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Evolution of the dinosaur flight feather: insights from 3-dimensional fossil feathers

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Evolution of the dinosaur flight feather: insights from 3-dimensional fossil feathers

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Content EVOLUTION OF THE DINOSAUR FLIGHT FEATHER:

INSIGHTS FROM 3-DIMENSIONAL FOSSIL FEATHERS

by

Nathan Robert Carroll

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

December 2021

© Copyright 2021 Nathan Robert Carroll
ii
DEDICATION
This dissertation is dedicated to my grandparents, Jim and Loryane Stermitz and
Lloyd and Betty Carroll. I was blessed to experience their work ethic, stewardship of the
landscape, and deep well of love and support for their family. I hope to continue to learn
from the lands and earn with my hands, and thanks to them I can.
iii
ACKNOWLEDGEMENTS
This list of acknowledgements is not full account of those responsible for the
production of this manuscript, but it is an attempt to acknowledge those that directly
contributed to the production of new information presented here. Thanks to my co-
advisors, Luis Chiappe and David Bottjer, for their patience, contributions, and editorials
to this dissertation, my experience at USC, and their support in past and future
publications. The insights made by this research would not have been possible without
the scanning expertise of Tea Jashashvili at the USC Keck School of Medicine Molecular
Imaging Lab, and to Rachel Racicot for teaching me how to use VGStudio. This research
provided the opportunity to utilize multiple departments outside the Dinosaur Institute of
the Natural History Museum of Los Angeles County and the many talented individuals
that run them. Images of feather specimens and their arthropod context would not have
been possible without the expertise of Giar-Ann Kung and Brian Brown of the
Entomology Department. Aaron Celestion was generous with his time and mastery of
equipment in Minerology Department, and the fine folks in the Education and Performing
Arts Department allowed me to expand my outreach skills. Invaluable mentorship from
Jingmai O’Connor has been provided since the start of my paleontological studies.
Thanks to David DeMar for discovering an exceptional fossil in an unexceptional place,
and to Gregory Wilson Mantilla for offering me the opportunity to work on such an
amazing discovery made by and housed by the Burke Museum of Natural History.
Thanks to Karen Chin, Nathan Myhrvold, David DeMar, Gregory Wilson Mantilla, and
iv
Thomas Tobin for comments and insights into the preservation of coprolite-preserved
feathers. Thank you to Cipriano Belser, Cindy Waite, and my colleagues of the USC
Earth Science department (particularly Snir Attia, Hank Wooley, Claire Johnson, Kirstin
Washington, Joyce Yager, and Kenny Bolster) for your encouragement in Los Angeles.
My studies in California would not have been possible without the continued support of
the Carter County Museum and the community of Ekalaka, Montana. Last but most
importantly, thank you to my parents Llane and Sharon Carroll and my partner Sabre
Moore for your love and support no matter the distance.
v
TABLE OF CONTENTS
Dedication ............................................................................................................................ ii
Acknowledgements ............................................................................................................ iii
List of Figures .................................................................................................................... vii
List of Institutional Abbreviations .................................................................................... viii
Abstract ............................................................................................................................... ix
Chapter 1: Introduction ........................................................................................................ 1
Chapter 2: Mid-Cretaceous Amber Inclusions Reveal Morphogenesis of Extinct Rachis-
Dominated Feathers. ............................................................................................................ 7

Chapter 3: Building the Feather Shaft: 3D Calamus-Rachis Transitions in Amber Provide
Insights into the Formation of Mid-Cretaceous Feathers. ................................................. 23

Chapter 4: Modern Bird Feather Architecture Preserved in Putative T. rex Coprolite ..... 39
Chapter 5: Conclusions and Discussion ............................................................................ 62
References ......................................................................................................................... 72
vi
LIST OF FIGURES
Figure 1.1 Feather Anatomy ................................................................................................ 6

Figure 2.1 Lithic preservation of Early Cretaceous rachis-dominated feathers from the
Yixian Formation ............................................................................................................... 18

Figure 2.2 Paired rachis-dominated feathers preserved in amber ..................................... 19

Figure 2.3 Rachis-dominated feathers in amber ................................................................ 20

Figure 2.4 Generalized overview of the morphogenesis of a modern chicken tail feather
and proposed morphogenesis of extinct rachis-dominated feather. .................................. 21

Figure 3.1 Anatomical illustration of the rachis-calamus transition in a modern flight
feather ................................................................................................................................ 32

Figure 3.2 Mid-Cretaceous bird wing (LACM 8001) in amber ........................................ 33

Figure 3.3 Segmented reconstruction of wing preserved in amber (LACM DI 8004) in
dorsal view. ........................................................................................................................ 34

Figure 3.4 Sagittal sections of primaries 4 and 5 of LACM DI 8004 from µCT slices .... 35

Figure 3.5 Cross sections of LACM DI 8004 primaries 4 and 5 from µCT slices. ........... 36

Figure 3.6 X-ray µCT renderings of isolated flight feather CCM V 2021-5 .................... 37

Figure 3.7 Illustration of the contiguity of the tubular epidermis and central dermal pulp.38

Figure 4.1 Optical image of nodule and exposed feather. ................................................. 54
vii

Figure 4.2. Details of surface-exposed feather under light microscopy ............................ 55

Figure 4.3. Preservational details of exposed feather under SEM. .................................... 56

Figure 4.4. Micro-CT reconstructions of definitive feathers in UWBM 103150 .............. 57

Figure 4.5. Fragmentary Inclusions ................................................................................... 59

Figure 4.6: Potential integumentary producing groups of the Hell Creek Formation and
evolutionary significance of described feathers ................................................................ 60

Figure 4.7. Coprolite (LACM 48121) from the Hell Creek formation. ........................... 61
viii
LIST OF INSTITUTIONAL ABBREVIATIONS
CCM ................................................................................................ Carter County Museum
BMRP ........................................................................... Burpee Museum of Natural History
LACM ...................................................... Natural History Museum of Los Angeles County
UWBM ............................................................... University of Washington Burke Museum

ix
ABSTRACT
Modern flight feathers have been historically viewed as appearing early in avian
evolution, and possibly originating in non-avian dinosaurs. The assumption that a modern
asymmetrical flight feather had evolved by the Late Jurassic and maintained relative
morphologic stasis for over 145 million years was informed by 2-dimensional lithic
feather preservation. This body of research utilizes morphogenetically informative 3-
dimensional characters of modern feathers and new information derived from 3-
dimensional Mesozoic fossils to demonstrate that key aspects of the modern bird feather
continued to evolve throughout the Cretaceous. Feathers preserved in mid-Cretaceous
amber reveal that stem birds produced feathers without medullary pith or the full ventral
geometry that typifies modern feather rachises. A new source of exceptional 3-D feather
preservation for the Mesozoic is identified (coprolites) and provides evidence for the
presence of modern rachis development by the latest Cretaceous. This new data
highlights the need for 3-dimensional feather preservation to make informed hypotheses
about the evolutionary development of the modern bird feather.

1
CHAPTER 1
INTRODUCTION
Feathers and their seemingly magical ability to imbue birds with flight have long
fascinated humans. Cultures across the globe have historically adorned themselves with plumes,
associating feathers and wings with their respective flighted deities and mythological stories of
flight. Early experiments in human flight often sought to replicate the feathered wing of a bird,
and flying models often utilized bird feathers because of their natural strength and lightness.
Feathers are so ubiquitous with birds and flight that the discovery of a small Jurassic dinosaur
skeleton from the Solnhofen Limestones with three clawed fingers, toothed skull, and long tail in
1861 was immediately identified as an ancient flighted bird-because it was preserved with
feathered wings. The earliest recorded discovery of a fossil feather, which appears to be
remarkably modern, was also discovered in a Solnhofen limestone quarry in 1861. These two
fossils were subsequently classified as belonging to the famous Archaeopteryx.
Following the celebrated discoveries of Archaeopteryx in the 19
th
th century, the study of
fossil feathers was done only at a minimal level until discovery of the Early Cretaceous Jehol
biota in China. The Jehol biota has revealed a diversity of feather types as well as a diversity of
dinosaur forms associated with them. Although many of these feather forms are found on stem
birds, feathers and feather-like integumentary structures have been found on increasingly wider
taxonomic groups of non-avialan dinosaurs.
The level of preservation from the Jehol deposits is truly remarkable. Despite these
examples of exceptional preservation, the compressed, two-dimensional nature of these lithic
fossils prevent examinations of the three-dimensional aspects of these feathers that would allow

2
for more accurate comparisons to modern feathers. Although barbs are commonly fully
discernible, barbule morphology, specifically the hooklets that allow modern feathers to create a
cohesive vane, are assumed to be present because of the macroscale appearance of a cohesive
vane. This window into the Early Cretaceous has been incredibly beneficial for tying derived
forms of feathers with skeletal material, allowing for the placement of these feather forms into a
phylogenetic context. However, to further test when certain three-dimensional components of the
modern bird feather evolved requires three-dimensional preservation.
Amber (fossilized tree resin) has long been the backbone of fossil arthropod research and
although the amber record is largely dominated by invertebrate inclusions, 3D- preserved
feathers have been reported from nearly every well studied amber deposit. Vertebrate remains
are the least common inclusion in any amber deposit, but feathers are the most common
vertebrate inclusion. Isolated feathers are reported in ambers from the Late Barremian of
Lebanon (Schlee 1973) the Late Aptian/middle Albian of Spain (Alonso et al. 2000) , Early
Cenomanian of Myanmar (Grimaldi, Engel, and Nascimbene 2002), Cenomanian of France
(Perrichot et al. 2008), Turonian of New Jersey (Grimaldi and Case 1995), Santonian of Siberia
(Kurochkin 1985), Santonian of Japan (Grimaldi and Case 1995), and Campanian of Canada
(McKellar et al. 2011). These early discoveries in Cretaceous amber show the potential of this
type of preservation for understanding the complex three-dimensional structure of feathers, but
only in the last few years has the true potential of these types of deposits been realized with the
advent of a wealth of new discoveries from the middle Cretaceous of Myanmar (Xing et al.
2017b; 2019; Xing, McKellar, and O’Connor 2020; Xing, Cockx, and McKellar 2020; Xing et
al. 2016).

3
Inclusions in amber from Myanmar were noted as early as 1892 (Noetling 1892; 1893)
but it would not be until geopolitical events in 1994 that significant collections of amber from
this region would enter scientific studies. Grimaldi et al. (2002) figures a feather cluster, but it
was only in 2010 that the surprising number of feathers preserved in this deposit became
apparent. There is extensive evidence on the paleobiology and paleoecology of organismal
remains from Burmese amber. The current latitude of Burmese amber deposits is 25.5°N, but
paleolatitude was a tropical 12°N (Zherikhin and Ross 2000). Many organisms in burmite,
including bark-growing liverworts, buthid scorpions, roaches (Blattodea), stem group ants,
termites, webspinners (Embiodea), scale insects (Coccoidea), Zoraptera, and Onychophora
resemble extant, tropical taxa, indicating that the amber was deposited in a moist tropical
paleoenvironment (Grimaldi et al. 2002). Discoveries of pholadid bivalve borings on amber
nuggets (Smith and Ross 2016), encrusting crinoids and corals (Mao et al. 2018), and encased
ammonites and isopods (T. Yu et al. 2019; Bolotov et al. 2021) suggest a nearshore marine or
brackish water setting.
The modern flight feather is an inspiring adaptation of a keratinous epidermal tube into
an airfoil component. At the exterior morphologic scale, a “basic” feather is composed of a
central shaft with a proximally hollow calamus that transitions to a pith-filled square rachis. The
interior, sponge-like medullary pith is key to the morphogenesis of the square cross section as
well as conveying mechanical efficiencies (Maderson et al. 2009; Chang et al. 2019b). Barbs
branch from the lateral walls of the rachis, and from the pith-filled barb ramus are tertiary-
branching barbules (Fig. 1.1). The barbules, which typically have a plate-like proximal base can
differentiate distally to a pennulum with cilia (or hooklets) that interlock with neighboring
barbules to form the feather vane (Fig. 1.1).

4
The mechanical efficiencies, composition, and underlying morphogenesis of the
hierarchical branched architecture of the modern bird feather are currently being discovered with
new techniques and technologies (N. Sullivan et al. 2016; Chang et al. 2019; Theagarten
Lingham-Soliar 2017; Sullivan et al. 2018). These recent advances have revealed how the central
shaft of a feather, termed the rachis, plays a major role in lift production, airfoil shape, and drag
reduction (KleinHeerenbrink, Johansson, and Hedenström 2017). The multiple performance
demands of flight on a single feather are accommodated by a rachis with variable cross-sectional
geometry coupled with a multi-component structure (Chang et al. 2019; B. Wang and Meyers
2017).
The external hierarchal nature of the feather is likely due in part to its internal material
construction and can be considered a fiber-reinforced composite (B. Wang and Meyers 2017). A
system of protein matrix-supported continuous keratin fiber bundles (3–5 μm in diameter) that
connect via nodes at the microscale, comprised largely of corneous beta-proteins (CBPs), some
intermediate filament (IF)(alpha) keratins, and other amorphous proteins form the feather
(Theagarten Lingham-Soliar 2017; Alibardi 2017). These fundamental structural fiber bundles
are organized into lamellae within the cortex of the feather, with the lamellae sheets varying in
the fiber direction (Fig 1.1). At the nanoscale, these bundles are constructed of even smaller
macrofibrils 50~400 nm in diameter, which are composed of beta-filaments.
The discovery of numerous fossils since the first Mesozoic feather was unearthed more
than 160 years ago has yielded a wealth of evidence for understanding the evolutionary history
of these singular structures. This has been assisted by detailed studies of their development and
molecular control. Nonetheless, many questions about the evolution of these unique epidermal
structures remain unanswered: When did many of their complex traits—from hooklets to pith-

5
filled rachises—arise? Did the seemingly modern feathers of Mesozoic stem birds develop in a
similar fashion as those of living birds? Can the general appearance of many lithic feathers
preserved in Mesozoic Lagerstätten—with distinct shafts, barbs, and vanes—be taken as
evidence for the presence of micro- and nano-scaled traits (hooklets, pith, and others)? These are
some of the questions addressed in the present study, which uses novel evidence from amber and
coprolite inclusions (as well as CT visualizations) to provide a deeper understanding of the
evolution of feather traits and their possible developmental pathways.

6

Figure 1.1. Feather Anatomy. A) Generalized primary feather in ventral view. B) Detail of
feather follicle. C) Cross section and components of a rachis. C’) Proximal to distal cross
sections of the feather shaft, here represented by the American White Pelican. Numbers correlate
to numbered positions in (A). D) Detail of trailing pennaceous vane and interlocking relationship
between hooklets and grooves. D’) barb detail, illustrating differentiation between proximal and
distal barbules. B) and D’) modified from Lucas and Stettenheim 1976, C’) modified from Wang
and Meyer 2017, D) modified from Prum and Brush 2014.

7
CHAPTER 2
MID-CRETACEOUS AMBER INCLUSIONS REVEAL
MORPHOGENESIS OF EXTINCT RACHIS-DOMINATED FEATHERS.

CHAPTER 2 ABSTRACT- This chapter includes the description of three-dimensionally
preserved feathers in mid-Cretaceous Burmese amber that share macro-morphological
similarities (e.g., proportionally wide rachis with a “medial stripe”) with lithic, two-
dimensionally preserved rachis-dominated feathers, first recognized in the Jehol Biota. These
feathers in amber reveal a unique ventrally concave and dorsoventrally thin rachis, and a dorsal
groove (sometimes pigmented) that we identify as the “medial stripe” visible in many rachis-
dominated rectrices of Mesozoic birds. The distally pennaceous portion of these feathers shows
differentiated proximal and distal barbules, the latter with hooklets forming interlocking barbs.
Micro-CT scans and transverse sections demonstrate the absence of histodifferentiated cortex
and medullary pith of the rachis and barb rami. The highly differentiated barbules combined with
the lack of obvious histodifferentiation of the barb rami or rachis suggests that these feathers
could have been formed without the full suite and developmental interplay of intermediate
filament alpha keratins and corneous beta-proteins that is employed in the cornification process
of modern feathers. This study thus highlights how the development of these feathers might have
differed from that of their modern counterparts, namely in the morphogenesis of the ventral
components of the rachis and barb rami. We suggest that the concave ventral surface of the
rachis of these Cretaceous feathers is not homologous with the ventral groove of modern
rachises. Our study of these Burmese feathers also confirms previous claims, based on two-

8
dimensional fossils, that they correspond to an extinct morphotype and it cautions about the
common practice of extrapolating developmental aspects (and mechanical attributes) of modern
feathers to those of stem birds (and their dinosaurian outgroups) because the latter need not to
have developed through identical pathways.

i. Introduction
Exceptional fossil feather preservation in lithic Lagerstätten, largely from the Lower
Cretaceous, has led to the recognition of several purportedly unique feather types that are
unknown in modern birds (Fucheng, Zhonghe, and Dyke 2006; Fucheng Zhang et al. 2008; Xu
and Guo 2009; Xu, Zheng, and You 2010; 2009; O’Connor et al. 2012a). Although some of these
unique morphotypes may have been altered taphonomicaly (Benton et al. 2008; Foth 2012), the
rachis dominated feather (RDF) is a commonly reported and morphologically consistent type of
extinct feather, likely representing a true morphology (J. O’Connor et al. 2015). A clear
definition for the morphology of RDFs has yet to be fully proposed, largely due to disagreement
in how to interpret the features exhibited. In general, these feathers have an elongate “racket-
plume” appearance consisting of a long proximal portion formed by a proportionally wide rachis,
a distally vaned section, and a dark “medial stripe” that runs the full length of the feather (Fig.
2.1). Although many of these feathers are exquisitely preserved with some structurally resistant
components (i.e., melanosomes) observable at the microscale (Peteya et al. 2017), the
preservation of these two-dimensional lithic fossils prevents an accurate three-dimensional
microstructural whole-feather assessment. Without three-dimensional, contiguous micro to
macro scale preservation, it is difficult to make accurate assessments of the detailed morphology
of these feathers, let alone their development, therefore hindering comparisons with modern

9
feather development. This is typified by differing interpretations of the “medial stripe” as
representing the rachis of a vaned feather with undifferentiated barbs (FuCheng Zhang, Zhou,
and Benton 2008) or a trait (e.g., longitudinal groove) within a broader rachis (O’Connor et al.
2012b; Chiappe et al. 1999; F. Zhang 2000; Xu, Zheng, and You 2010).
As the number of reported RDFs has increased, so have the reported variations in
morphology and preservation. The greatest disparity is related to the extent of the vaned portion,
with pennaceous vanes running the full length of the feather in the Chinese Early Cretaceous
enantiornithines Parapengornis (Hu, O’Connor, and Zhou 2015) and Eopengornis (Xiaoli Wang
et al. 2014), and more distally restricted in most other coeval taxa (Chiappe and Meng 2016; Liu
et al. 2017). Likewise, the shape of the distally restricted pennaceous portion varies between taxa
(and sometimes intraspecifically), ranging from variably racket-shaped in the basal pygostylian
Confuciusornis, and the enantiornithines Paraprotopteryx and Dapingfangornis, to morphologies
in which the differentiation of the vanes is more gradual (e.g., Brazilian enantiornithine
Cratoavis) (Xiaoli Wang et al. 2014; de Souza Carvalho et al. 2015). Furthermore, the “medial
stripe”, observable on a number of Early Cretaceous specimens as a thin, pigmented line or a
longitudinal groove (de Souza Carvalho et al. 2015), is not apparent in some specimens (Peteya
et al. 2017). These morphologies, all documented in lithic fossils, are clearly subject to
taphonomic alteration, and the degree by which these biases modify morphology is not fully
known (Saitta et al. 2017). Regardless of these shortcomings, the nature of these unique feathers
has been the center of much debate.
In recent years, spectacular discoveries of avian fossils and putative non-avian dinosaurs
in mid-Cretaceous amber from northern Myanmar have provided important three-dimensional
and micro-structural information about Mesozoic feathers (Xing et al. 2016; 2017; 2018).

10
Among these new findings are a number of feathers with morphologies that closely match that of
RDFs at the macroscale, with preservation of features down to the microscale. A combination of
transmitted light microphotography and micro-CT scanning was used to elucidate important
three-dimensional, microscale features previously unattainable from the lithic record. Here we
present a set of new amber specimens to identify previously unknown features of RDFs and
highlight differences in the development of these feathers when compared to their modern
counterparts.

ii. Materials and Methods
All specimens described here are reposited at the Natural History Museum of Los
Angeles County. LACMDI 158032 is a 4 x 3 cm amber nugget containing two distal RDFs
(likely paired rectrices) and the distal tip of a wing. LACMDI 158557 is 3x2 cm amber nugget
containing the distal tip of an isolated feather and the middle section of an RDF. LACMDI
158490 is a 4 x 5 cm amber billet containing a single isolated distal portion of an RDF.
LACMDI 158555 contains an isolated middle portion of an RDF with the distal tip truncated
perpendicular to the long axis of the rachis.
Photomicrographs of all specimens were taken with a Keyence VHX-500 digital
microscope with a transmitted light base. Focused images were created using the Keyence
multiple image stacking software. One of the RDF inclusions of LACMDI 158032 was imaged
using x-ray microtomography. The scan was conducted on a GE Phoenix Nanotom M microCT
scanner at the Molecular Imaging Center, Department of Radiology, University of Southern
California Keck School of Medicine using a current of 400 µA and voltage of 60 kV. A
molybdenum target with no filter was used for the scan. The images were reconstructed from the

11
raw dataset with voxel size of 3.5 µm. VGStudioMax 3.0 software was used for visualization,
segmentation, and measurements. The feather was digitally isolated from the surrounding amber
matrix by using a variety of threshold values with the “region growing” and other “region of
interest” tools during the segmentation process, after applying a Gaussian filter. Original CT files
of the segmented feather are available from the Dryad database at
https://doi.org/10.5061/dryad.bzkh1894f upon request.

iii. Results
Our study is based on feathers preserved in 5 amber specimens (Figs 2.2; 2.3) in the
collection of the Natural History Museum of Los Angeles County’s Dinosaur Institute
(LACMDI). These specimens are from the Tanai Township (Myitkyina District) in Myanmar’s
Kachin Province, and they date to the middle Cretaceous (98.8±0.6 Ma) (Zherikhin and Ross
2000). The pennaceous feathers contained in these amber pieces range in total preserved length
from 23 mm to 6.5 mm, and display minor variations in the details of their morphology and
preservation. While some of these feathers are isolated (LACM-DI 158490, 158555), most occur
alongside other feather synclusions. In the case of LACM-DI 158032 (Fig. 2.2c) the feathers of
interest are preserved as parallel-aligned pairs.
Despite the variation in size and preservation, these feathers share a common rachis
construction. In planar view, the rachis is proportionally wide and bears a “darkened” medial
stripe running its full preserved length; this characteristic is observable with transmitted light in
all studied specimens (Figs 2.2c,d, 2.3a,d,f). It should be noted that due to the back-lit nature of
amber photomicrographs, it is difficult to discern whether darkening is due to a thickened keratin
cortex, pigmentation, or a combination of both factors. The dorsal surface of the rachis is slightly

12
convex with a dorsal groove that corresponds to the medial stripe. Ventrally, the concave surface
mirrors the convex dorsal surface, with a longitudinal medial ridge consequent with the medial
groove of the dorsal surface. Transverse cross sections of the rachis reveal an overall ventrally
concave morphology defined by an incredibly thin cortex (Fig. 2.2b). The cortex is thinnest in
the areas lateral to the medial stripe but medial to where the barbs attach, with thicknesses
between specimens ranging from approximately 3 μm (LACMDI 158555) to 10 μm (LACMDI
158205). The cortical thickness does not appear to vary along the preserved proximal-distal axis.
The lateral walls, where the barbs attach to the rachis, achieve the greatest cortical thickness,
ranging approximately between 10-36 μm (Figs 2.2a, 2.3b,c,e). The dorsal groove, present in all
specimens, is variable in the details of its morphology and preservation. In the case of LACMDI
158032, the groove is shallow, with a granulated texture distinct from the longitudinally aligned
fibrous texture of the rest of the rachis (Fig. 2.2d). In LACMDI 158557, a darkened strip of
material lies within the dorsal groove and appears to be loosely adhered to the cortical surface.
The dorsal groove maintains a constant width along the preserved length of the rachis, even as
the overall width of the rachis tapers distally. In feathers where the distal-most tip is preserved
(LACMDI 158205 and LACMDI 158557), the groove shallows and fades in prominence near the
point where the rachis narrows to the width of the dorsal groove and is not observable at the
distal-most tip of the feather.
The vanes of all feathers described here appear to be symmetric, although barb separation
and truncation prevents accurate measurements of total vane width. The vanes are formed by
interlocking barbs, which are comprised of a central ramus with distally and proximally
projecting barbules (Fig. 2.2 d,e). The thickness of the barb rami is comparably thin to that of the
rachis (3-10μm) and has a simple, ribbon-like morphology. The proximal and distal barbules

13
share a similar morphology in their attaching base, which is a long narrow plate with a dorsal
flange that connects with the ramus at an angle of 41-46° to the long axis of the barb. The bases
of the distal barbules attach to the dorsal aspect of the distal face of the rami, while the bases of
the proximal barbules attach to the ventral aspect of the proximal face of the rami. The proximal
barbules continue their insertion proximally beyond the junction of the barb rami and the rachis
as far as the insertion of the next proximal barb (Figs 2.2d, 2.3b). The pennuli of the proximal
barbules is demarcated by the presence of dorsal teeth and a tapering of the dorsoventral width.
The pennuli of the distal barbules are marked by an abrupt increase in angle and the presence of
weakly to strongly hooked barbicels that curve ventrally (Fig 2.3b).
iv. Discussion
Because the feathers here described only include relatively short (and presumably distal)
portions of vaned, RDFs, this study does not provide direct comparisons for the proximal, vane-
less portions of the rachis described from lithic deposits. Nonetheless, the new fossils
significantly expand our knowledge of the morphology of RDFs. In particular, these fossils show
that the rachis of these feathers was (1) dorsoventrally extremely thin (albeit their incomplete
preservation prevents determining if such condition extended throughout their entire length), (2)
ventrally concave, and (3) scarred by a dorsal groove and a ventral ridge. Most notably, they also
show that these feathers lack obvious medullary pith within the rachis or barb rami, an important
structural and developmental component of a modern feather (Lucas and Stettenheim 1972;
Maderson et al. 2009). Our observations also indicate that the “medial stripe” visible in many
RDFs preserved as lithic fossils corresponds to a dorsal, median groove that extended throughout
the length of the rachis (Figs 2.1b, 2.2b, 2.3). The fact that these traits are unknown among
modern feathers indicates that as previously claimed (O’Connor et al. 2012a), the unique RDFs

14
of many Mesozoic avians represent an extinct morphotype, which existence is thus far
conclusively known from only the first half of the Cretaceous (interpretations of the Late Jurassic
Praeornis sharovi as an RDF continue to be controversial [26]). Also of note are the
differentiated proximal and distal barbules with definable bases and ciliated pennuli exhibited by
these specimens.
The remarkably thin cross-sectional morphology of the rachises described here is a
surprising departure from modern bird rachises, which are generally four-sided with a compact
outer cortex encasing an inner medulla composed of spongey pith (Lucas and Stettenheim 1972).
This “composite foam sandwich” (Hertel 1966) construction is found even in specialized feathers
that have a broadened rachis, such as the feathers of penguins (Kulp et al. 2018)or the specialized
feather tips of various birds (Brush 1967). The functional significance of the extremely thin
rachises described here is currently not understood, nor is it clear if this construction scales to the
larger sizes more commonly reported from lithic fossils (O’Connor et al. 2012a; Chiappe et al.
1999; Xiaoli Wang et al. 2014; Agnolin, Rozadilla, and de Souza Carvalho 2019).
To understand the significance of the morphologies observed in these amber preserved
mid-Cretaceous feathers, it is useful to review the morphogenesis of a developing modern
symmetrical pennaceous feather, with a focus on the components of the rachis and barb rami.
Like all features of a feather, the rachis and barb rami develop from the tube of elongating
epidermis by the proliferation of cells at the base of a feather follicle (Prum 1999). This initially
undifferentiated epithelial cylinder begins branching in the ramogenic zone of the follicle
through a complex spatio-temporal cell differentiation program in which some cells accumulate
proteins that will form the body of the feather and others accumulate proteins that regulate the
scaffolding function and programmed cell death of intermediate cells (Alibardi et al. 2016; Wu et

15
al. 2015a; M. Yu et al. 2002). A cross section at the level of the ramogenic zone would reveal
identifiable presumptive rachis and barb ridges (each ridge containing the ramus and barbules of
a single barb) as the accumulation of various proteins begins (Fig. 2.4a). Subsequent
morphogenetic events occur as the differentiating tube of cells moves distally and early-
accumulating intermediate alpha-filament keratins (IF keratins) are rapidly replaced with beta-
keratins and other specific proteins to complete the keratinocyte differentiation and eventual
death (Alibardi 2017). The cells destined to form the rachis and barbs begin accumulating
various “Corneous beta-proteins” (CbetaPs, sensu Alibardi 2017). Mature feather cells,
especially in barbs and barbules, are comprised almost entirely of CbetaPs, while detectibly more
IF keratins are present in the calamus, ventral rachis, and ventral barb rami (Gregg and Rogers
1986; Ng et al. 2012; 2015; Rice et al. 2013; Wu et al. 2015a) A cross section of the cornifying
feather tube near the emergence of the epidermal surface would reveal the cells of the rachis and
barb rami differentiating into the inner medulla and outer cortex (Fig. 2.4b). Medullary pith cell
expansion within the rachis and rami extends the ventral aspects of these structures medially and
laterally. This process ends as the cells fully cornify and the outer constraining sheath desiccates
and is preened away, allowing for the feather to deploy (Fig. 2.4c). Of interest to this study is
that the differentiation of cells destined to become the CbetaP rich dorsal and lateral aspects of
the rachis, as well as those of the barbules, occurs earlier in the development of the feather than
the ventral aspects of the rachis and barb rami (Alibardi 2017).
Although the exact molecular mechanisms by which the epithelial cells of the medulla
vacuolate and expand are not well understood, recent work on the molecular basis of the
distinctive mutant frizzle feather phenotype found in chickens provides important insight into
this process. Ng et al. 2012 found that the rachis of frizzle feathers has a smaller medulla

16
compared to the normal leghorn controls and suggest that the frizzle phenotype is caused by a
defect in the ventral part of the rachis, via a misexpression of KRT75, an IF keratin. Their
research found that KRT75 is expressed in the ventral part that is destined to become the
medulla, whereas ß-keratin is expressed in the dorsal part of the rachis and ramus that is destined
to become the cortex.
The unique morphology of the RDFs of many stem avian lineages is difficult to reconcile
with our extensive knowledge about the development of modern feathers; the conservative
developmental circuits that produce a modern feather do not regularly generate a feather with the
morphology of these extinct feathers, namely one that lacks medullary pith and has the structural
traits described for these feathers. The cross-sectional morphology of a modern rachis is reliant
on the internal expansion of medullary pith as the feather cells mature and keratinize within the
sheath (Maderson et al. 2009). The extremely thin nature of the RDFs described here, along with
the absence of any medullary pith or structures known to rely on medullary pith development
appears to necessitate a different developmental explanation (Fig. 2.4e-h)
The high degree of barbule differentiation combined with the lack of obvious
histodifferentiation of the barb rami or rachis suggests that these feathers could have developed
without the full suite and developmental interplay of IF keratins and CbetaPs that is employed in
the cornification process of modern birds and could be produced with modifications to the
subperiderm layer (Alibardi et al. 2016; Alibardi 2017). This hypothesis provides one alternative
pathway (perhaps not the only one) of how the extinct RDFs could have developed. Clearly
further studies are needed to test this hypothesis but the realization that certain extinct feathers
are unlikely to have developed through identical developmental mechanisms that produce a
modern feather cautions the use of modern developmental pathways and mechanical properties

17
of feathers to infer aspects of the plumage of extinct, Mesozoic avians, a practice that has been
common among researchers (Nudds and Dyke 2010; X. Wang et al. 2012; Lees et al. 2017). If
the RDFs preserved as lithic fossils share the same construction and cross-sectional profile as
RDFs in amber, as suggested from semi three-dimensional remains from China (Fig. 2.1b) and
Brazil, then previous assumptions about their functional performance need to be reevaluated. The
consistently straight, un-bent preservation of RDFs in lithic fossils (O’Connor et al. 2012a; J.
O’Connor et al. 2015; Carvalho et al. 2015) is understandably suggestive of a rigid mechanical
nature and is seemingly at odds with the extreme rachis construction described here. However,
numerous feathers figured by (Xing, Cockx, et al. 2018) from the same mid-Cretaceous deposit
display consistent morphologies with those presented in this study, suggesting that this rachis
construction was the dominate developmental pathway to produce RDFs in the mid-Cretaceous.
Evaluating incongruences between inferred mechanical aspects of preserved RDFs from the
entire Mesozoic in the light of the unexpected three-dimensional morphologies described here is
outside of the scope of this study, but a greater understanding and consideration of the
construction of RDFs in three dimensions at multiple scales will be critical in understanding their
mechanical performance (Lees et al. 2017). The excellent three-dimensional and micro-structural
preservation in amber allows for unprecedented comparisons to modern feathers and can provide
insight into extinct and extant feather development.

18

Figure 2.1. Lithic Preservation of Early Cretaceous rachis-dominated feathers from the Yixian
Formation. (a) Confuciusornis pair with and without rectrices. (b) Paired rectrices of an
indeterminate enantiornithine displaying limited 3D preservation. (c) Junornis; an
enantiornithine with proportionately long rachis-dominated rectrices. Abbreviations: ms, medial
stripe; r, rachis.

19

Figure 2.2. Paired rachis-dominated feathers preserved in amber. (a) X-ray μCT rendering of
rachis-dominated feather in dorsal view preserved in LACMDI 158032. (b) Digitally sectioned
segment of rachis from boxed region in (a) with medial stripe highlighted in green. (c) Whole
specimen view of LACMDI 158032 with paired rectrices in ventral view. (d) Ventral view of
rachis and barbs from location indicated in (c). (e) Ventral view of separated barbs from location
indicated in (c). Abbreviations: db, distal barbule; hk, hooklets; ms, medial stripe; r, rachis; rm,
ramus.

20

Figure 2.3. Rachis-dominated feathers in amber. (a) LACMDI 158557 with two partial feathers
in dorsal view (b) Magnified dorsal view of feather from region in (a) showing rachis, medial
stripe, barbs, and barbules. (c) Transverse view from blue bar in (a) of truncated distal rachis.
Blue line traces the ventral surface profile of the rachis. (d) LACMDI 158490 in ventral view. (e)
Transverse view from box in (d) of truncated proximal rachis with blue line tracing the ventral
surface profile. (F) LACMDI 158555 in ventral view. (g) Transverse view from box in F of
truncated distal rachis with blue line tracing the ventral surface profile. Abbreviations: db, distal
barbule; hk, hooklets; ms, medial stripe; r, rachis; rm, ramus.

21

22
Figure 2.4. Generalized overview of the morphogenesis of a modern chicken tail feather and
proposed morphogenesis of extinct rachis-dominated feather. (a-c) Cross sectional views of the
developing epidermal feather tube of a modern chicken tail feather. Sections exhibit increasing
maturity and cornification as the location moves distally. (d) Illustrated cut section of a mature
barb from the deployed pennaceous vane of a modern chicken, modified from [24]. (d-g) Cross
sectional views of the proposed developmental progression in the epidermal feather tube of an
extinct rachis-dominated feather. (h) Illustrated cut section of a mature barb from the deployed
pennaceous vane of rachis-dominated feather in amber.

23
CHAPTER 3
BUILDING THE FEATHER SHAFT: 3D CALAMUS-RACHIS TRANSITIONS
IN AMBER PROVIDE INSIGHTS INTO THE FORMATION OF MID-
CRETACEOUS FEATHERS.

CHAPTER 3 ABSTRACT- The square cross section and pith-filled interior of a modern feather
rachis are characteristic features of modern flying birds. The expansion of medullary pith within
the interior of the rachis during development is crucial for the formation of the square cross
section. A consequence of this developmental pathway is the formation of proximally-extending
lateral swellings of the pith as the main shaft transitions from a foam filled rachis to a circular
calamus with a hollow lumen that tapers distally beyond the superior umbilicus. Analysis of the
flight feathers within a wing and isolated flight feather preserved in mid Cretaceous Burmese
amber reveal that the rachis-calamus transition differs from that of modern birds and that these
fossil feathers have a hollow, ovoid rachis. These findings suggest that ventral supporting
components of the rachis (and their development) were adaptations that occurred later or
separately in crown group birds than previously recognized or assumed. This study further
highlights that the use of modern bird feathers as proxies for inferring flight performance in
extinct taxa should be used with caution.

i. Introduction
The mechanical advantages of the 3D composite architecture of the rachis in flight have
been only recently explored (B. Wang and Meyers 2017; T. Lingham-Soliar, Bonser, and

24
Wesley-Smith 2010; Sullivan et al. 2017). The central shaft provides the main mechanical
support of the modern flight feather by providing lightweight, stiff, and strong, yet sufficiently
flexible, properties (B. Wang and Meyers 2017). The variability in properties is due to the
variability in construction of the shaft, which begins as an undifferentiated circular tube filled
with air at the calamus (proximal end) and changes cross-sectional shape from round to square at
the rachis (middle and distal shaft, Fig. 3.1B) while also differentiating into an outer cortex and
an interior fibrous closed-cell foam called medullary pith (Lucas and Stettenheim 1972; B. Wang
and Meyers 2017). Recent studies (B. Wang and Meyers 2017; B. Wang et al. 2016; T.
Lingham-Soliar, Bonser, and Wesley-Smith 2010) discovered that the feather cortex can be
considered as a fiber-reinforced composite with a hierarchal construction of β-keratin filaments
and macrofibrils, ranging from ≈3 nm in diameter to ≈200 nm in diameter. The orientation of
these fibers was found to vary along the length of the shaft, with the entire cortex of the calamus
displaying an inner layer of axially oriented fibers covered by an outer layer of circumferential
fibers. The dorsal and ventral cortex are composed of axially aligned fibers and the lateral walls
for the entire rachis show a crossed-fiber structure. This cross-sectional morphology combined
with the fibrous construction make the rachis “longitudinally strong, dorsal-ventrally stiff, and
torsionally rigid, yet capable of prescribed deflection and twisting at a minimum of weight,
modulated along the shaft length,” (B. Wang and Meyers 2017). Furthermore, the tailored
flexibility conveyed to the rachis by its cross-sectional geometry is controlled by the expansion
of medullary pith during the formation of the feather. So while the medullary pith contributes to
the lightweight and possibly structural functionality of the feather, it also plays a crucial role in
the morphogenesis of the rachis. The extent of medullary pith formation within the rachis varies
across feather types but derived characteristics of pith formation are consistently displayed in the

25
primary and secondary flight feathers of volant modern birds (Chang et al. 2019a). For this
reason, an examination of well-preserved wings and flight feathers preserved in amber reposited
at the Natural History Museum of Los Angeles will be the focus of this study.
Feather formation is a complex spatiotemporal process that can be broadly defined in two
stages: the initial patterning of an undifferentiated keratin tube and the subsequent differentiation
and cornification of that tube. Rachis formation begins in the feather follicle as the initially
undifferentiated epidermal tube receives nutrients and instructions from the dermis. A rachidial
ridge of cortex and medullary keratinocytes is identifiable shortly after the epithelial tube
progresses past the ramogenic zone. The dorsal cortex begins to differentiate first, followed by
the lateral cortex and lastly the medullary cells and ventral cortex (Alibardi 2017). During
anagenesis (growth phase of the feather), the dermal pulp expands into the center portion of
the feather cylinder and extends distally well beyond the follicle. The dermal pulp extension and
turgor pressure provided cede to the expansion of the medullary pith formation of the ventral
cortex. This expansion of the pith cells begins laterally and progresses ventrally and inward, with
both lateral sides eventually meeting in the middle. This process often pinches and captures the
dermal pulp epithelium into the interior of the rachis, the mature form of which is now
occupying the interior of the feather tube once occupied by the dermal pulp.
As the feather reaches the end of the vaned growth phase, barb ridge formation decreases
until the feather tube ceases to differentiate entirely, entering the formation of the calamus. It is
at this transition that the barbs of the vane shift from emerging along the dorsolateral walls of the
rachis to the ventral surface where they converge as a series of short tufts (termed umbilical
barbs). In a contour feather the ventral convergence of the vanes is occupied by a hyporachis,
which can look like a full feather that attaches distal to the calamus (but lacks one itself) and can

26
be as long and prominent as the main feather (Lucas and Stettenheim 1972). Internally, this
transition from a medullary pith filled rachis to the calamus is not abrupt, and results in a cone-
like hollow space that extends distally into the dorsal aspect of the vaned rachis and ventrolateral
lobes of pith extending proximally into the hollow space of the calamus (lumen). Once the
feather sheath is dehydrated and preened away, the exterior transition between the calamus and
rachis (termed the superior umbilicus) is visible on the ventral surface, often with remnants of
the pulp caps observable. This is often the site of quill mite invasion, where quill mites can enter
into the hollow calamus to feed on the still receding dermal pulp and lay eggs within the calamus
(Casto 1974). As the dermal pulp regresses in the later stages of anagen, it leaves behind a series
of internal conically shaped epithelial layers (pulp cups) that are composed of alpha keratin,
rather than the cornifying beta-Keratin that composes the structural parts of the feather (Alibardi
2009). These internal pulp cups are often visible through the un-pigmented calamus wall. As the
feather ends its growth phase and enters its mature resting phase, the dermal pulp regresses and
reduces its diameter to the size of the dermal papilla, resulting in a tapered proximal terminus of
the calamus.
Much as the umbilical cord belies the unique development of a placental mammal the
superior umbilicus of a mature feather reveals the early development of a feather shaft.
Externally, the ventrally located superior umbilicus is the position where medullary pith
expansion of the rachis transitions to dermal pulp turgor pressure as internal supporting force
needed for the keratinocytes to properly cornify into the mature feather. Umbilical barbs also
mark this developmental transition as barb and rachis differentiation shifts to the relatively
undifferentiated calamus.

27
This chapter will investigate whether the developmentally indicative morphological
characters of the calamus-rachis transition of a modern flight feather shaft are present in mid-
Cretaceous birds.

ii. Materials and Methods
The two specimens described here (LACM DI 8004 and CCM V 2021-5) are from the
amber producing mines in northern Myanmar, located in the Hukawng Valley (Hukawng Basin)
of Kachin State, and specifically on Noije Bum, a hill that rises some 250 m above a broad
alluvial plain that lies between two rivers, Idi Hka and Nambyu Hku. LACM DI 8004 contains
the feathers of a right bird wing and CCM V 2021-5 contains an isolated flight feather.
LACM DI 8004: A uniquely splayed wing preserved in Burmese amber
The main inclusion comprises feathers of the dorsal tract of the distal half of a right wing.
Standard microscopy and computer tomographic images reveal that a complete ungual phalanx,
presumably belonging to digit II (major digit), and the articulated distal end of its corresponding
intermediate phalanx, are preserved. These are the only osteological elements preserved. CT
imaging also reveals the presence of 10 primary feathers and at least 5 secondary feathers (1-5).
Primaries X-VIII are clustered together but can be resolved through CT imaging. The remaining
primaries (VII-I) are regularly spaced, defining the surface of the distal wing. A reduction in the
space separating the rachises as well as a change in the orientation and the dimensions of the
rachis, define the boundary between the primaries and secondaries. The rachises of the latter
(secondaries 1-5) are preserved closer to one another. Both primaries and secondaries are
attached to what appears to be the remnant of a postpatagium. Near the middle of the preserved
leading edge of the wing, there are at least two feathers interpreted as part of the alula; these

28
feathers are relatively short and their rachises are parallel to the leading edge. CT scans reveal
that proximally, the rachises extend to the level of primary I.
Although the feathers of this wing are truncated on their distal portions, preventing a
complete approximation of wing shape and overall bird size, the proximal portion of the primary
and secondary feathers are well preserved. This allows for the unique observation of multiple
flight feathers of a single individual. The rachis-calamus transition of these flight feathers, both
primaries and secondaries, can be observed optically and through CT segmentation.
Optically, the calami of preserved primaries and secondaries are more transparent and
appear to be hollow with transmitted light (Fig. 3.2). The transition to the rachis is marked by a
distinct change to an opaque shaft with the appearance of the barbs of the vanes on the lateral
sides of the feather. Notably, the emergence of the barbs of these feathers begin on the lateral
walls of the shaft and do not converge on the ventral face of the shaft. The opacity of the rachis
portion of the primary and secondary remiges varies among the feathers, suggesting variability in
the preservation and infill of the rachises. There is no clear evidence of a superior umbilicus or
umbilical barbs present at the rachis-calamus transition.
Micro-CT investigations of the specimen allows for more accurate observations of the
internal geometry of the calami lumen and interior rachises than relying on differences in opacity
(Fig. 3.3). Segmentation of CT slices show that the lumens of the calami are infilled with fossil
resin, likely from the exposed open inferior umbilicus and were hollow in vivo. Cross sectional
analysis of the rachis-calamus transition reveals an abrupt cap of the lumen followed by a
variably hollow rachis (Fig. 3.4). The distal most extent of the lumen does not extend beyond the
emergence of the vane. The rachises of the feathers preserved here are largely hollow (preserving
a negative void) and circular to sub-ovoid in geometry. Variations from this hollow, ovoid

29
morphology occur even within a single feather where the ventral cortex of the feather appears to
have split open, allowing the infill of either resin or in some cases, a denser mineral or
sedimentary infill. It is of note that where the full circumference of the rachis cortex is preserved,
a hollow air void is also preserved (Fig. 3.5 C, D, F). In regions where the ventral aspect of the
rachis cortex is split open, the interior of the rachis is supported by amber-density infill or
higher-density material.
CCM V 2021-5: Isolated flight feather
CCM V 2021-5 is an isolated asymmetric feather in a small billet of Burmese amber
resin. Truncation of the feather occurs distally but the proximal portion of the feather containing
the rachis to calamus transition is well preserved. While the proximally preserved portions of the
feather appear to have fully intact cortical surfaces and the barbules and hooklets are optically
visible and intact distally towards the truncated portion of the feather show evidence of
degradation including broken and cracked barbs and notable splitting of the ventral portion of the
rachis. This degradation looks similar to that described by (Theagarten Lingham-Soliar, Bonser,
and Wesley-Smith 2010) in experiments where feathers were exposed to keratinophagous fungi.
Degradation of feathers by fungi in modern environments begins by preferential removal of the
amorphous keratin matrix, revealing the more resistant ß-keratogenic components of the keratin
matrix.
There is no evidence of medullary pith within the rachis or barb rami and the rachis cross
sections (where the cortex is complete) is ovoid in geometry. Unlike the rachis-calamus
transitions of LACM 8004 there is no clear division within the interior of the shaft in CCM V
2021-5. A continuous hollow space infilled with fossil resin persists from the calamus
throughout the rachis (Fig. 3.6). Within the outer cortex of the calamus a secondary interior

30
collar of similar thickness to the exterior cortex is discernible. The inner collar has a convex
dorsal perimeter with a nearly flat ventral perimeter for the first proximal third of the calamus, at
which point it constricts abruptly to approximately half the diameter of the outer calamus wall
and assumes a finger-like appearance (Fig. 3.6D) This inner collar then transitions ventrally at
the point where the barbs of the vane begin to emerge, occupying the ventral lateral half of the
interior of the rachis and does not extend dorsally along the lateral walls beyond the point where
the barbs emerge from the outer cortex. For the first half of the preserved rachis this inner
structure forms a complete secondary inner wall to the ventral aspect of the rachis, but as it is
traced distally it transitions to a series of ventrolateral ribbons that interweave with the outer
cortex of the ventral rachis (Fig. 3.6E).

iv. Conclusions and Discussion
Despite some taphonomic variation in the preservation of the rachises of LACM 8004,
the cross-sectional geometry is ovoid to sub-ovoid, with no indication of square or rectangular
geometry. The preserved air voids within the rachis interior where the cortex is unbroken
suggests that this was a hollow void in life. No evidence of medullary pith is present in the
interior of the rachises or within the thin-walled barb rami. The abrupt truncation of the calamus
lumen and separation between calamus and rachis by a thickened wall is consistent amongst
primary and secondary remiges. The calami do not taper proximally, and inferior lumens are
large and roughly equal to the mid-length diameter of the calami. The lack of a proximally
tapered calamus and comparatively large inferior umbilicus is shared by isolated feather CCM V
2021-5, as is the lack of medullary pith in the rachis or barb rami. Both of these specimens lack

31
the morphology of the rachis-calamus transitions seen in modern bird feathers that are indicative
of medullary pith development of the rachis.
The unexpected interior morphology of the isolated feather CCM V 2021-5 is especially
intriguing. As an isolated feather taphonomic and preservational factors cannot be entirely ruled
out. It is possible that the interior of the rachis was biodegraded by fungus or an ectoparasite,
creating a continuous hollow shaft. However, this morphology is reminiscent of the rachis-
calamus transition of the first molt of birds, where the distal tips of a new juvenal feather connect
to the base of the tubular calamus of the older natal feather (Fig. 3.7).
Feather growth and ultimate size is constrained by the size of the feather follicle (Jenni et
al. 2020). Modern bird feather development has optimized this constraint with an extended
feather sheath and protracted series of cornification events that occur beyond the epidermal
surface. The late-stage cornification and expansion of medullary pith within the extended feather
sheath allows the ventral and lateral aspects of the rachis to expand into the interior part of the
tube formally occupied by the dermal pulp that had previously provided nutrients and signaling.
With this innovation, the initial portion of epidermal collar dedicated to the rachidial ridge can be
reduced (maximizing the portion dedicated to barb formation and wider vanes) with a mature
rachis diameter that can be nearly equal to the constraining diameter of the feather follicle.
Because this late-stage expansion of pith in the rachis also occurs at the same time as the barb
rami, overall vane width is optimized because the mature supporting barb rami can be expanded
and grow into space previously occupied by the dermal pulp. If earlier birds were forming
feathers without the controlling advantage of medullary pith, overall feather length and vane
width would be constrained.

32

Figure 3.1. Anatomical illustration of the rachis-calamus transition in a modern flight feather. A)
distal portion of a flight feather in the ventral view. B) Sagittal section of the rachis-calamus
transition with corresponding cross sections. Lumen is highlighted in blue and medullary pith in
yellow. Note that the distal extent of the lumen extends beyond the emergence of the vane.
Sagittal section is oriented with ventral side up and cross sections are oriented with dorsal aspect
to the right, ventral side to the left.

33

Figure 3.2. Mid-Cretaceous bird wing (LACM 8001) in amber. A) Multifocal stacked image of
entire LACM 8001 specimen in ventral view, transmitted light, white balanced. B) Enlarged
portion of red inset of a showing the proximal portions of primaries 5 -1 and secondaries 1-5.
Abbreviations: cl, calamus lumen; iu, inferior umbilicus; v, vain; r, rachis.

34

Figure 3.3. Segmented reconstruction of wing preserved in amber (LACM DI 8004) in dorsal
view. The splayed fashion of this specimen presents a unique opportunity to examine the
proximal rachis-calamus transition across all ten primary feathers not observable in previously
reported wing specimens from the same deposit. Note the small ungual claw preserved near the
base of P9 and P8. Abbreviations: S, secondary; P, primary.

35

Figure 3.4. Sagittal sections of primaries 4 and 5 of LACM DI 8004 from µCT slices. Note the
abrupt transition of the calamus lumen Abbreviations; cl, calamus lumen; P4, Primary 4; P5,
Primary 5; r, rachis.

36

Figure 3.5. Cross sections of LACM DI 8004 primaries 4 and 5 from µCT slices. (A-D) Cross
sections from primary 4. A) Calamus infilled with resin. B) Calamus-Rachis transition. C) Mid-
rachis with intact cortex and air-filled void. D) Distal rachis with intact cortex and air-filled void.
(E-H) Cross sections from primary 5. E) Calamus infilled with resin. F) Proximal rachis with
intact cortex and air-filled void. G) Mid-rachis with broken cortex and resin-filled interior. H)
Distal rachis with high-density infill. All cross sections to same scale.

37

Figure 3.6. X-ray µCT renderings of isolated flight feather CCM V 2021-5. A) Dorsal view of
feather with translucent rendering of cortex. B) Lateral view of feather. C) Oblique ventral view
of feather with inner cortex rendered in red and outer cortex rendered in translucent blue. D)
Proximal calamus with inner cortex constricted. E) Distal portion of rachis with inner cortex
emerging as ventrolateral ribbons.

38

Figure 3.7. Illustration of the contiguity of the tubular epidermis and central dermal pulp between
generations of feathers that grow from the same follicle shown by the natal down and juvenal
contour feathers of a White Pekin Duck, from Lucas and Stettenheim (1972, Fig. 229). (A) The
natal feather has been replaced by the new juvenal feather growing out of the same follicle. (A’ )
The distal tips of the new juvenal feather are connected to the base of the tubular calamus of the
older natal feather. The opening into the dermal pulp cavity of the natal feather (called the
inferior umbilicus) is contiguous with the central dermal pulp lumen of the juvenal feather germ.

39

CHAPTER 4:
MODERN BIRD FEATHER ARCHITECTURE PRESERVED IN PUTATIVE
T. REX COPROLITE

CHAPTER 4 ABSTRACT- We report a feather assemblage of avian affinity preserved in a
phosphatic coprolite fragment from the Upper Cretaceous Hell Creek Formation, northeastern
Montana, USA. Preservation of three-dimensional (3D) macro- to nanoscale feather structures
characteristic of modern birds is observed, including a central shaft that transitions from a
proximally circular and hollow calamus to a square/rectangular pith-filled rachis, barbs with
pith-filled rami, and synticial fibers within the barbules, rami, and rachis cortex. This complex
internal feather architecture allows optimization of flight efficiency and thermoregulation. The
combination of selective biodegradation and multiphase phosphatization of these fossil feathers
likely allowed for this exceptional view into the evolution of the complex, hierarchal, fiber-
reinforced composite construction of the modern-type feather. The mainly longitudinally aligned
feather and bone inclusions, partial digestion of bones, and coprolite diameter (>7 cm) suggests
that a large carnivorous theropod dinosaur such as Tyrannosaurus rex was potentially the
producer.

i. Introduction
The Maastrichtian Hell Creek Formation (HCF) is one of the most celebrated dinosaur-
rich deposits worldwide, and together with the overlying Ft. Union Formation, its exposures are
the most well-studied terrestrial sediments for understanding the Cretaceous-Paleogene (K-Pg)

40
mass extinction (e.g., Wilson et al., 2014; Fastovsky and Bercovici 2016). However, the majority
of vertebrate fossils derived from this area are vertebrate hard parts, such as bones, teeth, and
scales (Horner, Goodwin, and Myhrvold 2011; Brown et al. 2013). This has resulted in a hard-
tissue bias of our understanding of the ecosystem leading up to and after the end-Cretaceous
mass extinction. Seemingly, the taphonomic conditions necessary to preserve information from
the soft tissue of animals are not present in the HCF as those of earlier Mesozoic or later
Cenozoic deposits (Davis and Briggs 1995a). These latter sites of exceptional preservation
(Lagerstätten) have provided invaluable insights into the ecology and evolution of many
taxonomic groups, notably that of birds and their associated feathers and other soft tissues
(Chiappe and Meng 2016).
The early evolution of the bird feather is recorded as two-dimensional carbonized or
imprinted remains, with some intriguing insights into their three-dimensional (3D) aspects from
mid-Cretaceous amber deposits (Xing, Cockx, and McKellar 2020). Still, many questions remain
about when certain composite and 3D aspects of the modern bird feather arose. One of these
relates to the “basic structure” of a modern feather, in which a central shaft with a proximally
hollow calamus transitions to a pith-filled square rachis, where the sponge-like medullary pith is
key to the morphogenesis of the square cross section as well as conveying mechanical efficiency
(N. Sullivan et al. 2016; Chang et al. 2019a; Theagarten Lingham-Soliar 2017; Sullivan et al.
2018).
Although the fluvial and flood-basin deposition of the HCF is not conducive to typical
feather-preserving conditions (i.e. carbonization, bacterial autolithification, imprintation, and
amber, sensu Davis and Briggs 1995) it does preserve an understudied mode of feather
preservation, namely coprolites (Chin et al. 1998; Hollocher, Hollocher, and Rigby 2010).

41
Coprolites (fossilized feces) might preserve feathers as three-dimensional voids but have yet to
be recorded from Mesozoic deposits. This lack of coprolite-preserved feathers in the Mesozoic
has been proposed to be associated with regurgitation of indigestible material (Myhrvold 2012)
but it may also be explained as a collection and study bias of fossilized gastric pellets and feces
(Qvarnström, Niedźwiedzki, and Žigaitė 2016).
Useful feather data preserved in modern feces is common, and its absence from the
Cretaceous record is perplexing. The stomach enzymes (pepsin) of vertebrate digestive systems
are unable to break down the complex disulfide bonds within the keratinous components of a
feather (Y. Zhang, Yang, and Zhao 2014). The ability to digest keratin proteins in general is
restricted to a few groups of arthropods (dermestid beetles, moth larvae, chewing lice) as well as
specialized bacteria and fungi (Joshi et al., n.d.) . Most feathers, therefore, either pass through the
digestive tract of an animal undigested or are avoided altogether during ingestion by the predator
(Myhrvold 2012; J. K. O’Connor and Zhou 2020). This indigestibility of feather keratin in
modern ecosystems has proven invaluable for ecological and forensic studies that utilize species-
level identifications of avian prey within modern scat (Dove 2000; Mondal, Sankar, and Qureshi
2012). Bird species are identifiable from feathers in Pleistocene feces of humans, hyenas, and
other predators (Reinhard and Bryant 1992; Bryant and Williams-Dean 1975), but so far feathers
in coprolites have only been reported from the Late Cenozoic. Despite being one of five
proposed preservation modes of fossil feathers (Davis and Briggs 1995b), there are only a few
brief reports of feather impressions in possible whale coprolites from the Miocene and Pliocene
(Wetmore 1943; Mehling 2010).
With the majority of the feather fossil record preserved as two-dimensional carbonized or
imprinted remains, the evolution of 3D composite features has been difficult to attain and track.

42
Here, we report the first fossilized feathers from the Upper Cretaceous HCF of Montana,
preserved three-dimensionally in a phosphatic coprolite.

ii. Materials and Methods
Material
Specimen UWBM 103150 is a 20 x 30 mm nodule found within a larger ovoid nodule
approximately 9-10 cm long and 8 cm in diameter and is currently on display in the paleontology
hall of the Burke Museum in Seattle Washington.

Optical Microscopy
Photomicrographs of the exposed feather were taken with a Keyence VHX-500 digital
microscope with multiple light sources. Focused images were created using the Keyence
multiple image stacking software.
SEM
To allow for future analysis and optical presentation, the specimen was not coated.
Scanning electron micrographs were produced using a Hitachi S-3000N SEM (Tokyo, Japan) at
an accelerating voltage of 4 kV and working distance of 26.5–12.3 mm in the SEM laboratory at
NHMLA.
Micro-Computed Tomography
Inclusions within UWBM 103150 were imaged using x-ray microtomography. The scan
was conducted on a GE Phoenix Nanotom M microCT scanner at the Molecular Imaging Center,
Department of Radiology, University of Southern California Keck School of Medicine using a
current of 400 µA and voltage of 60 kV. A molybdenum target with no filter was used for the

43
scan. The images were reconstructed from the raw dataset with voxel size of 3.5 µm.
VGStudioMax 3.0 software was used for visualization, segmentation, and measurements.
Inclusions were digitally isolated from the surrounding groundmass by using a variety of
threshold values with the “region growing” and other “region of interest” tools during the
segmentation process, after applying a Gaussian filter.
X-ray fluorescence
In situ X-ray fluorescence (XRF) data were collected on a Horiba XGT-7200 using a 50
µm beam diameter, 30 s acquisition rate, Rh X-ray tube settings of 15 kV, and a current of 1.0
mA. Data were collected in partial vacuum mode that keeps the X-ray optics under vacuum, but
the sample chamber was left in normal atmospheric pressures to allow for fast sample
preparation and the use of standard tubing and fittings.
iv. Description
Geologic context/discovery
The coprolite described herein (UWBM 103150) was discovered on July 9, 2016 by
David DeMar at the Nitocris 1 locality (UWBM loc. C2365) of the uppermost Cretaceous
(Maastrichtian) HCF, McCone County, northeastern Montana, USA, and is now on display at
Burke Museum in Seattle, WA. The coprolite-bearing horizon is ~18 m below the nearest HCF-
Fort Union formational contact (~140 m to the NE). At several local geologic sections, this
contact is nearly coincident with the K-Pg boundary (eg., Moore et al. 2014; 2014; Sprain et al.
2015), which has a reported age of 66.052 ± 0.008/0.043 Ma (Sprain et al. 2018). On the basis of
nearby magnetostratigraphic sections, we infer that Nitocris 1 was deposited during
magnetochron C29r and within the last 300,000 years (Ka) of the Cretaceous (Sprain et al. 2018).

44
The coprolite-bearing sediments are olive gray (5Y 4/1), massive, clay-rich siltstones.
The dominant clay minerals are likely mixed-layer smectite/illite species given the “popcorn
weathering” of the outcrop (D.E. Fastovsky 1987). Excavation of these sediments exhibited
blocky to crude platy parting. No other fossils were found in the surrounding siltstones. In
combination with the lack of other sedimentary features (e.g., laminations, root traces), we
interpret these data as indicative of a shallow lacustrine depositional environment (i.e., pond or
lake), although currently we cannot rule out the possibility of Nitocris 1 representing an
overbank or floodplain deposit. Substantial concentrations of likely associated skeletal material
of the large bowfin fish Melvius thomasi and gar fish (Lepisosteidae) were scattered on the
surface above and across the coprolite-bearing horizon, and down to the base of the ~3 m tall
outcrop. Fossils of these and other less common taxa at Nitocris 1 (e.g., turtles) likely originated
from sediments above the coprolite-bearing horizon, which have since eroded away; no in situ
fossils of these larger-bodied taxa are known.
The fossil-bearing coprolite (UWBM 103150) was found within an ovoid nodule
inclusion approximately 9-10 cm long and 8 cm in diameter (Fig 4.1a), alongside two other
nodules in contact proximity that are roughly equal in size and shape for a total length of about
26 cm, based on Fiji image measurements. An eroded end of the chalky phosphatic nodule
revealed a dark brown cryptocrystalline center revealing a feather and a small hollow bone in
cross section. Three other similar-sized but variably shaped vertebrate-bearing phosphatic
nodules were found within the same stratigraphic horizon and within ~28 m of UWBM 103150.

45
Feather Inclusions
The fractured discovery surface of the UWBM 103150 nodule allows for observations of
a small partial feather in planar view, with portions of the ventral surface exposed and variably
preserved. The broken surface exposes internal and external morphologies, various oblique
cross-sections, and embedded views of the feather due to the semi-translucent nature of the
matrix. The exposed feather shaft is ~9.3 mm long, with the distal-most rachis truncated at a
width of 0.15 mm. As the shaft transitions from the vaned rachis to the tubular calamus, a large
section of the shaft is broken off, but its impression is traceable proximally to where the hollow
calamus dives into the coprolite groundmass, with a diameter of 0.3 mm. Medullary pith cells are
preserved throughout the distal half of the interior rachis. The white pith walls preserve what we
interpret as vacuolated, air-cell spaces that range in diameter from ~3 µm to 5 µm (Fig. 4.2b). In
planar view, the barbs are visible with the naked eye, and attach to the rachis asymmetrically
with the barbs of the right vane at an angle of ~23° and those of the left vane at angles ~35–40°.
Broken surfaces of the barb ramus reveal a thin cortex cored with medullary pith cells. Barbules
are visible in multiple tangential, longitudinal, and oblique views and cross-sections, but a
complete view of a single barbule from base to pennulum is not discernable (Fig. 4.2c).
Using Scanning Electron microscopy (SEM), we investigated the surface of the white
cortex and medullary pith cell walls that define the morphology of the feather. We interpret that
the morphologies observed with light optics are preserved by a combination of moldic
impression and replacement. The barbules, which are white under light microscopy, are seen as
small valleys (~5 µm wide) that are variably filled with globular bodies separated by walls of
smooth matrix (Fig. 4.3). A preserved proximal portion of the rachidial cortex has a surface that
is composed of axially diverting striated fibers. These fibers (~3–7 µm in diameter) are variably

46
packed in bundles and are covered in globular microbodies (~2–4 µm in diameter). This same
fibrous architecture is present where barbules are exposed and overlying the matrix (Fig. 4.3).
The irregular shape and relatively large size of the globular microbodies are not consistent with
the shape and size of previously reported fossil feather melanosomes, which can display
considerable size variation (.5 µm~2 µm for eumelanosomes) (Moyer et al. 2015).
Digital reconstructions of the surface-exposed feather derived from µCT scans (Fig. 4.4a,
b) demonstrate a correlation of densities between areas of presumptive cortex, pith, and voids.
The 3D model of the feather, which is defined by a range of density threshold values, shows that
the shaft transitions from a hollow, circular calamus proximally to a square rachis distally (Fig.
4.4c).
A slightly smaller feather (6.3 mm long) of similar morphology and density variation was
discovered via µCT imaging aligned perpendicular to the exposed feather, with the distal-most
portion truncated by the fracture surface. This feather also preserves a hollow, circular calamus
that transitions to a presumably pith-filled rachis that is square in cross-section (Fig. 4.4d). The
proximal portion of this feather displays regions of the cortex and a barb that have been infilled
by high-density material, rather than by the low-density microfabric preserving these features
elsewhere. Although barbules are not fully discernable at the reconstruction size of 8 microns,
the barbs appear uniformly locked in a planar vane, and are likely symmetrical.
Several other feather or filamentous integumentary structures are visible through µCT
imaging within the nodule, but have less distinctive morphology and internal preservation. A
high-density infill has preserved two smaller filamentous feathers (Fig. 4.4). One of these
feathers (Fig. 4.4e) displays loosely branching barbs that radially coalesce proximally and
terminate to a solid, short base that we interpret as the calamus. This morphology closely

47
matches that of a basally joining filamentous feather observed in non-avialan dinosaurs and
commonly produced as natal down in modern birds (Xu 2020). Several flattened ovoid
inclusions with similar density but distinct microfabric appear entangled in the distal portions of
the filamentous strands. A second filamentous feather is also discernable from the matrix (Fig.
4d). This feather features a thin rachis roughly equal in diameter with the branching barbs that
show indications of barbules.
Using the microfabric textures and morphologies of the definitive feathers in Figure 4, we
identified 12 elongate structures within the matrix that we tentatively identify as rachis fragments
(Fig. 4.5a, b). These display square cross sections variably cored with material matching the
microfabric of previously identified pith. Some of these rachises display remnants of branching
barbs, whereas others display periodically occurring patches of high-density infill along the
lateral walls. This pattern is generally consistent with the presumptive location of barb junctures
with the rachis.

Other Inclusions
Several other elongate fibrous structures with similar density ranges as the identified
feathers were visualized through CT imaging, but do not provide recognizable morphology.
These structures are largely aligned on the same axis as the elongate rachis fragments, with some
running the full length of the nodule. Additionally, several hard-tissue inclusions are optically
observable on the surface of the nodule and CT imaging reveals two partial bones (Fig. 4.5e, f).
The conspicuously observable smaller of these skeletal elements is elongate with a hollow shaft
featuring a prominent medially curved flange that decreases in prominence towards the terminus
preserved within the nodule. The terminal end of this bone is more trabecular than the shaft and

48
intergrades into the surrounding groundmass preventing identification of definitive diagnostic
morphology (Fig. 4.5e. The larger bone features a largely trabecular internal structure with a less
definitive boundary with the groundmass but appears to preserve the terminal end of an elongate
element that transitions to a hollow shaft (Fig. 4.5f). Two other elements, identified by a distinct
bimodal density, are interpreted to be fish scales. The cross section of one is optically visible on
the surface of the nodule and displays a roughly diamond shape with a small projection in µCT
reconstruction. A fan shaped scale in close proximity to the surface-exposed scale was also
identified by its similar density and internal structure. Both scales delineated by a low-density
perimeter with a radiating internal structure and are ~1.6 mm in length. (Fig. 4.5d).

v. Discussion
Feather Inclusion Affinities
The varying morphology of these feather inclusions of UWBM 103150 allow their
identification to varying archosaurian groups. The downy-type feather (with a short calamus and
lacking a rachis) is likely assignable to Dinosauria, although further integument discoveries of
pterosaurs may reveal that this simple feather type can be produced by the more inclusive group
Archosauria (Yang et al. 2019). The plumaceous feather, with a slender rachis sub-equal in
diameter to its branching barbs is assignable to Maniraptora (Fig 4.6). The fact the plumaceous
feathers are distinctly preserved with a higher density infill may reflect an originally distinct
keratin composition than the contour feathers, as adult and natal down of modern birds contains a

49
higher alpha-keratin component that more derived feather types (Wu et al. 2015b). Based on
external morphology alone, the contour feathers are assignable to Penneraptora, but the internal,
3-D architecture of the rachis and barbs allow assignment to the more exclusive group Aves, and
more specifically to Neornithes.
The contour feathers preserved in UWBM 103150 provide the oldest unquestionable
evidence of medullary pith and a square rachis in the fossil record. The co-occurrence of a square
rachis and pith may not be surprising given the integral role that medullary pith fills in the
formation of a square rachis in modern birds (Maderson et al. 2009), but also suggests that the
evolution of a square rachis requires prior acquisition of medullary pith (S. Wang et al. 2020).
Although numerous, exceptionally preserved feathers have recently been reported from
Cretaceous amber (Xu 2019; Carroll, Chiappe, and Bottjer 2019; Xing, Cockx, and McKellar
2020), they have failed to provide clear evidence of medullary pith or rachises with a square
cross section. Until now, the oldest reported fossil medullary pith was preserved in a neornithine
contour feather from the lower Eocene Fur Formation of Denmark (Gren et al. 2017). The lack of
medullary pith in feathers attributed to Mesozoic stem birds (e.g., Enantiornithes) supports the
argument that this key component of the modern feather evolved within the ornithuromorph
lineage (i.e., the lineage that includes modern birds and their most immediate outgroups) and it
was an integral novelty of the crown clade, Neornithes. Although it is currently impossible to
pinpoint the origin of this structure in avian phylogeny, the existing fossil record is congruent
with the idea that the medullary pith of modern feathers evolved late in dinosaur evolution, and
closer to (if not at) the origin of modern birds. Furthermore, the discernibility of fiber orientation
of individual layers within the rachis cortex of these feathers also suggests that the fiber-

50
reinforced rachis construction was being utilized in small contour feathers prior to crown bird
radiation.
Therefore, the available evidence indicates that some of the feathers included in UWBM
103150 belong to neornithine birds, which are known to have evolved by the Late Cretaceous
(Field et al. 2020b). It is tempting to ascribe the small size of the feathers preserved in this
nodule to a small sized bird. However, the difference in size between the largest and smallest
feather within the plumage of an individual bird can be a factor of 1000 (Leeson and Walsh,
2004) and the length of contour feathers across different tracts of an adult Single Comb White
Leghorn Chicken have a range of .9-200 mm (Lucas and Stettenheim 1972). Additionally,
studies of modern crocodiles show that while the largest indigestible feathers are regurgitated
(Fisher 1981), small contour, downy and fragmented portions of larger feathers are passed fully
through the digestive tract (Milàn 2012). Given that only the smallest contour and downy
feathers of a considerably sized bird are likely to pass fully through the digestive system of a
carnivore, more diagnostic elements are needed before prey size can be estimated.

Coprolite Assignment and Producer Affinities
UWBM 103150 is identified as a large carnivore coprolite based on its phosphatic
composition, ovoid external morphology, presence of phosphatic matrix-supported bone
inclusions, and longitudinally aligned fibrous internal void architecture.
Although the initial field observations of UWBM 103150 did not present obvious diagnostic
coprolite characteristics, additional laboratory analysis provided favorable coprolite assignment.
Microvertebrate assemblages can be concentrated by abiotic (hydraulic, aeolian sorting) and
biotic (predators, scavengers, burrowing) means. The shallow lacustrine and possible overbank

51
or floodplain deposit interpretation of this depositional environment is not conducive to the
multi-taxa accumulation of both skeletal and soft tissue elements described here (Hollocher,
Hollocher, and Rigby 2010). The disarticulated and broken nature of the skeletal elements
preserved in this nodule, along with the indistinct boundaries of the epiphyseal portions suggest a
digestive accumulation rather than a burrow infill origin (Weaver et al. 2021). Regurgitated
pellets of modern owls and raptors can provide similar element accumulations to those observed
here but are dominated by keratin and skeletal elements that are not supported with as much
phosphatic groundmass that is observed in UWBM 103150 (Dodson and Wexlar, 1979;
Andrews, 1990). Given the limited fossil identification of regurgitates (Myhrvold 2012) and
knowledge of Late Cretaceous carnivore digestive systems (Zheng et al. 2018) we cannot
completely rule out the possibility of UWBM 103150 being a regurgitated pellet.
Studies on scat from modern crocodilians show a consistent relationship between fecal
diameter and body length, whereas the length of the scat is diet dependent. With a diameter
greater than 8 cm, the estimated body length (>4.5 m) of a crocodilian needed to produce
UWBM 103150 exceeds that of the crocodilians known from the well-studied HCF including the
approximately 2.5–3-m-long Brachychampsa montana and Borealosuchus sternbergii of the
study area (e.g., (Gilmore 1910; 1911; M. A. Norell, Clark, and Hutchison 1994), and the much
smaller (~1.5 m) Stangerochampsa (BMRP 2008.4) from Carter County, Montana.
This leads to the hypothesis that this coprolite was produced by a larger animal. Several
large-bodied, predatory dinosaurs are known from the HCF. These include ornithomimids and
the 200-300 kg oviraptorosaurian Anzu wyliei (Lamanna et al. 2014). However, Late Cretaceous
ornithomimids have been reinterpreted as likely herbivorous (Kobayashi et al. 1999) and the
trophic ecology of Anzu is poorly understood (Lamanna et al. 2014). Given that only a single

52
large confirmed (although see DePalma et al. 2015; Arbour et al. 2016) predator, Tyrannosaurus
rex, is known from the HCF ecosystem, it is likely that this is the producer of the coprolite. As
such, the T. rex individual that produced UWBM 103150 would have been of substantially
smaller body size, and presumably younger, than the one that produced the coprolite reported
from the Maastrichtian Frenchman Formation (Chin et al. 1998), which had a diameter roughly
twice that of the specimen described herein. The importance of juvenile tyrannosaurs in the HCF
ecosystem has recently been emphasized (Schroeder, Lyons, and Smith 2021; Holtz 2021), who
hypothesized that these dinosaurs filled the predatory role of smaller carnivorous species. The
fossil content of this coprolite implies that juvenile or subadult T. rex preyed on birds,
reinforcing the idea of ontogenetic dietary shifts, with evidence of predation by juveniles on
smaller-bodied prey than previously recognized (Woodward et al. 2020).

vi. Conclusion
It is of note that the described specimen was only collected because of a chance field
identification of an optically identifiable feather from the fragmented center of an otherwise non-
descript nodule. It was only during laboratory investigations that the specimen was understood to
not only be a coprolite, but that it contained more feathers and elements than were exposed at the
surface. Traditional investigations of coprolites have involved petrography, SEM, or acid
dissolution (Chin 2002; CHIN et al. 2003); techniques that would have difficulty recognizing the
feathers within. Thin sectioning and SEM surface analysis alone would require intersections
through recognizable feather structures, and acid dissolution would have destroyed the fine 3D
feather structures. After µCT scanning and reconstruction revealed internally preserved feathers
their exposed intersections with the surface could be identified with traditional optical

53
microscopy; a linear series of v-shaped depressions (barbs) centered by a square hole (rachis)
locates the internal contour feather while trapezoidal to rectangular pits cored by medullary pith
locate the fragmentary rachis intersections with the surface.
As demonstrated by (Qvarnström et al. 2017; 2021; 2019), the use of phase-contrast
propagation synchrotron microtomography is ideal for discerning the possible range of soft tissue
and hard tissue inclusions that may be in a coprolite. This study shows that the use of laboratory-
grade µCT scanners (which are more accessible), when operated by a technician familiar with
the requirements for paleontological investigations can reveal important data on feather forms
(Fig. 4.7). Recognizing coprolites (especially larger specimens that do not exhibit obvious
morphology in the field) can provide Konservat-Lagerstätte preservation for feathers in
otherwise under-sampled formations will certainly provide a powerful sampling method for
investigating feather evolution throughout the Mesozoic. Coprolites, such as UWBM 103150,
offer a fossil record that is complementary to the amber fossil record in providing critical data to
the study of the evolution of feathers and other keratinous structures.

54

Figure 4.1. Optical image of nodule and
exposed feather. (a) Nodule from coprolite
studied (b) Exposed feather.

55

Figure 4.2. Details of surface-exposed feather under light microscopy. (a) Exposed medullary
pith of rachis and barb ramus. (b) Detail of exposed barbs and barbules.

56

Figure 4.3. Preservational details of exposed feather under SEM. (a) Rachidial cortex
showing fibrous texture. (b) Globular microbodies covering fiber bundles. (c) Enlarged
view of rectangle in (b) of microbodies covering fiber bundles. (d) Barb with exposed
medullary pith in ramus. (e) Enlarged view of (d) showing interstitial smooth matrix
between valleys of presumed barbule plate positions filled with globular microbodies. (f-
h) SEM of feather rachidial (cortex) fibres (syncitial barbules). (f,g) Biodegraded fibres of
Gallus gallus (resin embedded and etched). (f) A detail showing fibres, syncitial nodes
and macrofibrils; arrows and arrowheads show hooked and ringed terminations of nodes,
respectively. (g) Group of fibres seen in cross section; the thicker cross sections indicate
proximity to the syncitial nodes; arrows show macrofibrils. (h)– Non-biodegraded
rachidial fibres. (c) Gallus gallus, showing ringed nodes (arrow). Images and descriptions
of (f-h) from (Lingham-Solair 2010).

57

58
Figure 4.4. Micro-CT reconstructions of definitive feathers in UWBM 103150. (a) The entire
nodule (semi-transparent) and inclusions colored in order of density in relation to average nodule
groundmass: gold- low to vacant; red- medium density; dark blue- higher than average density;
light blue- highest density (b) Surface exposed contour feather in ventral view. (c) Surface
exposed contour feather in dorsal view with cross sections of the shaft from proximal calamus to
distal end of rachis. (d) Encased contour feather in dorsal view with cross sections of the shaft
from proximal calamus to distal end of rachis. (e) Downy-type feather with short calamus and
long barbs. (f) Plumaceous feather with central thin rachis.

59

Figure 4.5. Fragmentary Inclusions. (a) The entire nodule (semi-transparent) and inclusions
colored in order of density in relation to average nodule groundmass: gold- low to vacant; red-
medium density; dark blue- higher than average density; light blue- highest density. (b) Possible
rachis fragments that display similar densities and morphologies to the rachises of contour
feathers displayed in Fig. 4.4. (c) elongate fibrous structures. (d) Possible fish scales, dark blue
indicates low density and light blue indicates higher density. (e) Small hollow bone element. (f)
Larger trabecular bone.

60

Figure 4.6: Potential integumentary producing groups of the Hell Creek Formation and
evolutionary significance of described feathers. The top phylogeny illustrates the potential
filament-producing fauna of the HCF, based on confirmed integument types of earlier related
taxa from other formations. The nested boxes under the phylogeny depict the conservative
placement of described feather types in this chapter.

61

Figure 4.7. Coprolite (LACM 48121) from the Hell Creek formation. a) Photographs of
LACM48121 in two views. b) Digital reconstruction from micro-CT scans of coprolite LACM
4812 in same orientation as (a). Coprolite groundmass is transparent, with hair-like inclusions in
blue and purple, possible scales or elytra in green, and arthropod cephalothorax in teal.

62
Chapter 5:
Conclusions and Discussion

i. Introduction
This study has identified key three-dimensional macro and micro-structural features of
modern bird feathers that have a more complex, mosaic distribution amongst Cretaceous avians
than previously recognized. By utilizing under-studied fossil resources with emerging
technologies, these new discoveries reveal that components currently thought to be integral to the
modern bird flight apparatus, as well as some developmental pathways, were likely not present in
some stem bird lineages. These new findings illustrate that the mechanical capabilities and
efficiencies of modern bird feathers, as well as their development, should not be inferred wholly
from two dimensionally preserved compression fossils. The recognition of ovoid, hollow
rachises in flight feathers suggests that while the asymmetric vane arose early in bird evolution,
adaptations to components of the main shaft evolved later. This study also demonstrated that
exceptional fine scale 3D preservation is not limited to amber deposits; coprolites can provide an
important and historically over-looked record for testing hypotheses about avian integument
evolution.

ii. Evolution of Medullary Pith and the Modern Rachis
The adaptation of medullary pith appears to be a key morphogenic factor in feather
evolution, given its importance in the development of a square rachis and the mechanical
lightness and strength it confers (B. Wang and Meyers 2017; Osváth et al. 2020). Its apparent
absence in middle Cretaceous amber from Myanmar, as well as its presence by the latest

63
Cretaceous Hell Creek Formation of Montana, supports the hypothesis that this feature may be
unique to crown-group birds, which begin to radiate by the Late Cretaceous (Field et al. 2020a;
Y. Yu, Zhang, and Xu 2021). Because all modern volant birds fly with feathers supported by a
square, pith-filled rachis, the general assumption has been that this feature is necessary for flight
(Pap et al. 2015), as the degree of rachis “squareness” is lessened in lineages of birds that have
lost flight compared to their close volant relatives (Mcgowan 1989). However, stem birds and
even non- avian theropods feature many skeletal and feather adaptations that suggest that they
were capable of powered flight, despite possibly not having developed all the components of a
fully modern rachis.
Despite the important developments that resulted from the discovery of different types of
feathered non-avian dinosaurs (Prum 2005; M. Norell et al. 2002; Prum 1999), the current
paradigm of feather evolution regards the asymmetric flight feather—already present in the Late
Jurassic Archaeopteryx—as the pinnacle of feather evolution. While this appears to be the case
at the macroscopic level, the results of the present study reveal that significant evolutionary
innovations of the modern feather took place late in the evolutionary history of birds, appearing
well after the development of the asymmetrically vaned feather. Therefore, the results of the
present study run somewhat counter to common knowledge indicating an evolutionary ‘stasis’ in
the development of the modern feather. In contrast, these results show that during the Cretaceous
(and perhaps beyond, see (Price-Waldman, Shultz, and Burns 2020) ), feathers were subject to
selective pressures leading to the evolution of important structures that cannot be identified from
lithic fossils (i.e., square-shaped rachis, medullary pith, hooklets). These selective pressures also
led to the evolution of feather morphotypes that are no longer in existence, such as the rachis-
dominated feathers (RDFs) adorning the tails of many stem birds (e.g., confuciusornithids,

64
enantiornithines). The results of this study show that along with the unique development of
ornamental RDFs, wing and body plumages of stem birds may have experienced divergent
developmental pathways within the rachis.
The mechanical advantages of a square rachis in modern birds are most evident for flight,
but the tailored stiffness or flexibility afforded by medullary pith development is equally useful
in body contour feathers for thermal regulation and for display structures, such as the train of a
peacock or the racket plumes of hummingbirds. Many modern birds utilize structural coloration
and the control of the body contour feather’s angle towards light sources to create visual displays
(Stavenga et al. 2011; McCoy et al. 2021). The rachises of enantiornithine contour feathers
appear to be very thin (Xing et al. 2017c; J. K. O’Connor et al. 2020) or consist of elongate barbs
that are basally attached to a proportionately short rachis (O’Connor 2020). This feather
morphology may be expected in lineages without the control of pith for rachis development and
has major implications for interpretations of plumage use and display in Mesozoic avifauna.

iii. Calamus-Rachis Transitions: Identifying a Modern Flight Feather
The transition of the calamus to the rachis that is characteristic of a modern flight feather
and its development was not present in the mid-Cretaceous flight feathers analyzed in this study.
A tapered hollow lumen of the calamus that extends distally beyond the start of vane formation,
lateral extensions of medullary pith that proximally extend into the calamus lumen, a clear
superior umbilicus, and formation of a rachis with a square cross section could not be identified
in associated or dissociated flight feathers in mid-cretaceous amber. Rather, these feathers
display an abrupt transition of the calamus to the rachis (separated by a thickened cortical wall)
or a continuous lumen from the calamus to the vaned rachis. The rachis of these feathers display

65
an ovoid cross-sectional geometry that would likely not convey the same mechanical
performance afforded by the square cross section of modern birds (KleinHeerenbrink Marco,
Johansson L. Christoffer, and Hedenström Anders 2017). These results suggest that a unique
rachis development in Mesozoic stem birds may have been employed in the formation of flight
feathers as well as the more obviously unique RDFs. Without the ability to form square cross-
sectional rachises, the controlled aerostatic flutter observed in slotted wing tips of modern birds
would have also been unlikely (Klaassen van Oorschot 2017; Sullivan et al. 2017). These results
raise questions about whether stem birds were capable of occupying the same wing
morphospaces occupied by modern birds (Serrano et al. 2018; Xia Wang and Clarke 2015). In
light of these findings, the application of modern molting patterns of modern birds should also be
applied to extinct birds with caution (Kaye, Pittman, and Wahl 2020; J. O’Connor et al. 2020).

iii. Coprolites: A Lagerstätte of keratinous structures
The study of feathers has traditionally relied on the Konservat-Lagertstätten of lacustrine
and lagoonal deposits, giving us exceptional albeit temporally disparate windows into the
evolution of feathers. Recent investigations of Permian and Triassic coprolites demonstrated that
otherwise rare chitinous and keratinous remains could be extracted with surprisingly high detail,
including that of insects and possible synapsid hair (Qvarnström et al. 2017; 2021; 2019). The
description of feathers in a Hell Creek coprolite presented here demonstrate that not only can the
external morphology of a feather be preserved, but that intricate internal components of a highly
derived keratinous structure can also be identified. This study reveals that coprolites can provide
high fidelity data on the presence of different feather morphologies from a well-studied deposit
that has produced phenomenal skeletal specimens, but until now has not yielded feathers. The

66
lack of feathers (or other keratinous structures) reported from the Hell Creek formation is likely
due to a collection bias of coprolites and the study of them with emerging technologies.
Preliminary investigations of other Hell Creek coprolites in the NHMLA collections suggest that
keratin preservation in coprolites from this formation is not rare, and that further reports of
feathers from this and other formations will only be limited by how many coprolites can be
collected and scanned.

iv. Further Research
Expanding the Fossil Amber Record
If medullary pith and the development of a square cross-sectional rachis is as integral to
the flight capabilities (and the diversity of wing morphologies) of modern birds as is currently
assumed, placing these features into a phylogenetic context may illuminate the relationship
between integument and skeletal evolution within Aves. To test this, additional data points from
coprolite or amber-preserved feathers that are coeval with well-studied lithic deposits (such as
the Jehol biota) that preserve compressed feathers and associated skeletons will be needed.
Amber deposits in Lebanon have produced feathers that predate the Jehol biota by at least 15
million years (Maksoud et al. 2017), and could provide important data on the construction of bird
feathers before the main radiation of stem birds. Late Campanian amber deposits from Canada
(McKellar et al. 2011) could provide important data on how early medullary pith evolved.
Amber research has traditionally been dependent on commercial mining operations to
collect the volumes of amber needed to find feather inclusions. Preliminary investigations on the
collection and stabilization of non-gem grade amber (Raritin Fm, Hell Creek Fm.) may also
provide an expanded temporal range to this record.

67

Taphonomic Factors
To test whether the signal observed in this study is truly biologic and a consequence of
taphonomy or influenced by facies it will also be important to demonstrate that medullary pith is
not selectively degraded by resins. Investigations of feathers from Baltic amber (S. Gabbott et al.
2019) and amber from the Dominican Republic (Laybourne, Deedrick, and Hueber 1994) should
be able to demonstrate that medullary pith can persist to at least the late Cenozoic. A collection
of feathers preserved in Columbian copal (Pleistocene) at NHMLA does preserve medullary pith,
and although copal is not fully polymerized, it does lack any volatiles and succinic acids.
Medullary pith does contain more IF-cornifying proteins than the cortex, but most of the pith is
comprised of similar feather beta-keratin as the cortex, so any mechanism of selective
biodegradation of pith would have to be extremely specific and is not yet observed in the modern
record.
Ecomorphological segregation between groups of birds may also introduce a bias into the
feathers that enter the amber record. The ecology of enantiornithines has been inferred to be
predominately arboreal, particularly for the Early-Middle Cretaceous, and since the majority of
resin capture happens in forest environments it is likely that enantiornithine feathers dominate
the amber record of this time. Previous research by (Field et al. 2018) has revealed through
ancestral state reconstructions that Late Cretaceous neornithine ecologies have strong bias
toward non-arboreal environments, so accessing complementary 3-D fossil feather record that
does not come exclusively from arboreal paleoenvironments will be important. As the results of
the present study indicate, the coprolite record plays a significant role in this respect.

68
Expanding the Coprolite-Preserved Feather Record

The remarkable results from this study on the preservation of feathers in a coprolite
demonstrate that a large-scale, systematic study of the fossil record for coprolites and feather
remains is warranted. This study provides both the oldest example of a feather preserved in
amber as well as the oldest example of medullary pith (latest Maastrichtian, ~66 MYA). Given
that crown birds originated in the Late Cretaceous, this prompts the question of whether or
medullary pith originated before or after the origin of crown birds. Feathers preserved in
coprolites of a known producer have the added benefit of being able to be placed into a
palaeoecological context and given that the chitin of insects is indigestible and also found within
coprolite matrix or attached to feathers, coprolites allow for studies of avian food chain
dynamics.
Coprolites are relatively abundant in the fossil record and throughout the Cretaceous, and
combining the amber and coprolite record of fossil feathers may truly lead to a fine-scale
understanding of how this remarkable integumentary feature, the feather, evolved.

V. Ethics, Amber, and the Quest for Exceptional Feathers
Although the study of paleontology is focused on dead organisms of the past, its progress
is reliant on living humans operating in the complexities of the present. This study has hopefully
acknowledged those that have previously published the ideas and information necessary for the
advances made by this study, but a full account of the individuals responsible for the discovery,
excavation, and securement of specimens into the public trust is not presented here. Instead, the
following endeavors to at least acknowledge why a full accounting of the labor needed to

69
produce this research is not possible and recognize the conditions that have brought the
specimens presented here to light.
The study of fossil inclusions in amber has traditionally relied on the commercial
excavation of amber for commercial gemological purposes to provide fossil specimens of interest
to the scientific community (Langenheim 2003). These economically driven operations have
provided exceptional views into ancient environments, specifically those of the Eocene and
Miocene of Baltic and Dominican Republic deposits (respectfully), that produce economically
viable fossilized resin (Poinar 1988). Although the Cretaceous amber deposits of Myanmar
(Burma) have been excavated and traded for 2,000 years, significant descriptions of inclusions in
amber from Myanmar have only entered into scientific literature in the early 21
st
century (Penney
2010; Grimaldi, Engel, and Nascimbene 2002), despite promising descriptions of inclusions from
the early 20
th
century (Cockerell 1916). The influx of Burmese amber into world markets by the
early 2000’s was due to ceasefire agreements between the Burmese government and the armed
groups controlling the northern amber-producing regions of Myanmar in the early 1990’s (Rippa
and Yang 2017). The following two decades of relatively stable trade across Myanmar’s borders
(particularly the 2010’s) resulted in the recognition of numerous fossil inclusions from this
deposit, notably those of vertebrates (Ross 2018). The recognition of spectacular fossils from this
region was also accompanied with justifiable scrutiny of the excavation and trade of these
deposits, which raised concerns about the labor conditions and use of funds generated by the
trade of Burmese amber (Lawton 2019). In April 2020, the Society of Vertebrate Paleontology
called for a publication moratorium on any fossil specimens purchased from sources in Myanmar
after June 2017, largely citing concerns that profits of amber sales in the Hukwang region of
northern Myanmar were funding an oppressive military regime that was killing unarmed

70
civilians (Rayfield, Theodor, and Polly 2020). Subsequent publications and letters by authors
(both local and abroad) pointed out that there was little to no evidence that profits from the
amber trade in this region were directly funding genocide, not all amber from Myanmar is
sourced from conflict regions, and that the export of amber specimens prior to 2017 was legal
according to Burmese laws at that time (Peretti 2021; Barrett, Johanson, and Long 2021; Zin-
Maung-Maung-Thein and Khin Zaw 2021; Shi et al. 2021). The labor conditions in which all
amber is excavated in Myanmar are not fully documented (as is the case for other economically
important amber deposits), but accounts of child labor do exist (Lawton 2019) . For what it is
worth, the specimens in amber utilized in this research from Myanmar were acquired or donated
to the Natural History Museum of Los Angeles County prior to 2017.
The recent spectacular discoveries of inclusions in Burmese amber and current cultural
climate have drawn the interest of the general public and scientific community to the
complications surrounding Burmese amber, but these complications are neither unique or
entirely new (Monarrez et al. 2021). Exceptionally preserved fossils (a category in which almost
any fossil feather falls into) attract the attention of science and monetary interests, which has
historically led to the exploitation of labor and resources. The first Archeopteryx skeleton was
described after it was sold to the London Museum by a doctor who had acquired from a
Solnhofen Limestone quarry worker who used it as payment to treat chronic pneumonia (Hanson
2011). The specimens from the “Bone Wars” of Cope and Marsh that ultimately resulted in
foundational collections at the Yale Peabody Museum of Natural History, the American Museum
of Natural History, and the Smithsonian Museum of Natural History (and arguably set the U.S. at
the forefront of paleontology at the time) were largely collected without permission from treatied
Indian territories (Bradley 2014). Many important avian specimens from the Jehol have entered

71
Chinese museums only after filtering through black market trades (Dalton 2000). Legal and
illegal excavations of amber in the Ukraine and elsewhere continue to have devastating
ecological impacts (Smaliychuk, Ghazaryan, and Dubovyk 2021).
The examples given above (which is not an exhaustive list) of exploitation of labor and
resources in pursuit of exceptional fossils is not intended to be a list of “whataboutisms” to
absolve the nature of amber excavations in Myanmar. Rather, these examples are given to
acknowledge that the current knowledge of feather evolution is built on exceptional fossils that
have inspired brilliant insights, and that there has been an unappreciated cost to those insights.
The discovery of exceptionally preserved fossil feathers does not require exploitative
excavation; ethical discoveries of feathers from amber deposits that are not economically mined
are being done by researchers in Canada, Spain, France, New Jersey, and elsewhere (McKellar et
al. 2011; Alonso et al. 2000; Perrichot et al. 2008; Grimaldi and Case 1995). The discovery of
coprolites as a potential source of exceptional feather preservation (a resource that is not
currently monetized) provides a potential avenue for ethically-sourced feather data if properly
acquired. The coprolites utilized in this study were obtained through permitted collection on
land currently administered by the federal Bureau of Land Management that is the ancestral land
of the Očhéthi Šakówiŋ, Michif Piyii (Métis), Niitsítpiis-stahkoii (Blackfoot), Apsaalooké
(Crow), and Tséstho’e (Cheyenne) peoples. It is with hope that acknowledging the unheard
voices and roles of the people who have suffered as the result of scientific exploits will open a
future chapter of ethical extraction of exceptionally preserved fossils.

72

REFERENCES
Agnolin, Federico L., Sebastián Rozadilla, and Ismar de Souza Carvalho. 2019.
“Praeornis Sharovi Rautian, 1978 a Fossil Feather from the Early Late Jurassic of
Kazakhstan.” Historical Biology 31 (7): 962–66.
https://doi.org/10.1080/08912963.2017.1413102.
Alibardi, Lorenzo. 2009. “Cornification of the Pulp Epithelium and Formation of Pulp
Cups in Downfeathers and Regenerating Feathers.” Anatomical Science
International 84 (4): 269–79. https://doi.org/10.1007/s12565-009-0033-2.
———. 2017. “Review: Cornification, Morphogenesis and Evolution of Feathers.”
Protoplasma; Vienna 254 (3): 1259–81. http://dx.doi.org/10.1007/s00709-016-
1019-2.
Alibardi, Lorenzo, Karin Brigit Holthaus, Supawadee Sukseree, Marcela Hermann, Erwin
Tschachler, and Leopold Eckhart. 2016. “Immunolocalization of a Histidine-Rich
Epidermal Differentiation Protein in the Chicken Supports the Hypothesis of an
Evolutionary Developmental Link between the Embryonic Subperiderm and
Feather Barbs and Barbules.” Edited by Michel Simon. PLOS ONE 11 (12):
e0167789. https://doi.org/10.1371/journal.pone.0167789.
Alonso, Jesus, Antonio Arillo, Eduardo Barrón, J. Carmelo Corral, Joan Grimalt, Jordi F.
López, Rafael López, et al. 2000. “A New Fossil Resin with Biological Inclusions

73
in Lower Cretaceous Deposits from Álava (Northern Spain, Basque-Cantabrian
Basin).” Journal of Paleontology 74 (1): 158–78.
Arbour, Victoria M., Lindsay E. Zanno, Derek W. Larson, David C. Evans, and Hans-
Dieter Sues. 2016. “The Furculae of the Dromaeosaurid Dinosaur Dakotaraptor
Steini Are Trionychid Turtle Entoplastra.” PeerJ 4 (February): e1691.
https://doi.org/10.7717/peerj.1691.
Barrett, Paul M., Zerina Johanson, and Sarah L. Long. 2021. “Law, Ethics, Gems and
Fossils in Myanmar Amber.” Nature Ecology & Evolution 5 (6): 708–708.
https://doi.org/10.1038/s41559-021-01478-0.
Benton, Michael J., Zhou Zhonghe, Patrick J. Orr, Zhang Fucheng, and Stuart L. Kearns.
2008. “The Remarkable Fossils from the Early Cretaceous Jehol Biota of China
and How They Have Changed Our Knowledge of Mesozoic Life: Presidential
Address, Delivered 2nd May 2008.” Proceedings of the Geologists’ Association
119 (3–4): 209–28.
Bolotov, Ivan N., Olga V. Aksenova, Ilya V. Vikhrev, Ekaterina S. Konopleva, Yulia E.
Chapurina, and Alexander V. Kondakov. 2021. “A New Fossil Piddock (Bivalvia:
Pholadidae) May Indicate Estuarine to Freshwater Environments near Cretaceous
Amber-Producing Forests in Myanmar.” Scientific Reports 11 (1): 6646.
https://doi.org/10.1038/s41598-021-86241-y.
Bradley, Lawrence W. 2014. Dinosaurs And Indians: Paleontology Resource
Dispossession From Sioux Lands: First Edition. Outskirts Press.
Brown, Caleb Marshall, David C. Evans, Nicolás E. Campione, Lorna J. O’Brien, and
David A. Eberth. 2013. “Evidence for Taphonomic Size Bias in the Dinosaur Park

74
Formation (Campanian, Alberta), a Model Mesozoic Terrestrial Alluvial‐paralic
System.” Palaeogeography, Palaeoclimatology, Palaeoecology, Vertebrate
palaeobiodiversity patterns and the impact of sampling bias, 372 (February): 108–
22. https://doi.org/10.1016/j.palaeo.2012.06.027.
Brush, Alan H. 1967. “Additional Observations on the Structure of Unusual Feather
Tips.” The Wilson Bulletin 79 (3): 322–27.
Bryant, Vaughn M., and Glenna Williams-Dean. 1975. “THE COPROLITES OF MAN.”
Scientific American 232 (1): 100–109.
Carroll, Nathan R., Luis M. Chiappe, and David J. Bottjer. 2019. “Mid-Cretaceous
Amber Inclusions Reveal Morphogenesis of Extinct Rachis-Dominated Feathers.”
Scientific Reports 9 (1): 1–8. https://doi.org/10.1038/s41598-019-54429-y.
Carvalho, Ismar de Souza, Fernando E. Novas, Federico L. Agnolín, Marcelo P. Isasi,
Francisco I. Freitas, and José A. Andrade. 2015. “A New Genus and Species of
Enantiornithine Bird from the Early Cretaceous of Brazil.” Brazilian Journal of
Geology 45 (2): 161–71. https://doi.org/10.1590/23174889201500020001.
Casto, Stanley D. 1974. “Entry and Exit of Syringophilid Mites (Acarina:
Syringophilidae) from the Lumen of the Quill.” The Wilson Bulletin 86 (3): 272–
78.
Chang, Wei-Ling, Hao Wu, Yu-Kun Chiu, Shuo Wang, Ting-Xin Jiang, Zhong-Lai Luo,
Yen-Cheng Lin, et al. 2019. “The Making of a Flight Feather: Bio-Architectural
Principles and Adaptation.” Cell 179 (6): 1409-1423.e17.
https://doi.org/10.1016/j.cell.2019.11.008.

75
Chiappe, Luis M., Shu’an Ji, QIANG Ji, and Mark A. Norell. 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: 89.
Chiappe, Luis M., and Qingjin Meng. 2016. Birds of Stone: Chinese Avian Fossils from
the Age of Dinosaurs. Johns Hopkins.
Chin, Karen. 2002. “Analyses of Coprolites Produced by Carnivorous Vertebrates.” The
Paleontological Society Papers 8 (October): 43–50.
https://doi.org/10.1017/S1089332600001042.
Chin, Karen, David A. Eberth, Mary H. Schweitzer, Thomas A. Rando, Wendy J.
Sloboda, And John R. Horner. 2003. “Remarkable Preservation of Undigested
Muscle Tissue Within a Late Cretaceous Tyrannosaurid Coprolite from Alberta,
Canada.” PALAIOS 18 (3): 286–94. https://doi.org/10.1669/0883-
1351(2003)018<0286:RPOUMT>2.0.CO;2.
Chin, Karen, Timothy T. Tokaryk, Gregory M. Erickson, and Lewis C. Calk. 1998. “A
King-Sized Theropod Coprolite.” Nature 393 (6686): 680–82.
https://doi.org/10.1038/31461.
Cockerell, T.D.A. 1916. “Insects in Burmese Amber.” American Journal of Science 4
(42): 135–38.
Dalton, Rex. 2000. “Chasing the Dragons.” Nature 406 (6799): 930–32.
https://doi.org/10.1038/35023182.
Davis, Paul G., and Derek EG Briggs. 1995. “Fossilization of Feathers.” Geology 23 (9):
783–86.

76
DePalma, Robert A., David A. Burnham, Larry D. Martin, Peter L. Larson, and Robert T.
Bakker. 2015. “The First Giant Raptor (Theropoda: Dromaeosauridae) from the
Hell Creek Formation.” Paleontological Contributions 2015 (14): 1–16.
https://doi.org/10.17161/paleo.1808.18764.
Dove, Carla J. 2000. “A Descriptive and Phylogenetic Analysis of Plumulaceous Feather
Characters in Charadriiformes.” Ornithological Monographs, no. 51: 1–163.
https://doi.org/10.2307/40166844.
Fastovsky, David E., and Antoine Bercovici. 2016. “The Hell Creek Formation and Its
Contribution to the Cretaceous–Paleogene Extinction: A Short Primer.”
Cretaceous Research 57 (January): 368–90.
https://doi.org/10.1016/j.cretres.2015.07.007.
Fastovsky, D.E. 1987. “Paleoenvironments of Vertebrate-Bearing Strata during the
Cretaceous-Paleogene Transition, Eastern Montana and Western North Dakota.”
PALAIOS 2 (January): 282. https://doi.org/10.2307/3514678.
Field, Daniel J., Juan Benito, Albert Chen, John W. M. Jagt, and Daniel T. Ksepka. 2020.
“Late Cretaceous Neornithine from Europe Illuminates the Origins of Crown
Birds.” Nature 579 (7799): 397–401. https://doi.org/10.1038/s41586-020-2096-0.
Fisher, Daniel C. 1981. “Crocodilian Scatology, Microvertebrate Concentrations, and
Enamel-Less Teeth.” Paleobiology 7 (2): 262–75.
Foth, Christian. 2012. “On the Identification of Feather Structures in Stem-Line
Representatives of Birds: Evidence from Fossils and Actuopalaeontology.”
Paläontologische Zeitschrift 86 (1): 91–102. https://doi.org/10.1007/s12542-011-
0111-3.

77
Fucheng, Zhang, Zhou Zhonghe, and Gareth Dyke. 2006. “Feathers and ‘Feather-like’
Integumentary Structures in Liaoning Birds and Dinosaurs.” Geological Journal
41 (3–4): 395–404. https://doi.org/10.1002/gj.1057.
Gabbott, S., V. McCoy, K. Penkman, M. Collins, S. Presslee, J. Holt, H. Grossman, et al.
2019. “Ancient Amino Acids from Fossil Feathers in Amber,” April.
https://doi.org/10.1038/s41598-019-42938-9'].
Gilmore, Charles W. 1910. “Leidyosuchus Sternbergii, a New Species of Crocodile from
the Ceratops Beds of Wyoming.” Proceedings of the United States National
Museum 38 (1762): 485–502. https://doi.org/10.5479/si.00963801.38-1762.485.
Gilmore, Charles W. 1911. “A NEW FOSSIL ALLIGATOR FROM THE HELL
CREEK.” Proceedings of the United States National Museum 41: 297–302.
Gregg, Keith, and George E. Rogers. 1986. “Feather Keratin: Composition, Structure and
Biogenesis.” In Biology of the Integument: 2 Vertebrates, edited by Jürgen
Bereiter-Hahn, A. Gedeon Matoltsy, and K. Sylvia Richards, 666–94. Berlin,
Heidelberg: Springer. https://doi.org/10.1007/978-3-662-00989-5_33.
Gren, Johan A., Peter Sjövall, Mats E. Eriksson, Rene L. Sylvestersen, Federica Marone,
Kajsa G. V. Sigfridsson Clauss, Gavin J. Taylor, Stefan Carlson, Per Uvdal, and
Johan Lindgren. 2017. “Molecular and Microstructural Inventory of an Isolated
Fossil Bird Feather from the Eocene Fur Formation of Denmark.” Edited by Sarah
Gabbott. Palaeontology 60 (1): 73–90. https://doi.org/10.1111/pala.12271.
Grimaldi, David A., and Gerard Ramon Case. 1995. “A Feather in Amber from the Upper
Cretaceous of New Jersey. American Museum Novitates; No. 3126.”
http://digitallibrary.amnh.org/handle/2246/3571.

78
Grimaldi, David A., Michael S. Engel, and Paul C. Nascimbene. 2002. “Fossiliferous
Cretaceous Amber from Myanmar (Burma): Its Rediscovery, Biotic Diversity,
and Paleontological Significance.” American Museum Novitates 3361 (March): 1–
71. https://doi.org/10.1206/0003-0082(2002)361<0001:FCAFMB>2.0.CO;2.
Hanson, Thor. 2011. Feathers: The Evolution of a Natural Miracle. Basic Books.
Hertel, H. 1966. Structure, Form, Movement. Rehnhold Publishing Corp.
Hollocher, K. T., T. C. Hollocher, and J. K. Rigby. 2010. “A Phosphatic Coprolite
Lacking Diagenetic Permineralization From The Upper Cretaceous Hell Creek
Formation, Northeastern Montana: Importance Of Dietary Calcium Phosphate In
Preservation.” PALAIOS 25 (2): 132–40. https://doi.org/10.2110/palo.2008.p08-
132r.
Holtz, Thomas R. 2021. “Theropod Guild Structure and the Tyrannosaurid Niche
Assimilation Hypothesis: Implications for Predatory Dinosaur Macroecology and
Ontogeny in Later Late Cretaceous Asiamerica.” Canadian Journal of Earth
Sciences, June, 1–18. https://doi.org/10.1139/cjes-2020-0174.
Horner, John R., Mark B. Goodwin, and Nathan Myhrvold. 2011. “Dinosaur Census
Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper
Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA.” PLoS ONE 6
(2). https://doi.org/10.1371/journal.pone.0016574.
Hu, Han, Jingmai K. O’Connor, and Zhonghe Zhou. 2015. “A New Species of
Pengornithidae (Aves: Enantiornithes) from the Lower Cretaceous of China
Suggests a Specialized Scansorial Habitat Previously Unknown in Early Birds.”

79
Edited by Andrew A. Farke. PLOS ONE 10 (6): e0126791.
https://doi.org/10.1371/journal.pone.0126791.
Jenni, Lukas, Kathrin Ganz, Pietro Milanesi, and Raffael Winkler. 2020. “Determinants
and Constraints of Feather Growth.” PLOS ONE 15 (4): e0231925.
https://doi.org/10.1371/journal.pone.0231925.
Joshi, Savitha G., M. M. Tejashwini, N. Revati, R. Sridevi, and D. Roma. n.d. Isolation,
Identification and Characterization of a Feather Degrading Bacterium.
Kaye, Thomas G., Michael Pittman, and William R. Wahl. 2020. “Archaeopteryx Feather
Sheaths Reveal Sequential Center-out Flight-Related Molting Strategy.”
Communications Biology 3 (1): 1–5. https://doi.org/10.1038/s42003-020-01467-2.
Klaassen van Oorschot, Brett. 2017. “Aerodynamics and Ecomorphology of Flexible
Feathers and Morphing Bird Wings.” Ph.D. Thesis.
https://ui.adsabs.harvard.edu/abs/2017PhDT........49K.
KleinHeerenbrink, Marco, L. Christoffer Johansson, and Anders Hedenström. 2017.
“Multi-Cored Vortices Support Function of Slotted Wing Tips of Birds in Gliding
and Flapping Flight.” Journal of The Royal Society Interface 14 (130): 20170099.
https://doi.org/10.1098/rsif.2017.0099.
Kobayashi, Yoshitsugu, Jun-Chang Lu, Zhi-Ming Dong, Rinchen Barsbold, Yoichi
Azuma, and Yukimitsu Tomida. 1999. “Herbivorous Diet in an Ornithomimid
Dinosaur.” Nature 402 (6761): 480–81. https://doi.org/10.1038/44999.
Kulp, Felicia B., Liliana D’Alba, Matthew D. Shawkey, and Julia A. Clarke. 2018.
“Keratin Nanofiber Distribution and Feather Microstructure in Penguins.” The
Auk 135 (3): 777–87. https://doi.org/10.1642/AUK-18-2.1.

80
Kurochkin, Evgeny N. 1985. “A True Carinate Bird from Lower Cretaceous Deposits in
Mongolia and Other Evidence of Early Cretaceous Birds in Asia.” Cretaceous
Research 6 (3): 271–78. https://doi.org/10.1016/0195-6671(85)90050-3.
Lamanna, Matthew C., Hans-Dieter Sues, Emma R. Schachner, and Tyler R. Lyson.
2014. “A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the
Latest Cretaceous of Western North America.” PLOS ONE 9 (3): e92022.
https://doi.org/10.1371/journal.pone.0092022.
Langenheim, Jean H. 2003. Plant Resins: Chemistry, Ecology, and Ethnobotany. Timber
Press, Inc.
Lawton, Graham. 2019. “Blood Amber.” New Scientist 242 (3228): 38–43.
https://doi.org/10.1016/S0262-4079(19)30790-0.
Laybourne, Roxie C., Douglas W. Deedrick, and Francis M. Hueber. 1994. “Feather in
Amber Is Earliest New World Fossil of Picidae.” The Wilson Bulletin, 18–25.
Lees, John, Terence Garner, Glen Cooper, and Robert Nudds. 2017. “Rachis Morphology
Cannot Accurately Predict the Mechanical Performance of Primary Feathers in
Extant (and Therefore Fossil) Feathered Flyers.” Royal Society Open Science 4
(2): 160927. https://doi.org/10.1098/rsos.160927.
Lingham-Soliar, T., R. H. C. Bonser, and J. Wesley-Smith. 2010. “Selective
Biodegradation of Keratin Matrix in Feather Rachis Reveals Classic
Bioengineering.” Proceedings of the Royal Society B: Biological Sciences 277
(1685): 1161–68. https://doi.org/10.1098/rspb.2009.1980.

81
Lingham-Soliar, Theagarten. 2017. “Microstructural Tissue-Engineering in the Rachis
and Barbs of Bird Feathers.” Scientific Reports 7 (March): srep45162.
https://doi.org/10.1038/srep45162.
Lingham-Soliar, Theagarten, Richard H. C. Bonser, and James Wesley-Smith. 2010.
“Selective Biodegradation of Keratin Matrix in Feather Rachis Reveals Classic
Bioengineering.” Proceedings of the Royal Society of London B: Biological
Sciences 277 (1685): 1161–68. https://doi.org/10.1098/rspb.2009.1980.
Liu, Di, Luis M. Chiappe, Francisco Serrano, Michael Habib, Yuguang Zhang, and
Qinjing Meng. 2017. “Flight Aerodynamics in Enantiornithines: Information from
a New Chinese Early Cretaceous Bird.” PLOS ONE 12 (10): e0184637.
https://doi.org/10.1371/journal.pone.0184637.
Lucas, Alfred Martin, and joint author.) Stettenheim Peter. 1972. Avian Anatomy :
Integument. [Washington] : U.S. Agricultural Research Service; for sale by the
Supt. of Docs., U.S. Govt. Print. Off. http://trove.nla.gov.au/version/26054060.
Maderson, Paul F.A., Willem J. Hillenius, Uwe Hiller, and Carla C. Dove. 2009.
“Towards a Comprehensive Model of Feather Regeneration.” Journal of
Morphology 270 (10): 1166–1208. https://doi.org/10.1002/jmor.10747.
Maksoud, Sibelle, Dany Azar, Bruno Granier, and Raymond Gèze. 2017. “New Data on
the Age of the Lower Cretaceous Amber Outcrops of Lebanon.” Palaeoworld,
Geologic and biotic events on the continent during the Jurassic/Cretaceous
transition, 26 (2): 331–38. https://doi.org/10.1016/j.palwor.2016.03.003.
Mao, Yingyan, Liang Kun, Su Yitong, JIANGUO LI, Xin Rao, Hua Zhang,
FANGYUAN XIA, Yanzhe Fu, Chenyang Cai, and Diying Huang. 2018.

82
“Various Amberground Marine Animals on Burmese Amber with Discussions on
Its Age.” Palaeoentomology 1 (December): 91.
https://doi.org/10.11646/palaeoentomology.1.1.11.
McCoy, Dakota E., Allison J. Shultz, Charles Vidoudez, Emma van der Heide,
Jacqueline E. Dall, Sunia A. Trauger, and David Haig. 2021. “Microstructures
Amplify Carotenoid Plumage Signals in Tanagers.” Scientific Reports 11 (1):
8582. https://doi.org/10.1038/s41598-021-88106-w.
Mcgowan, C. 1989. “Feather Structure in Flightless Birds and Its Bearing on the
Question of the Origin of Feathers.” Journal of Zoology 218 (4): 537–47.
https://doi.org/10.1111/j.1469-7998.1989.tb04997.x.
McKellar, Ryan C., Brian DE Chatterton, Alexander P. Wolfe, and Philip J. Currie. 2011.
“A Diverse Assemblage of Late Cretaceous Dinosaur and Bird Feathers from
Canadian Amber.” Science 333 (6049): 1619–22.
Mehling, Carl. 2010. “Turds of a Feather.” Journal of Vertebrate Paleontology Annual
Meeting Program and Abstracts 30 (sup2): 138A.
https://doi.org/10.1080/02724634.2010.10411819.
Milàn, Jesper. 2012. “Crocodylian Scatology - a Look into Morphology, Internal
Architecture, Inter- and Intraspecific Variation and Prey Remains in Extant
Crocodylian Feces.” New Mexico Museum of Natural History and Science,
Bulletin 57: 65–71.
Monarrez, Pedro M., Joshua B. Zimmt, Annaka M. Clement, William Gearty, John J.
Jacisin, Kelsey M. Jenkins, Kristopher M. Kusnerik, et al. 2021. “Our Past

83
Creates Our Present: A Brief Overview of Racism and Colonialism in Western
Paleontology.” Paleobiology, August, 1–13. https://doi.org/10.1017/pab.2021.28.
Mondal, Pooja Chourasia Krishnendu, K Sankar, and Qamar Qureshi. 2012. “Food
Habits of Golden Jackal (Canis Aureus) and Striped Hyena (Hyae,” 8.
Moore, Jason R., Gregory P. Wilson, Mukul Sharma, Hannah R. Hallock, Dennis R.
Braman, and Paul R. Renne. 2014. “Assessing the Relationships of the Hell
Creek–Fort Union Contact, Cretaceous-Paleogene Boundary, and Chicxulub
Impact Ejecta Horizon at the Hell Creek Formation Lectostratotype, Montana,
USA.” In Through the End of the Cretaceous in the Type Locality of the Hell
Creek Formation in Montana and Adjacent Areas, by Gregory P. Wilson, William
A. Clemens, John R. Horner, and Joseph H. Hartman. Geological Society of
America. https://doi.org/10.1130/2014.2503(03).
Moyer, Alison E., Wenxia Zheng, Elizabeth A. Johnson, Matthew C. Lamanna, Da-qing
Li, Kenneth J. Lacovara, and Mary H. Schweitzer. 2015. “Melanosomes or
Microbes: Testing an Alternative Hypothesis for the Origin of Microbodies in
Fossil Feathers.” Scientific Reports 4 (1): 4233.
https://doi.org/10.1038/srep04233.
Myhrvold, Nathan P. 2012. “A Call to Search for Fossilised Gastric Pellets.” Historical
Biology 24 (5): 505–17. https://doi.org/10.1080/08912963.2011.631703.
N. Sullivan, Tarah, Andrei Pissarenko, Steven A. Herrera, David Kisailus, V.A. Lubarda,
and Marc Meyers. 2016. A Lightweight, Biological Structure with Tailored
Stiffness: The Feather Vane. Vol. 41.
https://doi.org/10.1016/j.actbio.2016.05.022.

84
Ng, Chen Siang, Chih-Kuan Chen, Wen-Lang Fan, Ping Wu, Siao-Man Wu, Jiun-Jie
Chen, Yu-Ting Lai, et al. 2015. “Transcriptomic Analyses of Regenerating Adult
Feathers in Chicken.” BMC Genomics 16 (1): 756.
https://doi.org/10.1186/s12864-015-1966-6.
Ng, Chen Siang, Ping Wu, John Foley, Anne Foley, Merry-Lynn McDonald, Wen-Tau
Juan, Chih-Jen Huang, et al. 2012. “The Chicken Frizzle Feather Is Due to an α-
Keratin (KRT75) Mutation That Causes a Defective Rachis.” Edited by Dennis
Roop. PLoS Genetics 8 (7): e1002748.
https://doi.org/10.1371/journal.pgen.1002748.
Noetling, F. 1892. “Preliminary Report on the Economic Resources of the Amber and
Jade Mines Area in Upper Burma.;” Records of the Geological Survey of India
25: 130–35.
———. 1893. “On the Occurrence of Burmite, a New Fossil Resin from Upper Burma.”
Records of the Geological Survey of India 26: 31–40.
Norell, Mark A, I James M Clark, and J Howard Hutchison. 1994. “The Late Cretaceous
Alligatoroid Brachychampsa Montana (Crocodylia): New Material and Putative
Relationships.” AMERICAN MUSEUM NOVITATES, no. 3116: 28.
Norell, Mark, Qiang Ji, Keqin Gao, Chongxi Yuan, Yibin Zhao, and Lixia Wang. 2002.
“Palaeontology:’Modern’feathers on a Non-Avian Dinosaur.” Nature 416 (6876):
36–37.
Nudds, Robert L., and Gareth J. Dyke. 2010. “Narrow Primary Feather Rachises in
Confuciusornis and Archaeopteryx Suggest Poor Flight Ability.” Science 328
(5980): 887–89.

85
O’Connor, Jingmai, Amanda Falk, Min Wang, Zheng Xiao-Ting, and Vertebrata
Palasiatica. 2020. “First Report of Immature Feathers in Juvenile Enantiornithines
from the Early Cretaceous Jehol Avifauna” 58 (January).
https://doi.org/10.19615/j.cnki.1000-3118.190823.
O’Connor, Jingmai K., Luis M. Chiappe, Cheng-ming Chuong, David J. Bottjer, and
Hailu You. 2012. “Homology and Potential Cellular and Molecular Mechanisms
for the Development of Unique Feather Morphologies in Early Birds.”
Geosciences 2 (4): 157–77. https://doi.org/10.3390/geosciences2030157.
O’Connor, Jingmai K., Xiaoting Zheng, Yanhong Pan, Xiaoli Wang, Yan Wang,
Xiaomei Zhang, and Zhonghe Zhou. 2020. “New Information on the Plumage of
Protopteryx (Aves: Enantiornithes) from a New Specimen.” Cretaceous Research
116 (December): 104577. https://doi.org/10.1016/j.cretres.2020.104577.
O’Connor, Jingmai K., and Zhonghe Zhou. 2020. “The Evolution of the Modern Avian
Digestive System: Insights from Paravian Fossils from the Yanliao and Jehol
Biotas.” Palaeontology 63 (1): 13–27. https://doi.org/10.1111/pala.12453.
O’Connor, Jingmai, Da-Qing Li, Matthew Lamanna, Min Wang, Jerald D. Harris, Jessie
Atterholt, and Hai-Lu You. 2015. A New Early Cretaceous Enantiornithine (Aves,
Ornithothoraces) from Northwestern China with Elaborate Tail Ornamentation.
Vol. 36. https://doi.org/10.1080/02724634.2015.1054035.
Osváth, Gergely, Orsolya Vincze, Dragomir-Cosmin David, László Jácint Nagy, Ádám Z
Lendvai, Robert L Nudds, and Péter L Pap. 2020. “Morphological
Characterization of Flight Feather Shafts in Four Bird Species with Different

86
Flight Styles.” Biological Journal of the Linnean Society 131 (1): 192–202.
https://doi.org/10.1093/biolinnean/blaa108.
Pap, Péter L., Gergely Osváth, Krisztina Sándor, Orsolya Vincze, Lőrinc Bărbos, Attila
Marton, Robert L. Nudds, and Csongor I. Vágási. 2015. “Interspecific Variation
in the Structural Properties of Flight Feathers in Birds Indicates Adaptation to
Flight Requirements and Habitat.” Functional Ecology 29 (6): 746–57.
https://doi.org/10.1111/1365-2435.12419.
Penney, David. 2010. Biodiversity of Fossils in Amber from the Major World Deposits.
Siri Scientific Press.
Peretti, Adolf. 2021. “An Alternative Perspective for Acquisitions of Amber from
Myanmar Including Recommendations of the United Nations Human Rights
Council.” Journal of International Humanitarian Action 6 (1): 12.
https://doi.org/10.1186/s41018-021-00101-y.
Perrichot, V., L. Marion, D. Neraudeau, R. Vullo, and P. Tafforeau. 2008. “The Early
Evolution of Feathers: Fossil Evidence from Cretaceous Amber of France.”
Proceedings of the Royal Society B: Biological Sciences 275 (1639): 1197–1202.
https://doi.org/10.1098/rspb.2008.0003.
Peteya, Jennifer A., Julia A. Clarke, Quanguo Li, Ke-Qin Gao, and Matthew D. Shawkey.
2017. “The Plumage and Colouration of an Enantiornithine Bird from the Early
Cretaceous of China.” Edited by Sarah Gabbott. Palaeontology 60 (1): 55–71.
https://doi.org/10.1111/pala.12270.
Poinar, George O. 1988. The Amber Ark: Natural History. Vol. 12.

87
Price-Waldman, Rosalyn M., Allison J. Shultz, and Kevin J. Burns. 2020. “Speciation
Rates Are Correlated with Changes in Plumage Color Complexity in the Largest
Family of Songbirds.” Evolution 74 (6): 1155–69.
https://doi.org/10.1111/evo.13982.
Prum, Richard O. 1999. “Development and Evolutionary Origin of Feathers.” The
Journal of Experimental Zoology 285 (4): 291–306.
———. 2005. “Evolution of the Morphological Innovations of Feathers.” Journal of
Experimental Zoology Part B: Molecular and Developmental Evolution 304B (6):
570–79. https://doi.org/10.1002/jez.b.21073.
Qvarnström, Martin, Erik Elgh, Krzysztof Owocki, Per E. Ahlberg, and Grzegorz
Niedźwiedzki. 2019. “Filter Feeding in Late Jurassic Pterosaurs Supported by
Coprolite Contents.” PeerJ 7 (August): e7375. https://doi.org/10.7717/peerj.7375.
Qvarnström, Martin, Martin Fikáček, Joel Vikberg Wernström, Sigrid Huld, Rolf G.
Beutel, Emmanuel Arriaga-Varela, Per E. Ahlberg, and Grzegorz Niedźwiedzki.
2021. “Exceptionally Preserved Beetles in a Triassic Coprolite of Putative
Dinosauriform Origin.” Current Biology, June, S0960982221006746.
https://doi.org/10.1016/j.cub.2021.05.015.
Qvarnström, Martin, Grzegorz Niedźwiedzki, Paul Tafforeau, Živil Žigaitė, and Per E.
Ahlberg. 2017. “Synchrotron Phase-Contrast Microtomography of Coprolites
Generates Novel Palaeobiological Data.” Scientific Reports 7 (1).
https://doi.org/10.1038/s41598-017-02893-9.
Qvarnström, Martin, Grzegorz Niedźwiedzki, and Živilė Žigaitė. 2016. “Vertebrate
Coprolites (Fossil Faeces): An Underexplored Konservat-Lagerstätte.” Earth-

88
Science Reviews 162 (November): 44–57.
https://doi.org/10.1016/j.earscirev.2016.08.014.
Rayfield, E. J., J.M. Theodor, and P.D. Polly. 2020. “Fossils from Conflict Zones and
Reproducibility of Fossil-Based Scientic Data,” 2020.
http://vertpaleo.org/GlobalPDFS/SVP-Letter-to-Editors-FINAL.aspx.
Reinhard, Karl J., and Vaughn M. Bryant. 1992. “Coprolite Analysis: A Biological
Perspective on Archaeology.” Archaeological Method and Theory 4: 245–88.
Rice, Robert H., Brett R. Winters, Blythe P. Durbin-Johnson, and David M. Rocke. 2013.
“Chicken Corneocyte Cross-Linked Proteome.” Journal of Proteome Research 12
(2): 771–76. https://doi.org/10.1021/pr301036k.
Rippa, Alessandro, and Yi Yang. 2017. “The Amber Road: Cross-Border Trade and the
Regulation of the Burmite Market in Tengchong, Yunnan.” TRaNS: Trans-
Regional and -National Studies of Southeast Asia, June, 1–25.
https://doi.org/10.1017/trn.2017.7.
Ross, Andrew. 2018. “Burmese (Myanmar) Amber Taxa, on-Line Checklist v.2018.2,”
September.
Saitta, Evan T., Christopher S. Rogers, Richard A. Brooker, and Jakob Vinther. 2017.
“EXPERIMENTAL TAPHONOMY OF KERATIN: A STRUCTURAL
ANALYSIS OF EARLY TAPHONOMIC CHANGES.” PALAIOS 32 (10): 647–
57. https://doi.org/10.2110/palo.2017.051.
Schlee, Von Dieter. 1973. “Harzkonservierte fossile Vogelfedern aus der unsterten
Kreide.” J. Ornithol. 114 (2): 207–19.

89
Schroeder, Katlin, S. Kathleen Lyons, and Felisa A. Smith. 2021. “The Influence of
Juvenile Dinosaurs on Community Structure and Diversity.” Science 371 (6532):
941–44. https://doi.org/10.1126/science.abd9220.
Serrano, Francisco J., Luis M. Chiappe, Paul Palmqvist, Borja Figueirido, Jesús
Marugán-Lobón, and José L. Sanz. 2018. “Flight Reconstruction of Two
European Enantiornithines (Aves, Pygostylia) and the Achievement of Bounding
Flight in Early Cretaceous Birds.” Palaeontology 61 (3): 359–68.
https://doi.org/10.1111/pala.12351.
Shi, Chao, Hao-hong Cai, Ri-xin Jiang, Shuo Wang, Michael S. Engel, Ji Yuan, Ming
Bai, et al. 2021. “Balance Scientific and Ethical Concerns to Achieve a Nuanced
Perspective on ‘Blood Amber.’” Nature Ecology & Evolution 5 (6): 705–6.
https://doi.org/10.1038/s41559-021-01479-z.
Smaliychuk, Anatoliy, Gohar Ghazaryan, and Olena Dubovyk. 2021. “Land-Use Changes
in Northern Ukraine: Patterns and Dynamics of Illegal Amber Mining during
1986–2016.” Environmental Monitoring and Assessment 193 (8): 502.
https://doi.org/10.1007/s10661-021-09317-2.
Souza Carvalho, Ismar de, Fernando E. Novas, Federico L. Agnolín, Marcelo P. Isasi,
Francisco I. Freitas, and José A. Andrade. 2015. “A Mesozoic Bird from
Gondwana Preserving Feathers.” Nature Communications 6 (June): 7141.
https://doi.org/10.1038/ncomms8141.
Sprain, Courtney, Paul Renne, William Clemens, and Gregory Wilson Mantilla. 2018.
“Calibration of Chron C29r: New High-Precision Geochronologic and

90
Paleomagnetic Constraints from the Hell Creek Region, Montana.” GSA Bulletin
130 (May). https://doi.org/10.1130/B31890.1.
Sprain, Courtney, Paul Renne, Gregory Wilson Mantilla, and William Clemens. 2015.
“High-Resolution Chronostratigraphy of the Terrestrial Cretaceous Paleogene
Transition and Recovery Interval in the Hell Creek Region, Montana.” Geological
Society of America Bulletin 127 (March): 393–409.
https://doi.org/10.1130/B31076.1.
Stavenga, Doekele G., Hein L. Leertouwer, N. Justin Marshall, and Daniel Osorio. 2011.
“Dramatic Colour Changes in a Bird of Paradise Caused by Uniquely Structured
Breast Feather Barbules.” Proceedings of the Royal Society B: Biological
Sciences 278 (1715): 2098–2104. https://doi.org/10.1098/rspb.2010.2293.
Sullivan, Tarah N., Michael Chon, Rajaprakash Ramachandramoorthy, Michael R.
Roenbeck, Tzu-Tying Hung, Horacio D. Espinosa, and Marc A. Meyers. 2017.
“Reversible Attachment with Tailored Permeability: The Feather Vane and
Bioinspired Designs.” Advanced Functional Materials, n/a-n/a.
https://doi.org/10.1002/adfm.201702954.
Sullivan, Tarah N., Yunlan Zhang, Pablo D. Zavattieri, and Marc A. Meyers. 2018.
“Hydration-Induced Shape and Strength Recovery of the Feather.” Advanced
Functional Materials 28 (30): 1801250. https://doi.org/10.1002/adfm.201801250.
Wang, Bin, and Marc André Meyers. 2017. “Light Like a Feather: A Fibrous Natural
Composite with a Shape Changing from Round to Square.” Advanced Science 4
(3): n/a-n/a. https://doi.org/10.1002/advs.201600360.

91
Wang, Bin, Wen Yang, Joanna McKittrick, and Marc André Meyers. 2016. “Keratin:
Structure, Mechanical Properties, Occurrence in Biological Organisms, and
Efforts at Bioinspiration.” Progress in Materials Science 76 (March): 229–318.
https://doi.org/10.1016/j.pmatsci.2015.06.001.
Wang, Shuo, Wei-Ling Chang, Qiyue Zhang, Menglu Ma, Feng Yang, De Zhuo, Harn I.-
Chen Hans, et al. 2020. “Variations of Mesozoic Feathers: Insights from the
Morphogenesis of Extant Feather Rachises.” Evolution 74 (9): 2121–33.
https://doi.org/10.1111/evo.14051.
Wang, X., R. L. Nudds, C. Palmer, and G. J. Dyke. 2012. “Size Scaling and Stiffness of
Avian Primary Feathers: Implications for the Flight of Mesozoic Birds.” Journal
of Evolutionary Biology 25 (3): 547–55. https://doi.org/10.1111/j.1420-
9101.2011.02449.x.
Wang, Xia, and Julia A. Clarke. 2015. “The Evolution of Avian Wing Shape and
Previously Unrecognized Trends in Covert Feathering.” Proceedings of the Royal
Society B: Biological Sciences 282 (1816): 20151935.
https://doi.org/10.1098/rspb.2015.1935.
Wang, Xiaoli, Jingmai K. O’Connor, Xiaoting Zheng, Min Wang, Han Hu, and Zhonghe
Zhou. 2014. “Insights into the Evolution of Rachis Dominated Tail Feathers from
a New Basal Enantiornithine (Aves: Ornithothoraces).” Biological Journal of the
Linnean Society 113 (3): 805–19.
Weaver, Lucas N., David J. Varricchio, Eric J. Sargis, Meng Chen, William J. Freimuth,
and Gregory P. Wilson Mantilla. 2021. “Early Mammalian Social Behaviour

92
Revealed by Multituberculates from a Dinosaur Nesting Site.” Nature Ecology &
Evolution 5 (1): 32–37. https://doi.org/10.1038/s41559-020-01325-8.
Wetmore, Alexander. 1943. “The Occurrence of Feather Impressions in the Miocene
Deposits of Maryland.” The Auk 60 (3): 440–41. https://doi.org/10.2307/4079268.
Woodward, Holly N., Katie Tremaine, Scott A. Williams, Lindsay E. Zanno, John R.
Horner, and Nathan Myhrvold. 2020. “Growing up Tyrannosaurus Rex :
Osteohistology Refutes the Pygmy ‘ Nanotyrannus ’ and Supports Ontogenetic
Niche Partitioning in Juvenile Tyrannosaurus.” Science Advances 6 (1):
eaax6250. https://doi.org/10.1126/sciadv.aax6250.
Wu, Ping, Chen Siang Ng, Jie Yan, Yung-Chih Lai, Chih-Kuan Chen, Yu-Ting Lai, Siao-
Man Wu, et al. 2015. “Topographical Mapping of α- and β-Keratins on
Developing Chicken Skin Integuments: Functional Interaction and Evolutionary
Perspectives.” Proceedings of the National Academy of Sciences 112 (49):
E6770–79. https://doi.org/10.1073/pnas.1520566112.
Xing, Lida, Pierre Cockx, and Ryan C. McKellar. 2020. “Disassociated Feathers in
Burmese Amber Shed New Light on Mid-Cretaceous Dinosaurs and Avifauna.”
Gondwana Research, February. https://doi.org/10.1016/j.gr.2019.12.017.
Xing, Lida, Pierre Cockx, Ryan C. McKellar, and Jingmai O’Connor. 2018. “Ornamental
Feathers in Cretaceous Burmese Amber: Resolving the Enigma of Rachis-
Dominated Feather Structure.” Journal of Palaeogeography 7 (1): 13.
https://doi.org/10.1186/s42501-018-0014-2.

93
Xing, Lida, Ryan C. McKellar, and Jingmai K. O’Connor. 2020. “An Unusually Large
Bird Wing in Mid-Cretaceous Burmese Amber.” Cretaceous Research, February,
104412. https://doi.org/10.1016/j.cretres.2020.104412.
Xing, Lida, Ryan C. McKellar, Jingmai K. O’Connor, Kecheng Niu, and Huijuan Mai.
2019. “A Mid-Cretaceous Enantiornithine Foot and Tail Feather Preserved in
Burmese Amber.” Scientific Reports 9 (1): 1–8. https://doi.org/10.1038/s41598-
019-51929-9.
Xing, Lida, Ryan C. McKellar, Min Wang, Ming Bai, Jingmai K. O’Connor, Michael J.
Benton, Jianping Zhang, et al. 2016. “Mummified Precocial Bird Wings in Mid-
Cretaceous Burmese Amber.” Nature Communications 7 (June): 12089.
https://doi.org/10.1038/ncomms12089.
Xing, Lida, Jingmai K. O’Connor, Ryan C. McKellar, Luis M. Chiappe, Ming Bai,
Kuowei Tseng, Jie Zhang, Haidong Yang, Jun Fang, and Gang Li. 2018. “A
Flattened Enantiornithine in Mid-Cretaceous Burmese Amber: Morphology and
Preservation.” Science Bulletin 63 (4): 235–43.
https://doi.org/10.1016/j.scib.2018.01.019.
Xing, Lida, Jingmai K. O’Connor, Ryan C. McKellar, Luis M. Chiappe, Kuowei Tseng,
Gang Li, and Ming Bai. 2017. “A Mid-Cretaceous Enantiornithine (Aves)
Hatchling Preserved in Burmese Amber with Unusual Plumage.” Gondwana
Research, June. https://doi.org/10.1016/j.gr.2017.06.001.
Xu, Xing. 2019. “Feather Evolution: Looking up Close and through Deep Time.” Science
Bulletin 64 (9): 563–64. https://doi.org/10.1016/j.scib.2019.03.027.

94
———. 2020. “Filamentous Integuments in Nonavialan Theropods and Their Kin:
Advances and Future Perspectives for Understanding the Evolution of Feathers.”
In The Evolution of Feathers: From Their Origin to the Present, edited by
Christian Foth and Oliver W. M. Rauhut, 67–78. Fascinating Life Sciences.
Cham: Springer International Publishing. https://doi.org/10.1007/978-3-030-
27223-4_5.
Xu, Xing, and Yu Guo. 2009. “THE ORIGIN AND EARLY EVOLUTION OF
FEATHERS: INSIGHTS FROM RECENT PALEONTOLOGICAL AND
NEONTOLOGICAL DATA.” Vertebrata PalAsiatica 47: 311–29.
Xu, Xing, Xiaoting Zheng, and Hailu You. 2009. “A New Feather Type in a Nonavian
Theropod and the Early Evolution of Feathers.” Proceedings of the National
Academy of Sciences 106 (3): 832–34. https://doi.org/10.1073/pnas.0810055106.
———. 2010. “Exceptional Dinosaur Fossils Show Ontogenetic Development of Early
Feathers.” Nature 464 (7293): 1338–41. https://doi.org/10.1038/nature08965.
Yang, Zixiao, Baoyu Jiang, Maria E. McNamara, Stuart L. Kearns, Michael Pittman,
Thomas G. Kaye, Patrick J. Orr, Xing Xu, and Michael J. Benton. 2019.
“Pterosaur Integumentary Structures with Complex Feather-like Branching.”
Nature Ecology & Evolution 3 (1): 24–30. https://doi.org/10.1038/s41559-018-
0728-7.
Yu, Mingke, Ping Wu, Randall B Widelitz, and Cheng-Ming Chuong. 2002. “The
Morphogenesis of Feathers” 420: 5.
Yu, Tingting, Richard Kelly, Lin Mu, Andrew Ross, Jim Kennedy, Pierre Broly,
Fangyuan Xia, Haichun Zhang, Bo Wang, and David Dilcher. 2019. “An

95
Ammonite Trapped in Burmese Amber.” Proceedings of the National Academy of
Sciences 116 (23): 11345–50. https://doi.org/10.1073/pnas.1821292116.
Yu, Yilun, Chi Zhang, and Xing Xu. 2021. “Deep Time Diversity and the Early
Radiations of Birds.” Proceedings of the National Academy of Sciences 118 (10):
e2019865118. https://doi.org/10.1073/pnas.2019865118.
Zhang, F. 2000. “A Primitive Enantiornithine Bird and the Origin of Feathers.” Science
290 (5498): 1955–59. https://doi.org/10.1126/science.290.5498.1955.
Zhang, FuCheng, ZhongHe Zhou, and Michael J. Benton. 2008. “A Primitive
Confuciusornithid Bird from China and Its Implications for Early Avian Flight.”
Science in China Series D: Earth Sciences 51 (5): 625–39.
https://doi.org/10.1007/s11430-008-0050-3.
Zhang, Fucheng, Zhonghe Zhou, Xing Xu, Xiaolin Wang, and Corwin Sullivan. 2008. “A
Bizarre Jurassic Maniraptoran from China with Elongate Ribbon-like Feathers.”
Nature 455 (7216): 1105–8. https://doi.org/10.1038/nature07447.
Zhang, Yiqi, Ruijin Yang, and Wei Zhao. 2014. “Improving Digestibility of Feather Meal
by Steam Flash Explosion.” Journal of Agricultural and Food Chemistry 62 (13):
2745–51. https://doi.org/10.1021/jf405498k.
Zheng, Xiaoting, Xiaoli Wang, Corwin Sullivan, Xiaomei Zhang, Fucheng Zhang, Yan
Wang, Feng Li, and Xing Xu. 2018. “Exceptional Dinosaur Fossils Reveal Early
Origin of Avian-Style Digestion.” Scientific Reports 8 (1): 14217.
https://doi.org/10.1038/s41598-018-32202-x.

96
Zherikhin, V., and Andrew J. Ross. 2000. “A Review of the History, Geology and Age of
Burmese Amber (Burmite).” Bulletin of the Natural History Museum, London
(Geology) 56: 3–10.
Zin-Maung-Maung-Thein and Khin Zaw. 2021. “Parachute Research Is Another Ethical
Problem for Myanmar Amber.” Nature Ecology & Evolution 5 (6): 707–707.
https://doi.org/10.1038/s41559-021-01472-6.

Abstract (if available)

Abstract Modern flight feathers have been historically viewed as appearing early in avian evolution, and possibly originating in non-avian dinosaurs. The assumption that a modern asymmetrical flight feather had evolved by the Late Jurassic and maintained relative morphologic stasis for over 145 million years was informed by 2-dimensional lithic feather preservation. This body of research utilizes morphogenetically informative 3-dimensional characters of modern feathers and new information derived from 3-dimensional Mesozoic fossils to demonstrate that key aspects of the modern bird feather continued to evolve throughout the Cretaceous. Feathers preserved in mid-Cretaceous amber reveal that stem birds produced feathers without medullary pith or the full ventral geometry that typifies modern feather rachises. A new source of exceptional 3-D feather preservation for the Mesozoic is identified (coprolites) and provides evidence for the presence of modern rachis development by the latest Cretaceous. This new data highlights the need for 3-dimensional feather preservation to make informed hypotheses about the evolutionary development of the modern bird feather.

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Asset Metadata

Creator Carroll, Nathan Robert (author)

Core Title Evolution of the dinosaur flight feather: insights from 3-dimensional fossil feathers

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Geological Sciences

Degree Conferral Date 2021-12

Publication Date 05/02/2022

Defense Date 08/25/2021

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Amber,coprolite,feather evolution,flight evolution,fossil feathers,OAI-PMH Harvest

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Bottjer, David (committee chair), Chiappe, Luis (committee member), Huttenlocker, Adam (committee member)

Creator Email ncarroll@cartercountymuseum.org,nrcarrol@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC16351275

Unique identifier UC16351275

Legacy Identifier etd-CarrollNat-10197

Document Type Dissertation

Format application/pdf (imt)

Rights Carroll, Nathan Robert

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given.

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA

Repository Email cisadmin@lib.usc.edu