquenornis volans ? ? ? ? 1 1 ? 1 ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? 1 1 ? ? ? ?
El Montsec Hatchling ? ? ? ? 1 1 ? ? ? ?
Iberomesornis romerali 1 1 ? ? 1 1 ? ? ? ?
Eocathayornis walkeri 1 ? ? ? 1 0 ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? 1 1 ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? 1 ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis 1 ? 1 ? 1 ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? 1 1 ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? 1 ? ? ? ? ?
Enantiornis leali 1 ? ? ? ? 1 1 1 ? 1
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis 1 ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? 1 ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? 1 1 ? ? ? 1
Noguerornis gonzalezi ? ? ? ? 1 0 ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
549
Appendix C: Character Matrix Continued.
Taxa\characters 161 162 163 164 165 166 167 168 169 170
Enan. indet. CAGS-IG-04-CM-023 1 1 1 1 ? 1 0 0 2 0
Alexornis antecedens 1 1 1 1 ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi 1 1 1 ? 1 1 ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis 1 1 1 0 ? ? ? ? ? ?
Martinavis vincei 1 1 1 0 ? ? ? ? ? ?
Gurilynia nessovi 1 1 1 ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea 1 1 ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
550
Appendix C: Character Matrix Continued.
Taxa\characters 171 172 173 174 175 176 177 178 179 180
Archaeopteryx (all ten) 0 0 ? ? 0 0 - 0 0 0
Jeholornis prima 0 0 0 1 2 1 0 0 1 0
Rahonavis ostromi 0 0 ? ? ? ? ? ? ? ?
Zhongornis haoae ? ? ? ? ? 0 - 0 0 ?
Confuciusornis sanctus 0 0 0 1 2 0 - 0 0 0
Sapeornis chaoyangensis 0 0 ? ? 2 0 - 0 0 0
Apsaravis ukhaana 1 0 1 ? 3 1 0 0 1 1
Patagopteryx deferrariisi ? 0 ? ? ? ? ? ? ? ?
Longicrusavis houi ? 0 ? ? 3 1 1 0 ? ?
Gansus yumenensis 1 ? 0 1 3 2 ? 0 1 1
Archaeorhynchus spathula 1 0 1 ? 0 ? ? 0 0 2
Yixianornis grabaui ? 0 ? ? 3 1 1 0 1 2
Ichthyornis dispar 1 0 1 ? 3 2 1 0 1 2
Hesperornis regalis ? - - - - - - - - -
Anas 1 0 1 2 3 2 0 1 3 2
Gallus 1 0 1 1 3 2 0 1 3 2
Longipteryx chaoyangia ? 0 0 - 0 1 0 0 0 0
Rapaxavis pani ? ? 0 - ? 1 ? 0 0 ?
Cathyaornis yandica 1 1 0 ? 3 1 0 0 0 1
Enan. n. sp. DNHM D2950/1 ? ? ? ? 0 ? ? 0 0 1
Dapingfangornis sentisorhinus ? ? ? ? [123] 1 0 0 0 0
Pengornis houi ? ? 1 [02] [23] 1 1 ? ? ?
Hebeiornis fengningensis ? ? 1 [02] 0 1 0 1 0 ?
Longirostravis hani ? ? 0 - 3 ? ? 1 0 ?
Longipteryx DNHM D2566 ? ? 0 - 0 1 ? ? ? ?
Gobipteryx minuta 1 1 ? ? ? ? ? ? ? ?
Alethoalaornis agitornis ? ? ? ? 3 [01] ? 0 0 1
Longipteryx DNHM D2889 ? ? ? ? ? 1 0 0 0 ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? 1 0 - [23] ? ? 0 0 0
Protopteryx fengningensis ? ? ? ? ? ? ? 0 0 0
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
551
Appendix C: Character Matrix Continued.
Taxa\characters 171 172 173 174 175 176 177 178 179 180
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? 0 0 ?
Eoalulavis hoyasi ? 1 ? ? ? ? ? ? ? ?
Shanweiniao cooperorum 1 ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? 1 0 0 0 ?
Elsornis keni ? 1 ? ? 3 ? ? ? ? ?
Sinornis santensis ? ? ? ? ? 1 ? ? ? ?
Neuquenornis volans 1 1 ? ? 3 ? ? 1 0 ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? ? 0 - [23] ? ? 0 0 1
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? 0 ? ? ? ? ?
Cathayornis caudatus ? ? ? ? [123] ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? 0 0 ?
Enantiornis leali 1 1 ? ? 3 1 1 ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? ? 2 ? ? ? 0 ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? 0 - ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 1 0 ? ? [23] ? ? 0 0 ?
Noguerornis gonzalezi ? 0 ? ? 3 ? ? 1 0 ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
552
Appendix C: Character Matrix Continued.
Taxa\characters 171 172 173 174 175 176 177 178 179 180
Enan. indet. CAGS-IG-04-CM-023 ? 0 1 ? ? 1 ? 0 0 0
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
553
Appendix C: Character Matrix Continued.
Taxa\characters 181 182 183 184 185 186 187 188 189 190
Archaeopteryx (all ten) 0 1 0 0 0 0 0 0 0 0
Jeholornis prima 0 0 0 1 0 0 0 0 0 0
Rahonavis ostromi ? ? ? ? ? ? ? ? ? ?
Zhongornis haoae 0 1 0 0 - 0 ? 0 0 0
Confuciusornis sanctus ? 1 0 0 - 0 0 0 0 0
Sapeornis chaoyangensis 1 0 0 0 - 0 2 0 0 0
Apsaravis ukhaana 1 ? 1 1 0 ? ? ? ? ?
Patagopteryx deferrariisi 0 ? ? 1 ? ? 1 ? ? ?
Longicrusavis houi 0 0 0 1 0 1 0 0 0 0
Gansus yumenensis 1 0 0 0 1 ? 0 1 0 2
Archaeorhynchus spathula ? ? 0 ? ? 0 ? ? ? 2
Yixianornis grabaui 1 0 0 0 0 1 0 ? 0 1
Ichthyornis dispar 1 0 1 0 0 1 0 0 0 ?
Hesperornis regalis - - - - - - - - - -
Anas 1 1 1 1 1 1 0 0 0 2
Gallus 1 0 2 1 0 1 0 1 0 2
Longipteryx chaoyangia 0 1 0 0 ? 0 ? 1 0 1
Rapaxavis pani 0 1 0 0 0 0 0 1 1 2
Cathyaornis yandica 0 ? [01] 0 0 0 2 1 0 2
Enan. n. sp. DNHM D2950/1 0 1 0 0 1 0 2 1 0 1
Dapingfangornis sentisorhinus 0 ? [01] 0 0 0 0 1 0 2
Pengornis houi 0 ? 0 1 0 0 0 1 1 ?
Hebeiornis fengningensis 0 0 [01] 0 ? 0 0 1 ? 2
Longirostravis hani 0 ? [01] 0 1 0 0 1 0 ?
Longipteryx DNHM D2566 0 1 ? 0 - 0 ? 1 0 1
Gobipteryx minuta 0 ? ? 0 ? 0 ? 1 ? ?
Alethoalaornis agitornis 0 0 [01] 0 ? 0 2 1 ? 2
Longipteryx DNHM D2889 0 0 0 0 - 0 2 1 ? 0
Concornis lacustris 0 ? ? 0 ? ? [12] ? 0 2
Eoenantiornis buhleri 0 ? 0 0 0 0 ? 1 ? 1
Protopteryx fengningensis ? ? [01] 0 0 0 0 1 0 0
Enan. indet. DNHM D2952/3 0 ? ? 0 ? 0 2 1 ? 2
554
Appendix C: Character Matrix Continued.
Taxa\characters 181 182 183 184 185 186 187 188 189 190
Enan. indet. DNHM D2130 0 ? ? 0 ? 0 2 1 0 2
Eoalulavis hoyasi 0 ? ? 1 ? 0 0 1 ? 1
Shanweiniao cooperorum ? ? ? ? ? ? ? ? ? [01]
Enan. indet. DNHM D2884 1/2 0 ? ? 0 ? 0 2 1 0 2
Elsornis keni 0 ? [01] ? 0 1 1 ? ? ?
Sinornis santensis 1 0 ? 0 0 0 0 1 0 2
Neuquenornis volans 0 ? [01] 0 0 0 ? 1 ? ?
Enan. indet. DNHM D2567/8 0 ? ? 0 ? ? 2 ? ? 2
El Montsec Hatchling 0 1 ? ? ? ? ? 1 0 [12]
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri 0 ? ? 0 0 0 2 1 ? 2
Enan. indet. DNHM D2836 ? ? ? 0 ? ? ? ? ? 2
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? ? ? ?
Cathayornis chabuensis 0 ? ? 0 ? 0 ? 1 ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera 0 ? ? 0 ? 0 0 1 ? 2
Cathayornis caudatus ? ? ? 0 ? 0 ? 1 ? ?
Paraprotopteryx 0 ? ? 0 ? 0 ? 1 ? [12]
Enantiornis leali 1 ? ? 1 0 ? ? ? ? ?
Cathayornis aberransis 0 ? [01] 0 ? 0 2 1 ? 2
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? ? 0 0 0 ? 1 ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? 0 ? 1 ? 2
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? 0 ? 1 ? ?
Noguerornis gonzalezi 0 ? ? 0 ? ? 2 1 ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
555
Appendix C: Character Matrix Continued.
Taxa\characters 181 182 183 184 185 186 187 188 189 190
Enan. indet. CAGS-IG-04-CM-023 0 ? [01] 0 0 0 1 1 1 2
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
556
Appendix C: Character Matrix Continued.
Taxa\characters 191 192 193 194 195 196 197 198 199 200
Archaeopteryx (all ten) 0 0 0 0 0 0 2 0 ? 1
Jeholornis prima 0 0 0 1 0 1 3 0 0 1
Rahonavis ostromi ? ? ? ? ? ? ? 0 0 1
Zhongornis haoae 0 0 0 1 0 0 1 ? ? 0
Confuciusornis sanctus 0 0 0 2 0 0 2 0 0 0
Sapeornis chaoyangensis 0 1 0 1 1 0 3 0 0 0
Apsaravis ukhaana 1 ? ? ? ? ? ? 1 ? 0
Patagopteryx deferrariisi 0 0 0 ? ? 2 0 ? 0 0
Longicrusavis houi 1 0 0 1 1 0 1 ? ? ?
Gansus yumenensis 1 1 0 0 1 3 2 1 0 0
Archaeorhynchus spathula 1 1 0 ? ? 2 3 0 ? 0
Yixianornis grabaui 1 1 0 1 1 0 2 1 ? 0
Ichthyornis dispar 1 1 1 - ? ? 3 1 0 ?
Hesperornis regalis - - - - - - 0 1 1 0
Anas 1 1 1 - 1 2 3 1 1 0
Gallus 1 1 1 - 1 2 1 1 1 0
Longipteryx chaoyangia 0 1 0 0 1 1 3 0 ? 0
Rapaxavis pani 0 1 1 - 1 2 3 0 ? 0
Cathyaornis yandica 0 1 0 1 1 2 2 0 ? 0
Enan. n. sp. DNHM D2950/1 0 1 0 1 1 1 3 0 ? 0
Dapingfangornis sentisorhinus 0 1 0 0 1 1 2 0 ? ?
Pengornis houi 0 1 0 ? ? [12] 3 ? ? ?
Hebeiornis fengningensis 0 1 0 [01] 1 2 2 0 ? ?
Longirostravis hani 0 1 1 - 1 2 2 ? 0 0
Longipteryx DNHM D2566 0 ? 0 0 ? 1 3 0 ? 0
Gobipteryx minuta 0 ? ? ? ? ? 2 0 0 ?
Alethoalaornis agitornis 0 1 0 0 1 1 2 ? 0 ?
Longipteryx DNHM D2889 0 1 0 0 1 1 3 0 ? ?
Concornis lacustris 0 1 0 [01] 1 2 2 ? ? ?
Eoenantiornis buhleri 0 1 0 1 1 2 2 ? ? ?
Protopteryx fengningensis 0 0 0 0 1 0 ? ? ? 0
Enan. indet. DNHM D2952/3 0 1 0 0 1 2 2 ? ? ?
557
Appendix C: Character Matrix Continued.
Taxa\characters 191 192 193 194 195 196 197 198 199 200
Enan. indet. DNHM D2130 0 1 0 0 1 1 2 ? ? ?
Eoalulavis hoyasi 0 1 ? ? ? 2 ? ? ? 0
Shanweiniao cooperorum 0 1 1 - ? 2 2 ? ? ?
Enan. indet. DNHM D2884 1/2 0 1 0 [01] 1 2 2 ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis 0 1 0 ? ? 2 ? 0 ? ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? 1 ? ? ? ? [23] ? ? ?
El Montsec Hatchling 0 1 0 ? ? 2 ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri 0 1 0 0 1 1 ? ? ? ?
Enan. indet. DNHM D2836 ? ? 0 0 ? 2 2 ? ? ?
Enan. indet. DNHM D2510/1 0 1 0 ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? ? ? ? ? 1 ? ?
Cathayornis chabuensis 0 1 ? ? 1 ? 2 ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera 0 1 0 ? 1 1 2 ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx 0 1 0 1 1 [12] 2 ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? 2 ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? 0 1 0
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? ? ? ?
Cuspirostrisornis houi ? ? 0 0 ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 0 1 0 ? 1 2 ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
558
Appendix C: Character Matrix Continued.
Taxa\characters 191 192 193 194 195 196 197 198 199 200
Enan. indet. CAGS-IG-04-CM-023 0 1 0 0 1 ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
559
Appendix C: Character Matrix Continued.
Taxa\characters 201 202 203 204 205 206 207 208 209 210
Archaeopteryx (all ten) 0 0 0 0 0 1 ? 0 0 0
Jeholornis prima 0 0 0 0 0 1 1 0 0 0
Rahonavis ostromi 0 0 0 0 - 1 1 0 0 0
Zhongornis haoae ? ? ? ? ? ? ? 1 ? ?
Confuciusornis sanctus 0 0 0 0 0 ? 1 0 0 0
Sapeornis chaoyangensis 0 ? ? 0 ? 1 1 0 ? 0
Apsaravis ukhaana 0 1 [01] 1 1 1 ? 0 ? 0
Patagopteryx deferrariisi 0 1 0 0 0 0 0 0 2 0
Longicrusavis houi ? ? ? ? 1 1 ? ? ? ?
Gansus yumenensis 0 1 1 1 1 0 1 1 ? 0
Archaeorhynchus spathula 0 ? ? 0 ? 1 0 0 0 0
Yixianornis grabaui ? 1 ? ? 0 0 ? 1 2 0
Ichthyornis dispar 0 1 0 1 1 ? ? 0 2 0
Hesperornis regalis 0 1 2 1 1 0 1 0 0 0
Anas 1 1 1 1 1 0 1 0 0 0
Gallus 1 1 2 1 1 0 1 0 0 0
Longipteryx chaoyangia 0 ? ? ? ? 1 1 0 ? 0
Rapaxavis pani 0 ? 0 ? ? 1 1 ? ? 1
Cathyaornis yandica 0 ? 0 ? ? 1 1 ? ? ?
Enan. n. sp. DNHM D2950/1 0 ? ? ? ? ? ? 0 ? 0
Dapingfangornis sentisorhinus ? ? ? ? ? ? ? ? ? 1
Pengornis houi ? ? ? ? ? ? ? ? ? ?
Hebeiornis fengningensis 0 ? ? ? ? ? ? 0 ? ?
Longirostravis hani ? ? ? ? ? 1 ? ? ? 0
Longipteryx DNHM D2566 0 ? ? ? ? 1 ? 0 ? 0
Gobipteryx minuta ? 0 ? ? ? ? ? ? ? ?
Alethoalaornis agitornis ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2889 ? ? ? ? ? ? ? 0 ? 0
Concornis lacustris ? ? ? ? ? ? ? ? ? 1
Eoenantiornis buhleri 0 ? ? ? ? ? ? 1 1 ?
Protopteryx fengningensis 0 ? ? ? ? 1 1 ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
560
Appendix C: Character Matrix Continued.
Taxa\characters 201 202 203 204 205 206 207 208 209 210
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? 1 ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? 1 ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? 0 ? 0 ? 1 1 1 ?
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? 0 0 0
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? 1 ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 ? ? ? 0 0 ? 1 0 [12] 0
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? 0 1 0
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? 1 ? ? ? ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? 1 1 ? ? 1
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? 1 ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? 0 0 0
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
561
Appendix C: Character Matrix Continued.
Taxa\characters 201 202 203 204 205 206 207 208 209 210
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
562
Appendix C: Character Matrix Continued.
Taxa\characters 211 212 213 214 215 216 217 218 219 220
Archaeopteryx (all ten) 0 0 0 2 0 ? 0 0 0 0
Jeholornis prima 1 1 0 1 0 ? ? 0 0 0
Rahonavis ostromi 2 0 0 1 0 1 0 0 0 0
Zhongornis haoae 1 1 ? 1 0 ? ? ? ? ?
Confuciusornis sanctus 1 1 0 1 0 1 0 1 0 0
Sapeornis chaoyangensis ? 1 0 1 0 1 1 1 ? 0
Apsaravis ukhaana 1 1 1 0 - 1 1 2 ? 1
Patagopteryx deferrariisi 2 1 1 2 ? 1 1 2 ? 0
Longicrusavis houi 1 1 ? ? ? ? ? [12] ? 0
Gansus yumenensis 1 1 0 2 0 1 0 2 0 0
Archaeorhynchus spathula 1 1 0 0 - ? 1 [12] 0 0
Yixianornis grabaui 1 1 ? 2 0 1 0 1 ? 0
Ichthyornis dispar 1 1 0 2 0 1 1 2 ? 1
Hesperornis regalis 0 1 0 0 - 1 1 2 0 1
Anas 0 1 1 2 2 1 0 2 0 1
Gallus 2 1 1 2 2 1 1 2 0 1
Longipteryx chaoyangia ? 1 0 1 1 1 1 [12] 1 0
Rapaxavis pani ? 1 0 1 ? ? 1 1 1 ?
Cathyaornis yandica ? ? ? ? ? ? ? ? 0 0
Enan. n. sp. DNHM D2950/1 ? 1 0 1 ? 1 0 1 ? ?
Dapingfangornis sentisorhinus ? ? ? ? ? ? 0 1 0 0
Pengornis houi ? ? ? ? ? ? ? ? ? ?
Hebeiornis fengningensis ? ? ? ? ? ? ? ? ? ?
Longirostravis hani ? 1 0 ? ? 1 ? ? 1 ?
Longipteryx DNHM D2566 0 ? ? 1 [01] ? ? [12] 1 ?
Gobipteryx minuta ? ? ? ? ? ? ? ? 0 ?
Alethoalaornis agitornis ? ? ? ? ? ? ? ? ? ?
Longipteryx DNHM D2889 0 1 0 1 [01] ? ? 2 ? ?
Concornis lacustris 0 1 0 1 ? ? 1 [12] ? 0
Eoenantiornis buhleri 1 ? ? ? ? ? ? [12] ? 0
Protopteryx fengningensis 1 ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? [12] ? ?
563
Appendix C: Character Matrix Continued.
Taxa\characters 211 212 213 214 215 216 217 218 219 220
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis 1 1 0 1 1 1 1 2 0 0
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? 1 ? 0
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 0 1 0 1 1 ? 0 2 0 0
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 0 1 0 1 ? 1 0 1 ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? 1 ? 0
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? ? [12] ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? ? ? ? 1 0 ?
Cuspirostrisornis houi ? ? ? ? ? ? ? 1 ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? 1 ? 0
Longchengornis sanyanesis ? ? ? ? ? ? ? 1 ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi 1 1 0 1 ? 0 ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
564
Appendix C: Character Matrix Continued.
Taxa\characters 211 212 213 214 215 216 217 218 219 220
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
565
Appendix C: Character Matrix Continued.
Taxa\characters 221 222 223 224 225 226 227 228 229 230
Archaeopteryx (all ten) 0 0 ? 1 0 - 0 0 0 0
Jeholornis prima 1 0 ? ? ? ? 0 ? 1 0
Rahonavis ostromi 0 0 0 1 1 2 0 0 1 0
Zhongornis haoae ? ? ? ? ? ? [02] 0 [01] ?
Confuciusornis sanctus 1 0 1 0 1 1 2 0 1 0
Sapeornis chaoyangensis 1 0 0 1 0 - ? 0 1 0
Apsaravis ukhaana 2 1 1 0 1 [12] ? 1 1 0
Patagopteryx deferrariisi 2 1 ? 0 ? ? 2 0 2 ?
Longicrusavis houi ? ? ? ? ? ? ? ? ? 0
Gansus yumenensis 1 1 0 0 1 [12] ? 1 1 0
Archaeorhynchus spathula 1 0 ? ? ? ? ? ? ? ?
Yixianornis grabaui 1 ? ? ? 1 ? 2 ? 1 0
Ichthyornis dispar 2 1 1 0 1 2 2 1 2 0
Hesperornis regalis 2 1 1 0 2 1 2 2 2 0
Anas 2 1 1 0 1 1 2 1 2 0
Gallus 2 1 1 0 1 1 2 1 2 0
Longipteryx chaoyangia 1 0 ? 0 1 1 1 ? 1 0
Rapaxavis pani 1 0 1 0 ? [12] ? ? ? ?
Cathyaornis yandica ? ? ? ? 1 2 ? 0 1 0
Enan. n. sp. DNHM D2950/1 1 0 ? ? ? ? ? ? ? ?
Dapingfangornis sentisorhinus 1 ? ? ? ? ? ? ? ? ?
Pengornis houi [01] 0 ? 0 1 [12] ? ? ? ?
Hebeiornis fengningensis ? ? ? ? ? ? ? ? ? ?
Longirostravis hani ? ? ? 0 ? 1 ? ? ? ?
Longipteryx DNHM D2566 1 0 ? 0 ? ? 1 ? ? ?
Gobipteryx minuta 1 1 ? ? ? ? ? ? ? ?
Alethoalaornis agitornis ? ? ? 0 ? ? ? ? ? ?
Longipteryx DNHM D2889 ? ? ? ? ? ? ? ? ? ?
Concornis lacustris 1 ? 0 ? ? ? ? 0 ? 1
Eoenantiornis buhleri [12] 0 ? ? ? ? 1 ? ? ?
Protopteryx fengningensis 1 0 ? ? ? ? 1 ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? 0 ? 1 [01] ? ? ?
566
Appendix C: Character Matrix Continued.
Taxa\characters 221 222 223 224 225 226 227 228 229 230
Enan. indet. DNHM D2130 1 0 ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? 1 ? 1 ? ? ?
Shanweiniao cooperorum [12] ? 0 ? ? ? ? ? [01] 0
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis 1 0 ? ? ? ? ? ? ? ?
Neuquenornis volans ? ? ? ? 1 1 1 0 ? 1
Enan. indet. DNHM D2567/8 1 ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? 0 ? ?
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? 0 ? 2 ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 [12] 1 ? 0 ? ? 1 1 1 0
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 [12] 1 ? ? ? ? 1 ? ? 0
Jibeinia luanhera 1 ? ? ? ? ? ? ? ? ?
Cathayornis caudatus 1 0 ? ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? ? ? ? ? ? ? ? ?
Largirostrornis sexdentornis [01] ? ? 0 ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 1 1 1 0 1 [12] ? 0 1 0
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? ? 1 ? ? 0
Enan. indet. CAGS-IG-06-CM-012 [12] 1 ? ? ? ? 1 ? ? 0
Cuspirostrisornis houi ? ? ? 0 ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? 0 1 0
567
Appendix C: Character Matrix Continued.
Taxa\characters 221 222 223 224 225 226 227 228 229 230
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? 0 1 0
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
568
Appendix C: Character Matrix Continued.
Taxa\characters 231 232 233 234 235 236 237 238 239 240
Archaeopteryx (all ten) 0 ? 0 0 0 1 0 [01] 0 ?
Jeholornis prima 0 ? 0 ? ? 0 - [01] 0 ?
Rahonavis ostromi 0 0 0 1 1 1 0 [01] 0 0
Zhongornis haoae ? 0 ? ? 0 0 - ? 0 ?
Confuciusornis sanctus 1 ? 2 ? 0 0 - 1 0 0
Sapeornis chaoyangensis 0 ? 2 0 0 0 - ? 0 ?
Apsaravis ukhaana ? ? 2 ? ? ? ? 2 0 1
Patagopteryx deferrariisi 1 ? 1 0 0 1 1 [12] 0 ?
Longicrusavis houi 1 ? [12] 0 0 2 - 2 [01] 1
Gansus yumenensis 1 ? 2 0 0 2 - 2 ? 0
Archaeorhynchus spathula ? ? 0 ? 0 ? ? 0 0 ?
Yixianornis grabaui 1 ? [12] 0 0 ? ? 1 ? ?
Ichthyornis dispar 1 ? 2 0 0 2 - 2 1 1
Hesperornis regalis 1 1 2 0 1 2 - 2 1 1
Anas 1 1 2 0 0 2 - 2 2 0
Gallus 1 1 2 0 0 2 - 2 2 0
Longipteryx chaoyangia ? ? ? ? 0 ? ? ? ? ?
Rapaxavis pani ? ? 0 ? 0 [01] ? ? 0 ?
Cathyaornis yandica 1 ? ? ? ? [01] ? ? ? ?
Enan. n. sp. DNHM D2950/1 ? ? 0 ? 0 ? ? ? ? ?
Dapingfangornis sentisorhinus ? ? 1 ? 0 [01] ? ? 0 ?
Pengornis houi ? ? 2 ? ? [01] ? ? 0 1
Hebeiornis fengningensis ? ? 0 ? ? [01] ? ? ? ?
Longirostravis hani ? ? ? ? 0 0 - ? ? ?
Longipteryx DNHM D2566 ? ? ? ? ? ? ? ? ? ?
Gobipteryx minuta ? ? 1 1 0 [01] ? 1 0 ?
Alethoalaornis agitornis ? ? [12] 1 1 ? ? ? 0 1
Longipteryx DNHM D2889 ? ? ? ? ? [01] ? ? ? ?
Concornis lacustris ? ? 2 1 1 1 0 ? ? ?
Eoenantiornis buhleri ? ? ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? ? 0 ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
569
Appendix C: Character Matrix Continued.
Taxa\characters 231 232 233 234 235 236 237 238 239 240
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? [12] ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? 0 ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? 0 1 ? ? ? ? ?
Neuquenornis volans ? ? ? ? ? 1 0 ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? 0 1 ? 0 - ? ? ?
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? 0 ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 0 ? 1 0 0 1 1 1 0 0
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? [01] ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus ? ? ? ? 1 ? ? ? ? ?
Paraprotopteryx ? ? 0 ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? ? 2 1 1 1 0 1 0 0
Largirostrornis sexdentornis ? ? ? ? 0 ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 1 ? [12] 1 1 [01] ? 1 ? ?
Enan. indet. CAGS-IG-07-CM-001 ? ? 0 ? ? ? ? [01] ? ?
Enan. indet. CAGS-IG-06-CM-012 ? ? 1 ? 0 ? ? ? 0 ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni 1 0 ? ? ? ? ? ? ? ?
570
Appendix C: Character Matrix Continued.
Taxa\characters 231 232 233 234 235 236 237 238 239 240
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens 1 ? ? 0 0 1 0 ? ? ?
Lectavis bretincola ? ? [12] 0 0 1 0 1 0 0
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? 1 1 1 1 0 1 0 0
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? 1 0 0
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
571
Appendix C: Character Matrix Continued.
Taxa\characters 241 242 243 244 245 246 247 248 249 250
Archaeopteryx (all ten) ? 0 0 2 ? 0 0 0 ? ?
Jeholornis prima 1 0 ? 0 0 1 1 ? ? ?
Rahonavis ostromi 1 0 1 0 0 1 ? 0 0 2
Zhongornis haoae ? 0 ? ? ? ? ? ? ? ?
Confuciusornis sanctus 0 0 0 1 ? ? ? ? ? 1
Sapeornis chaoyangensis 1 1 0 2 ? ? ? ? 1 ?
Apsaravis ukhaana 2 1 0 1 0 1 1 ? ? ?
Patagopteryx deferrariisi 0 0 1 1 1 1 ? 1 1 1
Longicrusavis houi 2 1 0 2 [02] ? ? ? ? 1
Gansus yumenensis ? 0 0 2 0 0 1 0 ? 2
Archaeorhynchus spathula ? ? ? ? ? ? ? ? ? 2
Yixianornis grabaui ? ? ? ? ? 0 ? 0 ? ?
Ichthyornis dispar 1 1 0 2 0 ? ? ? ? 2
Hesperornis regalis 1 1 0 2 0 0 0 0 1 2
Anas 1 1 0 2 2 1 1 0 1 2
Gallus 1 1 0 2 1 0 0 0 1 2
Longipteryx chaoyangia 0 0 ? 0 ? ? ? ? 1 ?
Rapaxavis pani 0 ? ? ? ? ? ? 1 1 ?
Cathyaornis yandica ? ? 1 ? ? ? ? ? 1 ?
Enan. n. sp. DNHM D2950/1 ? ? ? ? ? ? ? ? ? ?
Dapingfangornis sentisorhinus 1 1 1 0 0 ? ? 1 ? ?
Pengornis houi [12] ? ? ? ? ? ? ? 1 ?
Hebeiornis fengningensis ? ? ? ? ? ? ? ? ? ?
Longirostravis hani ? ? ? ? ? ? ? ? 1 ?
Longipteryx DNHM D2566 ? ? 1 ? ? ? ? 0 ? ?
Gobipteryx minuta 0 1 1 1 [01] ? ? 1 1 ?
Alethoalaornis agitornis [01] 1 1 [01] 0 1 ? ? ? ?
Longipteryx DNHM D2889 ? ? ? ? ? ? ? ? ? ?
Concornis lacustris ? ? ? ? ? ? ? ? ? ?
Eoenantiornis buhleri ? ? ? ? ? ? ? ? ? ?
Protopteryx fengningensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2952/3 ? ? ? ? ? ? ? ? ? ?
572
Appendix C: Character Matrix Continued.
Taxa\characters 241 242 243 244 245 246 247 248 249 250
Enan. indet. DNHM D2130 ? ? ? ? ? ? ? ? ? ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 ? ? ? ? ? ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis ? ? ? ? ? 1 1 0 ? 0
Neuquenornis volans ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? ? ? ? ? ? ? ? ? ?
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 0 0 1 [01] 0 1 1 1 ? 0
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 ? ? ? ? ? ? ? ? ? ?
Jibeinia luanhera ? ? ? ? ? ? ? ? ? ?
Cathayornis caudatus 1 1 1 ? ? ? ? ? ? ?
Paraprotopteryx ? ? ? ? ? ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis 0 1 1 1 1 1 1 1 ? ?
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 ? ? ? ? ? ? ? ? 1 ?
Enan. indet. CAGS-IG-07-CM-001 ? ? ? ? ? 0 ? ? ? ?
Enan. indet. CAGS-IG-06-CM-012 0 ? ? ? 0 ? ? 0 ? ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
573
Appendix C: Character Matrix Continued.
Taxa\characters 241 242 243 244 245 246 247 248 249 250
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola 0 0 1 0 2 1 1 1 ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos 0 0 1 0 1 ? ? 1 ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca 0 ? 1 [12] ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
574
Appendix C: Character Matrix Continued.
Taxa\characters 251 252 253 254 255 256 257 258 259 260
Archaeopteryx (all ten) 0 0 0 0 ? 0 0 0 0 0
Jeholornis prima 1 1 0 0 ? 0 0 0 0 0
Rahonavis ostromi 1 0 0 0 ? ? 0 1 0 0
Zhongornis haoae 1 ? 0 0 ? ? 0 0 0 0
Confuciusornis sanctus 1 1 0 0 ? 0 0 0 0 0
Sapeornis chaoyangensis 1 1 0 0 ? 0 0 0 0 0
Apsaravis ukhaana 1 1 [12] 0 ? 1 0 0 1 0
Patagopteryx deferrariisi 1 1 2 0 0 1 0 0 0 0
Longicrusavis houi 1 1 2 0 ? 1 0 0 1 0
Gansus yumenensis 1 1 2 0 0 1 0 0 1 0
Archaeorhynchus spathula 1 1 [01] 0 ? 1 0 0 0 0
Yixianornis grabaui 1 1 [12] 0 ? 1 0 0 ? ?
Ichthyornis dispar 1 1 2 0 0 1 2 0 1 0
Hesperornis regalis 1 1 2 0 0 1 2 0 1 0
Anas 1 1 2 0 0 1 1 0 1 0
Gallus 1 1 2 0 0 1 1 0 1 0
Longipteryx chaoyangia 1 ? 0 ? ? 1 0 0 0 0
Rapaxavis pani 1 0 0 ? ? 1 0 0 0 1
Cathyaornis yandica 1 ? ? ? ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 ? 0 0 ? ? ? 0 1 0 ?
Dapingfangornis sentisorhinus 1 1 0 0 ? ? 0 1 0 ?
Pengornis houi 1 1 0 0 ? ? 0 1 0 0
Hebeiornis fengningensis ? 0 0 ? ? ? 0 1 0 0
Longirostravis hani 1 1 [01] ? ? 1 0 0 0 0
Longipteryx DNHM D2566 1 ? 0 ? ? ? 0 0 0 0
Gobipteryx minuta 1 1 0 0 ? 1 0 1 0 0
Alethoalaornis agitornis 1 1 0 ? ? ? ? 1 ? ?
Longipteryx DNHM D2889 ? ? 0 ? ? ? ? [01] 0 0
Concornis lacustris 1 1 1 0 ? ? 0 1 0 1
Eoenantiornis buhleri ? 1 1 ? ? ? 0 1 0 ?
Protopteryx fengningensis ? 0 0 ? ? ? 0 0 0 ?
Enan. indet. DNHM D2952/3 1 1 0 ? ? ? ? 1 0 ?
575
Appendix C: Character Matrix Continued.
Taxa\characters 251 252 253 254 255 256 257 258 259 260
Enan. indet. DNHM D2130 1 1 0 ? ? ? ? [01] 0 ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum 1 1 0 ? ? ? 0 0 0 0
Enan. indet. DNHM D2884 1/2 1 1 0 ? ? ? ? 1 0 ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis 1 1 0 ? ? 1 0 1 0 ?
Neuquenornis volans ? 1 0 ? ? ? ? 1 0 1
Enan. indet. DNHM D2567/8 1 ? 0 ? ? ? ? 1 0 ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali ? 0 0 ? ? 1 0 0 0 ?
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 ? ? 0 ? ? ? ? 1 0 ?
Enan. indet. DNHM D2510/1 ? 1 0 ? ? ? 0 [01] 0 ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 1 1 0 0 1 ? 0 1 0 0
Cathayornis chabuensis 1 ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 1 1 0 ? ? ? ? 1 0 1
Jibeinia luanhera ? ? 0 ? ? ? ? ? 0 ?
Cathayornis caudatus 1 1 0 ? ? ? 0 1 0 0
Paraprotopteryx ? ? 0 ? ? ? ? 1 0 ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis 1 ? ? ? ? ? ? ? ? ?
Soroavisaurus australis ? 1 [01] 1 1 1 0 1 0 1
Largirostrornis sexdentornis 1 1 0 ? ? ? 0 1 0 ?
Enan. indet. CAGS!IG!04!CM!007 1 1 0 ? ? 1 ? 1 ? ?
Enan. indet. CAGS-IG-07-CM-001 1 0 0 ? ? 1 0 1 0 ?
Enan. indet. CAGS-IG-06-CM-012 1 1 0 0 ? ? 0 1 0 1
Cuspirostrisornis houi ? ? [01] ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? 1 0 ? ? ? 0 ? 0 ?
Longchengornis sanyanesis ? ? 0 ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
576
Appendix C: Character Matrix Continued.
Taxa\characters 251 252 253 254 255 256 257 258 259 260
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola ? 1 1 0 0 ? 0 1 0 0
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae ? 1 0 1 1 ? 0 1 0 1
Yungavolucris brevipedalis ? 1 1 0 0 1 0 1 0 0
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
577
Appendix C: Character Matrix Continued.
Taxa\characters 261 262 263 264 265 266 267 268 269 270
Archaeopteryx (all ten) 0 0 0 ? 0 0 0 - 0 ?
Jeholornis prima 0 ? 0 0 0 0 0 - 0 2
Rahonavis ostromi 0 0 0 0 0 1 [23] 1 0 [01]
Zhongornis haoae ? 0 ? 0 ? 0 ? ? 0 [12]
Confuciusornis sanctus 0 1 0 0 1 1 2 1 0 0
Sapeornis chaoyangensis 0 0 0 0 0 0 0 - 0 0
Apsaravis ukhaana 2 1 [12] ? 1 2 3 ? 0 1
Patagopteryx deferrariisi 2 1 0 1 1 2 0 - 0 ?
Longicrusavis houi ? ? ? ? 1 2 2 0 0 1
Gansus yumenensis 2 0 ? ? 1 [12] 3 0 0 2
Archaeorhynchus spathula ? ? ? ? 0 0 0 - 0 1
Yixianornis grabaui 2 1 1 1 0 2 ? ? 0 1
Ichthyornis dispar [23] 0 0 0 2 2 3 0 0 2
Hesperornis regalis 2 0 1 0 2 [01] 2 0 3 2
Anas 3 0 0 0 2 2 3 0 0 2
Gallus 3 0 0 0 2 2 3 0 0 1
Longipteryx chaoyangia 0 0 0 0 0 0 2 1 1 2
Rapaxavis pani ? ? ? ? 0 0 3 1 0 1
Cathyaornis yandica ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 ? ? ? ? 0 ? ? ? 0 [01]
Dapingfangornis sentisorhinus ? ? ? ? 0 0 ? ? 0 0
Pengornis houi 0 1 2 0 0 0 3 1 0 1
Hebeiornis fengningensis ? ? ? ? 0 0 2 1 [01] 2
Longirostravis hani ? ? ? ? 0 0 ? ? 0 1
Longipteryx DNHM D2566 ? ? ? ? 0 0 ? ? [01] ?
Gobipteryx minuta 0 0 0 0 ? ? 2 1 0 ?
Alethoalaornis agitornis 0 ? ? 1 0 [01] ? ? 0 0
Longipteryx DNHM D2889 ? ? ? ? ? ? ? ? 1 [12]
Concornis lacustris ? ? ? ? 0 0 ? ? 0 0
Eoenantiornis buhleri ? ? ? ? ? ? ? ? 0 ?
Protopteryx fengningensis ? ? ? ? 0 0 ? ? 0 [01]
Enan. indet. DNHM D2952/3 0 0 ? ? 0 0 ? ? 0 1
578
Appendix C: Character Matrix Continued.
Taxa\characters 261 262 263 264 265 266 267 268 269 270
Enan. indet. DNHM D2130 0 0 ? ? 0 0 ? ? 0 0
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum ? ? ? ? 0 0 2 1 [01] [01]
Enan. indet. DNHM D2884 1/2 ? ? ? ? 0 ? ? ? 0 ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis 0 1 2 1 0 ? ? ? 0 0
Neuquenornis volans ? 1 ? 1 ? ? ? ? 0 ?
Enan. indet. DNHM D2567/8 0 ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali 0 ? ? ? 0 0 ? ? 0 0
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 0 1 1 1 ? ? ? ? 0 ?
Enan. indet. DNHM D2510/1 ? ? ? ? ? ? ? ? 0 ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 0 1 2 ? 0 ? 2 1 0 ?
Cathayornis chabuensis ? ? ? ? ? ? ? ? 0 ?
Enan. indet. CAGS-IG-05-CM-004 ? 1 2 1 0 [01] 2 1 0 2
Jibeinia luanhera ? ? ? ? 0 ? ? ? ? ?
Cathayornis caudatus ? ? ? ? 0 [01] ? ? 0 1
Paraprotopteryx ? ? ? ? 0 ? ? ? ? ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis 0 1 1 1 1 1 [12] 1 0 1
Largirostrornis sexdentornis ? ? ? ? ? ? ? ? 0 0
Enan. indet. CAGS!IG!04!CM!007 0 1 2 1 0 [01] ? ? 0 0
Enan. indet. CAGS-IG-07-CM-001 0 1 2 1 0 0 ? ? 0 1
Enan. indet. CAGS-IG-06-CM-012 ? ? ? ? 0 [01] 3 1 0 2
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla ? ? ? ? ? ? 1 1 [01] ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
579
Appendix C: Character Matrix Continued.
Taxa\characters 261 262 263 264 265 266 267 268 269 270
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ? ? ? ? ?
Lectavis bretincola 1 1 1 1 0 ? 2 0 ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae 0 0 0 ? [01] 1 1 2 0 0
Yungavolucris brevipedalis 0 0 0 1 0 ? 1 [12] 1 2
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
580
Appendix C: Character Matrix Continued.
Taxa\characters 271 272 273 274 275 276 277 278 279 280
Archaeopteryx (all ten) 0 0 0 0 0 ? ? ? 0 0
Jeholornis prima 0 0 0 0 0 ? ? 0 0 0
Rahonavis ostromi 0 0 0 0 1 0 0 0 0 0
Zhongornis haoae 0 0 0 0 0 ? 0 ? 0 0
Confuciusornis sanctus 0 0 0 0 0 0 0 0 2 0
Sapeornis chaoyangensis 0 0 0 0 0 ? 0 0 0 ?
Apsaravis ukhaana 0 0 0 0 0 ? 0 0 ? ?
Patagopteryx deferrariisi 0 0 0 0 0 ? 0 0 0 0
Longicrusavis houi 0 ? 0 0 0 ? 1 ? 0 0
Gansus yumenensis 2 0 0 0 0 0 1 ? 0 1
Archaeorhynchus spathula 0 0 0 0 0 ? 0 ? ? ?
Yixianornis grabaui 0 1 ? 0 0 ? 0 ? 0 1
Ichthyornis dispar 0 0 0 0 1 0 0 ? ? ?
Hesperornis regalis 1 0 0 1 0 1 0 0 ? 0
Anas 1 0 0 0 0 0 1 0 3 0
Gallus 2 1 0 0 0 1 0 0 3 0
Longipteryx chaoyangia 0 0 0 0 0 0 0 0 0 0
Rapaxavis pani 0 0 0 0 0 ? 0 ? 0 0
Cathyaornis yandica ? ? ? ? ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 0 0 0 0 0 ? ? ? 2 ?
Dapingfangornis sentisorhinus 0 0 ? 0 0 ? 2 ? [01] 0
Pengornis houi 0 0 1 0 0 ? ? 0 1 0
Hebeiornis fengningensis 0 ? 1 1 0 ? ? ? 1 0
Longirostravis hani 0 0 0 0 0 ? ? ? ? ?
Longipteryx DNHM D2566 0 0 ? 0 0 ? ? ? ? ?
Gobipteryx minuta 0 0 1 1 0 ? ? 0 1 ?
Alethoalaornis agitornis 0 0 0 0 0 ? 0 0 1 0
Longipteryx DNHM D2889 0 0 0 0 0 ? ? ? 0 0
Concornis lacustris 0 0 0 0 0 ? 0 ? [01] 1
Eoenantiornis buhleri ? 0 1 0 0 ? ? ? ? ?
Protopteryx fengningensis 0 0 1 0 0 ? ? ? 0 0
Enan. indet. DNHM D2952/3 0 0 1 0 0 ? ? ? ? ?
581
Appendix C: Character Matrix Continued.
Taxa\characters 271 272 273 274 275 276 277 278 279 280
Enan. indet. DNHM D2130 0 0 0 0 0 0 ? ? 2 ?
Eoalulavis hoyasi ? ? ? ? ? ? ? ? ? ?
Shanweiniao cooperorum 0 0 0 0 0 ? ? ? ? ?
Enan. indet. DNHM D2884 1/2 0 0 ? 0 0 ? ? ? ? ?
Elsornis keni ? ? ? ? ? ? ? ? ? ?
Sinornis santensis [01] 0 ? 0 0 ? ? ? 1 1
Neuquenornis volans 1 1 1 0 ? 1 0 1 2 0
Enan. indet. DNHM D2567/8 ? ? ? ? ? ? ? ? ? ?
El Montsec Hatchling ? ? ? ? ? ? ? ? ? ?
Iberomesornis romerali 0 0 ? 0 0 ? ? ? 1 0
Eocathayornis walkeri ? ? ? ? ? ? ? ? ? ?
Enan. indet. DNHM D2836 0 0 ? 0 0 ? ? ? 1 ?
Enan. indet. DNHM D2510/1 0 0 ? 0 0 ? ? ? ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 [01] ? 0 0 ? ? ? ? 1 1
Cathayornis chabuensis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 [01] ? 0 0 0 ? 0 ? 1 1
Jibeinia luanhera 0 0 ? 0 0 ? ? ? ? ?
Cathayornis caudatus 0 0 0 0 0 ? 0 ? [01] ?
Paraprotopteryx ? ? ? 0 ? ? ? ? [01] ?
Enantiornis leali ? ? ? ? ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ? ? ? ? ?
Soroavisaurus australis 0 0 1 1 0 1 0 1 2 0
Largirostrornis sexdentornis 0 0 ? 0 1 ? 0 ? ? ?
Enan. indet. CAGS!IG!04!CM!007 0 0 ? 0 0 0 1 0 2 ?
Enan. indet. CAGS-IG-07-CM-001 0 0 1 0 0 0 0 0 1 1
Enan. indet. CAGS-IG-06-CM-012 0 0 0 0 0 ? ? ? 1 ?
Cuspirostrisornis houi ? ? ? ? ? ? ? ? ? ?
Enantiophoenix electrophyla 0 0 ? 0 ? ? ? ? ? ?
Longchengornis sanyanesis ? ? ? ? ? ? ? ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ? ? ? ? ?
582
Appendix C: Character Matrix Continued.
Taxa\characters 271 272 273 274 275 276 277 278 279 280
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ? ? ? ? ?
Alexornis antecedens ? ? ? 0 ? 1 ? ? ? ?
Lectavis bretincola ? ? ? ? ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ? ? ? ? ?
Avisaurus gloriae 0 0 1 0 0 1 0 1 ? ?
Yungavolucris brevipedalis 0 0 1 0 1 0 0 1 ? ?
Martinavis cruzyensis ? ? ? ? ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ? ? ? ? ?
583
Appendix C: Character Matrix Continued.
Taxa\characters 281 282 283 284 285 286
Archaeopteryx (all ten) 0 1 0 0 0 0
Jeholornis prima 1 1 0 ? ? 0
Rahonavis ostromi 1 0 0 ? ? ?
Zhongornis haoae 1 1 0 1 ? ?
Confuciusornis sanctus 1 1 0 0 0 0
Sapeornis chaoyangensis 1 1 0 ? ? ?
Apsaravis ukhaana ? ? ? ? ? ?
Patagopteryx deferrariisi 0 1 0 1 ? ?
Longicrusavis houi 1 1 ? 0 ? ?
Gansus yumenensis 1 1 0 0 ? ?
Archaeorhynchus spathula ? ? 0 ? ? ?
Yixianornis grabaui 1 1 0 1 ? 1
Ichthyornis dispar ? ? ? ? ? ?
Hesperornis regalis ? ? 0 ? 0 ?
Anas 1 0 0 1 1 1
Gallus 1 0 0 1 1 1
Longipteryx chaoyangia 1 [01] 0 0 ? ?
Rapaxavis pani 1 1 1 0 ? ?
Cathyaornis yandica ? ? ? ? ? ?
Enan. n. sp. DNHM D2950/1 1 ? 2 ? ? ?
Dapingfangornis sentisorhinus 1 2 2 1 ? 0
Pengornis houi ? ? 0 ? ? ?
Hebeiornis fengningensis 1 1 ? 1 ? ?
Longirostravis hani ? ? ? ? ? ?
Longipteryx DNHM D2566 ? 1 0 0 ? ?
Gobipteryx minuta ? ? 0 ? ? ?
Alethoalaornis agitornis 1 1 2 0 ? ?
Longipteryx DNHM D2889 1 1 0 0 ? 0
Concornis lacustris 1 ? 0 ? ? ?
Eoenantiornis buhleri 1 1 0 ? 1 0
Protopteryx fengningensis 1 1 ? 0 1 0
Enan. indet. DNHM D2952/3 1 1 ? 1 1 0
584
Appendix C: Character Matrix Continued.
Taxa\characters 281 282 283 284 285 286
Enan. indet. DNHM D2130 1 1 0 0 1 ?
Eoalulavis hoyasi ? ? ? ? 1 ?
Shanweiniao cooperorum 1 [01] 2 0 ? 1
Enan. indet. DNHM D2884 1/2 1 1 ? 0 ? 0
Elsornis keni ? ? 0 ? ? ?
Sinornis santensis 1 1 2 1 ? ?
Neuquenornis volans 1 [12] 0 ? ? ?
Enan. indet. DNHM D2567/8 1 [12] 0 ? ? ?
El Montsec Hatchling ? ? ? ? ? ?
Iberomesornis romerali 1 1 ? ? ? ?
Eocathayornis walkeri ? ? ? ? ? ?
Enan. indet. DNHM D2836 1 1 0 0 ? ?
Enan. indet. DNHM D2510/1 1 1 0 0 ? ?
Enan. n. sp. CAGS 05-CM-006, 04-CM-006 1 [01] 0 1 ? ?
Cathayornis chabuensis 1 0 ? ? ? ?
Enan. indet. CAGS-IG-05-CM-004 1 1 1 ? ? 0
Jibeinia luanhera 1 1 ? 0 ? ?
Cathayornis caudatus ? ? ? ? ? ?
Paraprotopteryx 1 1 ? 0 ? 0
Enantiornis leali ? ? ? ? ? ?
Cathayornis aberransis ? ? ? ? ? ?
Soroavisaurus australis 1 ? 0 ? ? ?
Largirostrornis sexdentornis ? ? ? ? ? ?
Enan. indet. CAGS!IG!04!CM!007 1 1 0 0 ? ?
Enan. indet. CAGS-IG-07-CM-001 1 [01] 0 1 ? 0
Enan. indet. CAGS-IG-06-CM-012 1 1 0 ? ? ?
Cuspirostrisornis houi ? ? ? ? ? ?
Enantiophoenix electrophyla 1 ? ? ? ? ?
Longchengornis sanyanesis ? [12] 0 ? ? ?
Enan. indet. CAGS-02-CM-0901 ? ? ? ? ? ?
Noguerornis gonzalezi ? ? ? ? ? ?
Halimornis thompsoni ? ? ? ? ? ?
585
Appendix C: Character Matrix Continued.
Taxa\characters 281 282 283 284 285 286
Enan. indet. CAGS-IG-04-CM-023 ? ? ? ? ? ?
Alexornis antecedens ? ? ? ? ? ?
Lectavis bretincola ? ? ? ? ? ?
Otogornis genghisi ? ? ? ? ? ?
Avisaurus gloriae ? ? ? ? ? ?
Yungavolucris brevipedalis ? ? ? ? ? ?
Martinavis cruzyensis ? ? ? ? ? ?
Martinavis vincei ? ? ? ? ? ?
Gurilynia nessovi ? ? ? ? ? ?
Nanantius eos ? ? ? ? ? ?
Explorornis nessovi ? ? ? ? ? ?
Enantiornis walkeri ? ? ? ? ? ?
Kizylkumavis cretacea ? ? ? ? ? ?
Sazavis prisca ? ? ? ? ? ?
Abavornis bonaparti ? ? ? ? ? ?
Enantiornis martini ? ? ? ? ? ?
Zhyraornis kashkarovi ? ? ? ? ? ?
Incolornis silvae ? ? ? ? ? ?
Lenesornis maltshevskyi ? ? ? ? ? ?
586

Abstract (if available)

Abstract Enantiornithes is a diverse group of Mesozoic birds, however little is understood about their interrelationships, and even their monophyly has been questioned. Repeated attempts to yield phylogenetic hypotheses at the species level have resulted in trees with low support that are largely inconsistent between matrices. These hypotheses consistently place Enantiornithes as sister group to Ornithuromorpha, together comprising the clade Ornithothoraces, which includes Neornithes. Because of their phylogenetic position, intermediate between Archaeopteryx and modern birds, as well as their success during the Cretaceous, enantiornithines are important for better understanding early avian evolution and the evolution of the anatomically modern bird. This large-scale study of enantiornithines has three main aspects

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Dental evolution and tooth cycling in Mesozoic birds

PDF

Evolution & ecology of Mesozoic birds: a case study of the derived Hesperornithiformes and the use of morphometric data in quantifying avian paleoecology

PDF

Evolution of the dinosaur flight feather: insights from 3-dimensional fossil feathers

PDF

Assessing the quality of the fossil record using a phylogenetic approach

PDF

Benthic and pelagic marine ecology following the Triassic/Jurassic mass extinction

PDF

The evolution and functional significance of the cetacean pelvic bones

PDF

Growth of the Cretaceous Tuolumne batholith and synchronous regional tectonics, Sierra Nevada, CA: a coupled system in a continental margin arc setting

PDF

The geobiological role of bioturbating ecosystem engineers during key evolutionary intervals in Earth history

PDF

The early Triassic recovery period: exploring ecology and evolution in marine benthic communities following the Permian-Triassic mass extinction

Asset Metadata

Creator O'Connor, Jingmai Kathleen (author)

Core Title A systematic review of Enantiornithes (Aves: Ornithothoraces)

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publication Date 10/22/2009

Defense Date 08/19/2009

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Birds,cretaceous,Enantiornithes,Evolution,Mesozoic,OAI-PMH Harvest,Ornithothoraces

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Bottjer, David J. (committee chair), Chiappe, Luis (committee member), Chuong, Cheng-Ming (committee member), Corsetti, Frank (committee member), Wang, Xiaoming (committee member)

Creator Email jingmai@usc.edu,jugolik.cakey@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m2682

Unique identifier UC1185159

Identifier etd-OConnor-3232 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-277998 (legacy record id),usctheses-m2682 (legacy record id)

Legacy Identifier etd-OConnor-3232.pdf

Dmrecord 277998

Document Type Dissertation

Rights O'Connor, Jingmai Kathleen

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu