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Early Jurassic reef eclipse: Paleoecology and sclerochronology of the "Lithiotis" facies bivalves

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Early Jurassic reef eclipse: Paleoecology and sclerochronology of the "Lithiotis" facies bivalves

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Content EARLY JURASSIC REEF ECLIPSE: PALEOECOLOGY AND SCLEROCHRONOLOGY OF THE “LITHIOTIS” FACIES BIVALVES Copyright 2002 by Nicole Marie Fraser A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements of the Degree DOCTOR OF PHILOSOPHY (EARTH SCIENCES) December 2002 Nicole Marie Fraser Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3093763 UMI UMI Microform 3093763 Copyright 2003 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY OF SOUTHERN CALIFORNIA The G raduate School U n iversity Park LOS ANGELES, CALIFORNIA 90089-1695 This dissertation, w ritte n b y Nicole Marie Fraser Under th e direction o f h & T L . . D issertation Com m ittee, and approved b y a ll its m em bers, has been p resen ted to an d accepted b y The Graduate School, in p a rtia l fulfillm ent o f requirem ents fo r th e degree o f DOCTOR OF PHILOSOPHY D a te December 18. 2002 DISSER TA TION COMMITTEE Chairperson SLa Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In memory of Laura Lynne Kinsey August 24, 1971 - December 29, 1999 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS Dr s. David Bottjer and A1 Fischer, my official and unofficial advisers, are the most responsible for me completing this dissertation. Dave’s careful mix of cheerleading, cajoling and when necessary tough talk pushed me to produce this even when I thought I wasn’t able to contribute “anything interesting.” My deepest thanks to Dave for all of his efforts to help me succeed. When things looked bleak, he never turned me away but welcomed me in to his office and helped devise a plan to overcome it. Dave is a St. Jude of paleontology, never giving up on lost causes, including his students. A1 Fischer is the inspiration for so much of this work. He and his wife, Winnie, accompanied me for two field seasons in Italy and Morocco. In the short span of weeks, I was immersed in one of the most amazing tutorials of my life, from Upper Triassic carbonate platforms of the Dolomites to Italian wines to the intricacies and diplomacy of marriage. My thanks to both of you for sharing your time and knowledge with me. I return it with my love and joy for being included in your remarkable lives. Their niece, Mary Bishop, made our trip to Morocco happen. She opened a country to us that is mysterious to many foreigners by bringing us into the homes of her many friends. Al’s tutelage continued when we returned to USC. I may have been timid at first to ask for his help but towards the end I became very emboldened and called him frequently. I can only hope that this work reflects his efforts to improve on my attempts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Also at USC, Drs. Donn Gorsline and Bob Douglas were walking resources for me to nag at any point of time for sedimentological information to index fossils. Dr. Gerry Bakus provided a modem reef ecologists perspective that enhanced the ancient work and helped me to place it in an appropriate context. Drs. Hong-Chung Li and Richard Ku helped me use the X-ray Diffraction Lab for the microstructure analyses. Dr. Will Berelson, curmudgeon ne plus ultra, provided hood space, a geochemist’s viewpoint for much of the conclusion section and humor at every turn. Dr. Frank Corsetti encouraged me to try stable isotopes on some of my samples and helped connect me to Alan Jay Kaufman at University of Maryland to mn many of my samples. Dr. Lowell Stott and Miguel Rincon ran the bulk of my stable isotope samples for the sclerochronologic analysis. Miguel persevered even when I “only had one more batch to mn” several times. At the Santa Barbara Museum of Natural History, Dr. Dan Geiger gave me a three-day personal workshop on cladistics and associated software. My many thanks for his time and interest in this work. This research was supported in part by an AAPG Raymond C. Moore Grant, the USC Department of Earth Sciences Graduate Student Research Fund, AMNH Lemer-Grey Marine Research Fund and the Wrigley Institute of Environmental Studies. John McRaney deserves special mention for all of his creative efforts to employ me during the summer and finagle funding, as well as his gift of friendship. A grant from SeaGrant to Will Berelson, also funded my living expenses and enabled much of the field work. In the last year, when I needed a place to write, Dr. Chris Poulsen generously gave me space and a computer to use. The College of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Letters, Arts and Sciences provided three important fellowships that provided a stipend in final two years. The generosity of the Tyler Prize for Environmental Studies provided much of my support for lab work. Ms. Carol Gordon of the Graduate School was instrumental for helping me receive to very important awards: The Luce Scholar Fellowship and The Tyler Prize. The Luce Scholars program took me to Indonesia and many other (mis)adventures. Along the way, I met my husband Harley, a Luce Scholar in Thailand. I returned to USC for my PhD and in the critical last year, Ms. Gordon helped me with the Tyler Prize at a time when financial support was critical for completion. She is a fairy godmother to me in so many ways, her efforts brought me great joy in both my personal and professional life. I am grateful to Roberto Zorzin and Anna Vaccari (Museo di Storia Naturale di Verona); Attilio Benetti (Museo Geopaleontologico di Campsilvano); Kiyotaka Chinzei (University of Kyoto); Adolf Seilacher and Hans Luginsland (Institut und Museum fur Geologie und Palaontologie, Tubingen); Carmen Broglio Loriga, Renato Posenato, Alfonso Bosselini (Istituto di Geologia Universita degli Studi di Ferrara); Driss Najid and Mohammed Boutakiout (Service Geologique du Maroc and Universite Mohammed V); Christopher Lee (University of South Wales) and John Warme (Colorado School of Mines) for access to samples and field site information. Property owners are thanked for their assistance: Scott Hess, Mike Keerins, Les Schnabele, and Ed Sturza (Suplee-Izee); Roberto Tomieri (Mt. Lessini); Mohammed Kharbouches (Ait Athmane). The Moroccan Postal Service and the agents in Casablanca helped me mail all of my rocks from Morocco safely home to Los Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vi Angeles. Mary Bishop, Harley Feldbaum, Jochen Halfar, Martha Forment-Halfar, Tran Huynh and Deanna Major were brilliant field assistants and made the schlepping of rocks much easier and fun than expected. There are so many people from my personal life to thank that made these last four years more fun than could be imagined. My parents, Deanna and Bill Major, Scott and Renee Fraser and grandparents, Pat and Jack Fraser, may have been exasperated with the timeline but never questioned the ultimate goal. Their support and love has been limitless. My siblings, David and Doug Major, Caneel and Skye Fraser, graciously accepted their quirky sister and her jags. Harley Feldbaum, Heather Moffat, Tran Huynh and Scott Frank nurtured me daily with affection and honesty. I have mentioned many individuals above but all of my friends, families and fellow graduate students (Masha Prokopenko; USC Paleolab: Nicole Bonuso, Stephen Dombos, Margaret Fraiser, Karina Hankins, Pedro Marenco, Sara Pruss; and UCR Paleolab: Diana Boyer, Seth Finnegan, Bob Gaines, Brenda Hunda) are appreciated for all of their companionship and laughter. I’m often asked to summarize my research: in times of great environmental crisis, entire ecosystems were replaced by unusual, aberrant organisms. This quote by Tennessee Williams is even more succinct: “Nature is most creative when she has a vacuum to fill.” Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vii TABLE OF CONTENTS Dedication i Acknowledgements ii List of Tables viii List of Figures ix Abstract xv Chapter 1: Introduction 1 Chapter 2: Stratigraphy and Sedimentology of Study Sites 23 Chapter 3: Morphology, Proposed Life Habits and Phylogeny of the “Lithiotis” Facies Bivalves 102 Chapter 4: Paleoecology and Biozonation of the “Lithiotis” Facies Bivalves 178 Chapter 5: Sclerochronology and Stable Isotopic Records of “Lithiotis” Facies Bivalves 200 Chapter 6: Conclusions 217 References 223 Appendix A: Phylogenetic character codes for bivalve families and “Lithiotis” facies bivalves after Waller (1990). 247 Appendix B: Bivalve stable isotope data 252 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Table 1. Summary of field site descriptions. Table 2. Summary of morphological characteristics of '‘ Lithiotis" facies bivalves. Table 3. Summary of the means of morphological measurements of Lithiotis problematica specimens. Table 4. Summary of the means of morphological measurements of Cochlearites loppianus specimens. Table 5. Summary of the means of morphological measurements of Gervilleiopema sp. specimens. Table 6. Summary of the means of morphological measurements of Mytilopema sp. specimens. Table 7. Summary of the means of morphological measurements of Lithiopema scutata specimens. Table 8. Summary table of number of samples from field sites and representative facies. Table 9. Faunal list. Table 10. Checklist of criteria for recognition of photosymbiosis in fossil bivalves. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IX LIST OF FIGURES Figure 1. Percent generic extinction rate as calculated by Raup and Boyajian (1988). 3 Figure 2. The Early Jurassic reef eclipse and range of “Lithiotis” facies bivalves. 7 Figure 3. Early Jurassic Pliesnbachian paleogeography and predicted ocean currents adapted from Parrish (1992) and Aberhan (2001). 11 Figure 4. Early Jurassic “Lithiotis’’ ’ facies bivalves. 16 Figure 5. Locality map of studied sites. 25 Figure 6. Legend of lithologic characters for stratigraphic . 26 Figure 7. Stratigraphy of field sites. 29 Figure 8. Overview map of the Suplee-Izee area and the four study sites. 30 Figure 9. Robertson Ridge buildups. 31 Figure 10. Photograph of the distinctive Robertson Formation volcaniclastic sandstone 33 Figure 11. Stratigraphic columns from the Robertson Ridge study area. 34 Figure 12. Fossils from Robertson Ridge. 36 Figure 13. Swamp Creek buildups. 37 Figure 14. Stratigraphic columns from the Swamp Creek study area. 38 Figure 15. Spongiomorpha ramosa(?). 40 Figure 16. Lithiotis problematica individual samples from Swamp Creek. 41 Figure 17. Cow Creek Bioherms. 43 Figure 18. Stratigraphic columns from the Cow Creek study area. 44 Figure 19. Lithiotis buildups at Cow Creek. 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 20. Fossils from Cow Creek. 47 Figure 21. Sedimentological features of Cow Creek sections. 48 Figure 22. Bivalve fauna from the Cow Creek assemblage. 49 Figure 23. Microfossils of Cow Creek . 50 Figure 24. Jackass Ranch. 51 Figure 25. Stratigraphic columns from Jackass Ranch. 52 Figure 26. Lithologic features at Jackass Ranch Column D. 54 Figure 27. Poker Ridge locality. 57 Figure 28. Stratigraphic column from the Poker Ridge locality, near Spring Creek. 59 Figure 29. Picture of base of Poker Ridge limestone facies with examples of bivalve fauna. 59 Figure 30. Photograph of the Lithiotis death assemblage at Poker Ridge. 61 Figure 31. Poker Ridge Nerinea bed. 62 Figure 32. Thompson Formation: distinctive red sandstone with limestone lenses facies. 63 Figure 33. Laura Canyon outcrop. 67 Figure 34. Dunlap Formation stratigraphic columns. 68 Figure 35. Lithiotis problematica of Laura Canyon. 69 Figure 36. Third Canyon outcrop. 71 Figure 37. Ponte dell’Anguillara outcrop. 75 Figure 38. Calcari Grigi stratigraphic columns. 76 Figure 39. Close-up of the Ponte dell’Anguillara “brown coal” facies (shallow water black shale) and wood fragment. 78 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xi Figure 40. Ponte dell’Anguillara thin section of micritic microfacies with very small burrows (approximately 1 mm wide burrows). 78 Figure 41. Ponte dell’ Anguillara microfacies. 79 Figure 42. Thin section of Ponte Dell’Anguillara microfauna. 80 Figure 43. Bellori outcrop. 82 Figure 44. Bellori bivalve assemblage. 83 Figure 45. Garzon di Sotto outcrop. 85 Figure 46. Microfossils of Garzon di Sotto. 86 Figure 47. Assemsouk buildup outcrop. 90 Figure 48. Facies and fossils of Assemsouk, Central Fligh Atlas, Morocco. 91 Figure 49. Assemsouk Cochlearites loppianus reef section. 92 Figure 50. Stratigraphic columns of Assemsouk reef. 94 Figure 51. Ait Athmane outcrops. 96 Figure 52. Stratigraphic columns of Ait Athmane area. 97 Figure 53. Photographs of Mytilopema sp. at Ait Athmane Column A. 98 Figure 54. Coral-algal-bivalve facies of at Ait Athmane Column C. 99 Figure 55. Burrows at Ait Athmane Column D. 99 Figure 56. Evaporite breccia of Ait Athmane Column D. 100 Figure 57. Schematic of Lithiotis problematica (interior of pedestal valve) with morphological terms and measurements. 104 Figure 58. Distribution of the “Lithiotis” facies bivalves. 109 Figure 59. X-ray diffraction analysis of Lithiotis problematica middle aragonitic prism layer. 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xii Figure 60. Microstructure of Lithiotis problematica. 115 Figure 61. Photographs of Lithiotis problematica morphotypes. 117 Figure 62. Length measurements of Lithiotis problematica. 118 Figure 63. Paleocurrent orientation of Lithiotis problematica. 121 Figure 64. Schematic of proposed Lithiotis problematica life habit based on field observations and paleocurrent orientations. 122 Figure 65. Schematic of Cochlearites loppianus (interior of pedestal, left valve) with morphological terms and measurements. 124 Figure 66. Photographs of Cochlearites loppianus morphotypes A. Moroccan form, B. Mt. Lessini form (Verona Museum). 128 Figure 67. Length measurements of Cochlearites loppianus. 129 Figure 68. Paleocurrent orientation of Cochlearites loppianus. 132 Figure 69. Schematic of proposed Cochlearites loppianus life habit based on field observations and paleocurrent orientations. 134 Figure 70. Schematic of Gerveilleiopema sp. (interior of right valve) with morphological terms and measurements. 136 Figure 71. Photograph of Gervilleiopema sp. specimen from the Geological Institute of Ferrara. 137 Figure 72. Schematic of proposed Gervilleiopema life habit based on field observations and Seilacher (1984). 143 Figure 73. Schematic of Mytilopema sp. (interior of right valve) with morphological terms and measurements. 151 Figure 74. Mytilopema microstructure after Broglio Loriga and Posenato (1996). 146 Figure 75. Morphotypes of Mytilopema based on Arkell’s (1933) obliquity angle. 148 Figure 76. Photographs of Mytilopema morphotypes 149 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xiii Figure 77. Length and obliquity angle measurements of Mytilopema. 150 Figure 78. Proposed life habits of Mytilopema based on field observations after Broglio Loriga and Posenato (1996). 151 Figure 79. Schematic of Lithiopema scutata (interior of right valve) with morphological terms and measurements. 155 Figure 80. Microstructure of Lithiopema scutata. 159 Figure 81. Morphotypes of Lithiopema scutata. 161 Figure 82. Photographs of Lithiopema scutata morphotypes. 162 Figure 83. Length measurements of Lithiopema scutata. 163 Figure 84. Proposed life habits of Lithiopema scutata based on field observations after Broglio Loriga and Posenato (1996). 164 Figure 85. Paleocurrent orientation of Lithiopema scutata. 165 Figure 86. Examples of other bivalve families. 169 Figure 87. Proposed phylogenetic tree for the “Lithiotis” facies bivalves with other lamellibranch bivalves. 174 Figure 88. UPGMA cluster with 1-Pearson coefficient distances for the Cow Creek Bioherm at Suplee-Izee, Oregon. 182 Figure 89. Trypanites-shaped burrows without calcareous linings, and circular boring or resting traces on a Lithiotis problematica. 186 Figure 90. Proposed biozonation diagram of "Lithiotis" facies bivalves. 190 Figure 91. Lithiotis problematica bouquet at the base of a buildup at Jackass Ranch, Suplee-Izee, Oregon. 194 Figure 92. Modem and fossil bivalve growth rates. 201 Figure 93. Scans of drilled specimens. 206 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 94. Growth rates of “Lithiotis" facies bivalves compared to Tridacna, Gryphaea and rudists. Figure 95. Stable isotope cross-plot of 5I 8 0 and 51 3 C data. Figure 96. Stable isotope (S1 8 0 and §1 3 C) data for specimens xiv 209 211 212-213 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. XV ABSTRACT Following extensive Late Triassic coral-constructed reefs and the aftermath of the end-Triassic mass extinction, Early Jurassic buildups are rare and constructed primarily by bivalves. The Pliensbachian exhibits a radiation of aberrant pterioid bivalves, the " Lithiotis" facies bivalves, which include: Lithiotis problematica, Cochlearites loppianus, Gervilleiopema sp., Mytilopema sp. and Lithiopema scutata. These large bivalves are ubiquitous in shallow, nearshore tropical waters and restricted to the Early Jurassic recovery interval. Lower Jurassic deposits with “Lithiotis” facies bivalves were examined in three field areas: Western North America, Northern Italy and the Central and High Atlas Mountains of Morocco. Museum and field specimens were examined and measured for a suite of morphological characters. Field and thin section observations indicate a strong zonation o f " Lithiotis" facies bivalves in shallow nearshore environments and a range of phenotypes. Gervilleiopema and Mytilopema are restricted to tidal flat facies and inner platform facies. Lithiopema scutata is found throughout the lagoonal subtidal facies and some low-oxygen environments. Lithiotis and Cochlearites are found in subtidal facies, constructing buildups. The largest buildups attain lengths over 60 m and are 3-5 m high. Phylogenetic analyses suggest that the “Lithiotis” facies bivalves are a paraphyletic group that is closely related to the Isognomonidae, within the bakevelliid clade. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xvi Sclerochonologic analyses were performed on specimens of Lithiotis, Cochlearites and Lithiopema. Stable isotope analyses were performed on Cochlearites, Lithiopema, Crassostrea titan and Isognomon janus. These data were compared to published results of other bivalves. Peaks and troughs in the 51 8 0 isotopes correspond to internal and external growth bands in both Lithiopema and Cochlearites specimens. Proposed rates of growth for the various bivalves were calculated: Lithiopema (17.6 mm/year), Cochlearites (11.2 mm/year), Italian Lithiotis (10.8 mm/year) and Oregon Lithiotis (34.1 mm/year). Due to their large size and reef-building habit, Lithiotis and Cochlearites, filled the relatively empty ecological niche of reef-building during the Lias, only to be replaced by their “predecessors,” the scleractinian corals, by the Middle Jurassic. It is proposed that the severe environmental changes and associated unusual seawater chemistry of the protracted Early Jurassic recovery led to suppressed coral reef growth and the rapid radiation of reef-building bivalves. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 CHAPTER 1: INTRODUCTION General statement The Early Jurassic (Lias), which directly followed the end-Triassic mass extinction, is an enigmatic time in Earth’s history. A period of protracted biotic recovery, it is characterized by dynamic environmental change, virtual disappearance of reef ecosystems and another smaller mass extinction in the early Toarcian, as well as the appearance of the aberrant “Lithiotis” facies bivalves, which dominated nearshore tropical regions. This chapter will introduce the setting of the Early Jurassic in the aftermath of the end-Triassic mass extinction and review the factors that control reef ecosystems today. Reefs and Carbonate Buildups Coral reefs are the most biologically diverse of modem shallow water ecosystems yet occupy only one-sixth of the world’s coastlines (Roberts et al., 2002). Reefs influence global climate and sea level, acting as a storehouse of carbon but also as important regulators of atmospheric C 02 (Birkeland, 1997). Not only is the biodiversity of reefs exceptional, but also the complexity of species interactions from symbioses and predation is unparalleled in marine ecosystems (Wood, 1999). Despite the significance of reefs, the very term “reef’ is fraught with controversy. The strictest definition of a reef is a “rigid wave-resistant framework constructed by large skeletal organisms” (Ladd, 1944). However, to conclusively prove a buildup’s ability to withstand wave action is very difficult in the extensive fossil record of reefs. In particular, as the major framework-building constituents of reefs have changed significantly throughout the Phanerozoic, it is even more difficult to use uniformitarian principles to define ancient reefs. Modem framework building Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 organisms in reefs are dominated by colonial corals with skeletons, in the geologic past however reefs have been made by solitary organisms (Cretaceous rudist reefs). Wood (1999) proposed a more encompassing definition of a reef as a “discrete carbonate structure formed by in situ or bound organic components that develops topographic relief on the seafloor.” The terms bioherm and biostrome, are commonly used to designate structures consisting of biological elements. The term “bioherm” designates a lens-shaped structure with some topographical relief constructed by in situ biota, but is not necessarily wave-resistant or created by skeletal elements; “biostrome” is used to denote a tabular body without significant topographic relief and consists of biological elements that are often but not always in life-position (e.g. a death assemblage; adapted from Wood, 1999). For the purposes of this study, I use the term “carbonate buildup” in an attempt to refrain from genetic implications associated with “biostrome,” “bioherm,” or “reef.” The term “reef’ or “bioherm” is used only when the criteria of Ladd (1944) have been sufficiently met. Mass Extinctions and Recovery Intervals Mass extinctions were recognized as early as 1840 when John Phillips designated the Paleozoic, Mesozoic and Cenozoic eras on the basis of faunal change (Hallam and Wignall, 1997). However, the statistical studies of mass extinctions began with a series of papers in the early 1980s and 1990s, with Raup and Sepkoski’s (1982) marine family diversity curve. Paleontologists have investigated effects of the “Big 5” mass extinctions (end-Ordovician, late Devonian, end-Permian, end-Triassic, end- Cretaceous; e.g. Hallam and Wignall, 1997; Droser et al., 2000) (Figure 1), but work has only recently focused on the recoveries from these biotic crises. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 50— 0 - 200 400 Time in Ma Figure 1. Percent generic extinction rate as calculated by Raup and Boyajian (1988). The major mass extinctions are marked with an arrow. The end-Triassic mass extinction is marked by a *. U > 4 Each recovery from a mass extinction appears to have a unique signature. Comparisons of biotic recoveries using paleobiology or paleoecology have challenged some widely held beliefs about ecosystems. Two assumptions about mass extinction recovery periods have recently been overturned. The first is that post-mass extinction radiations were presumed to have proceeded rapidly at high rates of speciation as previously occupied niche space was emptied and release from predation pressure occurred (Erwin, 1992; Stanley, 1999). While this is true for the Early Tertiary period (Koutsoukos, 1996), it is not observed at other mass extinction biotic recoveries, such as the Early Jurassic. Some recovery intervals are unusually long, leading some researchers to suggest that lingering deleterious environmental conditions associated with the mass extinction may have delayed recovery. The second assumption, that many paieoecological features of recovery environments indicate brackish or estuarine conditions, is based on strict uniformitarian interpretations of faunas and biogenic structures recorded from those environments (Bottjer, 1998). For example, Schubert and Bottjer (1992) used a non-uniformitarian approach in the Early Triassic. They demonstrated that an increase of level-bottom stromatolites in the Early Triassic recovery period was because metazoan-imposed barriers to stromatolite development in nearshore normal-marine environments were removed by the end-Permian mass extinction. Throughout the Phanerozoic, nearshore tropical carbonate environments (i.e. reefs) contain the highest biodiversity. Droser et al. (1997) noted that reef ecosystems formed by colonial organisms are the first decimated in biotic crises and often the last to return. Because reef and carbonate buildup communities are typified by their complex species interactions, it is understandable that millions of years may pass Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 before the community returns to the pre-crisis state. Other highly specialized fauna exhibit a similar delayed recovery rate. For example, keeled pelagic foraminifera appear 10 my after the end-Cretaceous mass extinction, attributed to be a relatively rapid recovery (A. G. Fischer, pers. comm. 2002). Understanding how biota has recovered from past mass extinctions is of great significance because through these studies we appreciate both the resiliency and fragility of Earth’s ecosystems, which are now under constant assault from anthropogenic causes (Droser et al., 2000). End-Triassic Mass Extinction The End-Triassic mass extinction is one of the least understood of the “Big Five” mass extinctions (Hallam and Wignall, 1997). An estimated 53% of all marine genera were eliminated (Erwin, 1998; Figure 1). Due to the worldwide paucity of stratigraphic sections and the regression-transgression couplet that spans the event, the cause(s) of the extinction remain equivocal. Bolide impact, climate change, volcanism, sea level change and anoxia have all been proposed as potential causes (Hallam, 1996). Olsen et al. (1987 and 2002) proposed that tetrapod faunal changes, as well as high levels of iridium and spores at a Newark Rift Basin site point to a bolide impact. However, evidence of an associated crater and a global iridium signal remain lacking. The proposed Manicouagan impact crater reveals a U-Pb zircon date of 214±1 Ma, preceding the proposed Triassic-Jurassic boundary in continental deposits (Newark Basin) of 199.6 ±.3 Ma (Hodych and Dunning, 1992; Palfy et al., 2000a). Massive volcanism and related anoxia, sea level and climate change are detailed below. The timing of the extinction is still hotly contested, however from some critical sections the terrestrial extinction preceded marine extinctions by at least several hundred thousand years (Palfy et al., 2000a). The terrestrial extinction resulted in a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 shift from non-dinosaurian to dinosaurian-dominated tetrapod communities (Olsen et al., 2002). Palynomorphs do not exhibit drastic changes across the boundary; however, palynological estimates of extinction tend to underestimate severity as different plants produce indistinguishable palynomorphs (Pedersen and Lund, 1980). Sepkoski (1986) wrote that 48% of all marine invertebrate genera became extinct at the end-Triassic event. In particular, cephalopods, bivalves, gastropods and brachiopods were hard hit; conodonts were completely wiped out (Hallam and Wignall, 1997). Of the Ammonoidea, only the genus Rhacophyllites (or a small number of closely related genera) survived the end-Triassic extinction (Dommergues et al., 1999). Just prior to the end-Triassic mass extinction, in the Norian-Rhaetian, corals and other reef-related organisms increased in both diversity and in ecological roles. Norian reefs are globally widespread and expand into northern latitudes of Europe, Asia and Western North America. Reef-construction by scleractinian corals was exceptionally productive, up to 700 meters of carbonate platform was deposited within only 10 million years (Fliigel, 1981). The advent of scleractinian corals and the acquisition of photosymbionts also occurred in the Late Triassic and led to immense reef building similar to reef systems today (Stanley and Swart, 1995). Coral reefs were decimated by the end-Triassic mass extinction. Of the 50 scleractinian genera known globally at the end-Triassic, only 11 are recognized to have survived into the Early Jurassic (Beauvais, 1984). Protracted Early Jurassic Biotic Recovery and Reef Eclipse The Early Jurassic, or Lias, which is divided into four stages (Hettangian, Sinemurian, Pliensbachian, Toarcian) and estimated to span about 26 million years, is a critical recovery interval in Earth’s history (Figure 2) (Palfy et al., 2000b). This Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. RANGE OF "LITHIOTIS" FACIES HETTAN GIAN BAJOCIAN NORIAN AALENIAN RHAETIAN PLIENSBACHIAN SINEMURIAN TOARCIAN LATE TRIASSIC MIDDLE JURASSIC LOWER JURASSIC Period Tim e in Ma o lo 00 o o CM IT) LO O CM LO 0 5 00 Figure 2. The Early Jurassic reef eclipse and range of “fdthiotis” facies bivalves. Early Jurassic stages after Palfy et al. (2000b), Rhaetian-Norian boundary from Gradstein et al. (1994). Jurassic reef curve from Kiessling et al. (1999) and Fliigel and Fltigel-Kahler (1992). - 4 8 recovery interval is typified by delayed radiations and blooms of opportunistic fauna. In the Lias, deep water facies are characterized by limestones and shales that are benthos-free, laminated, organic-rich deposits alternating with beds containing high- density, low-diversity faunas suggestive of opportunistic colonization in dysaerobic conditions (Hallam and Wignall, 1997). Reefs were globally rare for 4-10 million years following the end-Triassic mass extinction (Stanley, 1994) (Figure 2). Hettangian carbonate facies, such as the Massicio Formation of Central Italy are relatively devoid of metazoans, while the possibility of non-metazoan reefs (i.e. stromatolites) has not been fully explored in the immediate aftermath of the extinction. Sinemurian reefs are known from volcanic islands in the Panthallassian Ocean (proto-Pacific), and Late Triassic coral species such as Phacelostylophyllum rugosum appear to have survived (Stanley and Beauvais, 1994). These reefs are interpreted as “refugia” because they contain a coral that is common in Late Triassic European reefs but does not survive to the Middle Jurassic. Only in the Bajocian (Middle Jurassic) did reefs become genuinely reestablished (Hallam, 1996). Stanley and Fautin (2001) suggested that the disappearance or decreased diversity of scleractinian corals is associated with elevated atmospheric C 02 . Three possible global environmental stresses linked to the rapid rise in C 02 may have inhibited scleractinian coral growth during the Early Jurassic: temperature, inhibition of calcification, and episodic eutrophication of shallow carbonate shelves. Early Toarcian Mass Extinction A minor extinction in the Early Toarcian is associated with a global oceanic anoxic event while most evidence of faunal turnover originates from Western European Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. marine sections (Hesselbo et al, 2000; Hallam, 1961). Nearly 84% of all bivalve species went extinct at the boundary (Hallam, 1996). Yet, any breakdown of species into ecological groups fails to reveal any extinction selectivity (Little and Benton, 1995). The extinction event corresponds closely to the widespread occurrence of laminated organic-rich shales: Jet Rock (Yorkshire, England), Schistes Carton (northern France) and the Posidonienschiefer (Germany; Aberhan and Fursich, 1996). Early Jurassic Paleoenvironments The Early Jurassic is characterized by dramatic change: continental reconfiguration, climatic warming, and rapid sea level change. The rifting of Pangaea and creation of the Atlantic Ocean is associated with the large outpouring of continental flood basalts over an area of 2.5 million km2 in the Central Atlantic Magmatic Province (CAMP; Marzoli et al., 1999). The peak of the volcanism occurred at 199 ±2.4 my, in the Hettangian and a second pulse occurred at 186.9 my, the Pliensbachian-Toarcian boundary (Marzoli et al., 1999). The following sections, paleogeography, paleocirculation, and paleoatmosphere, present the most current models available with attention to conditions that may have affected the study areas. Paleogeography During the Early Jurassic, the supercontinent Pangea, surrounded by the superocean Panthalassa or paleo-Pacific, was nearly symmetrical about the equator (Figure 3). However, this aggregation was not long-lived; rifting began in the Late Triassic. As the supercontinent pulled apart, sea level changed rapidly, resulting in a series of marine transgressions. In Morocco, this activity is associated with Late Triassic continental distension and the development of a clastic-filled graben system Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 3. Early Jurassic Pliensbachian paleogeography and predicted ocean currents adapted from Parrish (1992), Aberhan (2001) and Westerman (1993). Thin dashed arrows indicate northern summer currents, thin solid arrows indicate northern winter currents; year-round currents are indicated by thick and solid arrows; thick dashed lines indicate the positions of the Hispanic Corridor (HC) and Viking Corridor (VC) currents (after Aberhan, 2001). Base map after Schettino and Scotese (2001). o 11 and a well-established marine system by the Early Jurassic (Dewey et al., 1973). The Trento Platform of Italy had begun subsiding by the Pliensbachian and drowned by the Middle Jurassic (Zempolich, 1993). Coinciding with the breakup of Pangea and the separation of Laurasia and Gondwana, was the widespread Early-Middle Jurassic terrane accretion and arc- continent collision and a surge of locally extensional arc magmatism in the Cordillera of Western North America (Monger, 1993; Jones et al., 1983). Faunal evidence and paleomagnetic evidence indicate that many of these terranes originated from a southerly position relative to the craton with subsequent movement northward before collision with other terranes and the craton (Gabrielse and Yorath, 1992). For example, many terranes have low-latitude tropical faunas and low paleomagnetic inclinationsbut now abut cratonic boreal faunal assemblages. Paleolongitudinal assignments of terranes lack rigorous control and are still hotly contested (see review in Belasky and Runnegar, 1993). The Western North American tectonic setting for the early Mesozoic is marked by two tectonic events: the Sonomian and the Nevadan orogens. The Sonomian is marked by truncation of the earlier Paleozoic continental margin, eastward directed thrusting of shallow back-arc and intra-arc basins, and deposition of late Paleozoic- early Mesozoic island arc sequences (Davis et al., 1978). In the Late Triassic, the northeast-southwest trend abruptly shifted to the new Nevadan mountain belts that trended northwest-southeast. This dramatic shift in the collision of the North American and oceanic plates is attributed to the reorganization of plates due to the global break up of Pangaea (Burchfiel et al., 1992). Two differing paleogeographic reconstructions of the Liassic Western North American coast line have been suggested: 1) embayment (McKee and Imlay, 1956); or Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 2) open coast (Hallam, 1965). McKee and Imlay’s (1956) embayment hypothesis proposed two separate areas of deposition, marine deposition in the west and mixed continental and marine sediments in the east. Ferguson and Muller (1949) proposed a north-facing shoreline for some of the western Nevadan sites. Hallam (1965) proposed a direct marine connection between British Columbian sites and the marine deposits of Sonora based on the similarity of species and overall lack of endemism, that one might expect in an embayment environment. Paleocirculation The effect of a large aggregation of continental area at the mid-latitudes has led to the description of the Late Triassic and Early Jurassic climates as driven by “monsoonal circulation” with strong seasonality (Parrish, 1992). The results of this “monsoonal circulation” are believed to include: 1) an equatorial region that is dry on the east and humid to the west, 2) absence of latitude-parallel climatic belts, and 3) alternating oceanic flow, including upwelling in the Western Tethys (Parrish, 1992). Oceanic circulation is predicted to have been influenced by this monsoonal system in the northwestern Panthallassa and the Tethys. The eastern Panthallassa Ocean is presumed to have currents similar to that of today with paleo-Califomia and paleo- Humboldt currents delivering relatively cool waters with upwelling (Parrish, 1993). Tethyan circulation is predicted to have been similar to the modem monsoon- influenced Indian Ocean circulation. Warm equatorial currents would have been directed northward during the northern hemisphere summers and southward during the southern hemisphere summer. Parrish and Curtis (1982) predicted seasonal (northern hemisphere summer) upwelling in the Eastern Tethyan Margin, just north and south of the equator. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 As the supercontinent began to break up and sea level rose during the Jurassic, several epeiric seaways became established, separating areas of exposed land (Hallam, 1996). The Hispanic Corridor opened by the Early Pliensbachian, connecting the eastern Panthallasa Ocean and the western Tethyan oceans based on the distribution of pectinoid bivalves (Aberhan, 2001; Figure 3). Apart from the Hispanic Corridor, another seaway, termed the Viking Corridor by Westermann (1993), opened in Late Pliensbachian time between Greenland and Norway and connected the Arctic and Tethyan oceans (Figure 3). Paleoatmosphere A rapid rise in C 02 levels across the Triassic-Jurassic boundary has been proposed due to the outpouring of the Central Atlantic Magmatic Province (CAMP) basalts, a result of the rifting of Pangaea (Marzoli et al., 1999). Some paleobotanical evidence and carbon isotopes from ooilitic goethites and pedogenic calcite estimate a 2,000 to 4,000 ppm increase in atmospheric C 02 levels, associated with 3-4°C “greenhouse” warming (McElwain, et al., 1999; Yapp and Poths, 1996). However, others propose a rise of only 250 ppm from carbon isotope paleosol data, approximately double that of pre-industrial Holocene atmospheric C 02 (Tanner et al., 2001). The link between this rapid rise in C 02 and ecosystems has not been explored in the Early Jurassic’s shallow tropical marine environments. One interpretation from the paleobotanical data is that the climate wanned dramatically from the Late Triassic into the late Early Jurassic (Toarcian), and cooled again in the Middle Jurassic (Vakhrameev, 1982). The most striking aspect of Jurassic climates is that subtropical conditions possibly reached to 60°N and global temperatures in the Early and Middle Jurassic may have averaged as much as 7° C Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 warmer than those of the present (Chandler et al., 1992). Crowley and North (1991) suggest that the earlier depictions of an "equable" Early Jurassic climate are not entirely accurate. Based on coupled atmospheric/ocean models, the large Pangaean supercontinent was coherent for much of the period and was likely to have experienced a strong seasonality, particularly the Western Tethys where large megamonsoons may have been common (Kutzbach and Gallimore, 1989; Chandler et al., 1992). Jurassic Carbonate Buildups Concurrent with the warmer climate, possibly sluggish oceanic circulation and dynamic tectonic history, buildup construction in the Early Jurassic was also appreciably different from both the modem and the Late Triassic. Two qualities of Early Jurassic reefs and bioherms separate them from the modem style of reef construction: 1) despite the acquisition of photosymbionts, scleractinian corals never gained their dominance characteristic of modem reef environments; and 2) volumetrically, more large epifaunal bivalves are common (Beauvais, 1977; Kiessling et al., 1999). Additional reef-inhabiting biota typical of Liassic reefs are calcareous algae, hydrozoans, bryozoans, encmsting and sessile foraminifera, assorted encrusting problematica (Tubiphytes sp., Bacinella sp. Thaumnatoporella sp.), calcareous algae (dasycladacean, blue-green, and coralline) and calcareous sponges (Warme, 1988). Beginning in the Late Lias, extensive siliceous sponge mudmounds attained 1.5 meters of relief appeared in deeper waters (Duarte et al., 2001). Middle and Late Jurassic reefs are of a somewhat deeper-water origin built by siliceous sponges or by algae where these framework builders still exceeded corals in both volume and diversity (Scott, 1988). Late Jurassic reefs were well developed and are preserved in Germany’s Southern Franconian Alb. Bioherms and reefs from this area attained heights of 60 m Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 on a shallow carbonate shelf (Leinfelder et al., 1994). Late Jurassic and early Cretaceous reef-builders were taxonomically heterogeneous; skeletal and non-skeletal algae, diverse calcareous and siliceous sponges, scleractinians and the rapidly emerging hippuritacean (mdist) bivalves (Fagerstrom, 1987). “Lithiotis” Facies Bivalves: Organisms Unique to the Early Jurassic “Lithiotis” facies bivalves (Figure 4) were ubiquitous benthic organisms in nearshore low latitude environments. The “Lithiotis” facies fauna include: Lithiotis problematica, Cochlearites loppianus, Gervilleiopema sp., Mytilopema sp. and Lithioperna scutata. The unique morphology of the “Lithiotis” facies fauna, their short stratigraphic range (limited to the Early Jurassic) and domination of Early Jurassic nearshore ecosystems make them a unique evolutionary and ecological recovery taxon of the Early Jurassic. “Lithiotis ” facies bivalves have been the subjects of controversy since the early eighteenth century. Lithiotis problematica was originally described as an alga, thought to be related to the modem Udotea by Gtimbel (1871). Later, Tausch (1890) and Reis (1903) correctly placed it within the mollusca. Lithiotis problematica is a sessile, monomyarian bivalve characterized by its unusual morphology, prismatic aragonite mineralogy and propensity to aggregate in rudist-like bioherms (Figure 4A). Lithiotis problematica has a stick-like shell, which reaches a height of 30 cm or more, has a width of 4-6 cm and an average thickness of 3 cm (Accorsi Benini and Broglio Loriga, 1982; Figure 4A). Cochlearites loppianus, also a bioherm-builder, is of a similar morphology but the opercular valve is thicker than that of Lithiotis problematica (Figure3B), and the ligamental area has a narrow groove in contrast to the multivincular ligament of “Lithiotis ” facies bivalves (Chinzei, 1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. adaoerturai a tta c h e d valve fre e valve lig a m e n t ^ V a d a p ic a l Lithiotis problem atica A le ft valve 1 right valve ligam ent g r o o v e a d a p ic a l Cochlearites loppianus adapertural h g a m e n ta l g r o o v e s a d a p ic a l Lithioperna scutata C _ a d a p ic a l Gervilleioperna sp. a d a p e rtu r a i i M ytiloperna sp. Figure 4. Early Jurassic “ Lithiotis ” facies bivalves; A - Lithiotis problematica, right valve; B - Cochlearites loppianus, left valve; C - Lithioperna scutata, right valve; D - Gervilleioperna sp., left valve; E - Mytiloperna sp. right valve. O s 17 Lithioperna scutata, ironically the most common bivalve of the “Lithiotis” facies, is most often 15-20 cm long but some specimens are as long as 70 cm (Debeljak and Buser, 1997; Figure 4C). The shell shape is subequivalve, with flattened to concave-convex massive shells that are rounded or subrectangular in outline (Broglio Loriga and Posenato, 1996). Gervilleioperna sp. is roughly equivalved with a vertically elongated cuneiform body, with massive shells, a narrow prominent umbo, a long posterior wing, and a prosogyrous beak (Cox et al., 1969; Figure 4D). Mytiloperna is an equivalve, mytiloform bivalve with massive shells and a ridge running from the subterminal beak to the lower edge (Cox et al., 1969; Figure 4E). Mytiloperna sp. is the only “Lithiotis” facies genus whose range extends beyond the Lias for the remainder of the Jurassic. Modem Coral and Bivalve Buildups Research on modem reefs focuses on the prodigious coral-constructed reefs. However, the technical definition of reef adopted by this study includes reefs constructed by bivalves. The factors that control reef construction by these two different phyla are integral to this study, Modem Carbonate Buildups and the Role of Nutrients Most modem coral reef growth occurs in “blue deserts” where annual average concentrations of nitrate are less than 2.0 mmol L'1 , and for phosphate are less than 0.20 mmol L'1 (Kleypas, 1995). In modem reef environments, increased eutrophication affects the physical environment by decreasing water clarity, increasing the sedimentation rate and destabilizing oxygen levels and pH (Braiser, 1995). Algae are highly nitrogen-limited when compared to the other oligotrophic-adapted fauna. High Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 nutrient levels enhance the growth of benthic macroalgae, which compete with corals for space and light (Wood, 1999). Modem coral reef workers have noted that nutrients appear to be the controlling factor of reef faunal development by changing phytoplankton and macrofauna distributions, predation and herbivory which all influence the reef community structure (Wood, 1999). However, heterotrophic bivalve, such as oyster reefs, buildups tend to occur in nutrient-rich environments. Modem Carbonate Buildups and the Effects of Increased Temperature and C 02 Modem scleractinian corals have been reported to “bleach” (i.e. lose their photosymbionts) and experience high rates of mortality when sea surface temperatures exceed 30°C (Carriquiry et al., 2001). Some studies of modem buildup-constructing bivalves (e.g. Crassostrea virginica) report a shut-off in shell calicification when water temperatures exceed 28°C and a presumed mortality should such high temperature conditions persist (Surge et al., 2001). Other bivalves, such as Tridacna maxima, do not exhibit similar “shut-offs” when water temperatures exceed those required for coral bleaching (Romanek and Grossman, 1989). Increases in atmospheric C 02 alter the saturation states of both aragonite and calcite thereby inhibiting calcification. Studies of modem scleractinian corals show that a 280 ppm increase in atmospheric C 02 lowers calcification rates by 60% (Langdon et al., 2000). The results are deadly to corals. These organisms experience weaker skeletons, reduced extension rates and increased susceptibility to erosion. There are no similar modem studies that assess the role of C 02 on bivalve calcification. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 Bivalves in Modem Carbonate Buildups Filter-feeding bivalves in modem bioherms and reefs are used as “sentinel” organisms because of their sedentary habits and their ability to bioconcentrate pollutants as well as the fact that their presence as filter-feeders signals a change in the nutrient regime (Tripp and Farrington, 1985). After mixotrophic scleractinian corals, filter feeders (usually bivalves) are second in benthic biovolume in modem coral reefs (Dubinsky, 1990). Some volumetrically important bivalves in modem oligotrophic settings include Tridacna and Hippopus. These bivalves differ from their smaller counterparts in that they are mixotrophs adapted to the low-nutrient setting and appear to have increased calcification rates due to the energetic subsidy of photosymbiosis (discussed below). Large mixotrophic bivalves (Tridacna and Hippopus) are common in modem Indo-Pacific reefs while absent from modem Atlantic reefs (Stoddart, 1969). As nutrient levels increase the number of filter feeding organisms (bivalves and polychaetes) also increases. Experiments with radiocarbon labeling have shown that the fine filterers of the reef reduce bacteria to concentrations less than 1 mg nr3 , levels one-third to one-half those in oligotrophic waters and 1 to 2 orders of magnitude below those in neritic mesotrophic waters (Sorokin, 1990). Thus, the efficiency of filtering reef fauna in oligotrophic systems is extremely high: for every 1 g of filter-feeder biomass, the bacteria of size 0.2 to 0.5 mm are removed from 400 to 600 L of sea water everyday (Sorokin, 1990). As particulate food matter increases with nutrient levels, the efficiency of filter-feeding organisms decreases while their populations increase. In contrast, the eutrophic end-member bioherm is typified by oyster reefs, constructed by Crassostrea virginica common off the coasts of Georgia and Texas and Ostrea edulis in the North Sea (Bahr, 1976). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 Photosymbiosis in Modem Bivalves The tropical giant clam family, Tridacnidae (including Tridacna gigas, T. maxima, T. derasa, T. squamosa, T. corocea, Hippopus hippopus and H. porcellanus), as well as the heart cockle, Corculum cardissa, have symbiotic relationships with the zooxanthella Symbiodinium microadriaticum, a dinoflagellate. The large size associated due to increased calcification rates as a result of mixotrophy is evident in T. gigas; one specimen was reported to exceed 1.2 m in length and 250 kg in weight (Yonge, 1936), only to be exceded in size by Late Jurassic-Early Cretaceous rudistid bivalves and late Cretaceous inoceramids. Unlike scleractinian corals, where the zooxanthellae are housed within the cells of the corals, these algae are found intercellularly in bivalves. It has been postulated that only organisms with “thin-tissues” (e.g. diploblastic - two layers of tissues such as corals and ctenophores) can effectively use the photosynthate produced by the zooxanthellae (Cowen, 1988). The success of photosymbiosis in the triploblastic bivalves is a result of this key difference of where the symbionts are housed in the host, intercellularly in mantle tissues. However, since bivalves are not clonal, like scleractinian corals, zooxanthellae are passed from adult to the veliger stage (Fitt and Trench, 1981). When submerged, adult tridacnid clams gape and extrude their mantle folds during the day only, while at night they are inactive (Yonge, 1936). This exposes the zooxanthellae located in the mantle tissue to light and permits photosynthesis to take place. Corculum cardissa, by contrast, keeps its valves shut and light is transmitted through the shell to the photosymbionts housed in the gills and anterior mantle (Carter and Schneider, 1997). The metabolic gain for the bivalves from the photosymbionts are the released photosynthate products (Muscatine, 1990). Tridacnid clams are referred to as "nutritional opportunists" in a nutrient poor environment, as Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 they are not dependent on the photosymbionts but are true mixotrophs (Ambariyanto and Hoegh-Guldberg, 1999). They filter feed on suspended particles including diatoms and crustaceans as well as on zooxanthellae released from heat-stressed corals. Focus of This Study “Lithiotis” facies bivalves radiated and became extinct within the end-Triassic mass extinction recovery, thus representing “failed crisis progenitors” (sensu Harries et al, 1996) as unique evolutionary and ecological mass extinction biotic recovery taxa. Many of these bivalves constructed carbonate buildups. “Lithiotis” facies bivalve bioherms have been assigned in previous studies to restricted nearshore environments of rapidly fluctuating salinity and temperature, based on the low diversity of the bioherms and morphological similarity to modem oysters. I question this assessment. Depleted diversity is to be expected after mass extinction events and not necessarily indicative of restricted nearshore environments (e.g., Bottjer, 1998). The purpose of this study is to re-evaluate the previous facies within a non-uniformitarianist context as the “Lithiotis” facies bivalves flourished during a time of global biotic recovery from the end-Triassic mass extinction. To accomplish this goal, a four-step approach was undertaken using: 1) stratigraphic setting, 2) morphology and phenotypic variation, 3) paleoecology and biozonation and, 4) geochemical-based sclerochronology. The second chapter details the stratigraphy of the various field sites with special attention to ancient water depth indicators. The third chapter deconstructs the various morphologies of the “Lithiotis” facies bivalves. The fourth chapter delineates biozonation of the “Lithiotis” facies bivalves using paleoecological techniques. The fifth chapter utilizes stable isotope and trace element techniques used to quantify the growth history and paleoenvironments Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 recorded by seasonal changes in three “Lithiotis’’ facies bivalve shells. The sixth chapter concludes with a summary of the research and proposed mechanism for the flourishing of the “Lithiotis” facies bivalves during the end-Triassic recovery. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 CHAPTER 2: STRATIGRAPHY AND SEDIMENTOLOGY OF STUDY SITES Introduction At the Triassic-Jurassic transition, dramatic changes affected the supercontinent o f Pangaea, which was subjected to extensional tectonics related to incipient Atlantic rifting (Veevers, 1989). The Italian Southern Alps and Moroccan Central High Atlas represent a section of a Jurassic passive continental margin and troughs of the neo-Tethys ocean. Meanwhile on Pangaea’s western edge, regional tectonics were slowly assembling what is now referred to as the Western North American Cordillera. Accreted terranes of Oregon and California or authocthonous sections of Nevada display sections of a Jurassic active continental margin, the eastern margin of the Panthallassa Ocean (Figure 3). Marine Liassic rocks in conterminous Western North America are confined to the Cordilleran region. The Liassic sea did not reach into the interior of the continent. However, several extensive continental formations are tentatively assigned to this interval (Hallam, 1965). During these large scale tectonic changes, the well-developed buildups and carbonate platforms of the Late Triassic suffered from the twin blows of the Triassic- Jurassic mass extinction and the afore-mentioned rifting. Not only the size of the carbonate platforms decreased in the Lias, but the major reef building organisms, namely scleractinian corals, were nearly decimated by the extinction (Cobianchi and Picotti, 2001; Stanley, 1988). In this relatively empty niche, the “Lithiotis” facies bivalves colonized the nearshore environments of the Early Jurassic. “Lithiotis” Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 facies bivalves are distributed globally in tropical and near tropical areas of the Pliensbachian and Early Toarcian. Three regions, Western North America, Italy and Morocco were compared in this study (Figure 5). Western North American sites are located in the Robertson Formation near Suplee-Izee, Oregon, the Thompson Formation at Mt. Jura, California and Dunlap Formation in the Garfield Hills and Shoshone Mountains, Nevada (Figure 5A). Tethyan sites are located in Northern Italy and Morocco. Northern Italian sites, Garzon di Sotto, Ponte delTAnguillara and Bellori are located in the Calcare Grigi Formation on the South Trento Carbonate Platform, north of Verona in the Monte Lessini district (Figure 5B). The two Moroccan field sites, Ait Athmane and Assemsouk, are located in the Central and Eastern High Atlas Mountains (Figure 5C). Methods Each field area was described on the basis of: 1) general setting and stratigraphy, 2) site description (lithofacies, macro- and microfossils, sedimentologic features, etc.) and 3) proposed depositional setting. Figure 6 contains a legend and key for symbols that were used during mapping and construction of stratigraphic profiles. Along the profiles, bedding thickness, dip of the stratal planes and the geometry of the buildups were measured. Samples for slabbing, acetate peels and thin-sections for detailed analyses of sediment fabric were collected to determine representative lithofacies horizons. Each site description ends with an analysis of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. j ' y t- oruanc / Suplee-Izee • ^It. Jura • / Garfield H ills r N 0 \ 250 Shoshone Range t 5dh|--as V e $ a s .„_ _ \\ A V \ I Bellorie*Ga^ 0,l f ^ 0tt0 Veropi V \ / J V X V.. ■ < # H om e X “ V . ( N 0 125 250 t -X / f j f km xFf ( " \ r B .. • V /* ’ i a n g ie r X Rabat,/ J / M a f r a k e d t AitAthmane \ \ . E r R a e h i d p A zilai Assefnsouk .... s' s N t 0 100 200 km Figure 5. Locality map of studied sites. A - Western North America sites: Suplee-Izee, Oregon, Mt. Jura, California; Garfield Hills, Nevada; Shoshone Range, Nevada. B - Northern Italy sites in the Monte Lessin; District: Ponte dell’Anguillara, Bellori, Garzon di Sotto. Central High Atlas Mountains, C- Morocco: Ait Athmane, Assemsouk, Jebel Azourki. 26 Figure 6. Legend of lithologic characters for stratigraphic columns adapted from Corsetti (pers. comm., 2002) and Tucker (1969). Key of symbols for stratigraphic columns adapted from Corsetti (pers. comm., 2002), Tucker (1969) and Swanson (1981). Lithologic Symbols Shale Buildup Mudstone Limestone Lignite (brown coal) Marl Limestone, sandy Conglomerate Sandstone Sandstone, parallel bedding Limestone, silty Breccia Sandstone, cross-bedded Limestone, oolitic Lava flow Limestone, shell bed Siltstone Siltstone, interbedded with limestone Dolostone sedimentary features other fossils " Lithiotis " facies bivalves oncoids gastropods Cochlearites paleocurrent trend Opisoma q Oq nodules Gervilleioperna pectinids mudcracks y bioturbation www microbial laminae Lithiotis, broken C r other bivalves Mytiloperna cross beds I Lithioperna, broken bracbiopods collapsed beds microfossils branching corals or spongiomoiphs speroidal weathering © Orhitopsella domal corals or stromatoporoids • • • chert Lituosepta graded bedding OOP other forams echinoderms teepee structures Palaeodasycladus undiffemtiated fossils <•> fenestrae ^ other alga ostracods corals, tabular ripples Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 depositional setting with a focus on water depth. Table 1 is a summary of the field site descriptions. Robertson Formation, Suplee-Izee, Oregon Upper Triassic to Lower Jurassic sections are exposed beneath a cover of Tertiary lavas in the Blue Mountains of Central Oregon. Lupher (1941) was the first to reconstruct the major stratigraphic relationships of rocks this age. Dickinson and Vigrass (1965) refined these observations and detailed the most complete and exposed succession in the Suplee-Izee area. The Robertson Formation of Late Pliesnbachian-Toarcian age has several exposures of lithiotid bioherms. Dickinson and Thayer (1978) suggested that the Robertson Formation and other sedimentary rocks of the Suplee-Izee Terrane were deposited in an intra-arc basin of the older volcanic arc Olds Ferry Terrane, which was active in the Permian and was accreted onto the craton during the Early Cretaceous. The Olds Ferry terrane has been correlated with the Quesnellia Terrane based on paleomagnetic data, deformational history and igneous rock trends (Vallier, 1995). The Robertson Formation is part of a largely volcaniclastic sequence called the Mowich Group located on the Suplee- Izee Terrane. It rests on an angular uncomformity over folded chert-pebble conglomerates of the Triassic Begg and Bribois Formations and is overlain by the Suplee, Nicely, Hyde and Snowshoe Formations of volcanic sandstones (Dickinson and Vigrass, 1965; Nauss and Smith, 1988) (Figure 7). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 1. Summary o f field site descriptions. Site Location Age Depositional Setting Paleodepth Buildup Form Reef-building r Faima "Lithiotis" Bivalves References Robertson Formation Suplee-Izee, Upper Volcanic intra- subtidal to bioherms and Lithiotis, OR Pliensbachian arc basin low intertidal biostromes Lithiotis spongiomorphs, algae Nauss and Smith, 1988 Nauss, 1986 Thompson Formation Mt. Jura, Upper CA Pliensbachian Volcanic intra- subtidal arc basin biostrome Lithiotis Batten and Taylor, 1976 Sunrise & Dunlap Formation W estern NV Pliensbachian- Siliciclastic subtidal Toarcian embayment on craton biostrome Lithiotis Muller and Ferguson, 1936 Silberling, 1959 Calcare grigi Mt. Lessini, Pliensbachian- Carbonate subtidal to Italy Early Toarcian platform intertidal lagoon bioherms and Lithioperna, biostromes Lithiotis, Cochlearites Lithiotis, Cochlearites, Lithioperna, Gervilleioperna, M ytiloperna Bosselini and Broglio Loriga, 1971 Ait Athmane & Central Pliensbachian- Rift basin and subtidal to bioherms and Assemsouk High Atlas, Early Toarcian carbonate supratidal biostromes Morocco platform Cochlearites, Opisoma, Lithioperna, corals, algae, spongiomorphs Cochlearites, Lithioperna, Gervilleioperna, M ytiloperna Lee, 1983 Crevello, 1988 to oo 29 Figure 7. Stratigraphy of field sites. The range of the “Lithiotis” facies bivalves is shaded gray. Mt Jura, California Central & Eastern High Alas, Morocco West Central Nevada Suplee-Izee, Oregon STAGES calcaires recifaux Lower AmmoiitioQ R( Mcrmon Sandstone m am esa posidonies Posidonia A£ina ... Beds Snowshoe Fm. Dunlap Fm. Form sft ion d'Aganane N ic ely F m I s s< Occ Fant Meta-andesite C aps Creek Beds Graylock Fm. Sunrise- Gabbs F m . Formation des AitBou Ouili unnmaed metarhyolite Rail Cabin HETTANGAN Fcreman Beds Water Canyon Fm. pelites rouges etbasaltes Luning Fm. Swearinger Slates CARMAN Fm. informal units after Du Dresnay.1965 Septfontaine, 1986 Zenploich, 1983 after Bosellini etal., 1981 M dler& Ferguson, 1939 Taylor etal., 1983 Bartel, 1994 Differ, 1892 Harwood, 1993 Dickinson & Vigrass, 1965 The Robertson Formation is comprised of a sandy pebble conglomerate, volcanic sandstone and minor gray limestone units and reaches thicknesses of 95 m. Lithiotis bioherms create a bafflestone biofacies and death assemblages of lithiotids form a rudstone facies. Outcrops of the bioherms are up to 10 m thick. Limestones in the Robertson Formation are generally fossiliferous, while sandstones are non- fossiliferous to sparsely fossiliferous. Thus, the formation is more fossiliferous in the northern exposures (Cow Creek and Jackass Creek) than in the southern Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 exposures (Robertson Ridge and Swamp Creek) where the proportion of limestone lithofacies is less (Figure 8). Figure 8. Overview map of the Suplee-Izee area and the four study sites. Dayville John Day Mt. Vernon Oregon map area Jackass Ranch Cow Creek .Seneca. Suplee Silvies' _Grant Co. _ Harney Co. Robertson Ridge '395 ' lu m s Robertson Ridge The Robertson Formation was named by Lupher (1941) for the Roberston Ranch, 8 miles southeast of Suplee; his type section is on “Robertson Ridge” in SE1/4, Sec. 28, T18S, R26E (Big Mowich Mountain Quad; 43°58.936’N; 119°37.728’W) (Figure 9). The outcrop band in this area extends eastward from Sec. 29, 518S, R26E, and the formation is not mappable east of Sec. 36. Beyond this Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 Figure 9. Robertson Ridge buildups. A - Map. Buildups believed to be in situ life assemblages are outlined. Biostromal, or death assemblages are marked by filled outlines. The extent of the Robertson Formation is outlined and infilled with gray. Positions of stratigraphic columns are denoted by letters and are depicted in detail in Figure 10. B - Photograph of the uppermost Robertson Ridge buildup outcrop visible from the road, the buildup depicted in stratigraphic column D, near the Robertson Formation type s e c t i o n . _____________________ Oregon Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 point, “intercalations of green volcanic sandstone of Robertson lithology, occur in the lower 6 meters of the Suplee Formation as far east as Big Flat” (about 5 miles NE of Little Mowich Mountain; Dickinson and Vigrass, 1965, p. 34). The volcaniclastic sandstone is a distinct green-gray to green-brown (Figure 10). Exposures are rare on rounded sage-covered slopes. Flowever, the area is unique, because it is the only continuous superposition of the “Suplee Platform” facies and the “Izee Basin” (Dickinson and Vigrass, 1965). The maximum thickness of the Robertson in the Robertson Ridge area is 72 m in the NW1/4, SE1/4, Sec. 29, T18S, R26E (Figure 11, Columns B & C). The formation thins abruptly to about 41 m in the NE1/4, SE1/4 of sec. 28, T18S, R.26E (Figure 11, Column A). The Robertson Formation beds dip between 10 and 50° and are sometimes offset by faults. In this area the formation rests with angular uncomformity on the Carnian (Upper Triassic) Begg Formation throughout this outcrop, except for a small area in SW1/4 of Sec. 26, where it rests on the Brisbois Formation. The basal conglomerate frequently forms resistant ledges along hillsides in this area. The Triassic-Jurassic uncomformity is most apparent where equally resistant ridges of Begg Conglomerate underlie the Robertson. The basal conglomerate is 30 m thick in SW1/4, NE1/4, Sec. 27, T18S, R26E (Figure 11, Column D). Only a small portion of the Roberstson exposed in this area is limestone; 60% of this limestone is a gray silty limestone and the rest is Lithiotis buildups. The buildups have a mean thickness of about 1 m and contain calcareous mud or calcareous sands between the Lithiotis valves. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 10. Photograph of the distinctive Robertson Formation volcaniclastic sandstone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 Figure 11. Stratigraphic columns from the Robertson Ridge study area. Column A - NW1/4, SE1/4, Sec. 29, T18S, R26E; Column B - Center of SW1/4, Sec. 28, T18S, R26E; Column C - NE1/4, SE1/4 of sec. 28, T18S, R.26E; Column D - SW1/4, NE1/4, Sec. 27, T18S, R26E. All stratigraphic columns are located within the Big Mowich Mountain Quadrangle. -*Z Q gwswn | | Q ) ■ y . (3 . " ■ ■ •■"i Y : - - 0( A 0 0 s 5 0 ■ w o . 0 o r- o s o © V * ) 0 s I O ~ < £) ( SB fjffS B B ih . . _ f : ; .. i l l •,o .r -0 .u . y.« y 0 ■ 0 o H < 2 ^ 0 ° 3 0 2 0 £ O o o :\0, 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Column A Column B Column C Column D 35 These buildups appear to grade laterally into sequences of muddy or silty limestones, or inter-buildup areas that are sometimes fossiliferous. The gastropod Nerinea occurs in some concentrations in these beds; forms similar to the bivalve Modiolus and terebratulid brachiopods are also common (Figure 12). Swamp Creek At Swamp Creek, the Robertson Formation is exposed as thin bands of outcrops about 3 km in length, trending roughly southwest-northeast (Figure 13). The southernmost exposure is in the north half of NE1/4, SE1/4, Sec.4, T18S, R26E (Figure 14, Column A) and the northernmost exposure is in the middle of Sec. 34, T17S, R26E. One of the best exposures is in the SE1/4, SW1/4, Sec. 26, T17S, R26E (44°02.299’N; 119°35.754’W) (Figures 13B and 14, Column D). The Packwood Creek exposure reported in Lupher (1941) is located about 4.8 km east of Swamp Creek in Sec. 6, T18S, R27E and Sec. 12, T18S, R26E. In this area the Robertson is deformed and poorly exposed. Several tributaries of Swamp Creek cut through the area, and the formation is well exposed on the hillsides and ridges between these streams. The basal conglomerate and Lithiotis buildups generally form resistant ledges, while the less resistant sandstones are usually covered by a thin layer of rubble and soil. The thickness of the Robertson formation is over 90 m at Column D (Figure 14). It is difficult to determine its thickness in other exposures but some thinning is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 Figure 12. Fossils from Robertson Ridge. A - Nerinea from the Robertson Formation. B- Modiolus from the Robertson Formation. C - Terebratulid brachiopod from Robertson Formation. HflH IflH Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 Figure 13. Swamp Creek buildups. A - Map. Buildups believed to be in situ life assemblages are outlined. Biostromal, or death assemblages are marked by filled outlines. The extent of the Robertson Formation is outlined and infilled with gray. Positions of stratigraphic columns are denoted by letters and are depicted in detail in Figure 14. B - Photograph of the uppermost Swamp Creek buildup outcrop visible from Suplee-Izee road, the buildup depicted in stratigraphic column D. Gate to Schnabele {Swamp Creek.) Ranch map area Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 Figure 14. Stratigraphic columns from the Swamp Creek study area. Column A - NE1/4, SE1/4, Sec.4, T18S, R26E; Column B - SW1/4, NW1/4, Sec. 3, T18S, R26E; Column C - NE1/4, NW1/4, Sec. 3, T18S, R26E; Column D - SE1/4, SW1/4, Sec. 26, T17S, R26E. All stratigraphic columns are located within the Funny Butte Quadrangle. /' 5 U & Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 evident, in particular at the southwest side of the buildup. The formation in this area dips between 25° and 30° to the northwest; it is not as extensively deformed or altered as at Robertson Ridge. The basal conglomerate rests on shales, sandstones, and limestones of the Brisbois Formation, except for the extreme southwestern exposures, where the Begg is found. As at Robertson Ridge, the angular conformity at the base of the Robertson is high; the Triassic rocks often display near-vertical dips. The conglomerate is the same as in other areas, with pebbles of chert, sandstone and Permian limestone characteristic of the Olds Ferry Terrane (Dickinson and Vigrass, 1965). The conglomerate is 40 m thick and comprises nearly half of the formation. Limestones account for very few of the exposures of the Robertson Formation at Swamp Creek, but slightly more than in the type area. While much of the limestone at Robertson Ridge is a gray silty limestone, in Swamp Creek Sections nearly all of the limestone is a green-gray argillaceous limestone. The rest of the limestones are Lithiotis buildups. The green-gray limestone layers are interspersed throughout the upper part of the formation and have a mean thickness of four feet, they are often fossiliferous, containing Nerinea gastropods and the bivalve Modiolus. At the Sec. 3 buildup (Columns B and C), the height of the buildup was 5 m in the center which then tapered to the presumed seafloor over a distance of 100 m (Figure 14). The buildup grades into a sandy, pebble-rich limestone with fragments of Lithiotis problematica. At the buildup margins, samples of a branching organism, Spongiomorph ramosa?, were collected (Figure 15). The slopes downhill of the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 Figure 15. Spongiomorpha ramosa ?. A - hand sample. B- Thin section cross- sectional view under plane polarized light at 2.5x magnification, field o f view is 5mm. Scale bar is 1 mm long. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Swamp Creek exposure are littered with individual specimens of Lithiotis that have weathered out of the matrix, which were used in later morphological analyses (Figure 16). Figure 16. Lithiotis problematica individual samples from Swamp Creek. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 Cow Creek The Robertson Formation is exposed in a narrow band running along Pine Creek and Cow Creek in a southwest-northeast direction, roughly parallel to the Suplee- Izee Road (Figure 17). One of the largest buildups is located in SE 1/4, SW1/4, Sec. 17, T17S, R26E (44°06.541’N, 119°30.641’W) (Figure 17B; Figure 18, Column B). Relief in this area is high and the exposures are the best in the area. Buildups and limestone facies resist weathering forming ridges, and sandstone layers are covered by a scattering of talus and other debris. Beds in this area dip between 20°-60° to the north or northwest. The thickness of the Robertson formation in this area is more than 60 m in the NE1/4, NW1/4, Sec. 17, T17S, R27E (Figure 18, Column D). The shales and limestones of the upper Triassic Brisbois Formation underlie the Robertson throughout this area; angular discordance is often slight to nonexistent. The overlying Warm Springs Member of the Snowshoe Formation (Middle Bajocian) is presumed to have been deposited after significant erosion of the Robertson (Dickinson and Vigrass, 1965). The basal conglomerate present, at all other exposures was not observed at Cow Creek. The defining characteristic of the Cow Creek Robertson exposures is the large percentage of limestone, almost half of the exposed outcrops, with much of the limestone consisting of Lithiotis buildups (Figure 19). The sediment between the Lithiotis valves in these reefs alternates between gray calcareous muds at the base to sandy limestones at the top of the buildups. The buildups vary in size from 1 -10 m thick, averaging about 6 m thick. Many of the inter-buildup areas are fossiliferous Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 Figure 17. Cow Creek bioherms. A - Map. Buildups believed to be in situ life assemblages are outlined. Biostromal, or death assemblages are marked by filled outlines. The extent of the Robertson Formation is outlined and infilled with gray. Positions of stratigraphic columns are denoted by letters and are depicted in detail in Figure 18. B - Photograph of the Cow Creek Bioherm outcrop from Suplee-Izee road, the buildup depicted in stratigraphic column B is at the top of the ridge. A. I zee. Oregon f l t t - i t i “ Lithiotis riiiiie B. w e * i - a y Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 Figure 18. Stratigraphic columns from the Cow Creek study area. Column A - NW1/4, SE1/4, Sec. 8, T17S, R27E; Column B - SE 1/4, SW1/4, Sec. 17, T17S, R27E; Column C - NW1/4, NW1/4, Sec. 17, T 17S, R27E; Column D - NE1/4, NW1/4, Sec. 17, T17S, R27E. All stratigraphic columns are located within the Funny Butte Quadrangle. 0 0 0 C l 0 -^5 0 © 0 ^ (& C l * Q □ fS 0 ® i o o V 0 A r r v ™ , o 8 o £ U > o O o © o Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Column A Column B Column C Column D Figure 19. Lithiotis buildups at Cow Creek. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 with Nerinea, other gastropods, crinoid columnals, hollow regular echinoid spines (diademoid) and plates, the branching spongiomorph Spongiomorpha ramosa?, the bivalve Weyla sp., other unidentified brachiopods and terebratulid brachiopods (Figures 12, 15 and 20). The remainder of the formation consists of sandstones, which are fine to medium grained, dark green to gray, resistant and calcareous in some areas. Spheroidal weathering is often present and some of the sandstones have cross bedding features (Figure 21). These beds average between 3-6m in thickness and are rarely fossiliferous. However, the interbuildup areas of Cow Creek have a variety of bivalves including: Modiolus, Trigonia, Camptonectes, Pholadomya, Ceratomya and Lucina (Figure 22). The interbuildup area supports a wide array of microfossils including red algae, small miliolid foraminifera, thin-shelled ostracods and dasycladacean algae (Figure 23). Geopetal cements fill some of the lithiotid shell cavities indicating that some of the bouquets at the Cow Creek site are in original upright orientation. Jackass Ranch A small exposure of the Robertson Formation is parallel to the axis of an anticline on Jackass Ranch in Sec. 18, T17S and R26E (44°05.841 N, 119°32.416’W) (Figure 24). The beds in this area dip away from the anticline axis at 75°. The thickness of beds in this area are approximately 60-90 m (Figure 25). The Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 20. Fossils from Cow Creek. A - Nerinea', B - Hollow regular echinoid spines (diademoid); C- Weyla sp. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Figure 21. Sedimentological features o f Cow Creek sections. A - Spheroidal weathering of sandstones at Cow Creek sections. B- Cross-bedding features. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 22. Bivalve fauna from the Cow Creek assemblage. A - Camptonectes, B Pholadomya, scale bar is 1 cm long; C- Ceratomya. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 Figure 23. Microfossils of Cow Creek A - Thin section of two ostracods at 2.5x under plane polarized light. The large ostracod is approximately 1 mm long, echinoderm debris is just below. B - Thin section of several bioclasts: red algae, small miliolid foraminifera, gastropods, thin-shelled bivalves and echinoderm debris at 2.5x magnification under cross polarized light. Scale bars are 1 mm long. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 Figure 24. Jackass Ranch buildups. A - Map. Buildups believed to be in place life assemblages are outlined. Biostromal, or death assemblages are marked by filled outlines. The extent of the Robertson Formation is outlined and infilled with gray. Positions of stratigraphic columns are denoted by letters and are depicted in detail in Figure 25. B - Photograph of the uppermost Jackass Ranch buildup outcrop visible from Suplee-Izee road, the buildup depicted in stratigraphic column B. map area Gate to Jackass Ranch Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 Figure 25. Stratigraphic columns from the Jackass Ranch study area. Column A - NE1/4, SE1/4, Sec. 3, T17S, R26E.; Column B - NE1/4, SW1/4, Sec. 18, T17S, R27E; Column C - SE1/4, NW1/4, Section 18, T17S, R26E; Column D - NE1/4, NW1/4, Section 18, T17S, R26E. All stratigraphic columns are located within the Funny Butte Quadrangle. •< £ > * < 0 ! \ ■M T s T fin d o°:&° <f IK . . V . T N fK ■ - o M 3 C j ® < 0§ I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Column A Column B Column C Column D 53 shales and limestones of the upper Triassic Brisbois Formation underlie the Robertson throughout this area; angular discordance is often slight to nonexistent. The Robertson Formation is overlain by the Warm Springs Member (Middle Bajocian) of the Snowshoe Formation, in the area. The basal conglomerate, prominent in other areas of Robertson Formation exposure is 11 m thick at Jackass Ranch. The Lithiotis buildup is approximately 20 m long and 6 m high. Column B traverses three Lithiotis buildups of varying thickness (Figure 25, Column B). The thickest section (Column D) is at the same site to the Nauss (1986) Section 3 at Spring Creek. At this site, Nauss (1986) reported mudcracks. Features that may have been interpreted as mudcracks are depicted in Figure 26A. These features lack the characteristic polygonal mudcrack features and may be a post-depositional feature or a microbially mediated dessication feature; indicated by bulges protruding above polygonal cracks (v. Gerdes et al., 2000; their Figure 3f). Another feature discovered at Column D in the same silty limestone facies, is a series of finely laminated beds that may have been algal mats (Figure 26B; N. Noffke, pers. comm. 2002). If the interbioherm areas had algal mats, this may inhibit the formation of polygonal mudcracks and might lead to a feature seen in Figure 26A. The interstices of the buildups at Jackass Ranch are almost entirely calcareous mudstones with some grading on either side of the buildup into sandier facies. The sandy facies are less fossiliferous than those at Cow Creek and contain only Nerinea and terebratulid brachiopods. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 Figure 26. Lithologic features at Jackass Ranch Column D, near Spring Creek. A - Microbially influenced dessication structures (?). B - Microbial laminae features. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 Proposed Depositional Setting Several lines o f evidence suggest that the Robertson Formation was deposited in a shallow-water, nearshore environment. Taphonomically, the shell beds consist of highly abraded and broken shells with rounded edges. In the shell beds of Cow Creek, the sizes of the individuals show little variation, and are found parallel to the bedding plane with their long axes aligned. These observations suggest significant wave energy and abrasion. However, some fossils exhibit the “butterfly” style of preservation (Figure 22C, Ceratomya). Aberhan (1994) described the “butterflying” of bivalves as indicative of post-mortem exposure without significant transport, leaving the valves still articulated but most often convex down on the substrate. Sedimentologically, the presence of coarse-grained clastic rocks and the “clean” texture of the sandstones indicate a high-energy environment (Dickinson and Vigrass, 1965). Biotically, many of the accessory epifaunal bivalves (Weyla, Camptonectes, Parallelodon, Modiolus) have robust shells acting as anchors or may have been byssally attached to the substrate. Encrusters and boring fauna are visible in thin section at the Cow Creek facies. These three lines of evidence suggest that the Robertson Formation was a high-energy environment, nearshore, with significant wave or current agitation of the deposits mixed with some areas of quiet deposition. In complete sections, the nearshore Robertson and Suplee Formations are succeeded by the deeper water Nicely Formation (Dickinson and Vigrass, 1965). This sequence may reflect the rapid rise in sea level observed in Tethyan Lower Jurassic deposits, or subsidence that occurred at a rate greater or equal to the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 sedimentation rate. The basal conglomerate is thickest in the eastern sites (Swamp Creek and Robertson Ridge) and is not present or very thin in the western sites (Jackass Ranch and Cow Creek). The lenticular nature of many of the Robertson beds and the wedge-shaped cross section of the formation over the entire area are typical of sedimentation styles in a transgressive systems tract (Walker and Flint 1992). Thompson Formation, Mt. Jura, California The Lias is poorly exposed in California. Outcrops are separated by faults and difficult to correlate to each other due to the tectonic overprint that alters most index fossils such as ammonites. Part of the section in the Mount Jura region of Plumas County was recognized as Liassic by Diller (1892). The Thompson Formation is exposed in a narrow band across the western slopes of Mt. Jura near Taylorsville, California (Crickmay, 1933) (Figure 27). The Thompson Formation is part of the Mt. Jura sequence that has been described as part of the Sailor Canyon- Gardnerville Basin Complex (SCGB; Davis and Schweikert, 1995). The SCGB Complex extends from Butt Lake and Burnside Lake in Calfornia to the Wassuk Range in Nevada. Basin fill consists of volcaniclastic sedimentary rocks with minor quartzite, limestone, lava flows and tuffs. The Thompson Formation named by Diller (1892), is a purplish-red stratified marine volcanic sandstone and conglomerate with 5% gray limestone, approximately 10-32 m thick (Steams, 1962). Underlying the Thompson is the Fant Meta-andesite, a porphyritic volcanic flow and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 Figure 27. Poker Ridge locality. A - Map. The extent of the Thompson Formation is outlined and infilled with gray (Steams, 1962). B - Photograph of the Poker Ridge outcrop visible from Beardsley Grade (USFS 27N10), north of Foreman Ravine off of Plumas County Road 112. map area Beardsley Grade California km 207 Taylorsville rm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 lesser tuff breccia (Harwood, 1993) (Figure 7). Overlying the Thompson Formation, the Mormon Sandstone, a fine-grained gray to yellow sandstone that grades laterally and vertically into conglomerate and shaly beds (Steams, 1962). The Sailor Canyon and Gardnerville Formation are time-equivalent basinal units to the nearshore Thompson and Mormon Formations (Harwood, 1993). The area is structurally very complex with numerous faults. The SCGB was a probable fore-arc basin between an eastern arc and a western subduction zone formed west of the Inyo Mountains transported north by the Mojave-Snow Lake Fault System (Davis and Schweikert, 1995). Poker Ridge The Poker Ridge locality was described by Batten and Taylor (1978) and Crickmay (1933) on the northwest side of Mt. Jura at about 1300 m elevation (SE 1/2, SW 1/4, sec. 24, T26N, R10W; 40°05.289’N; 120°48.002’W). On a north facing slope on the NW side of Mt. Jura, a small east-west trending outcrop of the Thompson Formation is located. From the closed logging road, a very steep talus slope leads to the base of the outcrop. The beds in the outcrop are overturned and dip to the SW at 30°. At the base of the outcrop, a yellow-colored sandstone unit was identified as the Mormon Sandstone by its brachiopod fauna (Crickmay, 1933) (Figure 28). Moving up the outcrop exposure is the Thompson Formation’s light gray limestone with pectenid bivalves, other unidentified bivalves and gastropods (Figure 29). Above a series of these limestones is the first Lithitois problematica Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 Figure 28. Stratigraphic column from the Poker Ridge locality. Column A - Taylorsville Quad, SE 1/2, SW 1/4, sec. 24, T26N, R10W located within the Taylorsville Quadrangle. Column is overturned in the field and represented here in original superposition. Column A Figure 29. Photograph of base of Poker Ridge limestone facies with examples of bivalve fauna. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 death assemblage bed overlain by a second death assemblage with a sandier matrix (Figure 30). The valves are disarticulated and not parallel to bedding and the breakage of the thick pedestal valve suggests significant energy transported the valves. The surrounding matrix is a pure calcareous mudstone in one bed, the upper bed is slightly sandier. In thin section, this matrix has an abundant variety of small foraminifera and algae as well as other thin-shelled bivalves that are also disarticulated and broken. Due to the tectonic overprint in the area, all of the fossils are recrystallized to a calcite spar. Directly overlying these Lithiotis death assemblages is a 20 cm thick bed comprised of only Nerinea gastropods and crinkle- texture suggestive of microbial laminations (Figure 31; N. Noffke, pers. comm., 2002). The gastropods are all aligned in the same direction. I propose that this is a transported death assemblage based on the density of the gastropods and their uniaxial direction. The remainder of the outcrop is dominated by a distinctive red sandstone with limestone lenses, other microbial-influenced features (Figure 32). The top of the outcrop is the purple-brown Fant Meta-andesite believed to be Hettangian in age (Harwood, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 1 Figure 30. Photograph of the Lithiotis death assemblage at Poker Ridge. A - hand sample B - thin section photograph of the same facies under cross polarized light, at 2.5x magnification, with a gastropod in the center. The scale bar is 1 mm long. S tM s S it Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 Figure 31. Poker Ridge Nerinea Bed A - hand sample B - thin section photograph of a gastropod under cross polarized light at 2.5x magnification. The length of the shell is approximately 5 mm. The scale bar is 1mm long. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 Figure 32. Thompson Formation: distinctive red sandstone with limestone lenses facies. Proposed Depositional Setting Unlike other outcrops of the lithiotid bioherms in Western North America, the Poker Ridge locality lacks significant siliciclastic input in the matrix. In the Thompson Formation, Poker Ridge is the only outrcrop reported to have Lithitois problematica or its junior synonym Plicatostylus gregarius (Batten and Taylor, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 1978). None of the shells at the site appear to be in situ and are broken by physical means. Based on these and other taphonomic observations, the site represents a nearshore environment with strong wave and current action. The Nerinea bed and overlying unit have a feature suggestive of microbially influenced laminae which are associated with other peritidal carbonate environments. Since all of the fossils appear to be transported and found in arrangements denser than corresponding life assemblages, it is unlikely that one can draw conclusions about paleoecology of Lithotis problematica from the Poker Ridge site. The formation indicates a deepening of units from the subaerially exposed Fant Meta-andesite through the peritidal carbonates to the nearshore sandstones, similar to the sea level trends noted at the other North American or Tethyan sites. The Lower Jurassic lava flows and volcaniclastics that cap the Thompson display evidence of subaerial exposure (Harwood, 1993). The depth of the Sailor Canyon- Gardnerville Basin System is poorly understood but believed to be dictated by tectonic activity, not global sea level trends (Davis and Schweikert, 1995). Sunrise and Dunlap Formation, Garfield Hills & Shoshone Range Nevada Fairly well-exposed marine Liassic units occur in a number of ranges in west- central Nevada. The successions in Nevada are intricately folded and faulted and can only be pieced together from discontinuous outcrops. The Lias of Nevada consists of two main formations, the Sunrise and Dunlap Formations, first described by Muller and Ferguson (1936) while studying the Mesozoic stratigraphy of the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 Tonopah and Hawthorne Quadrangles of Western Nevada (Figure 7). Other workers have shifted the boundary between the Sunrise and the Dunlap Formations in specific study areas based on lithofacies or faunal changes that are not necessarily correlated to each other (e.g. Silberling, 1959; Hallam, 1965; Taylor et al., 1983). The Mina Peak and Joker Peak Members of the Sunrise as defined by Taylor et al. (1983) include Pliensbachian fauna. However, Silberling (1959), working near lone in the Shoshone Range, included Sinemurian faunas in the Dunlap Formation. For the purposes o f this study, I will focus on members of both formations that have documented Pliensbachian and Toarcian faunas. The Dunlap Basin is interpreted as the down-thrown block of a half-graben basin, open to the sea on the north and northwest (Bartel, 1994). Coarse clastic material was derived mainly from the horst block to the southwest where the Mina Formation derived chert clasts were eroded and transported into the basin; chert-rich clastic units are common in the Sunrise and lower Dunlap sequences (Stanley, 1971). Sands entered the basin from the southeast or were funneled down the northwest trending axis of the basin. The lithofacies of the Sunrise and Dunlap vary greatly from the Garfield Hills to the Shoshone Range. Much of the Pliensbachian and Toarcian lithofacies consists of sandstone, commonly coarsely cross-bedded with locally thick conglomerates, that include volcaniclastics and tuffaceous sandstones, and beds of bioclastic limestone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 Laura Canyon, Garfield Hills The Garfield Hills locality was described by Muller and Ferguson (1939), “Plicatostylus Basin” in what they term the Dunlap Formation (center of Sec. 8, T7N, R33E, 38°29.725’N, 118°21.534’W; Silberling, pers. comm., 2001) (Figure 33). The principal areas of the Dunlap formation in the Garfield Hills lie within a broad belt bordering the southern margin of the Upper Triasic Luning Formation. In the Garfield Hills, the Dunlap is deposited uncomformably on an eroded surface of the Luning Formation (Figure 34, Laura Canyon Column). The calcareous facies Dunlap Formation is overlain by several hundred feet of volcaniclastic rocks. These are in turn overlain by the Excelsior Formation which has massive cherts interbedded with the volcaniclastic sandstones (Muller and Ferguson, 1939; Ponsler, 1977). The Dunlap Formation in the Garfield Hills Range south o f Mable Mountain is thinner, about 900 m, than at its the type section of the Pilot Mountains, which is over 1500 m thick. Ferguson and Muller (1949) proposed that the Dunlap here was deposited in a synclinal trough, but it is very difficult to match up individual beds since the lithofacies are variable. The Dunlap Formation is exposed in the narro Laura Canyon dipping 45° to the SE. Near the base of the Dunlap in the Garfield Hills are transported assemblages of Lithiotisproblematica (Figure 35). The Lithiotis valves are completely recrystallized to a white sparry calcite, while the surrounding matrix is a dark gray micritic limestone. In this area the Dunlap Formation is blue-gray to tan, with mixed siliciclastic and limestone facies. Limestone lenses are found interspersed with large Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 Figure 33. Laura Canyon outcrop. A - Map. The extent of the Dunlap Formation is outlined and infilled with gray (Muller and Ferguson, 1936). Position o f the stratigraphic column is denoted by the letter A and is depicted in detail in Figure 34. B - Photograph of the Laura Canyon outcrop. A. • Kincaid L uning N evada 2 -A. km Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 Figure 34. Dunlap Formation stratigraphic columns. Laura Canyon, Garfield Hills is located in the center of Section 8, T7N, R33E, 38°29.625 N, 118°21.534 W in the Garfield Hills quadrangle. Third Canyon, Shoshone Range starts in SE1/4 of Sec 20 and ends in SW1/4 of Sec. 21 of T1 IN, R39E. o o o o • <5. a ■ c s i . -J3 . 2 'ft- < 2 I:r.dbs3 E E E 3 F=F=Fa S 3 EEEEE3 E E E 3 L aura C anyon Third Canyon Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 Figure 35. Lithiotis problematica of Laura Canyon. A - Upper bed. B - Lower bed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 lenticular beds of angular bioclasts. These fossil-rich beds contain broken Lithiotis valves, gastropods, unidentified bivalves, brachiopods, echinoderm debris and foraminifera. Some of the sandier limestone facies are bioturbated, indicated by features similar to Thallasanoides. Chert-rich sandstones and conglomerates are found in younger units. Microbial features are found in the siltstone facies above the limestone facies. Third Canyon, Shoshone Range Lithiotis (its junior synonym Plicatostylus) was tentatively reported from the Shoshone Range of Nevada (Silberling, 1959). Exposures in the Shoshone Range were mapped by Silberling (1959). The Third Canyon sequence of the Dunlap Formation extends for approximately 160 meters starting in the SE1/4 o f Sec. 20 and ending in the SW1/4 o f Sec. 21 of T1 IN, R39E (Figure 36). Beds dip from 60-70° in the south, crossing the Third Canyon Thrust the beds are overturned dipping 80° to the north. Silberling’s (1959) “Unit J” o f the Dunlap Formation contains a sequence of conglomerate and sandstone lithologies with lenses of limestone, similar in age and lithology to the Dunlap Formation of the Garfield Hills (Figure 34B). While many of these limestones contain Pliensbachian-Toarcian fossils, examination and thin section work on samples collected from these lenses revealed large fragments of bivalve shells resembling Weyla and other pectinids rather than Lithiotis. The original identification o f these bivalves as Lithiotis was doubtful, it was reported as “Plicatostylus ? ’’(Silberling, 1959). Other reports of Lithiotis in the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 Figure 36. Third Canyon outcrop. A - Map. The extent of the Dunlap Formation is outlined and infilled with gray (Silberling, 1959). Position of the stratigraphic column is denoted by the letter A and depicted in detail in Figure 34. B - Photograph of the Third Canyon outcrop. A. !84T ferlin-Icthyosaur Sate Park Nevada jnap area 9 Union • GrantsviUe ird Canyon Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 Clan Alpine Mountains (Nauss and Smith, 1988), could not be substantiated also. However, I would suggest returning to the detailed sections of the Dunlap Formation in the Pilot Mountains by Bartel (1994). He has reports of large “pelecypods” in limestone units above large scale conglomerate units, that could possibly be Lithiotis. Proposed Depositional Setting Previous authors suggested a non-marine origin for most or all of the Dunlap Formation based on red color and large sequences of conglomerates and conglomerate sandstones (Muller and Ferguson, 1939; Nielsen, 1964; Wetterauer, 1977). Bartel (1994) suggested that the conglomerates were deposited in submarine environments. The red coloration o f the sediments may indicate either the sediments were oxidized during deposition or were derived from an oxidized sediment source. Mudcracks are also used as evidence of subaerial deposition (Nielsen, 1964), but unequivocal mud cracks were observed only at one locality in upper part of the Dunlap member in the Pilot Mountains. Many of the reported mudcrack horizons are not mudcracks associated with subaerial exposure but are structures related to sediment dewatering and/or shearing during loading (Bartel, 1994). Stanley (1971) reported grayish-orange laminated dolomite and dolomitic limestone units of probable intertidal or supratidal origin in the uppermost Sunrise Formation. I was unable to find these in the field. The presence of Thalassinoides- style burrows in the sandier limestone units indicates a marine environment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 While the evidence for subaerial exposure may remain equivocal, the limestone facies within the Dunlap is undoubtedly marine based on the fossils: Weyla sp., other bivalves, brachiopods and echinoderm debris. The Lithiotis problematica shell beds display signs of transportation, including broken disarticulated valves not in life position, as in the Thompson Formation. Calcare Grigi, Mt. Lessini, Italy The Calcare Grigi Formation is the most extensive Liassic carbonate succession among those deposited on the Trento Platform (Bossellini and Broglio Loriga, 1971). The Trento Platform is a structural high formed by Early Jurassic rifting, between the Belluna Trough on the east and the Lombardy Basin on the west. It is located in the northern paratropics near the westem-end of the Tethys. The Calcare Grigi, whose thickness exceeds 400-500 m in places, overlies the Dolomia Principale (Norian-Rhaetian), a succession of peritidal cycles (Bosellini and Hardie, 1985) (Figure 7). The Calcare Grigi Formation is in turn directly overlain by the Toarcian-Aalenian San Vigilio Group or by the Upper Baj ocian-Tithonian Ammonitici Rosso. The Calcare Grigi Formation is subdivided into four members: Lower, Middle, Rotzo and Massone Members (Bosellini and Broglio Loriga, 1971; Boomer et al., 2001). The Lower Member (around 100 m thick) comprises sub-, inter- and supratidal successions (Masetti et al., 1998), conformable with the underlying Dolomia Principale (Bosellini and Borlgio Loriga, 1971). Dinosaur tracks and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 traces, rare small benthic foraminifera, brachiopods, bivalves and gastropods and calcareous green dasyclad algae are present in this unit (Mietto and Roghi, 1993). The Middle Member is an ooidal limestone (30-200 m thick) and contains rare inverebrate fossils (small benthic foraminifera, porifera and pectinid bivalves). The Rotzo Member is about 35-250 m thick from east to west (Masetti et al., 1998), and mainly comprised of ooidal, peloidal, bioclastic and intraclastic limestones; marls and clays are also common with occasional lignites (sometimes referred to as “brown coals” a direct translation from Braunkohle from German geologic literature) which have been identified as shallow water black shales (Boomer et al., 2001). The “Lithiotis” faces bivalves are the most distinctive faunal assemblages. The overlying Massone Member (30-80 m thick) consists of oolitic limestones, locally rich in bioclasts and oncoids. The last occurrence of the “lithiotis'' bivalve facies is found is within the Massone unit. Ponte dell ’ Anguillara At Ponte dell’Anguillara the Rotzo Member of the Calcare Grigi is exposed at the northernmost turn of the road between Erbezzo and Bosco Chiesanuova (45°29.535’N, 11°01.029’E) (Figure 37). The outcrop has a long history and has been the source of many studies since Zigno (1856-1895 in Wesley, 1965). The lignite at the base of the outcrop has yielded an excellently preserved fossil fauna and flora (Figure 38 Column A). The lignite is dark brown to black in color due to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 Figure 37. Ponte dell’Anguillara outcrop. A - Map from Bosco Chiesanuova Map, Foglio 49, IV no. 1. The extent of the Calcari Grigi is outlined and infilled with gray (Zampieri et al., 1993). B - Photograph of the Ponte dell’Anguillara outcrop. Ponte dell \n-_iiiILu B. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 Figure 38. Calcari Grigi stratigraphic columns (Ponte dell’Anguillara, Bellori and Garzon di Sotto). C giBglS&ji. /T fqgSBBfc. V© ( S ^ ~< £ Q Q ) ^0 © o o 0 3 | | 3 O 0 3 U C O 3 f e f i = < E ? 'o U < D T 3 8 B O a . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. large amounts of phytoclast material but is also rich in calcium carbonate, hence it’s designation as a shallow water black shale (Bassi et al, 1999). Lithioperna, Mytiloperna and Gervilleioperna are common in this unit; however, Lithioperna is the only bivalve that appears to be in place. Eomiodon, Astarte, Cytherea and Myrene are “accessory” bivalves in the lignite facies (Posenato, pers. comm., 2000). The remainder of the unit consists of small sized disarticulated shells and shell fragments and plant remains (roots, cuticles and spores) often encrusted with pyrite (Figure 39). Millimeter-scale scale bioturbation is seen also in thin section (Figure 40). Thin sections reveal numerous ostracod carapaces (Figure 41A). The overlying units are a series of limestones and marls which consist mainly of disarticulated bivalves and brachiopods; with subordinate small gastropod and crinoid fragments. In thin section, many of these units are dominated by peloids, bioclasts and micritic intraclasts (Figure 4 IB). Due to the rare occurrence of ammonites, the bio stratigraphy of the Calcare Grigi is based on the large benthic foraminifera and algae that were first described in detail by Septfontaine (1986) for the Moroccan Central High Atlas, discussed later. According to a recent revision of the foraminiferal associations of the Rotzo Member, three biozones are recognized: the older Orbitopsella praecursor zone, the middle Lituosepta compressa zone and the younger Paleodasycladus mediterraneous zone (Fugagnoli and Broglio Loriga, 1996). All of these are observed in succession at Ponte dell’Anguillara (Figure 42). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 Figure 39. Close-up of the Ponte dell’Anguillara lignite facies (shallow water black shale) and wood fragment. Figure 40. Ponte dell’Anguillara thin section of micritic microfacies with very small burrows (approximately 1 mm wide burrows). Photograph was taken at 2.5x magnification under plane polarized light, field of view is 5 mm. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 Figure 41. Ponte dell’Anguillara microfacies. A. Thin section of ostracod in a micritic matrix (width of shell is about .5 mm) B. Peloidal facies with diverse microfauna: foraminifera, echinoderm spine, gastropods, algae (field of view is 5 mm). Both photographs were taken at 2.5x magnification under plane polarized light. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 Figure 42. Thin section of Ponte Dell’Anguillara microfauna: A. Orbitopsella praecursor, (5x magnification), B. Lituosepta compressa about 1 mm high (5x magnification), C. Palaeodasycladus mediterraneus, (2.5x magnfication). All images photographed under plane polarized light, scale bars are 1 mm long. s. A > * Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 Bellori, Mt. Lessini, Italy By the side of a stream near a string of houses in the village of Bellori (45°35.360’N, 10°59.298’E), a 55 m long outcrop exposes the Massone Member of the Calcare Grigi (Figure 43). The base of the streambed is a marl and in the upper reaches of the streambed are beds of in situ Lithoitis problematica (Figures 38 Column B and 44A). Above this bioherm unit an oolitic limestone that lacks fossils is overlain by a silty limestone with small bivalve shells that are disarticulated. A thin shell bed of Lithiotis hash is in turn overlain by a silty limestone with large Thallassinoides. In thin section, this silty limestone contains crinoids, chaetitids, green algae and foraminifera (v. Fugagnoli and Broglio Loriga, 1996 for photomicrographs). A series of massive shell beds dominated by Lithoperna scutata, in the recliner morphology (described in the following chapter) are observed in the upper portion of the section. These beds are similar to the most common “Lithiotis” facies beds seen in the Calcare Grigi: densely packed beds o f large, reclining, articulated Lithioperna (Figure 44B). Above this unit is a large Lithiotis biohermal unit approximately 10 m thick. However, tracing out individual bioherm horizons, the vertical extent of these bioherms is only 1-1.5 m. In between the bioherms are occasional incursions of an oolitic facies followed by reestablishment of bioherm construction. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 Figure 43. Bellori outcrop. A - Map from Bosco Chiesanuova Map, Foglio 4 9 IV, No. 1. The extent of the Calcari Grigi is outlined and infilled with gray (Zampieri et al., 1993). B - Photograph of the Bellori outcrop from across the streambed. A. Corbiolo tp area Italy Cerro Veronese Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 Figure 44. Bellori bivalve assemblage. A - Close up of stream bed with outcrop of Lithiotis problematica. B - Lithioperna recliners in upper section. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 Garzon di Sotto, Mt. Lessini, Italy In a dense pine forest, a small outcrop of the Rotzo Member of the Calcare Grigi is found near the village Garzon di Sotto (Selva di Pregno, Foglio 49, IV, No. 11, 45°35.118’N, 11°08.141’E) (Figure 45). The outcrop is only 7.5 mhigh and about 10 m wide (Figure 38, Column C). At the base of the outcrop is a lignite facies similar to that found at Ponte dell’Anguillara, however the fossils are a well- preserved death assemblage of Lithiotis problematica and brachiopods (.Lychnothyrisl). A silty limestone above the lignite unit is a silty limestone, lacks macrofossils but contains Orbitopsellapraecursor (Figure 46A). Thin marls alternate with the silty limestone, followed by a thin limestone bed with several thin- shelled bivalves, Paleodasycladus mediterraneus, small foraminifera and echinoderm plates. At the top of the outcrop is an oolitic limestone, with pellets and intraclasts. Microfossils in this unit are extremely rare and only one miliolid foraminiferan was found (Figure 46B). Proposed Depositional Setting The Rotzo and Massone Members of the Calcare Grigi have been interpreted as a lagoonal environment (Rotzo), protected towards the open sea by oolitic bars and shoals forming barrier island complexes at the margins of the Trento Platform (Massone; Bosselini and Broglio Loriga, 1971; Masetti et al., 1998). Recently the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 Figure 45. Garzon di Sotto outcrop. A - Map from Selva di Pregno, Foglio 9 IV, No. 11. The extent of the Calcari Grigi is outlined and infilled with gray (Zampieri et al., 1993). B - Photograph of the Garzon di Sotto outcrop. Garzon di Sotto Velo Veronese Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 Figure 46. Microfossils of Garzon di Sotto. A - Orbitopsella praecursor (approximately 1.5 mm across). B - Miliolid foram (approximately 1mm across). Both thin sections were photographed at 5x magnification under cross-polarized Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 Rotzo Member has been interpreted as a “ramp-lagoon” environment, protected towards the west by a distal littoral complex (Monte Baldo area) represented by the Massone Member (Masetti et al., 1998). With the exception of the Lithiotis beds at Bellori, all of the other limestone facies studied in the Calcare Grigi appear to have been transported. The shell accumulations occur with most shells convex upward; but some specimens occur in convex-up “butterfly” preservation. The Lithiotis death assemblage at Garzon di Sotto is associated with open marine fauna: brachiopods, crinoids and the macroforaminifera Orbitopsella praecursor (Posenato et a l, 2000). The shallow water black shales of Ponte dell’Anguillara have been interpreted as a “parautochthonous deposit” (Bassi et al., 1999). No shells show evidence of boring or encrustation; signs of abrasion are rare and broken shells usually exhibit sharp edges. Large variations in size among individuals, good preservation and occasional convex-down patterns of shell orientations, also point to short post-mortem transport. Weakly corroded and thinned aragonitic shells in the shallow water black shales are common. Some of the accessory bivalves are very thin, the outermost surfaces are corroded. The accessory bivalves, Eomiodon and Myrene, are also thought to have been restricted to mesohaline (5-18% o) or brachyhaline environments (18-30%o; Fursich, 1993; Aberhan, 1994). These taphonomic and paleoecologic attributes indicate that the Ponte dell’Anguillara lignite deposits formed in low-energy conditions in a nearshore, brackish, organic- rich facies with significant terrestrial input. Unlike most lignites, the lignites or “brown coals” of the Calcare Grigi are calcareous (Bassi et al., 1999). This is similar Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 to mangrove peats in the Florida Keys or the South Caost of Puerto Rico, where mud available is entirely carbonate (Fischer, pers. comm., 2002). Macrofossils are very abundant and are represented by brachiopods, bivalves, gastropods, echinoids, corals and crinoid fragments (Broglio Loriga and Neri, 1976). Overlying the Calcare Grigi is the Ammonitico Rosso, a deeper marine environment. Zempolich (1993) suggested that the flooding of the Trento Platform and disaggregation was related to the rapid sea level rise and rifting of Pangea, respectively. Liassic Carbonate Platform Facies, Central High Atlas Mountains, Morocco The Central and Eastern High Atlas Mountains are composed almost wholly of Jurassic limestones, marls and shales. Within the mountains, there is one of the few complete, well-exposed and structurally simple stratigraphic sequences of Lower Jurassic carbonate platforms. The rocks of this sequence form a part of the sedimentary fill of a rift zone that developed during the initial breakup of Pangaea (Dewey et al., 1973). Middle Sinemurian deposits are the initial marine deposits in the Atlas; they overlie Upper Triassic continental red beds (marls and fine-grained sandstones and interbedded flood basalts) (Figure 7). Flooding of the rifting trough by waters from the Tethys initiated an episode of Liassic carbonate sedimentation (Warme, 1988). By the late Toarcian, shallow water micrites and marls became capped by a distinctive shallow-water reef facies of early Bajocian age (Septfontaine, 1986). The carbonate sedimentation within the basin continued until the late Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 Bajocian or early Bathonian when the open marine waters terminated (Lee and Burgess, 1978). During Pliensbachian and early Toarcian times, the middle of the basin was occupied by a topographic high where sponges, algae and problematic framebuilding and baffling organisms formed builidups and the preponderance of coated grains and algae are distinctive (Burgess and Lee, 1978). The perimeter of the basin was characterized by of buildups constructed by “Lithiotis” facies bivalves, scleractinian corals and spongiomorphs (Warme, 1988). The foraminiferal successions of the Lower Jurassic of Morocco in the High and Middle Atlas have been described in detail by Septfontaine (1984 and 1986). In his biostratigraphic arrangment the author defines six biozones which are supported by his taxonomic and phylogenetic revision o f the Orbitopsellids and which have been correlated to ammonites and brachiopods from basinal equivalents. Septfontaine’s (1984) exhaustive study helps identify facies on the platform and has been calibrated to Southern Tethyan margin sites including Spain, Trento Platform, Apennines, Slovenia and the Middle East. Assemsouk A well-exposed, large reef structure is found on the north flank of Jebel Azourki (30°43.002’N, 9°04.002’W), approximately 35 km to the east of the town of Ait Mohammed on the road to Zaoui Ahansal (Figure 47) (Lee, 1983). The overall structure is 90 m high and 1250 m in length, and runs east-west parallel to the road. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 Figure 47. Assemsouk buildup outcrop. A - Map. Buildups believed to be in life position are outlined. B - Photograph o f the Assemsouk buildup from the north flank of Jebel Azourki. Morocco Quaouisarhte Azilal Ait Mohammed 'Z a u o o i Ahansal Assemsouk Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 It consists of massive beds of pure limestone with four distinct biotic successions: basal Opisoma facies, coral-algal bivalve facies, spongiomorph-coral facies and a Cochlearites climax (Figures 48 and 49) (Lee, 1983; Copper, 1994). The underlying formation is not visible but the base of the structure starts from a small bioherm of Opisoma in growth position, which to the west grades into a pure limestone with few bivalves and a rich gastropod fauna, to the east it disappears into thinly bedded black shales, with intermittent limestone rich beds with normal bedding (Figure 50, Columns B and C). Above the colonizing Opisoma bioherm, the second bed is dominated by branching and encrusting corals, spongiomorphs, gastropods and a thick-shelled heterodont bivalve similar to Durga described from other Moroccan localities (v. Agard and du Dresnay, 1965). The western portion of the bed shows a rich fauna of high-spired gastropods (Figure 50, Column A). When traced further to the west, these beds grade into cross- and parallel-bedded, quartz- rich limestones with some ooids. The eastern portion of the buildup, terminates abruptly with some brecciated blocks appearing (Figure 50, Column C). The third bed is dominated by large, thin-valved, reclining Lithioperna, and branching and encrusting corals forming small patch reefs (Figure 48C). The western area of the reef has more Lithioperna shells, some Gervilleioperna sp. and oncoliths. The final stage is tightly packed beds of Cochlearites loppianus in life position, the bioherm is approximately 2-7 m tall, but it is difficult to discern if this reef stage had significant relief off o f the seafloor (Figure 49). In thin section the Cochlearites beds show acicular synsedimetary cements (Lee, 1983). The individual Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 Figure 48. Facies and fossils of Assemsouk, Central High Atlas, Morocco. A - Opisoma, a bivalve. B - unidentified spongiomorph, C - Lower coral-algal-bivalve facies. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 It consists of massive beds of pure limestone with four distinct biotic successions: basal Opisoma facies, coral-algal bivalve facies, spongiomorph-coral facies and a Cochlearites climax (Figures 48 and 49) (Lee, 1983; Copper, 1994). The underlying formation is not visible but the base of the structure starts from a small bioherm of Opisoma in growth position, which to the west grades into a pure limestone with few bivalves and a rich gastropod fauna, to the east it disappears into thinly bedded black shales, with intermittent limestone rich beds with normal bedding (Figure 50, Columns B and C). Above the colonizing Opisoma bioherm, the second bed is dominated by branching and encrusting corals, spongiomorphs, gastropods and a thick-shelled heterodont bivalve similar to Durga described from other Moroccan localities (v. Agard and du Dresnay, 1965). The western portion of the bed shows a rich fauna of high-spired gastropods (Figure 50, Column A). When traced further to the west, these beds grade into cross- and parallel-bedded, quartz- rich limestones with some ooids. The eastern portion of the buildup, terminates abruptly with some brecciated blocks appearing (Figure 50, Column C). The third bed is dominated by large, thin-valved, reclining Lithioperna, and branching and encrusting corals forming small patch reefs (Figure 48C). The western area of the reef has more Lithioperna shells, some Gervilleioperna sp. and oncoliths. The final stage is tightly packed beds of Cochlearites loppianus in life position, the bioherm is approximately 2-7 m tall, but it is difficult to discern if this reef stage had significant relief off of the seafloor (Figure 49). In thin section the Cochlearites beds show acicular synsedimetary cements (Lee, 1983). The individual Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 Figure 50. Stratigraphic columns of Assemsouk reef. Column A is the western side of the outcrop. Column B center of outcrop and Column C is the eastern side of the outcrop. 6 0 5 0 4 0 3 0 20 10 C ' T . O ~ i i r eW Ep ~ r ........ e :i o 3 i lor E..P . 1 ° . pT'V'fT'" I I p 1 A I . ...I ° j _ l i p I lQ > ...to t - t - t 0 1 T o T I i° ' i i° o i I o j m & r W □ B e r " i'"t i" i° I i° i i° W S . s> STa'a' • ^ < 3 ’ < ? < > 4 < P ■ ■ £ > . C W Column A Column B Column C Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 beds exhibit lower, sharp, erosional contacts. The individual valves often are eroded but do not show evidence of significant transport. The entire sequence is overlain by black to dark-green fissile shales. Ait Athmane The Ait Athmane site was described by Crevello (1988) and is located in Oued Ziz (31°55.914’N, 4°25.464’W) between the cities of Rich and Er Rachiddia (Figure 51). The underlying formations are Upper Triassic red beds with gypsum followed by red shales of Hettangian or Sinemurian age (Crevello, 1988). The overlying sediments are fissile Toarcian red and green shales with Toarcian ammonites and brachiopods. The first stratigraphic column (Figure 52, Column A) was measured on a platform just to the east of Provincial Route 21. The section is dominated by thick- to massive-bedded limestones with bioclasts of Opisoma, Gervilleioperna and Mytiloperna that appear to be transported and not in life position (Figure 53). Contacts between the beds are well-defined. Oncoid and ooid lime sands occur interbedded and mixed with the bioclasts. The second stratigraphic column (Figure 52, Column B) contains teepee- bedded structures and a diverse transported fossil assemblage of Lithioperna, oncoids, foraminifera (Orbitopsella and Lituosepta) and algae. These units are capped by limestones with fenestral features. Typically, the bioclasts are coated and reworked in the coarse-grained teepee sediments. The third sratigraphic column lacks the teepee structures and most of the bioclasts lack the coating seen at the previous sites but has mudcracks and fenestrae. The lower 8-14 m of the section has Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 Figure 51. Ait Athmane outcrops. A - Map. Position of the stratigraphic columns are denoted by letters and are depicted in detail in Figure 52. B - Photograph of the Ait Athmane outcrop visible from the road, the section is depicted in stratigraphic Column A. A. Kerrandou map area iorocco km Ait Athmane Er Raehidia Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 Figure 52. Stratigraphic columns of Ait Athmane area. $ ' o o o I I M e* $ I S i © o o < N o o c < • > <K $ < g C) ” <9 ~ = 30 6 § > J '’ S i 9 J (j2i ~ < £ > Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Column A Column B Column C Column D 98 Figure 53. Photographs of Mytiloperna sp. at Ait Athmane Column A. very large, thin-valved Lithioperna specimens that appear to be in situ. At the top of the section an extensive coral-algal-bivalve facies similar to Assemsouk is seen (Figure 54). The final stratigraphic column contains thin beds of mud-rich dolomites and marly dolomites (Figure 52, Column D). Characteristic sedimentary features include burrows, stromatolites, fenestrae, mudcracks, ripples and cross- and parallel bedding (Figure 55). An evaporite breccia occurs in the middle of the section (Figure 56) (A. G. Fischer, pers. comm., 2001). Gervilleiopema and Lithioperna are found below and above the evaporite breccia. In the upper portion of the section, bioclast rich limestones occur and these are interbedded with peloidal limestones reminiscent of Ponte dell’Anguillara site. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 Figure 54. Coral-algal-bivalve facies at Ait Athmane Column C. Figure 55. Burrows at Ait Athmane Column D. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 Figure 56. Evaporite breccia of Ait Athmane Column D. 1 b O T Proposed depositional setting Both the Ait Athmane and the Assemsouk sections represent high-energy nearshore environments on a carbonate platform. The Ait Athmane sections represent a sequence from outer margin, shoal, inner platform and restricted lagoon Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 with repeated emergence as indicated by the fenestrae, mudcracks and evaporite breccia (Crevello, 1988). Very large teepee structures, 2 m wide, are reported from a nearby locality, Jebel bou Dahar (Burri et al., 1973). The Assemsouk section represents a very shallow subtidal to low intertidal reef system that was within the photic zone and high energy. The western portion of the reef is similar to the back-reef or reef lagoon facies. It has a more restricted fauna, oncoliths, higher terrestrial input (the quartz grains), small scale, cross-bedded features and intermittent hardgrounds indicative of a sublittoral environment. The reef core changed significantly over the history of reef development from the colonizing community of Opisoma to the climax community of Cochlearites. However, from the acicular synsedimentary cements surrounding the reef fauna, it appears that the reef was subtidal with rare exposures during high tide. The eastern flank beds are interpreted as the reef front, with reef blocks falling off of the reef face (the brecciated facies) or limestone turbidites into a deeper water environment (the black shales). Lee (1983) interpreted the reef as having developed at the shelf edge/basin boundary with the platform carbonates to the west and the more open marine conditions to the east. Most Liassic sections in Morocco contain a Toarcian event that is typified by deeper water micrites and marls overlying Pliensbachian or Early Toarcian carbonate rocks. The Moroccan Toarcian sections have not been tied in to the Early Toarcian event beds found in other areas but could be explored as a possible link in further studies. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 CHAPTER 3: MORPHOLOGY, PROPOSED LIFE HABITS AND PHYLOGENY OF “LITHIOTIS” FACIES BIVALVES Introduction The “Lithiotis” facies bivalves include: Lithiotis problematica, Cochlearites loppianus, Gervilleioperna sp., Mytiloperna sp. and Lithioperna scutata (Broglio Loriga and Neri, 1976). These bivalves are common in low-latitude Tethyan deposits of the Pliensbachian and Early Toarcian (Geyer, 1977). However, the term “Lithiotis” has been haphazardly applied to many of these buildups without close examination. All five of the “Lithiotis” facies bivalves are typified by aberrant large morphologies with thick (20-30 mm) and high shells (up to 700 mm in some individuals) (Figure 4). Previous studies assigned the “Lithiotis” facies bivalves to restricted nearshore environments of rapidly fluctuating salinity and temperature, based on the morphological similarity of several of these bivalves to modern oysters. One of the purposes of this chapter is to elucidate the morphological differences between “Lithiotis” facies bivalves and oysters and the variety of morphologies and life habits. Methods and Materials Over 500 individual specimens of “Lithiotis” facies bivalves were collected from study sites or observed in museum collections (University of Tubingen, Natural History Museum of Verona and the Geological Institute of the University of Ferrara). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 General information about the hinge, ligament, valve shape and shell microstructure were collected from individual specimens as well as the literature when specimens were not well-preserved. For all of the “Lithiotis” facies individual specimens, five morphological measurements were examined when visible: the length (mm) and thickness (mm), number of ligamental grooves, and exterior concentric band height (mm/period). The angle of incidence to the furrowed plate was measured for Lithiotis and Cochlearites, while the angle of obliquity was measured for Lithioperna, Mytiloperna and Gervilleioperna sp. (e. g. Figure 57). Following standard bivalve conventions, the length of the shell is the distance between two planes perpendicular to the hinge axis and just touching the anterior and posterior extremities of the shell. Height is the greatest dimension perpendicular to length. The measurement of width usually requires both valves intact. Only rarely were both valves preserved, therefore thickness was used, referring to the distance between two parallel planes, one parallel to the commissural plane, the second tangent to the exterior of the valve. The angle of incidence of the growth bands to the furrowed plate is the angle between the central growth axis of the pedestal valve and the line tangent to the angle to the central axis of the exterior concentric band. The obliquity angle is the angle between the hinge and the line tangent to the beak and the more anterior point of the anterior margin, these measurements roughly approximate the terms acline (80-90°) to prosocline (less than 80°; Arkell, 1933). The uppermost complete exterior concentric band preserved was used for measurement. Only in a few of the specimens was height of specimens recorded Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 Figure 57. Schematic of Lithiotis problematica (interior of pedestal valve) with morphological terms and measurements. adductor muscle scar" adapterual [ length umbonal s pedestal valve opercular valve feathered region ligament grooves c r O Q. * < O 0 ) < I thickness I — d width of ligamental area height of exterior bands angle of incidence adapical 10 cm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 because of the rarity of complete specimens. Morphological descriptions are summarized in Table 2. Phenotypic variability was assessed by plotting the various lengths to thickness ratios, histograms of lengths and observations of reoccurring forms. The various life habits of the five “Lithiotis” facies bivalves were assessed by field observations of various morphotype orientation of in situ specimens, relationship to the substrate from slabbed blocks, and orientation to paleocurrent of clustering morphotypes (Lithiotis, Cochlearites and Lithioperna). To test for orientation to paleocurrent, the orientation of valves was recorded from well-exposed bedding planes or sawed large buildup blocks containing gregarious assemblages of Lithioperna, Lithiotis or Cochlearites. The orientation of the valves was recorded on a scale of 0-180° with a compass, since it was difficult to determine which valve is right or left in bedding planes. These orientation values were analyzed for significance when compared to an established paleocurrent value by a modified Rayleigh test (Durand and Greenwood, 1958). The established paleocurrent value was obtained through orientations of ripple marks or valves in contiguous death assemblages. Using this test, a V ’ value more than 1.645 at the 95% confidence level is needed to reject alignment with a preferred orientation. Using all of the above descriptions of “Lithiotis” facies bivalves, the chapter closes with a suggested phylogenetic placement of the various “Lithiotis” facies bivalves. The phylogenetic placement was assessed by comparison of key Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 Table 2. Summary o f morphological characteristics o f “Lithiotis ’ ’facies bivalves Characteristic Lithiotis problem atica Cochlearites loppianus G ervilleiopema sp. M ytilopem a sp. Lithioperna scutata Valve Shape stick-shaped, strongly stick-shaped, discordant valves (pedestal valve 10-25 mm thick, opercular valve 1 -2mm thick), elongated dorso- ventrally discordant valves (pedestal valve 10-38 mm thick, opercular valve 5-20 mm thick), elongated dor so- ventrally subequivalve and Myaliniform to subequivalve to subrectangular shape, mytiliform, equivaived inequivalve, asymmetrical, slightly discordant valves (thickness 20-35 mm) to slightly subequivalved, thick valves (15-40 mm) subrectangular (valves 10-30 mm thick) Size 30-75 mm long, 200- 350 mm high 55-118 mm long, 200- 500 mm high 35-75 mm long, 30-60 mm high 70-80 mm long, 85- 100 mm high 190-250 cm long, 250- 300 mm high Hinge structure edentulous; hinge plate on central pedestal valve, not articulated at maturity edentulous; modified hinge plate on pedestal valve, spur and groove structure ligamental area teeth present in smaller (juvenille?) specimens, but not found in larger specimens teeth are found above ligamental area in adult specimens teeth present in few specimens Ligament multivincular single ligmaental groove multivincular variant of multivincular, multivincular, fewer opisthodetic grooves widely spaced # o f ligaments 25-30 7-10 7-10 (maybe 16) 7-16 Shell microstructure 1) outer layer - prismatic calcite 2) middle layers - alternating irregular prisms with lenticular nacre 3) inner layer-altered to brown, compact calcite 1) outer layer - prismatic calcite 2) middle layers - alternating irregular prisms with lenticular nacre 3) inner layer-altered to brown, compact calcite 1) outer layer- prismatic calcite 2) middle layer - nacre 3) inner layer-fibrous prismatic aragonite 1) outer layer - prismatic calcite 2) inner layer-fibrous aragonite prisms 1) outer layer - prismatic calcite 2) inner layers - alternating irregular prisms with lenticular nacre Exterior ornamentation exterior well-defined sheet-like appearance rare concentrically growth rugae in periodic increments arranged features fine, small scale undulations Morphotype stick-shaped mudsticker A) Mt. Lessini - thin broad pedestal valve B) Oregon - thick stick-shaped mudsticker A) Mt. Lessini - thin narrow pedestal valve B) Assemsouk - thick narrow pedestal valve broad pedestal valve pleurothetic cup shaped recliner A) orthotethic to pleurothetic epifaunal recliner B) ortbothetic epifaunal recliner C) orththetic semi- infaunal recliner A) orthothetic mudsticker B) pleurothetic recliner (thick -cup shaped heavyweight recliner, thin - snowshoe recliner) radiated not alligned to radiated not alligned to solitary Growth Habit current current radiated aligned to current solitary Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 morphological features with an emphasis on shell microstructure. The five “Lithiotis” facies bivalves are compared to the several orders of eulamellibranch bivalves including Ostreidae and Pterioidae including the pterioid families Isognomidae and Bakevellidae, resulting in 23 taxa. Phylogenetic patterns were determined by parsimony analysis of 77 binary character states Waller (1998) and other sources (Appendix A). These data were subjected to a constrained “branch and bound” search using PAUP 4.0 (Swofford, 1998) with a stepwise addition sequence with 100 random replications, ACCTRAN setting and the TBR option. The constrained search was conducted with the “Lithiotis” facies bivalves within the Pterioida using the Ostreioida as an outgroup Lithiotis problematica Giimbel, 1871 Subclass Pteriomorpha Beurlen, 1944 Order Pterioida Newell, 1965 ?Suborder Lithiotina Accorsi Benini & Broglio Loriga, 1977 ?Superfamily Lithiotacea Accorsi Benini & Broglio Loriga, 1977 ?Family Lithiotidae Reis, 1903 Genus Lithiotis Giimbel, 1871 Originally described by Giimbel (1871) as a calcareous algae, Lithiotis problematica is an unusual bivalve that has been the source of many studies for the past two centuries. Giimbel (1890) revised his assessment of Lithiotis as an alga and named it Ostrea problematica. Lithiotis problematica is notable for its initial Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 8 appearance in the Pliensbachian and rapid rise to dominance in nearshore low- latitude ecosystems and abrupt extinction at the end of the Toarcian (Broglio Loriga and Neri, 1976; Figure 58). Independent of the European workers, Lupher and Packard (1930) described Plicatostylus gregarius which Broglio Loriga and Neri (1976) and Accorsi Benini and Broglio Loriga (1977) determined to be the junior synonym of Lithiotis problematica. Some of the literature from Western North America in the intervening years uses the junior synonym (e.g. Batten and Taylor, 1978). Lithiotis problematica populated the extensive and interconnected shallow marine areas of the western and southern margins of the Tethys and the Eastern Pacific. Because of the confusion of Lithiotis problematica and “Lithiotis” facies bivalves, many of the localities are uncertain and may not refer specifically to Lithiotis but other lithiotid bivalves. Various authors have reported this species in southern Spain, western France, northern Italy, the south-central Apennines, Croatia, Slovenia, Herzegovina, Montenegro, Greece, Morocco, Tibet, Indonesia (Timor), United States (Oregon, Nevada, California), Chile and Peru (Rey et al., 1990; Broglio Loriga and Neri, 1976; Accorsi Benini and Broglio Loriga, 1977; Geyer, 1977, Nauss and Smith, 1988; Buser and Debeljak, 1996; Figure 58). Unconfirmed reports of “Lithiotis” include Albania, Turkey, Somalia, Oman, Iran and Iraq (Broglio Loriga and Neri, 1976; Buser and Debeljak, 1996; C. Lee, pers. comm., 2001). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. / • / Lithiotis problemdtic a I *(_ Cochlekrites loppianus Lithioperna scutata Mytilop^rna sp. 1 i # Genhlleioperna sp. $ '1 s.'-: i * ■ ■ ■ / . T y ■ ■ s ' 1 1 V -' f i f % T .....~ T .... < $ > r —.— .......j- - -X! T 'f v i ..........- V - 4 ..- W - : ....S .. / ... i/ .y * ’ 1 ' " ' / V T V " * " / / rpF A % - \ - Figure 58. Distribution of the ‘ ' ‘ Lithiotis’ ’' ' facies bivalves. Base map of the Early Jurassic from Schettino and Scotese (2001). o 1 1 0 Materials Over 400 individual specimens of Lithiotis problematica, mainly shell fragments several centimeters high with clearly recognizable characteristics were used in this study. Three hundred thirty-three individual specimens from the Suplee- Izee area were used. Seventy-eight specimens were used from the Monte Lessini site, Garzon di Sotto. Forty-five specimens from the museum collections of University of Tubingen and the Natural History Museum of Verona, collected from the same Monte Lessini sites, were also used. Very rarely was a complete specimen of Lithiotis collected, in only six specimens was the apex observed. Only the pedestal valves were used in the analyses as the opercular valve was only visible in thin-section or peels. Description Morphology Lithiotis problematica has been called “ribbon-shaped” by several workers as it is elongated dorso-ventrally, usually 200-350 mm high, although some specimens are reported to be as high as 500 mm (Debeljak and Buser, 1997). While both valves are of similar height, one valve is much thicker (20-25 mm) than the other (1-2 mm), a condition that has been termed discordancy (Newell and Merchant, 1939) (Figure 57). This valve, variously regarded as the left or right in the literature (e.g. Accorsi Benini and Brogli Loriga, 1977 v. s. Chinzei, 1982 and Seilacher, 1984), is massive Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I l l and houses a short, obliquely conical body cavity at its ventral or adapterual margin. The apex is pointed. Because these organisms are so grossly elongated the terms dorsal and ventral are of little utility and for further discussion the terms adapterual (for ventral) and adapical (for dorsal) are used. This valve is referred to as the “pedestal” valve and its opposite as the “opercular” valve. The commonly-preserved pedestal valve was often cemented to solid objects in its early stages. The pedestal valve often has a curved habit referred to as a “bent knee” by Debeljak and Buser (1997). In some closely-packed Lithiotis bioherms the pedestal valve is contorted or twisted. The outer surface of the pedestal valve has regular undulations that could be analogous to growth bands, another superficial similarity to oysters. Only in very well preserved specimens can these concentric bands be seen. The morphological measurements of the Lithiotis pedestal valve are summarized in Table 3. The central area of the interior of the pedestal valve consists of a series of ligament grooves numbering 20-35 grooves in most specimens. On either side of the ligamental area is a series of small fine lines referred to as the feathered region. These fine lines are arranged in bundles which are bordered by furrows which connect to the exterior concentric bands. The pedestal valve also contains a series of cavities that run roughly longitudinally, are elliptical and about 2-5 mm in diameter (Figure 57). These cavities, termed “umbonal cavity” by Chinzei (1982), do not connect with the body cavity and are presumably analogous to those in oysters ('Gryphaea and Exogyra) where the body advanced in steps and abandoned umbonal space. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 3. Summary o f the means o f morphological measurements o f Lithiotis problematica specimens, standard deviation is reported in parentheses. Region Site Length (mm) Thickness (mm) Height of growth band (mm) Angle of growth hand f°l a of ligaments Oregon Swamp Creek 47.11 (7.14) 24.73 (5.33) 28.36 (6.68) 62.5 (9.53) 19.49 (2.95) t / 5 C 3 Cow Creek 46.40 (6.84) 25.87 (5.19) 27.63 (6.14) 62.5 (9.35) 19.21 (2.93) C S O Robertson Ridge 47.96 (7.11) 25.17(5.26) 27.75 (6.60) 63.13 (9.84) 19.85 (2.94) s Vail Bioherm 47.58 (6.61) 25.62 (6.15) 27.29 (6.86) 65.52 (11.58) 19.67 (2.73) Total 47.20 (6.99) 25.30 (5.35) 27.86 (6.50) 63.00 (9.78) 19.53 (2.89) Minimum 30.73 15.38 16.40 43 13 Maximum 61.04 41.10 42.76 82 25 Mt. Lessini C O £ Field 65.40 (7.64) 14.78 (3.39) 16.10(4.03) 69.76 (6.92) 24.62 (4.20) a Museum 62.05 (6.82) 13.91 (3.38) 16.00(4.17) 66.70 (6.30) 24.38 (4.24) B Total 64.17(7.40) 14.46 (3.37) 16.06 (4.05) 68.63 (6.73) 24.53 (4.18) Minimum 48.91 10.05 6.13 57 14 Maximum 77.62 23.10 26.38 79 33 113 The opercular valve has been reconstructed as either similar in outline and height to the other only extremely thin (Chinzei, 1982; Savazzi, 1996), or alternatively shorter and operculum-like (Accorsi Benini and Broglio Loriga, 1977). Savazzi (1996) found resilia in the interligament grooves of a well-preserved specimen. Therefore, he proposed in view of the attachment of the opercular valve was attached through the full height of the ligamental area, shell closure was achieved by the flexibility of the opercular valve. The majority of individual specimens are from the Oregon localities (Swamp Creek, Robertson Ridge, Cow Creek and Vail Bioherm), found on hill slopes weathered out of the matrix. These shells at these localities average 30-50 mm wide, with an average length of 47.20 mm. The thickness of the Oregon specimens ranges from 15-40 mm. The angle of incidence of bands to the furrowed plate is also variable with ranges between 53-82° and the height of the bands varies from 16 to 43 mm with an average height of 27.86 mm. The Monte Lessini specimens, collected from Garzon di Sotto or observed in museums, were incomplete, without apices or the body cavity. However, the detail of the interior of the pedestal valve was often very well preserved. The range of lengths of shells of these specimens, presumably all originally collected from the same area, is from 49-78 mm with an average of 65 mm. The Monte Lessini specimens range in thickness from 10-23 mm and an average of 15 mm. The height of the growth bands is less than that of the Oregon specimens, 6-26 mm with an average of 16 mm. This may be in part due to the difficulty of discerning boundaries Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 in major growth rugae. The angle of incidence of the growth bands range from 57- 79° with an average of 69°. Microstructure The first attempt at Lithiotis microstructure description was based on specimens obtained by Lupher and Packard (1930). Cox (1969, p. N1200) reported: “the interior wall of the umbonal cavity consists of vertically oriented, calcitic prisms, and the shell has minor tubular cavities extending dorso-ventrally.” These samples have been heavily altered by the regional tectonism and only have ghosts of the original microstructure observed in other specimens from the Tethyan sites. Later studies by Accorsi Benini and Broglio Loriga (1977) and Chinzei (1982) offer slightly different accounts of Lithiotis problematica shell microstructure. Lithiotis valves consist of three layers: 1) outer layer - prismatic calcite; 2) middle layers- alternating irregular prisms with lenticular nacre; 3) inner layer- usually altered brown, compact calcite (Accorsi Benini and Broglio Loriga, 1977). X-ray diffraction analysis confirms the presence of aragonitic layers in Lithiotis as described by Accorsi Benini and Broglio Loriga (1997) and Chinzei, (1982) (Figure 59). Aragonite layers are found mainly along the outer part of the shell and the adductor myostracum, where the shell is soft and chalky in appearance. Aragonitic parts of the wall extend inwards along growth lamellae and wedge out irregularly. Lithiotis shows slender subparallel needles of aragonite growing perpendicular to the growth laminae (Figure 60). These prisms are far smaller in diameter (2-5 mm) than Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 Figure 59. X-ray diffraction analysis of Lithiotis problematica from Crespadoro (CV-1), middle aragonitic prism layer. O ? O f 'aragonite calcite j ; “ |v - . j v I | ) ^ p j | | | s ^ ip rX T r r - r v ? 'r |,T -f ? ! v p 1 f 5”r T s | 4 |'-n :, , i~ P 'T T j'* * r - f T r r j 'T y 'r ; iY 'r f ^ r 3 Y ’ r Y'*k 'T1’ T“ ?'’ P f”|' 1C. 15.. 20, 25. 30. 35, 40. 45, 50.. m Figure 60. Microstructure of Lithiotis problematica. A. Sketch o f Lithiotis problematica longitudinal microstructure with x-section to show internal tubes adapted from Chinzei (1982). B. Thin section of cross-section of a Lithiotis problematica sample from Crespadoro (CV-1), the outer calcite layer is not preserved, but the middle layer of irregular prisms with lenticular nacre are preserved (2x magnification, field of view is 5 mm across, in plane polarized light). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 the ordinary prisms seen in pterioids and other bivalves (compare to Carter, 1990). They are rather irregular in shape. Voids are observed between the subparallel prisms. The outer shell microstructure is rarely preserved, in most specimens it has been altered to a micritic envelope. A series of small vesicles or internal tubes is visible in cross-section. The individual tubes are approximately 0.2 to 0.5 mm in diameter and composed of radially arranged aragonite (in almost all cases calcite, presumed to be recrystallized from the original aragonite). They have a void hole at the center, now filled with transparent sparry calcite. The thin free valves are composed of alternating prismatic and nacreous aragonite layers, the proportion of aragonitic parts being higher in the opercular valve than in the attached valve (Savazzi, 1996), which may also be the cause for the opercular valve’s rare preservation. Phenotypic variability and life habit Two features differ in the specimens from Oregon and than those from Monte Lessini. Pedestal valves from the Oregon sites are typically more robust than the Monte Lessini specimens (Figure 61). The length to thickness ratio of Oregon specimens is 1.87, while the length to thickness ratio of Monte Lessini specimens is 4.4 resulting in thinner and broader shells (Figure 62A). The mean height of the growth bands is also very different between the two regions; 16 mm at Monte Lessini specimens and 28 mm in Oregon. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 61. Photograph of Lithiotis problematica morphotypes A. Oregon form, B. Mt. Lessini form (GPIT 1550, Tubingen). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 118 Figure 62. Length measurements of Lithiotis problematica. A - Plot of length vs. thickness for two morphotypes of Lithiotis problematica. B - Normalized frequencies of the lengths of two Lithiotis problematica morphotypes. 50 40 30 Oregon form • • • • • • • m m m • t • Oregon □ Mt. Lessini < U a 10 - fii a a * D ° d % • • % o o » ■ * - I — Mt. Lessini form J i i i i I i i i i— I— i— r i *i 20 30 40 50 60 70 80 A. Length (mm) 20 ■ Mt. Lessini @| Oregon 15 O a < D =3 a* P. o 5 0 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 B . Length (mm) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 The normalized frequencies of the lengths of the two different sample sets are plotted in Figure 62B. Normalized frequency (the frequency divided by the number of samples multiplied by 100) was used because the large sample size from the Oregon sites drowned the comparison to the Monte Lessini samples. The distribution of the Oregon specimens is bimodal, while that of the Monte Lessini specimens’ approaches uniform or normal. Normal distributions of shell remnants signifies transport or sorting, while a bimodal distribution is thought to capture two different size classes and may represent a more accurate representation of the population (Olszewski and West, 1997). It is difficult to propose a cause for such phenotypic variation. At first glance, the different hydrodynamic regimes between the Oregon (siliciclastic, active margin) and Mt. Lessini (carbonate, passive margin) might be responsible for the variation. The more robust Oregon forms conform with such a premise. However, one of the other Western North America Lithiotis sites, Mt. Jura, is similar to the Oregon forms, while in a dominant carbonate matrix. These specimens cannot be extracted from the matrix for individual specimen studies, yet qualitatively they have a similar length: thickness ratio to the Oregon specimens. Therefore, it is unlikely that the two different forms were selected for by environmental regimes, but may represent a geographical morphotype between Tethyan and Panthallassian populations. Clusters of Lithiotis are closely packed and appear to radiate away from the base of the clusters, resulting in an upside down “banana-bunch” morphology that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 can be seen in Mt. Lessini and Oregon bioherms (Figure 63A). Lithiotis specimens at the perimeters of the cluster are contorted resulting in a bent-knee morphology described by Debeljak and Buser (1997) and some specimens exhibit torsion. Morphologically, these clusters are similar to heads of branching corals seen in modern scleractinian-constructed reefs. To test for the orientation of the clusters, well-exposed bedding planes at the Vail bioherm in Oregon were compared to paleocurrent directions. When the Lithiotis buildup orientations at the Vail bioherm in Oregon are compared to the estimated paleocurrent of 270° (or 0° on a converted 180° scale) established by the orientation of Lithiotis in death assemblages contiguous to the reef core, a V’ value of 6.261 was computed (Figure 63B). Therefore, Lithiotis problematica valves do not appear to be aligned with currents (see discussion in Selley, 1968 for a complete review of paleocurrent models). In situ reef blocks of the Cow Creek reef were collected for slabbing and exposing cross sections through the clusters of Lithiotis. The body chambers of the bivalves are infilled with a fine calcareous silt matrix darker than the carbonate shells and a different grain size and color from the sediments at the base and lower sections of the reef. Nauss (1986) proposed that although the bases of the bivalves were anchored in sediment the majority of each valve was not, resulting in reef mounds with up to 5.5 m relief above the sea floor. Most of the matrix sediment was deposited after the bivalves were well established, resulting in the drowning of various reef sectors. Therefore, the life habit of Lithiotis was semi-epifaunal to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 121 Figure 63, Paleocurrent orientation o f Lithiotis problematica. A - Clusters of Lithiotis problematica in vertical section from Suplee-Izee, Oregon, an individual cluster is outlined in white. B - Radiation diagram of Lithiotis problematica from a bedding plane at the Vail Bioherm site, Suplee-Izee Oregon. Established paleocurrent direction is 270°, converted to 90° on a 1-180° scale. 0 o > ----------------------------------------------------- 1 180 Lithiotis problem atica at Vail Bioherm, Cow Creek, Oregon Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 122 epifaunal arranged in radiating clusters, valves not aligned to paleocurrent and with relief above the sea-floor (Figure 64). Figure 64. Schematic of proposed Lithiotis problematica life habit based on field observations and paleocurrent orientations. 5 cm Cochlearites loppianus (Tausch, 1890) Family Cochlearitidae Accorsi Benini & Broglio Loriga, 1977 Genus Cochlearites Reis, 1903 Cochlearites loppianus (Tausch, 1890) First described by Tausch (1890), Cochlearites loppianus was named as Trichites loppianus. Giimbel (1890) identified specimens of Cochlearites as Ostrea problematica, the same designation as Lithiotis problematica at the time. Reis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 123 (1903) created the genus Cochlearites. Cochlearites loppianus has been found in Slovenia, northern Italy, the south-central Apennines, Montenegro, Greece and Morocco (Debeljak and Buser, 1997; Broglio Loriga and Neri, 1976) (Figure 58). It may possibly occur in western France, Somalia and the island of Timor in Indonesia (Broglio Loriga and Neri, 1976; Accorsi Benini and Broglio Loriga, 1977). Material Forty-nine individual specimens from the Italy and Morocco field areas were used in this study. Italian specimens include mostly fragments of the pedestal valves at the Natural History Museum of Verona and the University of Tubingen. These specimens from the two different museums came from the same site, Marzana in the Monte Lessini district. Marzana is no longer accessible as it is under the operation of a rock quarry (R. Zorzin, pers. comm. 2000). Ten of these specimens have both valves partially preserved. The apex and ligament groove structures are preserved in some of the Marzana specimens. From Morocco only 5 specimens were successfully removed from the matrix from the Assemsouk site. The upper portion of the shell where the body cavity was located was not preserved in the Moroccan specimens. Description Morphology The shell is narrow and strongly dorso-ventrally elongated with a tapered apex (Figure 65). It is also stick-shaped with discordant valves like Lithiotis, yet the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 124 Figure 65. Schematic of Cochlearites loppianus (interior of pedestal, left valve) with morphological terms and measurements. adapterual ifsnnth thickness a d d u c to r m u sc le s c a r width of ligamental, area height of exterior bands left valve angle of incidence right valve fe a th e re d region cen tral a re a ligam ent groove- I ----------------------------------------1 adapical 10 cm discordancy is not as pronounced. Adult specimens measure from about 200 mm to more than 500 mm in height; their length is 55 to 118 mm (Table 4). The left valve is the pedestal valve, based on muscle attachment sites, and is 10-38 mm thick. The Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 4. Summary o f the means o f morphological measurements o f Cochlearites loppianus specimens, standard deviation is reported in parentheses. Region Site Length (mm) Thickness (mm) Height of growth band (mml Angle of growth band (°) # o f ligaments Morocco S Assemsouk 78.20(5.61) 24.97(1.61) 16.83(1.10) 60.24(11.00) 1 (0.00) Minimum Maximum 60.06 96.40 22.93 26.99 16.29 17.84 61 85 Mt. Lessini S Field I Museum Total 65.40 (7.64) 62.05 (6.82) 14.78 (3.39) 13.91 (3.38) 16.10(4.03) 16.00(4.17) 69.76 (6.92) 66.70 (6.30) 24.62 (4.20) 24.38 (4.24) 64.17(7.40) 14.46(3.37) 16.06(4.05) 68.63(6.73) 24.53 (4.18) Minimum Maximum 56.39 117.91 14.32 37.80 4.72 31.74 32 89 to Ln 126 right valve is the opercular valve and is 5-20 mm thick. The shell is usually straight, some specimens are slightly curved but do not exhibit any torsion, unlike Lithiotis. The interior of the surface of the pedestal valve consists of three regions, a characteristic of most “Lithiotis” facies bivalves. The central (cardinal) area is usually about 20-40 mm wide, bordered by two feather-like areas. The feather-like appearance is created by growth lines, which often are bundled together. In specimens where both valves are preserved, there is a gape at the posterior and anterior margins. The body cavity of the shell was very small when compared to the total shell size. A wide depression bordered by two ridges runs down the center of the pedestal valve and a central crest of the opercular valve fits tightly into it, similar to a spur and groove structure. Semicircular traces are often found on the central cardinal area; these may be growth lines which the edge of the mantle left behind as the organism’s soft parts migrated towards the adapertural margin. In the body cavity area there is a well-developed, internal buttress extending from the edge of the hinge area to the posterior edge of the single adductor muscle. At the apical margin, near the middle of the cardinal area of both valves, runs a deep and narrow groove (resilifer) in which the fibrous ligament was attached. The lamellar part of the ligament was attached at both sides of the groove. The depth of the ligament groove varies with specimens from 30-60 mm. Chinzei (1982) reports “secondary” or “accessory” ligament grooves from specimens at the University of Tubingen and the Geological Institute of Ferrara. I was not able to locate these specimens. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 127 The majority of individual specimens are from the museum specimens of the University of Tubingen and the Natural History Museum of Verona from the Mt. Lessini district site Marzana. These samples were exceptionally preserved and exhibited original shell microstructure (shell microstructure is described below). However, the outer calcitic layer was often missing, leaving bare the alternating nacreous and irregular prismatic layers which were difficult to distinguish as growth bands. The morphological measurements of the Cochlearites pedestal valve are summarized in Table 4. The range of lengths of fragmented shells of these specimens collected from the same area is from 60-97 mm with an average of 78 mm. The Moroccan specimens range in thickness from 23-27 mm with an average of 25 mm (Figure 66A). The height of the growth bands is larger than that of the Italian specimens, 16-18 mm with an average of 16.83 mm (Figure 67A). The angle of incidence of the growth bands ranges from 61-85° with an average of 60°. The Moroccan specimens from the Assemsouk reef were in situ and difficult to remove. The range of lengths of the shells at Mt. Lessini localities is 57-118 mm with an average length of 78.20 mm (Figure 66B; Figure 67B). The thickness of the Mt. Lessini specimens ranges from 14-39 mm, with an average of 14.46 mm. The angle of incidence of bands to the furrowed plate is also variable, with ranges between 32- 89°, and the height of the bands varies from 5 to 32 mm, with an average height of 15 mm. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 Figure 66. Photograph of Cochlearites loppianus morphotypes A. Moroccan form, B. Mt. Lessini form (Verona Museum). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 129 Figure 67. Length measurements of Cochlearites loppianus. A - Plot of length vs. thickness o f Cochlearites loppianus. B- Normalized frequencies of the lengths of Cochlearites loppianus. 40 — .... f----- r----------j-----j----- 1 ----- |-----| i i T -----[— — -v.. 1 1 t □ 35 □ B 30 □ D H • ? 25 0 1 % ® " J g © “ J" ■ 0 ■w n a a t/3 ° a fca a j S 20 S cP O □ B 8 9 ” ^ D 3 B B 15 a H 15 : a ■ 10 - -j « Assemsouk 5 . □ Verona Museum J a Tubingen Museum 0 » ■ ■ ■ « -----■ ------1 ____ 1 ____ 1 ____ I ____ 1.....1. ... j,..,.,... 1 I 1 1 ...... 1 - - - 1 ..... J 1 ----- L 20 40 60 80 100 120 A . Length (mm) 40 ! » g 20 o c 10 Assemsouk Verona □ Tubingen I ■HI ■ I 1 - 100 105 110 115 B. Length (mm) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Microstructure Similar to Lithiotis, Cochlearites microstructure consists of three layers: 1) outer layer - prismatic calcite; 2) middle layers - alternating irregular prisms with lenticular nacre; 3) inner layer - usually altered brown, compact calcite (Accorsi Benini and Broglio Loriga, 1977; Chinzei, 1982). According to Broglio Loriga and Neri (1976), Cochlearites has intercalated aragonitic prismatic and nacreous shell layers (presumably middle and inner shell layers). Chinzei (1982) wrote that this genus, like Lithiotis, has an inner shell layer which was “now altered to brown, compact calcite, but which originally consisted of a very porous structure, similar to oyster chalky layers (but presumably aragonitic originally).” Cochlearites lacks the internal vesicles seen in Lithiotis. Phenotypic variability and life habit Individual specimens of Cochlearites loppianus within the bioherm of the Assemsouk section do not differ considerably from one another as seen in the low standard deviation values (1.61 for thickness v. 3.39 for the thickness of the Mt. Lessini), but again between sites the differences are quite noticeable. Such variations may be phenotypic, resulting from the tightly packed communities. The small sample size of the Assemsouk Cochlearites may contribute to the low standard deviation values. It is assumed based on the museum collection curation notes that all of the museum specimens are from the same localities, yet it is difficult to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131 document this because of the inaccessibility of the Marzana site. No two specimens have identical central areas and most of the different form types described by previous authors have focused on the depth and length of the ligamental groove. When Reis (1903) created the genus Cochlearites, he designated three types based on the ligament groove. By closely examining mantle growth lines, Accorsi Benini and Broglio Loriga (1977) combined these three to two types: the “normal” type (forma A) in which the ligament was connected to the mantle, and the “abnormal” type (forma B) in which a short stunted fibrous ligament no longer had connection with the body cavity and therefore the soft tissue. Chinzei (1982) noted that practically all adult specimens belong to the “abnormal” type. This discovery makes the considerations of different types or subspecies based solely on ligament structure irrelevant. In life position, Cochlearites aggregations are closely packed and are vertically oriented (Figure 68A). Cochlearites specimens observed in situ in Assemsouk lack the torsion or curved morphologies seen in Lithiotis. However, individual specimens of Cochlearites are slightly curved, often in adapical region (Figure 66A). Morphologically, Cochlearites aggregations are consistent to the stick-shaped mudsticker habit proposed by Seilacher (1984). To test for the orientation of the valves within the aggregation, well-exposed bedding planes at the Assemsouk reef, Jebel Azourki, Morocco were examined. Cochlearites from Assemsouk have a V ’ value of 1.919 when compared to a paleocurrent of 120° (or 0° on a converted 180° scale) established by the orientation of other fossils in death Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 Figure 68. Paleocurrent orientation of Cochlearites loppianus. A - Cochlearites loppianus in the field from Assemsouk reef, Jebel Azourki Morocco, bedding plane view. B - Radiation diagram of Cochlearites loppianus from the same bedding plane. Established paleocurrent direction is 120° converted to 30° on a 0-180° scale. B, Cochlearites loppianus at Assemsouk, Jebel Azourki, Morocco Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 133 assemblages contiguous to the reef (Figure 68B). Therefore, Cochlearites loppianus, like Lithiotis, valves did not align with currents. In situ reef blocks of the Assemsouk reef were collected for slabbing and exposing cross sections through the aggregations of Cochlearites. The body chambers of the bivalves are infilled with a fine calcareous mud that is indistinguishable from matrix below or to the sides of the reef complex. The gentle curving of the bioherm structure at Assemsouk is only visible in the Cochlear itesfacics suggesting that Cochlearites did maintain some amount of its shell above the substrate. It is difficult to pinpoint how high Cochlearites maintained itself above the substrate, but it would have been less than that proposed for Lithiotis problematica as the Cochlearites reefs do not have similar relief. As a result, the Cochlearites life habit reconstruction suggests the minimum amount of elevation above the substrate, just slightly below the shell’s midpoint resulting in an overall semi-infaunal mudsticker habit (Figure 69). Gervilleioperna Krumbeck 1923 Suborder Pteriina Newell, 1965 Superfamily Pteriacea Family Isognomidae Woodring, 1925 Genus Gervilleioperna Krumbeck 1923 The first description of Gervilleioperna was written by Krumbeck (1923) from two examples, both from the Pliensbachian of the island of Timor, Indonesia. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 134 Figure 69. Schematic of proposed Cochlearites loppianus life habit based on field observations and paleocurrent orientations. Krumbeck (1923) selected this generic name as he observed features from both Gervilleia Rominger 1846 and Perna Brugiere 1789. These characters included: 1) strongly inequivalved, 2) a protruding beak, 3) presence of a byssal furrow situated posterior to the byssal gape, 4) a variation of the multivincular ligament (fewer grooves, widely spaced) and 5) the presence o f a “coniform” shelf under the ligamental area. Dubar (1948) in his monograph of Liassic fauna of the High Atlas Mountains of Morocco named two species Gervilleioperna atlantis and termieri. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 Cox (1969) consolidated both species to G. timorensis. Individual specimens of Gervilleioperna have also been collected in the Veneto, near Ponte dell’Anguillara (Broglio Loriga and Neri,1976). Material Seven individual specimens of Gervilleioperna were studied, 5 from the Geological Institute of Ferrara (labeled as collected from Vaio Anguillara) and 2 from the Ponte dell’Anguillara site (very near if not the same site as Vaio Anguillara). No complete specimens were found but specimens for this study were included if the entire ligament area was intact. Many more specimens are visible in cross-section in the field from the Ait Athmane site. The Moroccan specimens were completely recrystallized and therefore, difficult to remove from the surrounding matrix for morphological studies. Description Morphology The outline of Gervilleioperna is subrectangular, slightly discordant and asymmetrical (Figure 70). Most of the specimens are 30-60 mm in height and 30-75 mm long (Figure 71). Krumbeck’s holotype (1923) from Timor was large, 115 mm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. adapaterual 136 anterior feathered region posterior Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 70. Schematic o f Gerveilleioperna sp. (interior o f right valve) w ith morphological term s a n d measurements. 137 Figure 71. Photograph of Gervilleioperna sp. specimen from the Geological Institute of Ferrara wide. The thickness of the shell varies and is at its greatest in the adapical region of the left valve (up to 35 mm), while it is thinnest, about 20 mm, at the adapertural margins on the right valve. The left valve has a well-developed prosogyrous beak. The cardinal margin is grooved in the anterior region. There is a furrow that begins at the beak and proceeds ventrally becoming less deep. Three distinct regions are observed in the shell interior: 1) multivincular ligament area (10-20 mm in height), 2) cardinal or subligamental platform and 3) the body cavity (30-60 mm high). A byssal gape and furrow are found in both valves. The ligamental area is multivincular with numerous ligamental grooves (7-10) and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 concentric striations occur within the grooves. The ligamental grooves are not equally spaced and have varying depths (about 23-45 mm). The area above the ligament extends to a platform parallel to the cardinal margin. This platform is not well preserved, but Broglio Loriga and Posenato (1996) report that one specimen collected at Ponte delT Anguillara but no longer in the Ferrara collections has “3-4 teeth of similar height oriented parallel or slightly oblique to the ligament area, similar to actinodont dentition.” Within the center of the small body cavity lies a semicircular muscle scar. The exterior of two specimens shows concentrically arranged growth lines. Measurements for the left valve and summarized in Table 5. Shells at these localities range from 13-75 mm long, averaging of 51.14 mm long. The thickness ranges from 7-34 mm, with an average of 26.97 mm. The angle of obliquity of the overall shell shape is also variable with ranges between 91-97°. Only two specimens have growth bands preserved, those two heights are 1.37 and 2.16. The number of ligaments ranges from 7 to 10, with an average of 8.71. Microstructure Macroscopically, three shell microstructures in Gervilleioperna sp. can be observed: 1) outer layer - prismatic calcite, 2) middle layer - nacreous, 3) inner layer - fibrous prismatic aragonite (Accorsi Benini and Broglio Loriga, 1982). The thick inner layer of fibrous prismatic aragonite is seen in other “Lithiotis” facies bivalves (Carter, 1990). The inner fibrous prismatic layer consists of long fibrous Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 5. Summary o f the means o f morphological measurements o f Gervilleioperna sp. specimens, standard deviation is reported in parentheses. Region Site Length (mm) Thickness (mm) Height of growth hand (mm) Angle of obliquity (°) # of ligaments Mt. Lessini a . Museum 1 Field Total 39.48(12.93) 24.61 (11.51) 2.16 91.00(2.83) 8.00(1.41) 55.80(15.00) 27.91 (6.57) 1.37 97.00(4.47) 9.00(1.00) 51.14(12.93) 26.97(7.31) 1.77 95.29(4.82) 8.71 (1.11) Minimum Maximum 12.93 75.35 6.57 33.70 1.37 2.16 89.0 103.0 7.00 10.00 uo VO 140 crystals, nearly all oriented to the “c” axis. The maximum length is about 1.2 to 2 mm (Accorsi Benini and Broglio Loriga, 1982). Bundles of these fibrous prisms are not easily distinguishable as in Mytiloperna (described below). The thickness of this layer increases from 1 to 7 mm as one traces back to the adapical margin. X-ray diffraction showed this layer to be composed of aragonite (Accorsin Benini, 1982). Phenotypic variability and life habit With only 7 specimens, it is difficult to propose any variability in shell forms. The two specimens collected from the Ponte dell’Anguillara site are smaller than those observed in cross section in field sites in Morocco. Gervilleioperna is found most often as individuals on shallow carbonate platforms. The life habit of Gervilleioperna is similar to that of gryphaeid oysters with the larger, thicker valve nestled in the sediment while the thinner valve functioned as an operculum. This form is similar to that described by Seilacher (1984) as a semi-infaunal cup-shaped recliner (Figure 72). Figure 72. Schematic of proposed Gervilleioperna life habit based on field observations and Seilacher (1984). 5 cm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141 Mytiloperna v. Ihering, 1903 Suborder Pteriina Newell, 1965 Superfamily Pteriacea Family Isognomidae Woodring, 1925 Genus Isognomon (Mytiloperna) v. Jhering 1903 The history of Mytiloperna begins with Forbes (1846 cited in Broglio Loriga and Neri, 1976) when he described a specimen of “Perna americana” from the Lias of Chile based on the apex and cardinal area of two valves. Jhering (1903) used a variety of features including the presence of an anterior furrow and the mytiliform contour shape to distinguish Mytiloperna from the genus Perna. Rollier (1914) independently discovered specimens o f a “Perna” that lacked a posterior wing but had a multivincular ligament similar to Isognomon but with wider interspaces, in the Middle Jurassic of Alsace and England. These were identified as Perna mytilioformis, a junior synonym of Mytiloperna. In Hayami (1957b), Mytiloperna was described from the Toarcian of Japan based on the wide interspaces of the multivincular ligament. Following Cox’s (1969) classification Mytiloperna v. Jhering, 1903 is a subgenus of Isognomon, which is found in modem intertidal mangrove root environments to subtidal environments. Mytiloperna occurs in northern Italy in the region near Asiago and the Seven Community areas of the Altoplano as well as Morocco, Chile, France, England and Japan (Accorsi Benini and Broglio Loriga, 1982) (Figure 58). In fact, many reports Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 of Mytilus in similar facies during the Pliensbachian and early Toarcian may be Mytiloperna. In the field, tangential sections of Mytiloperna are easily confused with Mytilus if the ligament area is not visible. Material Twenty-seven individual specimens were observed only in museum collections from the Geological Institute of Ferrara and the University of Tubingen. Measurements were made from specimens that had the ligamental area preserved. Two specimens of small size from the Ferrara collections were articulated. The Moroccan Mytiloperna specimens were completely recrystallized, and therefore difficult to remove from the surrounding matrix for morphological studies, but are incorporated into the discussion of life habit. Description Morphology The outline of the shell is mytiliform, elongated dorsal-ventrally with a slight rounding at the adapertural margin (Figure 73). The shell dimensions are about 70 tol30 mm in height, 62-124 mm wide and 40-80 mm thick. Mytiloperna is equivalved or slightly subequivalved and has a prominent beak area that twists and projects forwards. This feature creates two anterior ridges that run from the beak to the ventral margin. The anterior feathered region is not as wide as seen in Gervilleioperna. The posterior wing is absent or not easily distinguished. The shell Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. muscle scar adapterual length subligamental platform ligament area adapical anterior eathered region conical tooth angle of obliquity thickness h 10 cm Figure 73. Schematic of Mytiloperna sp. (interior of right valve) with morphological terms and measurements. 144 walls are thick and increase at the anterior ridge areas to 40 mm. Mytiloperna has no distinct byssal gape, unlike Gervilleioperna sp. or Lithioperna scutata. The posterior and ventral margins of the shell are rarely preserved, presumably because these areas are thinner than other regions. Three distinct regions are observed in the shell interior: 1) multivincular ligament area (5-35 mm in height), 2) cardinal or subligamental platform and 3) the body cavity (40-70 mm high). The multivincular ligament consists of about 8 to 10 ligamental grooves, although there are reports of specimens with up to 20 (Seilacher, 1984). Striae occur between the grooves. The grooves are about 3-4 mm wide. The cardinal platform in the adult stage carries 1-7 teeth, which vary in size and are oblique or perpendicular to the dorsal margin. Occasionally, two or three teeth join to form one conical tooth. The adult body cavity is small in comparison with the shell size and has a deep and narrow umbonal region edged by the flat subligamental platform. A semicircular, small muscle scar occurs in the anterior region of the body cavity. The external surface lacks ornamentation, yet some white lamellae are visible at the shell margins. In the field, Mytiloperna is easily distinguished from the other large “Lithiotis” facies bivalves because of its triangular shape in antero-posterior cross section (Figure 73). The morphological measurements of the Mytiloperna sp. valves are summarized in Table 6. The range of lengths is 63-123 mm with an average length of 98.46 mm. The thickness of the Mt. Lessini specimens ranges from 30-63 mm, with an average of 39.81 mm. The angle of obliquity plate is also Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 145 variable with ranges between 36-79°. The average number of ligaments is 8, ranging from 7-10. Table 6. Summary o f the means o f morphological measurements o/Mytiloperna sp. specimens, standard deviation is reported in parentheses. „ . v . Length Thickness Angle of # of e§lon a U C ________ (mini________fmml______ obliquity ligaments Mt. Lessini M ean 9 8 .4 6 (1 3 .2 6 ) 39.81 (6.57) 59.81 (14.59) 8 (1 .0 2 1 ) M inimum 62.60 30.01 36 7 M aximum 123.26 62.90 79 10 Microstructure Two microstructure layers are identifiable in Mytiloperna: a fibrous, aragonitic inner layer and a prismatic calcite outer layer (Accorsi Benini and Broglio Loriga, 1982) (Figure 74). The inner layers are characterized by lenticular nacre, 1-2 mm thick, which is also found on the ligamental surface. The inner fibrous layer consists of long, thin crystals that are perpendicular to slightly oblique (15°) to the shell surface. Powder obtained from a fragment of the inner layer was analyzed using XRD and was found to be aragonitic in composition; Feigel solution also tested positive for aragonite (Broglio Loriga and Posenato, 1996). The thin outer layer consists of short calcitic prisms and is only preserved on the lunule. Dark and light growth bands and sheets of homogeneous microstructures are readily observed in hand sample. The fibrous inner layer is thick, up to 40 mm, at anterior ridges but does not reach the ventral and posterior margins. It is in this layer that Mytiloperna accomplished the “heavy-weight” strategy of Seilacher’s (1984) terminology. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 146 Figure 74. Mytiloperna microstructure after Broglio Loriga and Posenato (1996). Outer irregular prismatic calcite layer are designated as small blocks, aragonite layers are depicted in white, recrystallized aragonite layers are black. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 147 Phenotypic variability and life habit Using the obliquity angle described by Arkell (1933) and valve discordancy, three morphotypes are observed: 1) subequivalved with an obliquity angle of 70-80°, 2) equivalved with an obliquity angle of 55-60°, and 3) equivalved with an obliquity angle of 36-41° (Figures 75 and 76). By plotting the angle of obliquity against length, the three morphotypes are readily distinguished (Figure 77). The first form has an obliquity angle of about 80°, nearly acline, and a wide lunule (Figures 75A and 76A). These are myaliniform in shape, similar to Hippochaeta in outline (Seilacher, 1984). The orientation on soft substrates is comparable to that of Orthomyalina, Newell 1942 or to Isognomon lusitnicum (Sharpe). Some specimens with this obliquity angle are strongly inequivalved and these are presumed to have a pleurothetic habit with the thicker valve lying on the bottom (Figure 78A). The second form has an obliquity angle of 55-60° and is equivalved (Figure 75B). The lunule area is large, the beak was very prominent and the umbo is twisted and projected forward but still with myaliniform shell outline. The obliquity angle in this form is similar to that in the presumed juvenile forms and the body cavity growth overall appears to be slower than that of the rest of the shell. The maximum thickness of the shell walls is found in the central-dorsal region and is typical of other edgewise recliners (Seilacher, 1984), but Broglio Loriga and Posenato (1996) proposed that this form was semi-infaunal (Figure 78B) The last form, an orthothetic semi-infaunal recliner, has a very low obliquity angle of only 38-40°, resulting in a mytiloform shape that is strongly prosocline Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 75. Morphotypes of Mytiloperna based on ArkelFs (1933) obliquity angle Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149 Figure 76. Photographs of Mytiloperna morphotypes A. Morphotype A with conical tooth (GPIT 1550, University of Tubingen) B. Morphotype C with strong prosocline form (Geological Institute of Ferrara, FEMlOa). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 Figure 77. Length and obliquity angle measurements of Mytiloperna sp. A - Plot of length vs. angle of obliquity for three morphotypes of Mytiloperna sp. B - Normalized frequencies of the angle of obliquity of three Mytiloperna sp. morphotypes. 80 70 60 Sf 50 3 c r 33 ■ § 40 C m e v “ 30 20 10 0 20 40 60 80 100 120 140 • angle of obliquity A □ angle of obliquity B • angle of obliquity C A. ■ Morphotype A a Morphotype B 4 - n □ Morphotype C > > U 8 , § ■ 3 " O < D N I d 2 - 0 1 . 1 ■ I . -I ■ 1 ■ L B -L . I m I w I , I . 1 . 1 JM 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 B . A ngle o f obliquity (°) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 Figure 78. Life habits of Mytiloperna. A - Subequivalved to inequivalved, pleurothetic epifaunal recliner. B - Equivalved orthetic epifaunal to seim-infaunal recliner. C - Equivalved orthothetic semi-infaunal recliner. ( r ^ \ \ 3 c. 5 cm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 152 (Figures 75C and 76B). The body cavity is high and narrow and the ligamental area and cardinal platform is shorter, while the teeth are fewer than those in previous forms or completely absent. The narrower lunule area, lack of byssal attachment and arched shape suggest that the shell was partially buried in the sediment, a mudsticker habit (Figure 78C). In life position one finds scattered individuals or small clusters of Mytiloperna sp.. The clustered arrangements tend to occur near the mud-mounds of the large and gregarious bivalves Lithioperna scutata and Cochlearites loppianus. Both Lithioperna and Cochlearites made very dense mono-specific communities and appear to have excluded colonization of substrates by other organisms. Therefore, the occurrence of other species in the Cochlearites and Lithioperna communities is very rare, and the settlement of Mytiloperna sp. is unusual. The availability of substrate could have been the primary factor in determining the growth habit of Mytiloperna. In areas of increased substrate availability, the myaliniform shape of the orthothetic and pleurothetic recliners may have dominated. The second form with retention of the juvenile obliquity angle may represent scattered individuals in areas with sufficient substrate availability for individual growth. The final growth form, a mudsticker, may be an adaptation to limited substrate availability resulting from the dense aggregations of Lithioperna and Cochlearites. Lithioperna scutata (Dubar, 1948) Suborder Pteriina Newell, 1965 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 153 Superfamily Pteriacea Family Isognomidae Woodring, 1925 Genus Lithioperna Accorsi Benini, 1979 - syn. Lithiopedalion Buser, 1965 Lithioperna scutata (Dubar, 1948) The genus Perna scutata was described by Dubar (1948) based on specimens from the Central High Atlas. The name Lithiopedalion was given to the genus by Buser (1965) in his doctoral thesis based on the characteristics of Lithiotis and Pedalion (an older synonym for Isognomon) from Slovenian specimens. The new genus and species were presented at the 42n d annual meeting of the Paleontological Society in Graz (Buser, 1972) but publication failed to meet the rules recognized by the ICZN. The name Lithiopedalion does occur in some of the literature (Bossellini, 1972; Broglio Loriga and Neri, 1976) but Accorsi Benini (1979) described the genus under the new genus Lithioperna revised from Dubar’s original collection and published according to the ICZM. Lithioperna is the most frequent large bivalves of the Liassic “Lithiotis” Facies of the Calcari Grigi in the Monte Lessini area. It is also cited in the Lower Jurassic of the Central and Southern Apennines, Slovenia, Albania, Greece, France Spain and Morocco (Broglio Loriga and Neri, 1976; Accorsi Benini, 1979; Buser and Debeljak, 1994; Rey et al., 1990) (Figure 58). Lithioperna scutata is most likely present at other localities but different authors have designated it under the names Perna or Isognomon, or in some places it has been classified as an oyster (e.g. Pernostrea of some Early Jurassic deposits of France; Buser and Debeljak, 1997). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 Material About 58 specimens were used in this study, most with only one valve preserved. Individual specimens were found in the collections of the University of Tubingen and the Geological Institute o f Ferrara, as well as collected from Ponte dell’Anguillara. Specimens from the Assemsouk section, Morocco were also used in this analysis. Fragments of the apical parts of the central plate with the ligament grooves dominate the collections. Marginal parts were generally missing. Description Morphology The shell is linguliform and often very large (Figure 79). On average, the shells are 200 to 700 mm high. Sections of field samples reveal that some specimens reached heights over 900 mm. The height is usually twice the length. The two valves have the same shape, size and thickness, and fit closely. Together they are 100 to 400 mm thick. In longitudinal sections, the shell appears compressed and has an undulating habit. The external surface of the valves is normally rough and irregular, in some rare specimens concentric growth lines are observed. Four distinct regions are observed in the shell interior: 1) multivincular ligament area (5-80 mm), 2) subligamental platform, 3) byssal notch and 4) the body cavity. The shell’s interior consists of a central plate consisting of ligament grooves and a cardinal platform and body cavity with feather-like areas on both the anterior Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. m uscle scar byssal notch subligam entaj platform ligamental are; length adapterual thickness 10 cm angle of obliquity adapical Figure 79. Schematic of Lithioperna scutata (interior of right valve) with morphological terms and measurements. L A LA 156 and posterior margin and a central plate. At the dorsal margin, the characteristic “Lithiotis” facies bivalve multivincular ligament is found. The ligament grew in 8- 20 sub-parallel ligamental grooves. As the bivalve grew the ligament shifted in the ventral direction and left behind thin convex semicircular traces; between the grooves these traces are concave. Some ligamental grooves appear to be “abandoned”, i.e. they are of similar width at the apical region to longer ligament grooves but terminate before reaching the upper margin of the ligamental area. In several specimens, the position and center of gravity of the shell may have changed over the organism’s growth history, so accordingly the ligament grooves were diverted often towards the anterior region. The subligamental platform was described by Seilacher (1984) as having a “broad tooth plate.” Any teeth structures are rarely preserved. The body space of this bivalve with a single muscle scar is very small in comparison to the overall size of the shell. It occupies only the ventral section of the shell and part of the space between the anterior border folds or lines. The depression for the soft tissue parts is very shallow. A byssal notch is present is some well- preserved specimens on the anterior side. When the byssal notch is not preserved, one can still distinguish between the right and left valves. First, trace a vertical boundary through the central plate and the feather-like area, and then connect this to a straight line to the edge of the ligamental grooves. The angle made by the two lines is more than 90° on the anterior side and less than 90° on the posterior (R. Posenato, pers. comm., 2000). The morphological measurements of the Lithioperna Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 valves are summarized in Table 7. The range of lengths of the shells at the Moroccan localities is 16-391 mm with, an average length of 163.46 mm. The thickness of the Mt. Lessini specimens ranges from 19-287 mm, with an average of 139.59 mm. The angle of obliquity varies between 70-145°. Growth bands tend to be very fine and only a few millimeters high. In six specimens where growth bands observed, height of the bands varies from 4-22 mm with an average height of 12.23 mm. The number of ligaments varies from 7-16 ligaments. Microstructure Lithioperna displays the same three-layer microstructure seen in other “Lithiotis ” facies bivalves (Figure 80). Broglio Loriga and Posenato (1996) detected on the outer surface a very thin calcific regular prismatic layer, which was not preserved in the specimens formerly examined by Accorsi Benini (1979). The inner shell layers are entirely aragonite and consist of alternating layers of irregular simple prismatic and lenticular nacreous sublayers of different thickness. Nacreous sublayers are dominant on the umbonal and ligamental areas. On the marginal regions the shell wall is predominantly nacreous. The prismatic sublayers become thicker toward the subligamental area where they make up almost all of the shell wall, thus forming a fibrous irregular simple prismatic structure. In cross sections, the prisms are polygonal and highly variable in shape. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 7. Summary o f the means o f morphological measurements o/Lithiopem a scutata specimens, standard deviation is reported in parentheses. Region Site Length (mm) Thickness (mm) Height of growth hand finirtt Angle of obliquity # o f ligaments M orocco § £ A ssem souk 163.46 (14.44) 20.74 (6.4) Minimum M axim um 15.85 391.54 10.86 37.80 Mt. Lessini 2 Ponte dell'Anguillara M useum (Ferrara) M useum (Tubingen) 51.71 (16.75) 111.59 (71.201) 82.21 (25.04) 11.56 (3.05) 12.43 (6.39) 10.46 (3-31) 6.66 13.15(8.52) 123.5 (.707) 105 (21.19) 87.74(11.00) 7.67 (0.58) 5.94 (3.16) 8.30(1.89) Total 139.59(109.26) 97.37(47.020 12.23 (8.15) 93.32(31.73) 9.125 (2.34) M inimum M aximum 19.29 287.53 6.17 31.70 4.04 22.45 70 145 7 16 U \ 00 159 Figure 80. Microstructure of Lithioperna. Outer irregular prismatic calcite layer are designated as small blocks, aragonite layers are depicted in white, recrystallized aragonite layers are black. Phenotypic variability and life habit As juveniles, Lithioperna scutata are generally rounded or elongated in outline, the beak is pointed and a byssal notch is already well developed. Broglio Loriga and Posenato (1996) postulated that in the juvenile stage Lithioperna used their byssus to attach to dead or living shells. In adult specimens, Seilacher (1984) recognized two main morphotypes, which are characterized by a different behavior Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 and adaptive strategy: spoon-shaped mud sticker with a flat and thin shell forming densely packed fan-like colonies (morphotype A; Figures 81A and 82A); and cup shaped isolated recliners, concave-convex in cross-section, with a rounded outline and thick or thin shells (morphotype B; Figure 81B and 82B). Plots of length when compared to thickness do not readily distinguish the three different morphotypes (Figure 83A). This in part reflects the delicacy of the anterior and posterior feathered regions that are rarely preserved. The thickness of the valves may be the best tool to recognize the various different morphotypes. A histogram of thickness when compared to the normalized frequency helps delineate between the two different morphotypes (Figure 83B). The “spoon-shaped” mudsticker morphotype inhabited areas with a maximum population density and grew in upright to oblique positions (Figure 84A). The shells were partially buried in the sediment and grew ventrally or adaperturally with their soft parts just at or above the sediment surface (Seilacher, 1984). Colonies of this morphotype of Lithioperna are seen at Ponte dell’ Anguillara site fanning outward, hence the term “fan-shaped” (Figure 85A). A bedding plane from Bellori was used, To test for orientation of this morphotype to paleocurrent. Since all specimens in these beds are articulated and are unlikely to have been transported, I believe these organisms were in situ. Lithioperna colonies at the Bellori site in Italy have a V’ value of 1.421 when compared to a paleocurrent of 5° (95° after conversion to 180° scale; Figure 85B). This V ’ (paleocurrent orientation) value is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 Figure 81. Morphotypes of Lithioperna. A - spoon-shaped mud sticker with a flat and thin shell forming densely packed fan-like colonies. B - thick inequivalved, cup shaped isolated recliner, concave-convex in cross-section, with a rounded outline. C - cross section of a thin equivalved recliner with a much longer valve length. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 162 Figure 82. Photographs of Lithioperna scutata morphotypes A. Morphotype A, two valves (GPIT 1550, University of Tubingen), B. Morphotype B thin valves (unnamed specimen from the Geological Institute of Ferrara), camera lens cap for scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 Figure 83. Length measurements of Lithioperna scutata. A - Plot of length vs. thickness for three morphotypes of Lithioperna scutata. B - Normalized frequencies of the thickness of three Lithioperna sp. morphotypes. ~ |— > r » T ' [ i1 i i > |—i — i—i— i— |— i— i— r - 35 30 i 1 * ■ * i s -8 15 ' A *A • 9 a A a A A . A A A • * Thickness A □ Thickness B Thick • Thickness B Thin 0 — I —I — 1 A a' 4 1 —L-dl— L_I—h-J—I —■ —k-J— I— J— I — 1 — 1 —L _ 50 100 150 200 250 300 350 400 A. Length (nun) 2 0 — i---- 1 — i— |---- 1 ---- 1 — r— j----- .— |----1 — )---- 1 — |---- 1 -----1 — r— ]---- 1 -----1 — i— |----^ ----- 1 ----1 — | - 15 o g 3 O " ^ 10 N l Morphotype A Morphotype B thick □ Morphotype B thin JJL 1 _ J i I III II tw B. 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Thickness (mm) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 Figure 84. Proposed life habits of Lithopema scutata based on field observations after Broglio Loriga and Posenato (1996). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 165 Figure 85. Paleocurrent orientation o f Lithioperna scutata. A. Clusters of Lithioperna scutata in the field from a vertical section at Ponte dell’ Anguillara. B - Radiation diagram of Lithioperna scutata from a bedding plane at the Bellori, Italy site. Established paleocurrent direction is 5° converted to 95° -180° scale. Lithioperna scutata at Ait Athmane, Morocco Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 less than 1.645, significant at the 95% confidence interval. Therefore, it is probable that fan-like Lithioperna morphotype A colonies aligned with currents, similar to modem oysters. The number of ligaments in this morphotype is relatively low, 7 - 10. The pleurothetic, cup-shaped recliner morphotypes are characterized by shells with rounded or obliquely ovoidal outlines (Figure 84B and C). When compared to the fan-like morphotype, the recliner morphotypes are less elongated, with a shorter byssal notch in most cases and above all, a smaller central plate giving the appearance of a larger body cavity. Shells rested on the convex valve with their commissure roughly parallel to the substrate, and thus were pleurothetic recliners. Some Lithioperna recliners grew in dense arrangements, appearing to have partially overlapped and imbricated with the heavier anterior-dorsal part of the shell partially buried (Figure 44B). Within the pleurothetic recliner morphotype, two different modes of valve thickness are observed. The thicker valve form (over 3 cm thick in some specimens) has a circular outline (Figure 84B). Thus it developed a “heavy weight” strategy for bottom stabilization in order to prevent capsizing (Seilacher, 1984) and is found in environments interpreted as high energy due to the high amounts of shell debris. The thinner shelled form, with valves up to 10 mm thick and 350 mm high has an ovoidal outline (Figure 80C). It inhabited calmer muddy substrates with a minor amount of skeletal debris. Therefore, a “lightweight” strategy or “snowshoe” function may have developed in this ecotype to prevent sinking into the mud Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 (Seilacher, 1984; Figures 82B and 84C). These forms have a greater number of ligamental grooves, with the “snowshoe” morphotype having the most (16-20 grooves). The strong morphological variability of Lithioperna scutata may be a result of the loss of byssal attachment during its ontogeny or the wide range of environmental conditions that the organism can be found in (shallow, low energy lagoons to banks in ooid shoals). Phylogenetic Affinities of the “Lithiotis” Facies Bivalves The taxonomic relationships of the “Lithiotis” facies bivalves are uncertain. Proposed clades include the pteriomorph families Bakevelliidae, Isognomonidae, and the order Ostreoida. This section will describe various characters of these families and their relation to the “Lithiotis” facies bivalves and will close with alternative phylogenies. Carter (1990) revised the taxonomy of many so-called problematic bivalves on the basis of microstructure. Shell microstructure provides an excellent base for discussion of the “Lithiotis” facies because many have similar microstructures and despite their aberrant morphologies this may well be the best link to recreating a phytogeny for the “Lithiotis” facies bivalves. Ligament structure is also a key character in differentiating between the “Lithiotis” facies bivalves and associations with other taxa. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 Family Bakevelliidae The endo-or epibenthic, byssally attached Bakevelliidae originated in the Late Permian, flourished during the Early and Middle Jurassic, and became extinct in the Late Cretaceous (Cox, 1969) (Figure 86A). They are characterized by a rhombic to trapezoidal outline with a more or less pronounced posterior wing (Hayami, 1957a). Ventral to a distinct ligamental area, which bears several ligament pits, they exhibit hinge teeth, which vary considerable in number and shape (Cox, 1969). At their pinnacle, the bakevelliid bivalves were common elements in benthic Jurassic shelf deposits, occurring in a wide range of lithofacies (Aberhan and Muster, 1997). Waller (1998) pointed out that the multivincular ligament systems of the bakevelliid bivalves consist of irregularly spaced resilifers that continue to expand during ontogeny. The result is a series of irregularly triangular resilifers rather than parallel-sided, more regularly spaced resilifers seen in the Inoceramidae and the Isognomonidae which may have evolved independently (Crampton, 1988). Plesiomorphic traits of the bakevilliids with other pteriomorphs include: a reduced anterior adductor muscle (but still dimyarian), nacreous inner shell layers and regular columnar prismatic calcitic outer shell layers (Waller, 1998). Most bakevelliids have calcitic, regular simple prismatic structure on both valves (Hayami, 1957a). Their regular simple prisms show irregular, wavy extinction under crossed polarized light (Carter, 1990). A few bakevelliids, such as the Jurassic Bakevellia and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 Figure 86. Examples of other bivalve families. A - Gervillaria ashcroftensis, a bakevelliid bivalve from the Early Jurassic of western Canada (interior view of the left valve, after Aberhan and Muster, 1997). B - Isognomon isognomon, a modem isognomonid collected from Cebu Island, Phillipines (interior view of left valve; Institut und Museum fur Geologie und Palaontologie, Tubingen). C - Crassostrea titan from the Upper Miocene, Santa Margarita Formation of central California (exterior view of left valve; University of Southern California collection). A, C. 'W fr y y Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 Cretaceous Gervillella, show irregular simple prisms on one or both valves (Carter, 1990). Nevesskaya et al. (1971) placed the bakevilliids in a superfamily with the Dattidae, Cassianellidae, and Isognomonidae. Ichikawa (1958) suggested that the Bakevelliidae, Pteriidae and Cassianellidae evolved from the pterinid Leptodesma. Nakazawa and Newell (1968) proposed a diphyletic origin for the bakevilliids. Cox (1969) indicated that this family was probably not monophyletic and he and Nakazawa (1959) favored a pterioid ancestry for at least some of its genera. Based on his theory of an independent evolution of the bakevelliid ligamental structure, Waller (1998) placed the Bakevelliidae and the Cassianellidae, outside of the Pteriidae, Isognomonidae, Malleidae and Pulvinitidae. Family Isognomonidae The Isognomon genus includes most species of “Perna” known from the Upper Permian to the Recent (Hayami, 1957b) (Figure 86B). Recent species are inequivalved and purse-shaped with a benthic, sessile habit and found in tropical or subtropical seas in nearshore areas. The left valve is usually more convex than the right (Cox, 1969). The posterior wing is undifferentiated to well defined and the anterior auricle is rarely present (Cox, 1969). Most characteristic is the multivincular ligamental area which is usually flat, with ligamental grooves reaching and indenting its lower margin. Beginning with a single groove, the number of ligamental grooves steadily increases during shell growth (Siung, 1980). The interligament areas are covered by periostracum and lamelllar ligament. As noted by Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 Waller (1978, Fig 1L) the fibrous part of the ligament is continuous between the two valves. All species are monomyarian with a discontinuous pallial line (Yonge, 1968). The exterior of the shell is smooth, concentrically lamellose or irregulary undulating, and radial ornament is absent except in Mulletia. Isognominids typically have calcitic regular simple prisms on both valves, excluding the ligament area, plus middle and inner nacreous layers. The calcitic prisms show mostly irregular, wavy, polycrystalline extinction in crossed polarized light (Carter, 1990). Similar symmetrical, calcitic prismatic outer shell layers occur in the Bakevellidae, Pteriidae, Maleidae, Ambonychiidae, Myalinidae and in Letodesma of the Pterineidae (Carter, 1990). With the exception of an extremely thin aragonitic ligostracum which may be locally developed, the ligament attaches directly to the nacreous shell layer (Yonge, 1968). In Recent isogonomid bivalves the lamellar ligament attaches to a thin layer of aragonitic, vertical, irregular simple prisms and irregular spherulitic prisms (Carter, 1990). This ligostracal layer covers the ligamental area between the ligament grooves. It extends slightly into the outer shell layer and does not extend over the ligament area. In this respect, isognomonids resemble pterineids, myalinids, bakevelliids, malleids, pinnids, cassianellids and pteriids, but they differ from ambonychiids and inoceramids (Waller, 1998). Living isognomids have much thinner shells than most fossil species. The Recent species Isognomon alatus is commonly found in mangrove swamps attached by a byssus to the prop roots of the red mangrove tree (.Rhizophora mangle L.), attached to jetty pilings, or growing in bottom sediments in shallow water (Siung, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 1980). The Recent species Isognomon ephippium has hinge teeth that are present in the earliest growth stages but become obsolete in the adult stage (Cox, 1969). Mesozoic isognomid bivalves are usually subequivalved or inequivalved, linguliform or mytiloform in outline except for several aberrant Cretaceous forms (e.g. Perm mullelli and Perna quintucoensis). Cox (1969) proposed that the Isognomonidae arose from the Bakevelliidae in Triassic time, losing the Pteria-like outline associated with the bakevelliids. Stanley (1972) noted that Permian Waagenoperna, the earliest known genus in this family, is subequivalve unlike most isognomonids that followed. He followed Cox (1969) in suggesting that isognomonids evolved from the Bakevellidae. Order Ostreoida Based on Waller (1978), the Order Ostreoida (Upper Triassic-Recent) is characterized by anisomyarian or monomyarian muscles, cemented early in ontogeny or lying free on the substrate on either the left or right valve and lacking a foot and byssal notch in the dissoconch stage (Figure 86C). One of the most diagnostic features of the order is the shell microstructure. The shell layers are primarily calcite, with simple-prismatic calcite tending to occur as an outer layer on both valves foliated calcite prominent, and aragonitic layers if present are crossed lamellar (Carter, 1990). The ligament is alivincular or irregularly multivincular. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173 Results of the Phylogenetic Analysis The constrained “branch and bound” search results yielded over 1080 trees. The 50% majority rule tree is presented in Figure 87. One most parsimonious tree was recovered with 97 steps length. The consistency index of the tree is 0.88, the retention index is 0.83, the rescaled consistency index is 0.73. The value of the consistency index is higher than the mean value of data sets this size, and is also within the range of consistency indices for phylogenies of this size (in terms of numbers of taxa; D. Geiger, pers. comm. 2002). The family Lithiotidae, which included Lithiotis problematica and Cochlearites loppianus, was described by Cox (1971, p. N 1199) as: Large thick-shelled, oblong, much elongated dorsoventrally, compressed, slightly to moderately inequivalve, with general resemblance to Crassostrea (Ostreidae) but attached possibly by RV, which is more convex than LV; umbones very acute, curved in some specimens, either to front or rear, hinge edentulous; ligamental area large, greatly elongated dorsoventrally differing from that of Ostreidae in absence or narrowness of median groove for fibrous ligament; monomyarian, commonly with thin internal buttress in each valve passing from lower margin of ligamental area to posterior margin of adductor scar; ostracum formed of lamellar calcite together with prismatic calcite developed as intercalate layers or as masses of radially disposed crystals surrounding tubular vesicles. Cox’s (1971) designation of the Lithiotidae may have been based on poorly preserved specimens that did not record the three-layered structure described by Chinzei (1982) and Carter (1990). Accorsi Benini and Broglio Loriga (1977) removed Cochlearites from the Lithiotidae and created the family Cochlearitidae despite the observations of Reis Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 Figure 87. Proposed phylogenetic tree for the “Lithiotis” facies bivalves with other lamellibrach bivalves. Tree was generated using a constrained ACCTRAN “branch and bound” parsimony analysis, with 50% majority rule consensus. Autobranchia Heteroconchiadae Mytiloida Arcoida Limoida Ambonychiodea Ostreoidea Gryphaeidae Monotoidea Anomnoidea Pectinoidea Aviuclopecinoidea Umburridae Pinnidae Pterinidae Bakevelliidae Pterioida Isognomonidae Lithiotis Cochlearites Lithioperna Mytiloperna Gervilleioperna Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 (1903) that these two genera are closely related. Carter (1990) proposed that they remain in the same family. Bohm (1892) considered both genera to be true ostreids. Nevesskaya et al. (1971) placed Lithiotis in the suborder Ostreina (now the order Ostreoida), along with the families Ostreidae, Gryphaeidae and Chondrodontidae. Meanwhile, both Mytiloperna and Gervilleioperna were placed by Cox (1969) in the family Isognomonidae. Chinzei (1982) suggested that “Lithiotis" facies bivalves and bakevelliids evolved from a common ancestral stock. Seilacher (1984) also favored derivation of the group from bakevelliids because these groups lived together in tropical, marine environments. Based on the “broad tooth plate” as some teeth occur below the ligamental area, Seilacher (1984) proposed that Mytiloperna also belonged to the family Bakevillidae. Also, bakevellids underwent a major evolutionary radiation in the Lower Jurassic, when “Lithiotis” facies bivalves first appeared (Aberhan and Muster, 1997). Bakevellids in general differ from the other four “Lithiotis” bivalves in having hinge dentition, a variation of a multivincular ligament (as described earlier), anisomyarianism and byssal attachment. However, there are significant exceptions to these generalizations within the Bakevelliidae. The bakevelliid genus Bakevellia shows a general evolutionary trend from anisomyarian to monomyarian (Carter, 1990). The bakevellids (e.g. Cretaceous Phelopteria) show ontogenetic reduction of their ligament from multi vincular to alivincular (Hayami, 1965). Finally, some bakevellids were edentulous, only slightly inequivalved and slightly taller than long (e.g. Panis) whereas others, like Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 Kobayashites had a septum in their umbonal cavity, as seen in Lithiotis (Hayami, 1957a). Cochlearites is the only “Lithiotis” facies bivalve without a multivincular ligament. All bakevellids have a multivincular ligament with the exception of the Cretaceous genus Phelopteria, whch shows ontogentic reduction o f its multivincular ligament into a single long, shallower resilifer (similar to Cochlearites-, Hayami, 1965). The shell structures of “Lithiotis” facies bivalves and the bakevelliids are relatively similar. A calcitic prismatic shell layer was not mentioned by Broglio Loriga and Neri (1976) and Accorsi Benini (1979) in their works on the Lower Jurassic Gervilleioperna, Mytiloperna and Lithioperna. However, a recent study by Broglio Loriga and Posenato (1996) verifies the presence of a thin, calcitic outer shell layer in Mytiloperna and Lithioperna. Because of the likelihood that lihtiotids evolved directly from bakeveliids, Carter (1990) placed the family Lithiotidae near the Bakevelliidae in the superfamily Pterioidea and collapsed the Cochlearitidae into the Lithiotidae. Not all characters of the “Lithiotis” bivalves are congruent with the diagnosis above. Following Cox’s classification (1969), some specimens of Mytiloperna were attributed to the Isognomidae (Broglio Loriga and Neri, 1976). According to Cox (1969), the Isognomidae have “hinge teeth present in the earliest growth stages, but soon become obsolete.” Therefore, the adult shell is without teeth. In contrast the Bakevelliidae have hinge teeth both in early growth shells and usually in the adult shells as well. In the adult Mytiloperna shell, teeth are present. The teeth of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill Mytiloperna show a broad variability with regard to number, orientation and height. Loriga and Posenato (1996) proposed that the retention of teeth of Mytiloperna into the adult stage is a morphological convergence with the Bakevelliidae. Yet, Mytiloperna and Lithioperna are characterized by a broad subligamental plate, the extreme development which has no correspondence with the Isognomidae or the Bakevelliidae. Another strange character is the fibrous irregular prismatic inner layer of the “Lithiotis” facies bivalves, the massive development of which is not recorded in other living or fossil bivalves (Taylor et al., 1969; Carter, 1990). The classification of “Lithiotis” facies bivalves as Ostreoids by Bohm (1892) and Nevesskaya et al. (1971) is unlikely based on shell microstructure and ligament arrangements described above, hence the placement of the ostreoids in the outgroup. The proposed phylogeny places four of the five “Lithiotis” facies bivalves within the node with the family Isognomonidae, hence the sister group. This placement is appropriate if the multivincular ligament is considered as an apomorphy and that the Bakevellidae is a paraphyletic group, which should be included with other multivincular ligament families. Gervilleiopema with its irregular multivincular ligament structure is placed outside of the node with the four other “Lithiotis” facies bivalves. Within the node, Lithiotis and Cochlearites share the highest number of similar character states. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 178 CHAPTER 4: PALEOECOLOGY AND BIOZONATION OF THE “LITHIOTIS” FACIES BIVALVES Previous chapters have focused on the wide range of aberrant morphologies from several different facies in nearshore tropical environments that the “Lithiotis” facies inhabit. However, the term “Lithiotis” facies has been applied haphazardly to these unique bivalves. As discussed earlier, Lithiotis problematica formed extensive rudist-like buildups, yet not all “Lithiotis” facies bivalves constructed bioherms (Broglio Loriga and Neri, 1976). The purpose of this chapter is to clarify the term “Lithiotis” facies by describing the observed ecological zonation of the five bivalves. Methods Sampling methods at each site were described in Chapter 2, in the context of a “lithofacies” assessment. To assess biofacies, bulk samples of 2.3 kg (5 pounds) were taken from discrete stratigraphic intervals less than 1 m in vertical extent; interbuildup facies are represented by single beds and within the various buildup facies (flanks, core, above and below) samples represent a single sediment type (Table 8). These samples were slabbed at 1-cm thick intervals, and attempts were made to identify organisms to the generic level when possible. Some representative faunal samples were prepared using acryloid and a mild formic acid bath to remove surrounding matrix, to aid in identification. For the Suplee-Izee Robertson Formation sites, R-mode cluster analyses were used to compare assemblages. R-mode clusters were performed only on these sites Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 8. Summary table of number of samples from field sites and representative facies Facies W estern U nited States Suplee-Izee, O R G arfield Hills, M t. Jura, CA NV Ponte dell'A neuilla M onte L essini, Italy Bellori G arzon di Sotto Central & H igh Atlas, M orocco A it A thm ane A ssem souk N on-R eef 10 4 3 9 4 4 1 R eef 13 5 3 2 4 R eef Flank 3 4 2 N erineid 3 2 2 Total 29 9 8 9 8 4 5 6 V O 180 because the number of samples collected was sufficient for a robust analysis (see Manly, 1994 for a discussion.). An R-mode cluster analysis groups the occurrence of taxa at a variety of different transects, on the basis of their dissimilarity or “distance.” The original data was recalculated so that each taxon was represented as a percentage of a one-meter transect. The cluster method in this study calculated the distances as a variation of the correlation coefficient (1-Pearson) and the taxa were linked using Unweighted Pair-Group Method Average (UPGMA). To determine the intensity of bioerosion and encrustation on “Lithiotis” facies bivalves, individual specimens were examined from field sites and museum collections at the California Academy of Sciences, Natural History Museum of Los Angeles County, University of Tubingen, the Natural History Museum of Verona and the University of Ferrara. Results Table 9 contains a faunal list of all the species identified in this study and their presence at each respective field site. Because of a touch of metamorphism that most of the sites have endured through various tectonic events, most organisms could not be identified at the generic or specific levels. Therefore, this faunal list represents only the few specimens that could be identified. Macrofossils Cluster analysis (Figure 88) was used to estimate the various communities at Suplee-Izee, Oregon for their diagnostic taxa. These sites also have a well- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 181 Table 9. Faunal list. Fauna Western United States Monti Lessini, Italy | Central & High Atlas Suplee- Garfield Mt. Jura, Izee, OR Hills, NV CA Ponte Bellori Garzon di Ait Assemsouk dell'Anguill Sotto Athmane "Lithiotis" Facies a V Lithiotis V V V V Cochlcearites V Lithioperna scutata a / V Gervilleiopema V V V Mytiloperna V V BIVALVIA "Astarte" V V Camptonectes V Cardinia V V Chlamys V V Coelastarte V Corbis V Ctenostreon V Entolium V Gervillia V Goniomya V Gramattodon V Gresslya V Isocyprina V Lima V V Lucitia V V Megalodon V? V? Meleagrinella V V Modiolus V V Mytilus V V Opisoma V? V Ostrea V Pachyrisma V? V Paralleolodon V Pecten juhanus V V Pholadomya V V V V Plagiostoma V Pleuromya V V Trigonia V V Weyla V V GASTROPODA Nerinea V V V V V ^ V V Scurria V BRACHIOPODA Rhyncbonellids V Terebratulids V V V V CNIDARIA Opelismilia V V V Phacellostylophyllum V V Cerioid corals V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 182 Figure 88. UPGMA cluster with 1-Pearson coefficient distances for the Cow Creek Bioherm at Suplee-Izee, Oregon. % Similarity 100 50 0 ' -------------------------------1 ---------------- i 1 Inter buildup Lim a Cam ptonectes Cardirria Chlam ys Parallelodon O strea Pieurom ya Isocyprina C ervillia G ram attod o n M odiolus Infaunal Lucina Trigonia P holadom ya C oelastarte [Spongiomorphsj Weyla Pinna Reg.echinoids Terebratulids N erinea Lithiotis T Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 183 developed interbuildup community of diverse infaunal bivalves, and a buildup flank community (phaceloid spongiomorphs and regular echinoids) delineated by the cluster analysis (Figure 7). The buildup core is represented by the monospecific aggregation of Lithiotis problematica. Rare, small nerineid gastropods and terebratulid brachiopods occur within the interstices of the lithiotid buildup. In selected sections at the Cow Creek site, this buildup core complex grades laterally into a buildup flank assemblage typified by regular echinoid debris including the hollow spines of diademoid urchins, a phaceloid spongiomorph (Spongiomorpha ramosa?) and the bivalve Weyla sp. (Figures 12, 15 and 20). The interbuildup assemblage is similar to the “infaunal bivalve facies” described by Batten and West (1976) for the Robertson Formation characterized by the bivalves Modiolus, Trigonia, Camptonectes, Pholadomya, Parallelodon and Lucina. Another facies commonly associated with Lithiotis problematica buildups in Western North America is one of densely packed nerineid gastropods, such as that found at Mt. Jura, California. The faunal composition of the European and Moroccan sites has been the subject of much research, including studies by Broglio Loriga and Neri (1976) and Accorsi Benini and Broglio Loriga (1982) in Italy, Buser and Debeljak (1994) in Slovenia and Septfontaine (1984 and 1986) in Morocco. The Italian and Moroccan sites contain all five of the “Lithiotis” facies bivalves, and a greater variety of facies can be recognized on the Tethyan carbonate platforms when compared to the accreted terranes of Western North America. Similar associations of buildup flank Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 184 fauna are found at the Tethyan sites, including the thick-shelled bivalve Opisoma menchikoffi, styllophyllid corals, unidentified cerioid colonial corals, regular echinoid debris, sponges and the solitary coral Opelismilia sp.. Aggregations of high-spired gastropods are common at many of the sites. Interbuildup macrofauna at the Tethyan sites are limited to Mytilus sp., Pecten juhanus, Lima sp., Pholadomya sp., and Ceratomya sp.. Microfossils The foraminifera Orbitopsella praecursor Gtimbel and Lituosepta recoarensis Cati, important biostratigaphic markers, are found in both the Italian and Moroccan sites. Other foraminifera including Mayncina termieri Hottinger, Haurania amiji Henson, H. deserta Henson, Involutina sp., Trocholina sp. and Frondicularia sp. are common elements (see Fugangnoli and Loriga Broglio, 1996 for review). The codiacean algae Palaeodasycladus mediterraneus (Pia) and Thaumatoporella parvovesiculifera (Raineri), are prevalent in Tethyan facies associated with Lithiotis and Cochlearites. The rhodophyte Cayeuxia sp. is found in association with Lithiopema scutata. At Suplee-Izee, the interbuildup area supports a wide array of microfossils including red algae, small miliolid foraminifera, thin shelled ostracods and possibly Palaeodasycladus sp.. The Cow Creek and Jackass ranch sites are particularly rich in algae. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 185 Encrustation and Bioerosion Clionid sponge borings, Entobia, are found on individual Lithiotis specimens in thin section and on hand samples. The limpet Scurria was found in the Assemsouk structure on a Cochlearites valve (Lee, 1983) and a shallow ovoid excavation, similar to the resting trace of a limpet was found on the interior of a transported Lithiotis. Trypanites-shaped burrows without calcareous linings, possibly the result of boring by lithophagid bivalves, were found on a few Lithiotis specimens (Figure 89). Several disarticulated lithophagid valves were found in the interbuildup facies of the Robertson Formation, in Suplee-Izee. Many of the algae and Lithiotis problematica were encrusted by serpulid worms. Most encrustation occurs on the interiors of disarticulated lithiotid shells and therefore is post-mortem. Bioerosion is conspicuously absent from the other “Lithiotis” facies bivalves: Gervilleiopema sp, Mytilopema sp. and Lithiopema scutata. The exclusion of bioeroders from estuaries, lagoons, bays and intertidal zones has been well- documented by the modem aquaculture industry (see White and Wilson, 1996 for review). Similar restrictions may have occurred in the Early Jurassic. Modem coral reefs, particularly reefs in mesotrophic waters, are eroded continuously by a host of bioeroding organisms (Hallock and Schlager, 1986; Wood, 1993). The dearth of bioeroders, encrusters and other shell-destructive taxa in the Early Jurassic “Lithiotis” facies bivalves could be explained by a variety of factors. Harper et al. (1998) attribute lack of evidence for Early Jurassic bioerosion in other Early Jurassic sites to taphonomy (i.e. poor preservation). However, even at some of the sites Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 186 Figure 89. Trypanites-shaped burrows without calcareous linings, and circular boring or resting traces on a Lithiotis problematica. Specimen from the Institut und Museum fur Geologie und Palaontologie, Tubingen. Trypamfcs shaped b u rrow s * C ircular boring or resting trace Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 187 where “Lithiotis” facies bivalves are well-preserved, bioerosion is rare. A second possibility is that bioerosion was diminished globally by the preceding mass extinction interval. Of all of the “Lithiotis” facies bivalves, Lithiotis problematica would have been most prone to predatory bioerosion. Its thin free valve, only a few millimeters thick, would have left it vulnerable to predatory drilling or shell-crushing. The other four “Lithiotis” facies bivalves had thick valves that would have required significant effort by a predator. The first predatory gastropod-like boreholes are known in the Cambrian (Conway Morris and Bengston, 1994) and possibly as early as the Precambrian (Bengston and Zhao, 1992). Predatory gastropods became ubiquitous predators in marine benthic systems by the Late Cretaceous (Kowalewski et al., 1998). Although very rare, drilling predators were present in Early Jurassic benthic ecosystems (Harper, et al., 1998; Kowalewski et al., 1998). Predatory asteroids had appeared in the Devonian, and the ability to feed extraorally (i.e. able to prey on bivalves) was acquired by the Early Mesozoic (Gale, 1987). And yet, as discussed below, it is Lithiotis problematica that most likely lived in a more open marine environment. A “non-uniformitarian” explanation - a reduction in the occurrence of predators in the preceding crisis , seems likely. Proposed Biozonation Field and thin section observations described in Chapter 2 when combined with faunal occurrence data indicate a strong zonation of "Lithiotis" facies bivalves Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 188 in shallow nearshore environments. Gervilleiopema and Mytilopema are restricted to intertidal facies. Lithiopema is found throughout the lagoonal subtidal facies and even in some low-oxygen environments. Lithiotis and Cochlearites are found in subtidal facies, constructing buildups. These associations and proposed life habits are discussed below and presented in Figure 90. Tidal Flat/Shoal facies: Gervilleiopema sp. and Mytilopema sp. Mytilopema and Gervilleiopema are typified by the facies found at Ait Athmane, representative of a tidal flat and exposed shoal environments (Crevello, 1988; Septfontaine, 1986). Two lithofacies are common: laminated carbonate mudstones and plane-bedded wackestones. The carbonate mudstones are flat-bedded to slightly mounded and locally have fenestral fabrics and desiccation cracks (Crevello, 1988). Teepee structures, another indicator of subaerial exposure, are common (Burri et al., 1973). In thin-section, the mudstones are formed by peloids and debris from ostracods, forams and gastropods. On some bedding surfaces, Ophiomorpha-type trace fossils are common, characteristic of a nearshore environment (see Figure 55). Beds of scattered individuals of Gervilleiopema sp. or small clusters of Mytilopema sp. at the Ait Athmane site are capped by an evaporite breccia. Thin sections from Ait Athmane Column D indicate possible primary dolomite, another line of evidence for an evaporitic nearshore environment. In cross-section, Gervilleiopema sp. appears to be a pleurothetic epifaunal recliner, thick-shelled and only slightly inequivalved with the thicker heavier valve Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 189 Figure 90. Proposed biozonation diagram of "Lithiotis" facies bivalves. From the lower left comer in a clockwise direction: A - Gervilleiopema-, B 1 - Mytilopema, orthothetic semi-infaunal recliner with expanded lunule morphotype; B2 - Mytilopema, orthothetic semi-infaunal equivalved morphotype; B3 - Mytilopema, pleurothetic inequivalved morphotype; C l - Lithiopema, spoon-shaped mudsticker morphotype; C2- Lithiopema, thick cup-shaped morphotype; C3 - Lithiopema, thin recliner morphotype; D - Lithiotis, spoon-shaped mudstickers in “banana-bunch” clusters; E - Cochlearites, semi-infaunal spoon-shaped mudstickers. Observations of life habit and mode compiled from Accorsi Benini (1979), Chinzei et al. (1982), Seilacher (1984), Broglio Loriga and Posenato (1996), Debeljak and Buser (1997). Proposed facies relationships are from this study and Broglio Loriga and Neri (1976). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 190 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 191 acting as the lower-valve, similar to gryphaeid oysters (Figure 90A). Unlike the other “Lithiotis” facies bivalves, it does not appear to form gregarious associations. However, Mytilopema sp. is commonly found in dense arrangements. In the less dense assemblages, the more common forms are the myaliniform shape of the orthothetic and pleurothetic recliners (Figure 90B1 and 2). The final growth form, a mudsticker, is common in dense arrangements near aggregations of Lithiopema and Cochlearites (Figure 90B3). The association of both Mytilopema and Gervilleiopema at Ait Athmane with lithologic evidence of subaerial exposure, suggests life in intertidal environments. Lagoonal subtidal: Lithiopema scutata Lithiopema scutata is common at most Moroccan and Italian sites. It occurs just behind the coral facies at Ait Athmane and in fan-like arrangements at Ponte dell’Anguillara and in solitary arrangements at Ait Athmane, Assemsouk and Bellori. Adult specimens of Lithiopema exhibit three different morphotypes which are characterized by different behaviors and different environments (Figure 84). The first Lithiopema morphotype has an elongated, ovoidal outline with a “spoon-shaped” mudsticker morphotype found in very dense “fan-like” arrangements (Figures 81A and 85). The presence of root traces penetrating into the interior of articulated Lithiopema morphotype A shells in life position lends credence to the idea that these organisms occupied the lagoonal habitat, near swamps (Posenato et al., 2000; Figure 90C1). However, Lithiopema morphotype A is also Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 192 common at Ait Athmane, Morocco, a high-energy carbonate setting along the outer platform margin. The pleurothetic, cup-shaped recliner morphotypes are characterized by shells with rounded or obliquely ovoidal outlines (Figures 8 IB and C). Lithiopema morphotype B has a circular outline and is found in deposits at Ait Athmane with cross-bedded features, shell debris and oncoliths, interpreted as inner platform and restricted lagoonal facies (Figure 90C2). It may have developed a “heavy-weight” strategy for bottom stabilization in order to prevent capsizing (Seilacher, 1984). Lithiopema morphotype C is a thinner-shelled form and ovoidal in outline, with valves up to 10 mm thick and 350 mm high (Figure 82B). This morphotype occurs in mud-rich substrates with a minor amount of skeletal debris; therefore, a “lightweight” strategy or “snowshoe” function may have developed to prevent sinking into the mud (Seilacher, 1984). This morphotype is common in the back-reef lagoonal environments at the Assemsouk site (Figure 90C3). Subtidal Buildup Constructors: Lithiotis problematica and Cochlearites loppianus This facies consists of massive lenticular, convex-upward calcareous buildups, which interfinger with and grade laterally into thinner beds of Lithiotis or Cochlearites fragments and in some places an echinoid-dasycladacean-bivalve flank facies. At the Suplee-Izee outcrops, the facies is light to medium gray, massive, cliff forming, and up to 6 m thick (Figure 17B). Geopetal sediment fills some of the lithiotid shell cavities. Fine to medium-grained packstone with a matrix of micrite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 193 and microspar is found between the buildups. Small cavities within the buildup framework are filled with carbonate mud and silt; peloids of an unknown origin fill the cavities of some fossils as does peloidal cement in many modem reefs (Macintyre, 1977). Both Lithiotis and Cochlearites have been described as upright, spoon-shaped mudstickers. Lithiotis as described earlier are found in vertically oriented “banana- bunch” clusters (Chinzei et al., 1982) with colonies starting on any available hard substrate (rocks or shells; Figure 91). Juveniles most likely attached themselves initially with a byssus, but became cemented later to older Lithiotis bivalves. In cross section, body chambers are filled with sediment at varying levels. Nauss (1986) proposed that “most of the (framework) matrix sediment was deposited after the bivalves were well established.” The result was well-cemented buildups that were certainly wave-resistant and rose above the surrounding seafloor (Buser and Debeljak, 1994). Cochlearites grew similarly to Lithiotis, vertical in life position (Figure 49). The orientations of Cochlearites in the Assemsouk section barely deviate from upright, without the twisting so common in Lithiotis buildups. There is not the same evidence of cementation or attachment to other clams as in Lithiotis. Therefore, it is presumed that Cochlearites buildups were not as well-cemented or wave-resistant and may have had less topographic relief. In Suplee-Izee, Lithiotis constructed buildups are laterally continuous with a buildup flank facies bearing a phaceloid spongiomorph as well as spines and plates Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 194 Figure 91. Lithiotis problematica bouquet at the base of a buildup at Jackass Ranch, Suplee-Izee, Oregon of regular echinoids, both of which would have been organisms restricted to open marine or at least normal salinity conditions. Lithiotis probably needed well- oxygenated, clear waters, as it is only found in position in clean, calcareous facies (Posenato et al., 2000; Figure 90D). At Assemsouk, the Cochlearites facies caps a well-developed reef containing scleractinian corals (Figure 47B). While not laterally continuous, it is likely that Cochlearites also inhabited more open marine conditions than the other “Lithiotis” facies bivalves (Figure 90E). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 195 Discussion of Photosymbiosis In an excellent review of algal symbiosis and its recognition in the fossil record, Cowen (1983) elaborated on the criteria for recognition for paleophotosymbiosis suggested by Vogel (1975) for rudists. These indirect criteria or correlates of photosymbiosis were proposed for evaluating the potential of photosymbiotic hosts among fossil foraminifera, corals, brachiopods or mollusks (Table 10). These criteria include growth habit, calcification, stable isotope signature, paleoenvironment, pseudocoloniality, and possible light-transmitting structures. From the growth habit of organisms, specifically the maintaining of a characteristic life position such that body tissues displayed to light, a hypothesis of algal symbiosis may be proposed (Cowen, 1983). One must first rule out other factors that may contribute to an up-right growth habit such as food gathering, current direction or even substrate competition which may also produce similar orientations. Modem oysters in reefs maintain a growth habit orientated towards a light source as an indirect consequence of the selection of that growth habit for current direction and substrate competition. As described earlier, one possible way to test for such alternative orientations is the paleocurrent test which was applied to Lithiotis, Cochlearites and Lithiopema. Lithiotis and Cochlearites, in contrast to many oysters, do not orient their commissure planes in a single direction. Instead, these two buildup-constructing genera radiate out from a central "bouquet." This Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Table 10. Checklist o f criteria for recognition of photosymbiosis in fossil bivalves. Criteria Lithiotis Cochlearities Gervilleiopema Mytilopema Lithiopema growth habit yes yes no no yes calcification yes yes yes yes yes stable isotope shift ? yes ? ? no paleoenvironment yes yes yes yes yes light-transmitting structures yes no no no no ON 197 arrangement does not select for maximizing filter-feeding, a trophic mode of many heterotrophic bivalves. It could be possible that the radiating growth habit exhibited by Lithiotis and Cochlearites was a result of selection to maximize exposure to another trophic niche: light. In general, hosts of algal symbionts secrete carbonate more rapidly than their non-photosymbiotic counterparts (Cowen, 1983). Several hypotheses have been advanced to account for this observation: 1) C 02 removal by photosynthesis helps drive bicarbonate to carbonate (Goreau, 1959); 2) algal uptake of phosphate which could otherwise act as a crystal poison to inhibit carbonate deposition (Simkiss, 1964); 3) release of photosynthetic energy for calcification (Chalker, 1976); and 4) energy release for organic matrix formation to aid calcification (Wainwright, 1963). However, some heavily calcified bivalves are not appropriate candidates for photosymbiosis. Bivalves with heavily calcified valves are common in areas of high predation, boring and other shell destructing fauna or high productivity (e. g. Crassostrea gigantissima\ Kirby, 2000). Some bivalve species are also exceptionally long-lived and their elaborate calcification may only be a record of many years of shell deposition (Heller, 1990). Another caveat is that some bivalves that are facultative photosymbiont hosts do not exhibit changes in their calcification rates from their non-photosymbiotic counterparts (Jones and Jacobs, 1992). Increased calcification alone is not a sufficient criterion to propose that a fossil bivalve is a candidate for a photosymbionts host, but is the most readily identified in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 198 the fossil record. All five of the “Lithiotis” facies bivalves exhibit heavy and elaborate calcification. During algal photosynthesis, the stable isotopes of carbon and oxygen are fractionated, and evidence of this fractionation may be preserved to varying degrees in the carbonate skeleton of the host (Cowen, 1983). Evidence for such patterns in bivalves were promising in early studies and the resolution declined as more species’ stable isotope profiles were compared. The modem symbiont-bearing Tridacna maxima exhibits a depletion in S1 3 C values of approximately 2%c, with no change in 51 8 0 values (Jones et al., 1986; Romanek et al., 1987). These studies led to hopes of documentation of photosymbiosis in fossil bivalve taxa. However, more recent studies have not shown similar shifts in other modem photosymbiotic bivalve taxa (Clinocardium nuttali, Jones and Jacobs, 1992). The issue of stable isotope signatures is explored in the following chapter for Lithiopema and Cochlearites. Photosymbiosis in benthic organisms is predominantly found in tropical, shallow water carbonates (i.e. reefs) today. The criteria that determine the distribution of reefs are correlated with the prevalence of photosymbiosis: shallow water depth, high water clarity and low nutrient concentrations (Hallock and Schlager, 1986; Wood, 1999). Recognizing this environment in the fossil record is the subject of numerous studies. Sedimentologic, faunal and other evidence are used to identify these paleoenvironments. The paleoenvironments of the “Lithiotis” facies bivalves were described in detail in Chapter 2. All of the “Lithiotis” facies bivalves Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 199 are associated with oligotrophic, shallow water settings in tropical paleolatitudes and have high population densities. Cowen (1983) also suggested as evidence of photosymbiosis the presence of “windows,” thin or transparent valves that may have let light transmit through closed valves as in the modem Fragum sp. or Corculum cardissa (Carter and Schneider, 1997). These organisms recline on the substrate and employ “windows” or localized transparent regions in the flattened upper surface of the thinned shell to enhance light penetration to the zooxanthellae in the underlying tissues (Kawaguti, 1950; Seilacher, 1972, 1973). Some of these organisms are epifaunal, some are semi- infaunal. Jones et al., (1988) pointed out that these organisms run contrary to the normal paradigm of bivalve photosymbiotic hosts as heavily calcified organisms, because they have relatively slow growth rates and maintain a small body size. The extremely thin, only 1-2 mm thick, free valve of Lithiotis problematica may have been thin enough to transmit light to a mantle that harbored photosymbionts. Whereas any one of these criteria or correlates is insufficient alone to document photosymbiosis for fossil bivalve taxa, together these criteria present a strong argument for the photosymbiosis. Lithiotis and Cochlearites are the most likely candidates for a photosymbiotic life habit. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 200 CHAPTER 5: SCLEROCHRONOLOGY AND STABLE ISOTOPIC RECORDS OF “LITHIOTIS” FACIES BIVALVES Introduction Sclerochronology, the study of periodic features recorded in the shells of organisms, records ontogeny and paleoenvironments of fossil organisms (Jones and Gould, 1999). An important goal of sclerochronology is the identification of the length of time associated with growth increments, which can quantitatively define growth rates and lead to the basis of further paleoenvironment and ontogenetic reconstructions (Jones, 1983). Many bivalve taxa from shallow water environments exhibit recognizable tidal, fortnightly, monthly, semi-annual and annual patterns. The semi-annual and annual patterns in bivalves are closely related to spawning activity (Lutz and Rhoads, 1980). In organisms with particularly high or slow growth rates, the identification of the annual band is very difficult but of paramount importance. Misidentification of the annual growth band in the coldwater species Spisula solidissima, led to the underestimation of growth rate in early life and overestimation in later years (Jones et al., 1978). Growth rates in bivalves are influenced by a bewildering number of factors, however the major factors include: age, water temperature and food availability/trophic niche. Rates of growth in bivalves tend to be very rapid in the early years and decrease over the course of the organism’s life history (Figure 92). Tridacna maxima grows annually 16 times faster Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. '5 J S 300 250 200 150 100 50 ---- 1 ---- 1 ---- 1 -----1 ---- QBE) < B > — 1 -----1 -----1 -----1 ---- ..--■ ’1---- i 1 1 -----,.....J -----1 ---- 1 ---- ------1 ---- 1 ■ ■ ■ " T " ! ---- , - T.—1 -----j ---- ..... vJ ■ — 1 O - © - O -m —---------- 1 1 1 ■ E l i ) i 1 " k " " ■ ■ t ? ----- - o -o - ■ . + m w F m • • • • . • • » • • • * : -o ■ n ■ ■ ■ • * A # • • v*» 9 • Tridacna ■ Tridacna ♦ Geukensi (R om anek & Gro (M cM illan, 1974 a demissa (Lutz a ssm an 1989) ) n d C astagn a, 1980) o ■ ■ o ^>< • ♦ # A A <f o o a a * o A Modiolus (C om ely, 1978) ▼ Nuculana (A n sell et al., 1978) O Pinna (B utler and Brewster, 1979) O Gryphaea gigantea (Jones and G ould, 1999) X Gryphaea mccullochi(Jones and G ould, 1999) + Gryphaea arcuata (Jones and G ould, 1999) X + , w X X X X X + + + + + <f ▼ v ▼ __ 1 ___L __1 ___1__ X x X X X + + + + + I I I ! XXX + + + I I I ! 10 15 20 25 30 years Figure 92. Modem and fossil bivalve growth rates. 202 than oysters (Bonham, 1965; Pannella and MacClintock, 1968). This rapid growth rate is attributed to Tridacna'& tropical habitat and photosymbiotic habit that enhances calcification (Jones et al., 1986). The sclerochronology of fossil organisms, such as Gryphaea, has also been studied and exhibits similar patterns as their modem counterparts (e.g. Steuber, 1996; Jones and Gould, 1999; Figure 92). Stable oxygen and carbon isotopic profiles of bivalve shells can provide indirect evidence of the environmental and physiologic conditions experienced by an individual throughout its life (e.g., Wefer and Killingley, 1980; Jones et al., 1986; Kirby, 2000). Isotopes of oxygen are more useful than those of carbon in interpreting these environmental variables because fewer factors influenced shell §1 8 0 and bivalves generally exert little physiologic control over the oxygen isotopic composition of their shells (Epstein and Lowenstam, 1953; Epstein et al., 1953; Krantz et al., 1984; Jones, 1985). The most significant environmental influences on the 51 8 0 values of bivalve shell carbonate are the ambient temperature and isotopic composition of the water in which the shell grew (Epstein et al., 1953; Epstein and Mayeda, 1953; Arthur et al., 1983). Because the 8lsO and salinity of water masses are correlated through processes of evaporation and freshwater dilution shell 5lsO is indirectly influenced by salinity (Grossman and Ku, 1986). Shell 5I3 C values are notoriously more difficult to interpret than 5lsO values. Shell S1 3 C is influenced by the ambient temperature and the carbon isotopic composition of water (Keith et al., 1964; Lloyd, 1964; Sackett and Moore, 1966; Mook and Vogel, 1968; Galimov, 1985; Grossman and Ku, 1986; Kirby 2000). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 203 Because freshwater bicarbonate is generally isotopically lighter than that of marine 13 13 waters shell 5 C is influenced indirectly by salinity-correlated changes in water 5 C, which reflect the proportion in which fresh and marine waters are mixed (Keith et al., 1964; Sackett and Moore, 1966; Mook and Vogel, 1968). Shell S1 3 C may be further affected by phytoplankton productivity (Killingley and Berger, 1979; Arthur et al., 1983; Krantz et al., 1987), metabolic effects (Tanaka et al., 1986; McConnaughey, 1989), and growth rate and ontogeny (Jones et al., 1983,1986; Krantz et al., 1987; Harrington et al., 1989; McConnaughey, 1989; Romanek and Grossman, 1989). Because the environments of the Early Jurassic Tethyan seaway are not quantitatively known, no attempt was made to link stable isotope profiles to paleotemperature or paleosalinity. The focus of this chapter is a sclerochronology of three “Lithiotis” facies bivalves, a reconstruction of the stable isotopic profiles of two “Lithiotis” facies bivalves and two younger bivalves for comparison to understand the growth history and in particular rates. Methods Growth band increment data were collected from complete specimens of Lithiotis problematica (one Oregon specimen and one Italian specimen), Cochlearites loppianus and Lithiopema scutata (both from the Institut und Museum ftir Geologie und Palaontologie, Tubingen). These data were compared to published growth results from the modem bivalve Tridacna (Jones et al., 1986), two Late Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 204 Cretaceous rudists Gorjanovicia cf. costata and Vaccinites ultimus (Steuber, 1996) and Early Jurassic Gryphaea mccullochi (Jones and Gould, 1999). Powder was drilled for oxygen and carbon isotopic profiles from specimens of Cochlearites loppianus, Lithiopema scutata, Crassostrea titan and Isognomon janus (Figure 93). Cochlearites and Lithiopema specimens represent the “Lithiotis” facies bivalves. The Lithiopema and Cochlearites specimens were the same used in the growth band analysis. The Lithiopema specimen was collected from the Ponte delTAnguillara field site. The Cochlearites specimen was collected from the Crespadoro site of Chinzei (1982). None of the Lithiotis problematica specimens were suitable for isotope analyses. While some specimens retained some the original aragonite, the preservation was patchy and did not allow for a continuous sampling transect. It is instructive to compare the oxygen isotopic profiles constructed from analyses of the shells with isotopic profiles from younger samples that might be less susceptible to recrystallization and/or may have some familial affinity. A Crassostrea titan specimen from the Upper Miocene Santa Margarita Formation was selected as comparison to the older Early Jurassic bivalves and its large size and prominent growth bands enabled easy and consistent sampling. Isognomon janus was collected from offshore in a depth of 6 m at Cabo Pulmo, near La Paz, Baja California, Mexico. It was selected for comparison to the Early Jurassic specimens because of its proposed phylogenetic affiliation and similar (reef) habitat. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 205 Shell material was removed using a press drill fitted with a 0.1 mm carbide twist bit. The press was fixed and excavation was guided by microscope stage fitted to the drilling platform, so the specimen could be moved in 1 mm or less intervals and recorded. Shells were first impregnated in epoxy for two reasons: 1) to decrease the amount of shell material lost during sawing; and 2) provide three flat surfaces to ease of manipulation of the microscope stage. Care was taken to target only aragonitic bearing layers of the shell. The specimens were sawed down the axis of maximum growth (perpendicular to shell growth increments), using a water-cooled rock saw. The exception was the Crassostrea sample, which was sampled in the ligamental area along the axis of maximum growth (see Kirby, 2000 for details about this sampling method). The sampling interval followed along this surface that appeared to cross one or more major growth increments, in hopes that these exterior rugae corresponded to divisions between the annual growth cycles. From this surface, a series of samples was drilled and distances measured by distance from the dorsal- most section of the shell. The average spacing of the sampling grooves was approximately 1 mm. Sectioning after sample excavation denoted which samples may have drawn from the epoxy or other shell layers; these samples were then excluded from further analysis. Excavations yielded between 0.1 and 1 mg of aragonite powder per sample drill hole and the number of samples between specimens varied greatly due to shell Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 206 Figure 93. Scans of drilled specimens. A - Cochlearites loppianus. B - Lithiopema scutata. C - Crassostrea titan. D - Isognomon janus. All bars are 1 cm long. C. wgm \ ' t ^ ■la, m m ' m m i M il 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 207 length. From the two “Lithiotis” facies bivalve specimens, 90 samples were collected from Cochlearites and 108 from Lithiopema (Figure 93A and B). The number of samples obtained from Isognomon janus was only 19 because of the shell’s small size (Figure 93C). Despite the shell’s large size, the number of samples from Crassostrea titan was 30 because samples were collected from the ligamental area to facilitate comparison with other published fossil Crassostrea data (Kirby, 2000 and 2001; Figure 93D). Data were also available from a Middle Jurassic isotope sclerochronology study, Isognomon murchisoni (Hendry et al., 2001) and will be used in subsequent discussions. Each sample was drilled over a square of wax paper, which allowed for easy collection and transfer of the powders to the University of Maryland Stable Isotope Lab (Lithiopema samples) or the Stable Isotope Lab of University of Southern California (all other samples). After drilling each sample, the bit was cleaned with alternating washes of dilute hydrochloric acid and double-deionized water and dried with a piece of filter paper. The modem samples were roasted in vacuo for one hour at 350°C to remove any remaining organic shell matrix. Roasted samples were reacted at 50°C for a minimum of four hours with concentrated phosphoric acid (density -1.92 g/cm3 ) and prepared C 02 was analyzed on a VG Isotech Prism2 Isotope Ratio mass spectrometer (USC) and Micromass U.K. Isoprime dual inlet mass spectrometer (University of Maryland). Each oxygen and carbon isotopic composition of samples is reported in the standard delta (s) notation as per mil (%c) deviation from the Pee Dee Belemnite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 208 (PDB) standard (Epstein et al., 1953); the average analytical precision of the University of Maryland Stable Isotope Calcite standard was typically ±0.048%c for S1 3 C and ±0.098 for 8lsO. The average analytical precision of the Stable Isotope Lab at USC was ± 0.007%c. for 81 3 C and ± 0.012%c for S1 8 0 . Results The results of the sclerochronology analyses are presented in Figure 94. There is a noticeable change in the length of the periodic shell increments from the Oregon and Italian Lithiotis specimens, as was observed also in the overall morphology of the two populations. The rate of periodic growth increments in the Oregon specimen is roughly double that of the Italian specimen. The surface periodicity is continuous with the inner shell structure of Lithiotis; when viewed in longitudinal cross section, the growth laminae are prominent. Periodic change of shell structure is also clearly recognized in Cochlearites. The periodicity of the growth bands is approximately 1 cm for the first six bands and then tapers off significantly. Growth periodicity is also recognized on the shell surface in the form of regularly prominent lamellar growth lines, and as regular growth lines on the central platform. More than thirty growth lines were visible, however those towards the shell’s aperture are so tightly spaced, they were difficult to discern. As growth periodicity appears at highly regular intervals in most specimens of Lithiotis and Cochlearites and is continuous with changes in the internal Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 250 200 S 150 100 50 t -------- 1 — “ i------ 1 -------- 1 ------- 1 -------- 1 -------- 1 ------- 1 ------- 1 --------1 -------- 1 ------- 1 --------1 -------- 1 -------- 1 ------- 1 — “ i------ r A • • O O---- o A O $ o ° A o o t n □ J * B I tDfl I □ □ □ □ C 3 □ 0 o _ l I I ______ 1 — J_____ 1 ______ ■ ■ ______L. o o o o o o o o -1 I I L . t 1 ------ 1 ------ r O O o o oo oo © O OOP O OO oo o ♦ ♦ ♦ ♦ • Lithiotis (OR) ■ Lithiotis (Italy) ♦ Cochlearites A Lithioperna A Gorjanovicia cf. costata (Steuber, 1996) O Vaccinites ultimus (Steuber, 1996) O Tridacna maxima (Jones et al., 1983) □ Gryphaea mccullochi (Jones and Gould, 1999) □ □ n E 3 □ □ s - J i— * — i ^ * i i t I i » i i 10 15 20 25 30 growth increment Figure 94. Growth rates of “Lithiotis” facies bivalves compared to Tridacna, Gryphaea and rudists 209 210 microstructure, this periodic increment is probably caused by the cyclicity of environmental conditions (annual, tidal or daily changes). Stable isotope data from four o f the five shells occupy overlapping fields that define a broad, positive covariant trend in O-C space (Figure 95). These results are reported in Appendix B. The S1 8 0 values mostly range from 0.5 to -4.2%o PDB and 51 3 C values range from 4.8 to -3.1 %c PDB. The exception to this trend is the Cochlearites specimen. The values from the Cochlearites specimen extend to lighter S1 8 0 values (-4.2 to -8.1 %o PDB) than those observed of other specimens, however the 51 3 C values are similar to that of the modem Isognomon janus. These data are plotted against the distance of the sample from the dorsal edge to produce an ontogenetic profile of 51 8 0 and 51 3 C for each shell (Figure 96). There is a pattern of gradual and synchronous change in 51 8 0 and 51 3 C for all specimens except Cochlearites. Some of the troughs coincide with shell “breaks” or distinct horizons in the shell microstructure as well as external band morphology. Discussion Positive covariant trends in bivalve O and C isotope composition have been interpreted as evidence for brackish or estuarine conditions form Middle Jurassic sediments (Hendry et al., 2001). This is most likely because fresh water has a lower 51 8 0 value than coeval seawater, and typically contains 1 3 C-depleted Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 1 Figure 95. Stable isotope cross-plot of S 1 8 0 and 81 3 C data. Values are reported in per mil (%c) notation relative to the PDB (Peedee Belemnite). Isognomon murchosoni data from Hendry et al. (2001). - l 1 ------- 1 ------ 1 ------- 1 -------1 ------- 1 ------ 1 ------- 1 -------1 ------- 1 ------ 1 ------- 1 -------j------- 1 -------1 ------- 1 ------ 1 ------- 1 ------ 1 ------- r u Sb 0 -5 # • Lithiopema ■ Cochlearites A I. janus V I. murchosoni □ Crassostrea □ J £ □ _)_____ ■ ■ I_____ I _____ I _____ L_ -10 -8 -4 5 180 0 2 dissolved C 02 from organic matter breakdown in soils (Kirby, 2001). Paleotemperatures for the Pliensbachian Northern Italian Alps are poorly constrained; therefore the Grossman and Ku (1986) fractionation relationship is not suitable for application to the S1 8 0 values. However, the 8lsO values of Lithiopema scutata are relatively similar to other bivalves found to be living in an estuarine Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 212 Figure 96. Stable isotope (8lsO and 81 3 C) data for specimens. A - Lithiopema scutata. B - Cochlearites loppianus. Closed circles are 81 3 C values and open circles are 5I S 0 values. Precision of the isotopic data is indicated by vertical error bars. ■ " I 1 I 3 T T j i i r - y — t - — i-----r ]-* t 1 i i ) "' " i i i E u CO * to A. E o CO Lithiopema scutata 3 . 2 3 . 4 3.6 3 . 8 4 . 2 4 . 4 » I i ......| ......"T 4 0 6 0 8 0 distance (mm) - I 1 1 1 -------- 1 --------1 --------1 -------- 1 -------- r - Cochlearites loppianus ■ ■ ■ __I —< * ■ J i_ J i 1 _ 20 B. 4 0 6 0 distance (mm) 8 0 - 8 .5 - 7 .5 - 7 oo 0 0 O 5 $ - 6 .5 ^ -6 - 5 .5 too Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 213 Figure 96 (continued). Stable isotope (51 8 0 and S1 3 C) data for specimens. C - Crassostrea titan. D - Isognomon janus. Closed circles are S1 3 C values and open circles are 51 8 0 values. Precision of the isotopic data is indicated by vertical bars - 7 U ro 1o 4 3 •2 1 0 Crassostrea titan 1 25 30 20 5 10 15 0 -6 - 5 - 4 oo -3 O 3 -2 c. distance (mm) u 2 .4 2.4 3 .2 3.2 _ Isognomon janus 30 25 10 15 20 0 5 °1 c o O 3 D. distance (mm) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 214 environment; Isognomon murchisoni and Crassostrea titan (Figure 95). When the Lithiopema stable isotope plot is compared to the Crassostrea titan stable isotope profile, the two profiles exhibit the same synchrony of 51 8 0 and 51 3 C (Figure 96A and C). Sedimentological evidence supports a similar habitat designation. The regular intervals of high and low S1 8 0 correspond to external growth ligaments of the Lithiopema specimen. If the intervals represent yearly cycles of fluctuating S 1 8 0 in the water due to evaporation or freshwater input, the average rate of growth of the Lithiopema specimen are approximately 17.66 mm/year. This rate is less than that of Tridacna maxima but higher than that of other bivalves. Further analyses with Mg/Ca trace element analyses could remove the salinity effect and approach a more accurate rendering of the Lithiopema’ ’ s paleoenvironments (paleotemperature and paleosalinity). The abnormally depleted 8lsO values (-4.2 to -8.1 %c PDB) of Cochlearites loppianus are typical of a recrystallized specimen. The 8i3C values overlap closely with the modem Isognomon (3.5 to 4.5%o PDB). These relatively high §1 3 C values are uncommon in most bivalves but are similar to S1 3 C values of Terebra areolata, a gastropod common to nearshore tropical environments (Jones et al., 1986). As mentioned earlier, the variations in S1 3 C are not well understood at present. There is evidence of repeated intervals of 8iS 0 and 81 3 C; these minima and maxima are well constrained with duplicates and correspond roughly to the external growth increments. While it is difficult to suggest a possible paleoenvironment based on the depleted S1 8 0 values, it is plausible to propose that the relative cycles observed are Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 215 accurate and may reflect an annual cycle. If these cycles are indeed annual, than the Cochlearites growth rates are on average 11.2 mm/year. This value is similar to the value proposed by Chinzei (1982, ~10mm/year). This growth rate is less than those of large bivalves that are photosymbiotic (Tridacna) or proposed to be photosymbiotic (Vaccinites and Gorjanovicia). However, as discussed earlier, not all photosymbiotic bivalves have increased growth rates (Jones and Jacobs, 1992). Modem Isognomon is very small and has life spans of a 3-4 years (e.g. Harper and Morton, 1994). The isotopic profile of Isognomon janus represents most likely one or two years of growth, as only one trough/peak set is easily discerned (Figure 96D). While the Lithiotis specimens did not undergo a stable isotope analysis, the growth band data may point to a possible growth niche. The external growth increments of Lithiotis can be traced to horizons in the internal shell microstructure (Chinzei, 1982). In Lithiopema the growth bands are most likely annual increments. If the same assumption is made of the Lithiotis specimens, then two very different growth rates are observed regionally. The growth rates of the Italian specimens are relatively slow at about 10.8 mm/year; these values are similar to that of Cochlearites and slower than that of Lithiopema (Figure 94). The Oregon specimens on the other hand have very rapid growth rates, on average 34.1 mm/year. These growth rates are more similar to those values obtained for large bivalves that are photosymbiotic or thought to be so. Another possible explanation of the differing growth rates between the Oregon and Monte Lessini Lithiotis specimens, relates to the differing tectonic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 216 regimes. The Oregon sites are located in a volcanic arc complex. Lithiotis bioherms would have grown on the growing slopes of volcanic islands. These islands had more relief and vigorous water exchange to offer clear water and higher nutrient delivery than would be expected in the passive carbonate platform of the Calcare Grigi. As a result, the difference in tectonic regime may have influenced the difference between the two Lithiotis growth rates. Accorsi Benini (1985) interpreted the ~1 mm growth increments in Lithiotis and Cochlearites to be annual and dismissed the hypothesis that these genera were symbiotic and attributed their great size to longevity. Most modem bivalves in nearshore tropical carbonates have relatively rapid growth rates and reach adult body size in a span of 3-4 years (Heller, 1990). It is more probable that the “annual” increment described by Accorsi Benini represents a lunar cycle and that the Italian Lithiotis specimens have a growth rate on the order of 10.8 mm/year. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 217 CHAPTER 6: CONCLUSIONS Summary 1) Early Jurassic deposits with “Lithiotis” facies bivalves were examined in three field areas: Western North America, Northern Italy and the Central and High Atlas Mountains of Morocco. Western North American sites are located in the Robertson Formation near Suplee-Izee, Oregon, the Thompson Formation at Mt. Jura, California and Dunlap Formation in the Garfield Hills and Shoshone Mountains, Nevada. Northern Italian sites are located in the Calcare Grigi Formation on the South Trento Carbonate Platform and north of Verona in the Monte Lessini district. The two Moroccan field sites, Ait Athmane and Assemsouk are located in the Central and Eastern High Atlas Mountains. The lithofacies of these deposits encompass a range of shallow subtidal to supratidal facies. 2) Five bivalves were studied: Lithiotis problematica, Cochlearites loppianus, Gervilleioperna sp., Mytiloperna sp. and Lithiopema. All of these bivalves display a wide variety of phenotypic variation but include similar features such as heavily calcified valves, a multivincular ligament and a relatively short strati graphic range during the aftermath of the end-Triassic mass extinction. Features studied include: valve shape, size, hinge structure, ligament structure, number of ligaments, shell microstructure, exterior ornamentation and growth habit. A phylogenetic analysis proposes that the “Lithiotis” facies bivalves are a paraphyletic group that is closely related to the Isognomonidae, with the bakevelliid clade. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 218 3) A strong biozonation of "Lithiotis" facies bivalves exists in shallow nearshore environments. Gervilleiopema and Mytilopema are restricted to tidal flat facies and inner platform facies. Lithiopema scutata is found throughout the lagoonal subtidal facies and even in some low-oxygen environments. Lithiotis and Cochlearites are found in subtidal facies, constructing buildups. Lithiotis and Cochlearites exhibit criteria associated with photosymbiosis in bivalves. These bivalves invaded the relatively open niche previously occupied by coral reefs, following their demise during the end-Triassic mass extinction. 4) Sclerochonologic analyses were performed on specimens of Lithiotis, Cochlearites and Lithiopema, stable isotope analyses on Cochlearites, Lithiopema, Crassostrea titan and Isognomon janus. These data were compared to published results of other bivalves, Middle Jurassic and modem. Peaks and troughs in the 8lsO isotopes correspond to internal and external growth bands in both Lithiopema and Cochlearites specimens. Proposed rates of growth for the various bivalves were calculated: Lithiopema (17.6 mm/year), Cochlearites (11.2 mm/year), Italian Lithiotis (10.8 mm/year) and Oregon Lithiotis (34.1 mm/year). Implications Bivalve-constructed buildups are traditionally placed in two models: oyster reefs and rudist reefs. Oyster reefs are common in restricted estuarine and lagoonal environments, and form relatively monospecific aggregations that are commonly but not always aligned with current direction, presumably to maximize passive filter- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 219 feeding capacity (Lawrence, 1971). Lithiopema scutata, with its fan like habit and associated restricted water lithofacies, clearly inhabited a niche similar to that of modem oyster reefs. Rudist constructed reefs are thought to inhabit a wide range of habitats on carbonate platform shelves, with some restricted to lagoonal environments and others found exclusively in the oligotrophic environments associated with modem scleractinian reefs (Perkins, 1974). Elongate radiolitid rudist bivalves, which are similar to Lithiotis and Cochlearites in morphology and habitat, interlock with mutual cementation of neighboring individuals as they grow upright (Kauffman and Johnson, 1988). These rudist aggregations, when at their climax, could be monospecific (Kauffman and Johnson, 1988), as Lithiotis and Cochlearites were in the Early Jurassic. Scott (1995) proposed that the rise of rudists over coral reefs during the Cretaceous was a result of global environmental stress linked to the rapid rise in atmospheric C 02 . The same scenario may be applied to the bivalve-constructed reefs of the Early Jurassic. The appearance of “Lithiotis” facies bivalves was delayed by ten million years after the end-Triassic mass extinction at a time when the nearshore tropical carbonate environments were relatively vacant. Scleractinian corals then recaptured this niche by the Middle Jurassic. Beauvais (1984) noted that middle Lias reefs are lower in coral diversity than the Upper Lias and Dogger coral reefs. Stanley and Fautin (2001) suggested that the disappearance or decreased diversity of scleractinian corals is associated with elevated atmospheric C 02. Three possible global stresses linked to the rapid rise in C 02 may have inhibited scleractinian coral Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 220 growth during the Early Jurassic: excessive temperature, inhibition of calcification, and episodic eutrophication of shallow carbonate shelves. Concomitant with the rise in atmospheric C 02 , was a proposed 3-4°C rise in global sea-surface temperatures (SST; McElwain et al., 1999). It is unclear whether the atmospheric C 02 returned to Late Triassic levels quickly or remained high until the Middle Jurassic (Retallack, 2001). Modem scleractinian corals have been reported to “bleach” (i.e. lose their photosymbionts) and experience high rates of mortality when SST exceed 30°C (Carriquiry et al., 2001). Global SST rise during the Early Jurassic could have caused a similar coral crisis that reduced the number of suitable environments for scleractinian coral growth that might not have similarly affected some bivalves. Increases in atmospheric C 02 alter the saturation states of both aragonite and calcite, thereby inhibiting calcification (Langdon et al., 2000). Because the “Lithiotis” facies bivalves have a thin outer prismatic calcite layer and thereby would have been less soluble than the aragonitic scleractinian coral skeleton, they may not have been as vulnerable to such lower saturation states and thereby were able to utilize the nearshore carbonate niche. “Lithiotis” facies bivalves do not appear until approximately 10 my after the end-Triassic event. The end-Cretaceous mass extinction is characterized by a rapid recovery rate; however, it was only until 10 my after the extinction that the appearance of highly-specialized fauna appear (e.g. keeled foraminifera, Koutsoukos, 1996). Therefore, it is likely that the specialization seen in the “Lithiotis” facies bivalves required a similar length of time. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 221 Kauffman and Johnson (1988) proposed that nutrient flooding of shelves by oceanic anoxic events enhanced the proliferation of rudists. In the Lias, deep water facies contemporaneous with the “Lithiotis” facies bivalves are benthos-free, laminated, organic rich limestones and shales that alternate with beds containing high-density, low-diversity faunas suggestive of opportunistic colonization in dysaerobic conditions (Hallam and Wignall, 1997). A minor extinction in the Early Toarcian is associated with a global oceanic anoxic event (Hesselbo et al., 2000). The demise of Pliensbachian platforms in Tunisia and Morocco has been suggested to be the result of eutrophication events (Soussi and Ben Ismail, 2000). “Lithiotis” facies bivalves, if they were mixotrophs or heterotrophs, may have been less at risk than the scleractinian corals to these anoxic and eutrophication events. If the Early Jurassic had a 1000 ppm increase in atmospheric C 02 as proposed by McElwain et al. (1999) or the minimal value 250 ppm proposed by Tanner et al., (2001), the effects on scleractinian corals, already diminished by the Triassic- Jurassic mass extinction would have been devastating. Regardless of source for such a rise in C 02, the rise would have cascading effects on paleotemperature, sea level change, carbonate platforms and organismal calcification. It may be more than coincidence that the two times of global bivalve reef-building occurred during elevated atmospheric C 02 , the Early Jurassic (McElwain et al., 1999; Tanner et al., 2001) and the Middle to Late Cretaceous (Poulsen et al., 1999; Johnson et al., 1996). The “Lithiotis” facies bivalves represent unique recovery taxa within the coral reef niche. Unlike disaster taxa that expand their distribution after a mass extinction, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 222 “Lithiotis” facies bivalves were uniquely adapted to the unusual conditions of the Early Jurassic. Be it increased atmospheric C 02 , nutrient flux to carbonate shelves, or a combination of both, “Lithiotis” facies bivalves thrived and dominated tropical facies only to become extinct when these environmental conditions disappeared as well. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 223 REFERENCES Aberhan, M., and Fursich, F.T., 1996, Diversity analysis of Lower Jurassic bivalves of the Andean Basin and the Pliensbachian-Toarcian mass extinction: Lethaia, v. 29, p. 181-195. Aberhan, M., 1994, Guild-stracture and evolution of Mesozoic benthic shelf communities: Palaios, v. 9, p. 516-545. Aberhan, M., 2001, Bivalve palaeobiogeography and the Hispanic Corridor: time of opening and effectiveness of a proto-Atlantic seaway: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 165, p. 375-394. Aberhan, M., and Muster, H., 1997, Palaeobiology of Early Jurassic bakevelliid bivalves from Western Canada: Palaeontology, v. 40, p. 799-815. Accorsi Benini, C., 1979, Lithiopema, un nuovo genere fra i grandi Lamellibranchi della facies "Lithiotis"; Morfologia, tassonomia ed analisi morfofunzionale: Bollettino della Societa Paleontologica Italiana, v. 18, p. 221-257. Accorsi Benini, C., 1985, The large Liassic bivalves: Symbiosis or longevity: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 52, p. 21-33. Accorsi Benini, C., and Broglio Loriga, C., 1982, Microstrutture, modalita di accrescimento e periodicita nei lamellibranchi liassici (facies a "Lithiotis"): II Simposio "Ecologia e Paleoecologia delle comunita bentoniche" Geologica Romana, v. 21, p. 765-793. Accorsi Benini, C., and Broglio Loriga, C., 1977, Lithiotis Gumbel 1871 e Cochlearites Reis 1903, 1° revisione morfologica e tassonomica: Bollettino della Societa Paleontologica Italiana, v. 16, p. 15-60. Agard, J., and du Dresnay, R., 1965, La region mineralisee du J Bou Dahar, pres de Beni-Tajjite: Notes Memoriales Service Geologique du Maroc, v. 181, p. 135-152. Ambariyanto, and Hoegh-Guldberg, O., 1999, Influence of field-based nutrient enrichment on the photobiology of the giant clam Tridacna maxima: Marine Biology, v. 133, p. 659-664. Arkell, W.J., 1933, A monograph of British Corallian Lamellibranchia, Part V: Journal of the Palaeontological Society, v. 85, p. 181-228. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 224 Arthur, M.A., Williams, D.F., and Jones, D.S., 1983, Seasonal temperature-salinity changes and thermocline development in the mid-Atlantic Bight as recorded by the isotopic composition of bivalves: Geology, v. 11, p. 655-659. Atkins, D., 1938, On the ciliary mechanisms and interrelationships of lamellibranchs. Part VII: Laterofrontal cilia of the gill filaments and their phylogenetic value: Quarterly Journal of Microscopical Science, v. 80, p. 345-436. Bahr, L.M., 1976, Energetic aspects of the intertidal oyster reef community at Sapelo Island, Georgia (USA): Ecology, v. 57, p. 121-131. Bartel, R.L., 1994, The Lower to Middle (?) Jurassic Dunlap Formation, west-central Nevada: Deposition in actively extending half-graben basins [unpublished Ph.D. dissertation, 101 pages thesis], Rice University. Bassi, D., Boomer, I., Fugagnoli, A., Loriga, C., Posenato, R., and Whatley, R.C., 1999, Faunal assemblage and paleoenvironment of shallow water black shales in the Tonezza area (Calcari Grigi, Early Jurassic, Southern Alps): Annali dell'Universita di Ferrara (Nuova Serie) Sezione: Scienza della Terra, v. 8, p. 1-16. Batten, B.L., and Taylor, D.G., 1978, Reassessment of the age of the Thompson Limestone, Lower Jurassic, Plumas County, California: Journal of Paleontology, v. 52, p. 208-209. Batten, B.L., and West, R., 1976, A study of the Robertson Formation, Grant County, Oregon: Oregon Museum o f Science and Industry, OMSI Technical Reports, v. 4, p. 1-37. Beauvais, L., 1977, Main characters of the Liassic coral fauna from Morocco, Proceedings -International Coral Reef Symposium, Volume 3: Miami, FL, Rosenstiel School of Marine and Atmospheric Science, University of Miami, p. 375-378. Beauvais, L., 1984, Evolution and diversification of Jurassic Scleractinia: Recent advances in the paleobiology and geology of the Cnidaria, Palaeontographica Americana, v. 54, p. 219-224. Belasky, P., and Runnegar, B., 1993, Biogeographic constraints for tectonic reconstructions of the Pacific region: Geology, v. 21, p. 979-982. Bengston, S., and Zhao, Y., 1992, Predatorial borings in late Precambrian mineralized exoskeletons: Science, v. 257, p. 367-369. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 225 Bernard, F.R., 1972, Occurrence and function of lip hypertrophy in the Anisomyaria (Mollusca, Bivalvia): Candian Journal of Zoology, v. 50, p. 53-57. Birkeland, C., 1997, Life and death of coral reefs: New York, Chapman and Hall, 536 p. Bohm, G., 1892, Lithiotisproblematica Giimbel: Naturforschenden Gesellschaft zu Freiburg im Breisgau, Berichte, v. 6, p. 55-80, pis. 2-4. Bonham, K., 1965, Growth rate of giant glam Tridacna gigas at Bikini Atoll as revealed by autoradiography: Science, v. 149, p. 300-302. Boomer, I., Whatley, R., Bassi, D., Fugagnoli, A., and Loriga, C., 2001, An Early Jurassic oligohaline ostracod assemblage within the marine carbonate platform sequence of the Venetian Prealps, NE Italy: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 166, p. 331-344. Bosellini, A., 1972, Paleocologia del calcari a " Lithiotis" (Giurassico inferiore Prealpi Venete): Rivista Italiana di Paleontolgia e Stratigrafia, v. 78, p. 441 - 466. Bosellini, A., and Broglio Loriga, C., 1971,1 "Calcari Grigi" di Rotzo (Giurassico inferiore, Altopiano di Asiago) e loro inquadramento nella paleogeografia e nella evoluzione tettonico-seimentaria delle Prealpi venete: Annali dell'Universita di Ferrara, v. 5, p. 1-61. Bosellini, A., and Hardie, L.A., 1985, Facies e cicli della Dolomia Principale delle Alpi Venete: Memorie della Societa Geologica Italiana, v. 30, p. 245-266. Bosellini, A., Masetti, D., and Sarti, M., 1981, A Jurassic "Tongue of the Ocean" infilled with oolitic sands; the Belluno Trough Venetian Italy: Carbonate platforms of the passive-type continental margins, Marine Geology, v. 44, p. 59-95. Bottjer, D.J., 1998, Phanerozoic non-actualistic paleoecology: Geobios, v. 30, p. 885-893. Brasier, M.D., 1995, Fossil indicators of nutrient levels. 1: Eutrophication and climate change, in Bosence, D.W.J., and Allison, P.A., eds., Marine Paleoenvironmental Analysis from Fossils, Volume Geological Society Special Publication, no. 83: London, United Kingdom, The Geological Society, p. 113-132. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 226 Broglio Loriga, C., and Neri, C., 1976, Aspetti paleobiologici e paleogeografici della facies a "Lithiotis" (Giurese Inf.): Rivista italiana di paleontologia e stratigrafia, v. 82, p. 651-706. Broglio Loriga, C., and Posenato, R., 1996, Adaptive strategies of Lower Jurassic and Eocene multivincular bivalves, in Cherchi, A., ed., Autecology of selected fossil organisms: Achievements and problems, Special Volume no. 3: Mucchi, Modena, Bollettino della Societa Paleontologica Italiana, p. 45- 61. Burchfiel, B.C., Cowan, D.S., and Davis, G.A., 1992, Tectonic overview of the Cordilleran Orogen in the western United States, in Burchfiel, B.C., Lipman, P.W., and Zoback, M.L., eds., The Cordilleran Orogen: Conterminous United States: Denver, Colorado, Geological Society of America, p. 407-479. Burgess, C.J., and Lee, C.W., 1978, The development of a Lower Jurassic carbonate tidal flat, central High Atlas, Morocco; 1, Sedimentary history: Journal of Sedimentary Petrology, v. 48, p. 777-793. Burri, P., Du Dresnay, R., and Wagner, C.W., 1973, Teepee structures and associated diagenetic features in intertidal carbonate sands (lower Jurassic, Morocco): Sedimentary Geology, v. 9, p. 221-228. Buser, S., 1965, Stratigrafski razvoj jurskih skladov najuznem Primorskem [unpublished dissertation], Geology Department, Faculty of Natural Sciences and Engineering, University of Ljubljana, 101 pgs. Buser, S., 1972, Die Charakteristik und systematische Stellung der Lithioden, Vortrag an 42, Jahresversammlung der Palaontologicschen Geselschaft: Graz, p. 9. Buser, S., and Debeljak, I., 1994, Lower Jurassic beds with bivalves in south Slovenia: Geologija, v. 37, p. 23-62. Carriquiry, J.D., Cupul-Magana, A.L., Rodriguez-Zaragoza, F., and Medina-Rosas, P., 2001, Coral bleaching and morality in the Mexican Pacific during the 1997-1998 El Nino and prediction form a remote sensing approach: Bulletin of Marine Science, v. 69, p. 237-249. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 227 Carter, J.G., 1990, Evolutionary significance of shell microstructure in the Palaeotaxodonta, Pteriomorphia and Isofilibra Skeletal Patterns, Processes and Evolutionary Trends, Volume I: New York, New York, Van Nostrand Reinhold, p. 136-296. Carter, J.G., and Schneider, J.A., 1997, Condensing lenses and shell microstructure in Corculum (Mollusca: Bivalvia): Journal of Paleontology, v. 71, p. 56-61. Chalker, B.E., 1976, Calcium transport during skeletogenesis in hermatypic corals: Compendium of Biochemistry and Physiology, v. 54,455-495. Chandler, M.A., Rind, D., and Ruedy, R., 1992, Pangaean climate during the Early Jurassic: GCM simulations and the sedimentary record of paleoclimate: Geological Society of America Bulletin, v. 104, p. 543-559. Chinzei, K., 1982, Morphological and structural adaptations to soft substrates in the Early Jurassic monomyarians Lithiotis and Cochlearites: Lethaia, v. 15, p. 179-197. Chinzei, K., Savazzi, E., and Seilacher, A., 1982, Adaptational strategies of bivalves living as infaunal secondary soft bottom dwellers: Neues Jahrbuch fur Geologie und Palaontologie, Bergrtindet 1807, Tubingen, v. Bd. 164, p. 229- 250. Cobianchi, M., and Picotti, V., 2001, Sedimentary and biological response to sea- level and palaeoceanographic changes of a Lower-Middle Jurassic Tethyan platform margin (Southern Alps, Italy): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 169, p. 219-244. Conway Morris, S., and Bengston, S., 1994, Cambrian predators: Possible evidence from boreholes: Journal o f Paleontology, v. 68, p. 1-23. Copper, P., 1994, Ancient reef ecosystem expansion and collapse: Coral Reefs, v. 13, p. 3-12. Cowen, R., 1983, Algal symbiosis and its recognition in the fossil record, in Tevesz, M.J.S., and McCall, P.L., eds., Biotic interactions in Recent and fossil benthic communities: New York, Plenum, p. 837. Cowen, R., 1988, The role of algal symbiosis in reefs through time: Palaios, v. 3, p. 221-227. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 228 Cox, L.O., 1969, Part N, Mollusca 6, Bivalvia Volumes 1-2: Lawrence, Kansas, Geological Society of America and University of Kansas, 952 p. Cox, L.R., 1971, ?Family Lithiotidae, Reis, 1903, in Moore, R.C., ed., Treatise on Invertebrate Paleontology, Part N, Mollusca 6, Bivalvia, Volume 3: Lawrence, Kansas, Geological Society of America and University of Kansas, p. N 1199-1200. Cragg, S.M., 1996, The phylogenetic significance of some anatomical features of bivalve veliger larvae, in Taylor, J.D., ed., Origin and Evolutionary Radiation of the Mollusca: Oxford, Oxford University Press, p. 371-380. Crampton, J.S., 1988, Comparative taxonomy of the bivalve families Isognomonidae, Inoceramidae, and Retroceramdae: Palaeontology, v. 31, p. 965-996. Crevello, P.D., 1988, Carbonate platform facies of the Southern Margin of the Central High Atlas Rift, in Warme, J.E., Crevello, P.D., Hazlett, B., H., Atmane, F., and Bouziane, M.B., eds., Evolution of the Jurassic High Atlas Rift, Morocco: Transtension, Structural and Eustatic Controls on Carbonate Facies, Tectonic Inversion, AAPG Mediterranean Basins Conference and Exhibit: Nice, France, AAPG, p. X-l-X-42. Crickmay, C.H., 1933, Mt. Jura Investigation: Geological Society of America Bulletin, v. 44, p. 895-926. Crowley, T.J., and North, G.R., 1991, Paleoclimatology: Oxford, United Kingdom, Oxford University Press, 349 p. Davis, D.A., and Schweikert, R.A., 1995, Analysis of the Early Jurassic Sailor Canyon-Gardnerville Basin (SCGB) of Western Nevada and Northeastern California: APPG Rocky Mountain Section Meeting Abstracts, American Association of Petroleum Geologists Bulletin, v. 79, p. 916-917. Davis, G.A., Monger, J.W.H., and Burchfiel, B.C., 1978, Mesozoic construction of the Cordilleran "collage" Central British Columbia to Central California, in Howell, D.G., and McDougall, K.A.M., eds., Mesozoic Paleogeography of the Western United States, Pacific Coast Symposium 2: Los Angeles, Society of Economic and Petroleum Mineralogists, p. 573. Debeljak, I., and Buser, S., 1997, Lithiotid bivalves in Slovenia and their mode of life: Geologija, v. 40, p. 11-64. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 229 Dewey, J.F., Pitman, W.C.I., Ryan, W.B.F., and Bonnin, J., 1973, Plate tectonics and the evolution of the Alpine system: Geological Society of America Bulletin, v. 84, p. 3137-3180. Dickinson, W.R., and Thayer, T.P., 1978, Paleogeographic and paleotectonic implications of Mesozoic stratigraphy and structure in the John Day inlier of central Oregon, in Howell, D.G., and McDougall, K.A., eds., Mesozoic paleogeography o f the Western United States (Pacific Coast Paleogeography Symposium 2): Los Angeles, Society of Economic paleontologists and Mineraologists, Pacific Section, p. 147-161. Dickinson, W.R., and Vigrass, T.P., 1965, Geology of the Suplee-Izee area, Cook, Grant and Hamey Counties, Oregon, State of Oregon Department of Geology and Mineral Industries, 109 p. Diller, J.S., 1892, Geology of the Taylorville region of California: Geological Society of America Bulletin, p. 369-392. Dommergues, J.-L., Laurin, B., and Meister, B., 1999, The recovery and radiation of Early Jurassic ammonoids: morphologic versus palaeobiogeographical patterns: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 165, p. 195- 213. Droser, M.L., Bottjer, D.J., and Sheehan, P.M., 1997, Evaluating the ecological architecture of major events in the Phanerozoic history of marine invertebrate life: Geology, v. 25, p. 167-170. Droser, M.L., Bottjer, D.J., Sheehan, P.M., and McGhee, G.R., Jr., 2000, Decoupling of taxonomic and ecologic severity of Phanerozoic marine mass extinctions: Geology, v. 28, p. 675-678. Drzewiecki, P.A., and Simo, J.A., 1997, Carbonate platform drowning and oceanic anoxic events on a mid-Cretaceous carbonate platform, south-central Pyrenees, Spain: Journal of Sedimentary Research, v. 67, p. 698-714. du Dresnay, R., 1965, Le gite de manganese de bou-Arfa, in Agard, J., and Diouri, M., eds., Colloque sur des gisements stratiformes de plomb, zinc et manganese du Maroc (2 mai-14 mai 1962): Rabat, Service Geologique du Maroc, p. 132-135. du Dresnay, R., 1977, Le milieu recifal fossile du Jurassique inferieur (Lias) dans le domaine des chaines atlasiques du Maroc: Memoires du Bureau de Recherches Geologiques et Minieres, v. 89, p. 296-312. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 230 Duarte, L.V., Krautter, M., and Soares, A.F., 2001, Bioconstructions a spongiares siliceux dans leLias terminal du Bassin lusitanien (Portugal); stratigraphie, sedimentologie et signification paleogeographique: Bulletin de la Societe Geologique de France, v. 172, p. 637-646. Dubar, G., 1948, La fauna domerienne du Lias marocain (domaine atlasique): Notes et Memoires Service Geologique du Maroc, v. 68. Dubinsky, Z., 1990, Coral Reefs: Ecosystems of the World: Amsterdam, Elsevier, 550 p. Durand, D., and Greenwood, J.A., 1958, Modification of the Rayleigh test for uniformity in analysis of two-dimensional orientation data: Journal of Geology, v. 66, p. 229-238. Epstein, S., and Mayeda, T., 1953, Variations in O1 8 content of waters from natural sources: Geochimica et Cosmochimica Acta, v. 4, p. 213-224. Epstein, S.R., Buschsbaum, R., Lowenstam, H.A., and Urey, H.C., 1953, Revised carbonate-water isotopic temperature scale: Geological Society of America Bulletin, v. 64, p. 1315-1326. Epstein, S.R., and Lowenstam, H.A., 1953, Temperature-shell growth relations of Recent and interglacial Pleistocene shoalwater biota from Bermuda: Journal of Geology, v. 61, p. 424-438. Erwin, D.H., 1992, A preliminary classification of evolutionary radiations: Historical Biology, v. 6, p. 133-147. Erwin, D.H., 1998, The end and the beginning: recoveries from mass extinctions: Trends in Ecology and Evolution, v. 13, p. 344-349. Fagerstrom, J.A., 1987, The Evolution of Reef Communities: New York, John Wiley & Sons, Inc., 600 p. Ferguson, H.G., and Muller, S.W., 1949, Structural geology of the Hawthorne and Tonopah quadrangles: Reston, VA, U.S. Geological Survey, 55 p. Fitt, W.K., and Trench, R.K., 1981, Spawning, development, and the acquisition of zooxanthellae by Tridacna squamosa (Mollusca, Bivalvia): Biological Bulletin, v. 161, p. 213-235. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 231 Fltigel, E., 1981, Paleoecology and facies of Upper Triassic reefs in the northern Calcareous Alps., in Toomey, D.F., ed., European fossil reef models, Volume Special Publication Number 30: Tulsa, Oklahoma, United States, Society of Economic and Petroleum Mineralogists, p. 291-359. Fltigel, E., and Fliigel-Kahler, E., 1992, Phanerozoic reef evolution: Basic questions and data base: Facies, v. 26, p. 167-278. Fugagnoli, A., and Broglio Loriga, C., 1996, Revised biostratigraphy of Lower Jurassic shallow water carbonates from the Venetian Prealps (Calcari Grigi, Trento Platform, northern Italy): Studi Trentini di Scienze Naturali: Acta Geologica, v. 73, p. 35-73. Fiirsich, F.T., 1993, Palaeoecology and evolution of Mesozoic salinity-controlled benthic macroinvertebrate associations: Lethaia, v. 26, p. 327-346. Gabrielse, H., and Yorath, C.J., 1992, Tectonic synthesis, in Gabrielse, H., and Yorath, C.J., eds., Geology of the Cordilleran Orogen in Canada: Ontario, Geological Survey of Canada, p. 679-705. Gale, A.S., 1987, Phylogeny and classification of the Asteroidea (Echinodermata: Zoological Journal of the Linnean Society, v. 89, p. 107-132. Galimov, E.M., 1985, The Biological Fractionation of Isotopes: Orlando, FL, Academic Press, 261 p. Gerdes, G., Klenke, T., and Nofflce, N., 2000, Microbial signatures in peritidal siliciclastic sediments: acatalouge: Sedimentology, v. 47, p. 279-308. Geyer, O.F., 1977, Die "Lithiotis-Kalke" im Bereich der unterjurassischen Tethys: Neues Jahrbuch fur Geologie und Palaeontologie, Abhandlungen, v. 153, p. 304-340. Goreau, T.F., 1959, The physiology of skeleton formation in corals: I, A Method for measuring the rate of calcium deposition by corals under different conditions: Biological Bulletin of the Marine Biology Laboratories, Woods Hole, v. 116, p. 59-75. Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, J., van Veen, P., Thierry, J., and Huang, Z., 1994, A Mesozoic time scale: Journal of Geophysical Research, B, Solid Earth and Planets, v. 99, p. 24051-24074. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 232 Grossman, E.L., and Ku, T., 1986, Oxygen and carbon isotope fractionation in biogenic aragonite: Temperature effects: Chemical Geology, v. 59, p. 59-74. Giimbel, C.W., 1871, Die sogennanten Nulliporen (Lithomammien und Dactylopora) und ihre, Bietheiligung an der Zusammensetzung der Kalksteine, pt 1 : Die Nulliporen dies Pflanzreichs (Lithothamnium): Abhandlungen der Mathematisch-Physikalischen Classe der Koniglich Bayerischen Akademie der Wissenschaften, v. 11, p. 13-52. Giimbel, C.W., 1890, Lithiotisproblematica Giimbel eine Muschel: Jahrbuch der Kaiserlich-Koniglichen Geologischen Reichsanstalt, v. 60, p. 64-73. Hallam, A., 1961, Cyclothems, transgressions and faunal change in the Lias of north west Europe: Transactions of the Edinburgh Geological Society, v. 18, p. 124-174. Hallam, A., 1965, Observations of marine Lower Jurassic stratigraphy of North America with special reference to the United States: Bulletin of the American Associations of Petroleum Geologists, v. 49, p. 1485-1501. Hallam, A., 1996, Recovery of the marine fauna in Europe after the end-Triassic and early Toarcian mass extinctions, in Hart, M.B., ed., Biotic Recovery from Mass Extinction Events, Volume Special Publication Number 102: London, Geological Society of London, p. 231-236. Hallam, A., and Wignall, P.B., 1997, Mass Extinctions and their aftermath: Oxford, Oxford University Press, 323 p. Hallock, P., and Schlager, W., 1986, Nutrient excess and the demise of coral reefs and carbonate platforms: Palaios, v. 1, p. 389-398. Harper, E., and B., M., 1994, The biology of Isognomon legumen (Gmelin, 1791) (Bivalvia: Pterioida) at Cape dAguilar, Hong Kong, with special reference to predation by muricids, in Morton, B., ed., The Malacofauna of Hong Kong and southern China III, Volume p. 405-425: Hong Kong, Hong Kong University Press. Harper, E.M., Forsythe, G.T.W., and Palmer, T., 1998, Taphonomy and the Mesozoic Marine Revolution: Preservation state masks the importance of boring predators: Palaios, v. 13, p. 352-360. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 233 Harries, P.J., Kauffman, E.G., and Hansen, T.A., 1996, Models for biotic survival following mass extinction, in Hart, M.B., ed., Biotic recovery from mass extinction events, Volume Geological Society Special Publications 102: London, Geological Society of London, IGCP Project No. 335, p. 41- 60. Harrington, R.J., Krantz, D.E., Jones, D.S., and Williams, D.F., 1989, Aspects of growth deceleration in bivalves: Clues to understanding the seasonal S1 8 0 and 51 3 C record - a comment on Krantz et al. (1987): Palaeogeography, Palaeoclimatology, Palaeoecology, v. 70, p. 399-403. Harwood, D.S., 1993, Mesozoic geology of Mt. Jura, Northern Sierra Nevada, California: A progress report, in Dunn, G., and McDoguall, K., eds., Mesozoic paleogeography of the Western United States - II, Volume Book 71: Los Angeles, Pacific Section SEPM, p. 263-274. Hayami, I., 1957a, Liassic Bakevellia in Japan (Studies on the Liassic pelecypods in Japan, 1): Recent Progress of Natural Sciences in Japan, v. 28, p. 47-59. Hayami, I., 1957b, Liassic Gervillia and Isognomon in Japan (Studies on the Liassic pelecypods in Japan, 2): Recent Progress of Natural Sciences in Japan, v. 28, p. 95-106. Hayami, I., 1965, Lower Cretaceous marine pelecypods of Japan, Part I: Memoirs of the Faculty of Science, Kyushu University, Series D, Geology, v. 15, p. 221- 349. Heller, J., 1990, Longevity in molluscs: Malacologia, v. 31, p. 259-295. Hendry, J.P., Perkins, W.T., and Bane, T., 2001, Short-term environmental change in a Jurassic lagoon deduced from geochemical trends in aragonitic bivalve shells: Geological Society of America Bulletin, v. 113, p. 790-798. Hesselbo, S.P., Grocke, D.R., Jenkyns, H.C., Bierrum, C., J., Farrimond, P., Morgans Bell, H.S., and Green, O., R., 2000, Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event: Nature, v. 406, p. 392-935. Hodych, J.P., and Dunning, G.P., 1992, Did the Manicougan impact trigger end-of- Triassic mass extinction?: Geology, v. 20, p. 51-54. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 234 Ichikawa, K., 1958, Aur Taxomonie und Phylogenie der triadischen "Pteriidae" (Lamellibranchia) mit besonderer Beriicksichtigung der Gattung Claraia, Eumorphtis, Oxytoma, undMonotis: Palaeontographica, Abteilung A, v. Ill, p. 131-212, pis. 21-24. Johnson, C.C., Barron, E.J., Kauffman, E.G., Arthur, M.A., Fawcett, P.J., and Yasuda, M.K., 1996, Middle Cretaceous reef collapse linked to ocean heat transport: Geology, v. 25, p. 376-380. Jones, D.L., Howell, D.G., Coney, P.J., and Monger, J.W.H., 1983, Recognition, character, and analysis of tectonostratigraphic terranes in Western North America, in Hashimoto, M., and Uyeda, S., eds., Accretion Tectonics in the Circum-Pacific Regions: Tokyo, Terra Scientific Publishing Company, p. 21- 35. Jones, D.S., 1983, Sclerochronology: Reading the record of the fossil shell: American Scientist, v. 71, p. 384-391. Jones, D.S., 1985, Growth increments and geochemical variations in the molluscan shell, in Broadhead, T.W., ed., Mollusks: Notes for a Short Course, Volume 13, University of Tennessee, Department of Geological Sciences, Studies in Geology, p. 72-87. Jones, D.S., and Gould, S.J., 1999, Direct measurement of age of fossil Gryphaea: the solution to a classic problem in heterochrony: Paleobiology, v. 25, p. 158- 187. Jones, D.S., and Jacobs, D.K., 1992, Photosymbiosis in Clinocardium nuttalli, implications for tests of photosymbiosis in fossil molluscs: Palaios, v. 7, p. 86-95. Jones, D.S., Williams, D.F., and Krantz, D.E., 1983, Combined stable isotope growth increment sclerochronology in modem and fossil bivalve molluscs: Geological Society of America 96th Annual meeting, abstracts with programs - Boulder, Colorado, v. 15, p. 605. Jones, D.S., Williams, D.F., and Romanek, C.S., 1986, Life history of symbiont- bearing giant clams from stable isotope profiles: Science, v. 231, p. 46-48. Kauffman, E.G., and Johnson, C.C., 1988, The morphological and ecological evolution of Middle and Upper Cretaceous reef-building rudists: Palaios, v. 3, p. 194-216. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 235 Kawaguti, S., 1950, Observations on the heart shell, Corculum cardissa (L.), and its associated zooxanthellae: Pacific Science, v. 4, p. 43-49. Keith, M.L., Anderson, G.M., and Eichler, R., 1964, Carbon and oxygen isotopic composition of mollusk shells from marine and freshwater environments: Geochimica et Cosmochimica Acta, v. 28, p. 1757-1786. Kiessling, W., Fliigel, E., and Golonka, J., 1999, Paleoreef maps: Evaluation of a comprehensive database on Phanerozoic reefs: American Association of Petroleum Geologists Bulletin, v. 83, p. 1552-1587. Killingley, J.S., and Berger, W.H., 1979, Stable isotopes in a mollusk shell: Detection of upwelling events: Science, v. 205, p. 186-188. Kirby, M.X., 2000, Paleoecological differences between Tertiary and Quaternary Crassostrea oysters, as revealed by stable isotope sclerochronology: Palaios, v. 15, p. 132-141. Kirby, M.X., 2001, Differences in growth rate and environment between Tertiary and Quaternary Crassostrea oysters: Paleobiology, v. 27, p. 84-103. Kleypas, J.A., 1995, A diagnostic model for predicted global coral reef distribution, in Bellwood, O., ed., Recent advances in marine science and technology: PACON International and James Cook University of N. Queensland, Townsville, Australia, p. 211-220. Koutsoukos, E.A.M., 1996, Phenotypic experiments into new pelagic niches in early Danian planktonic Foraminifera: Aftermath of the K/T boundary event, in Hart, M.B., ed., Biotic Recovery from Mass Extinction Events: London, Geological Society Special Publication No. 102, p. 319-336. Kowalewski, M., Dulai, A., and Fiirsich, F.T., 1998, A fossil record full of holes: The Phanerozoic history of drilling predation: Geology, v. 26, p. 1091-1094. Krantz, D.E., Jones, D.S., and Williams, D.F., 1984, Growth rates of the sea scallop, Placopecten magellanicus, determined from the 1 8 0 / 1 6 0 record in shell calcite: Biological Bulletin, v. 167, p. 186-199. Krantz, D.E., Williams, D.F., and Jones, D.S., 1987, Ecological and paleoenvironmental information using stable isotopes from living and fossil mollusks: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 58, p. 249- 266. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 236 Krumbeck, L., 1923, Zur Kenntnis des Juras der Insel Timor sowie des Aucellen Horizontes von Seran und Burn: Stuttgart, 1-20 p. Kutzbach, I.E., and Gallimore, R.G., 1989, Pangaean climates; megamonsoons of the megacontinent: Journal of Geophysical Research, D, Atmospheres, v. 94, p. 3341-3357. Ladd, H.S., 1944, Reefs and other bioherms: National Research Council, Division of Geology and Geography, Annual Report, v. 4, p. 26-29. Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., and Goddard, J., 2000, Effect o f calcium carbonate saturation state on the calcification rate of an experimental coral reef: Global Biogeochemical Cycles, v. 14, p. 639-654. Lawrence, D.R., 1971, Shell orientation in Recent and fossil oyster communities from the Carolinas: Journal of Paleontology, v. 45, p. 347-349. Lee, C.W., 1983, Bivalve mounds and reefs of the central High Atlas, Morocco: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 43, p. 153-168. Lee, C.W., and Burgess, C.J., 1978, Sedimentation and tectonic controls in the Early Jurassic central High Atlas trough, Morocco: Geological Society of America Bulletin, v. 89, p. 1199-1204. Leinfelder, R.R., Rrautter, M., Latemser, R., Nose, M., Schmid, D. U., Schweigert, G., Werner, W., Keupp, H., Brugger, H., Herrmann, R., Rehfeld-Kiefer, U., Schroeder, J. H., Reinhold, C., Koch, R., Zeiss, A., Schweizer, V., Christmann, H., Menges, G., Luterbacher, H., 1994, The origin of Jurassic reefs: Current research developments and results: Facies, v. 31, p. 1-56. Little, C.T.S., and Benton, M.J., 1995, Early Jurassic mass extinction; a global long term event: Geology, v. 23, p. 495-498. Lloyd, R.M., 1964, Variations in the oxygen and carbon isotope ratios of Florida Bay mollusks and their environmental significance: Journal of Geology, v. 72, p. 84-111. Lupher, R.L., 1941, Jurassic stratigraphy of Central Oregon: Bulletin of the Geological Society of America, v. 52, p. 219-270. Lupher, R.L., and Packard, E.L., 1930, The Jurassic and Cretaceous rudistids of Oregon: Oregon University Geology series, v. 1, p. 203-212. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 237 Lutz, R.A., and Rhoads, D.C., 1980, Growth patterns within the molluscan shell: An overview, in Rhoads, D.C., and Lutz, R.A., eds., Skeletal Growth of Aquatic Organisms: New York, Plenum Press, p. 203-254. MacIntyre, I.G., 1977, Distribution of submarine sediments in a modem Caribbean fringing reef, Galeta Point, Panama: Journal of Sedimentary Petrology, v. 46, p. 503-516. Manly, B.F.J., 1994, Multivariate Statistical Methods: London, Chapman & Hall, 215 p. Marzoli, A., Renne, P.R., Piccirillo, E.M., Emesto, M., Bellieni, G., and De Min, A., 1999, Extensive 200-million-year-old continental flood basalts of the Central Atlantic Magmatic Province: Science, v. 284, p. 616-618. McConnaughey, T., 1989,13C and 1 8 0 isotopic disequilibrium in biological carbonates: I. Patterns: Geochimica et Cosmochimica Acta, v. 53, p. 151-162. McElwain, J.W., Beerling, D.J., and Woodward, F.I., 1999, Fossil plants and global warming at the Triassic-Jurassic Boundary: Science, v. 285, p. 1386-1389. McKee, E.D., and Imlay, R.W., 1956, Paleotectonic maps, Jurassic system: Reston, VA, U. S. Geological Survey, United States. Mietto, P., and Roghi, G., 1993, Nuova segnalazione di impronte di dinosauri nel Giurassico Inferiore del Sudalpino: Le Piste di Revolto (Alti Lessini Veronesi): Paleocronache, v. 2, p. 39-43. Monger, J.W.H., 1993, Canadian Cordilleran tectonics: from geosynclines to crustal collage: Canadian Journal of Earth Sciences, v. 30, p. 209-231. Mook, W.G., and Vogel, J.C., 1968, Isotopic equilibrium between shells and their environment: Science, v. 159, p. 874-875. Muller, S.W., and Ferguson, H.G., 1936, Triassic and Jurassic formations of west- central Nevada: Geological Society of America Bulletin, v. 47, p. 241-251. Muller, S.W., and Ferguson, H.G., 1939, Mesozoic stratigraphy of the Hawthorne and Tonopah quadrangles, Nevada: Bulletin of the Geological Society of America, v. 50, p. 1573-1624. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 238 Muscatine, L., 1990, The role of symbiotic algae in carbon and energy flux in reef corals, in Dubinsky, Z., ed., Coral Reefs: Ecosystems of the World, Volume 25: Amsterdam, Elsevier, p. 75-87. Nakazawa, K., 1959, Permian and eo-Triassic Bakevellias from the Maizuru zone, southwest Japan: Memoirs of the Faculty of Engineering, Kyoto University, v. 26, p. 193-209. Nakazawa, K., and Newell, N.D., 1968, Permian bivalves of Japan: Memoirs of the Faculty of Science, Kyoto University, Series of Geology and Mineralogy, v. 35, p. 1-108. Nauss, A.L., 1986, Lithiotis bioherms in the Pliensbachian (Lower Jurassic) of North America [Unpublished master's thesis], University of British Columbia, 102 Pgs- Nauss, A.L., and Smith, P.L., 1988, Lithiotis (Bivalvia) bioherms in the Lower Jurassic of East-Central Oregon, U.S.A.: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 65, p. 253-268. Nevesskaya, L.A., Scarlato, O.A., Starogogatov, Y.I., and Eberzin, A.G., 1971, New ideas on bivalve systematics: Paleontological Journal, v. 5, p. 141-155. Newell, N., and Merchant, F., 1939, Discordant valves in pleurothetic pelecypods: American Journal of Science, v. 237, p. 175-177. Nielsen, R.L., 1964, Geology of the Pilot Mountains and vicinity, Mineral County, Nevada [Doctoral dissertation, 161 p. thesis], University of California, Berkeley. Olsen, P.E., Kent, D.V., Sues, H.-D., Koerberl, C., Huber, H., Montanari, A., Rainforth, E.C., Fowell, S.J., Szajna, M.J., and Hartline, B.W., 2002, Ascent of dinosaurs linked to iridium anomaly at the Triassic-Jurassic boundary: Science, v. 296, p. 1305-1307. Olsen, P.E., Shubin, N.H., and Anders, M.H., 1987, New Early Jurassic tetrapod assemblages constrain Triassic-Jurassic tetrapod extinction event: Science, v. 237, p. 1025-1029. Olszewski, T.D., and West, R.R., 1997, Influence of transportation and time- averaging in fossil assemblages from the Pennsylvanian of Oklahoma: Lethaia, v. 30, p. 315-329. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 239 Palfy, J., Mortensen, J.K., Carter, E.S., Smith, P.L., Friedman, R.M., and Tipper, H.W., 2000a, Timing the end-Triassic mass extinction; first on land, then in the sea: Geology, v. 28, p. 39-42. Palfy, J., Smith, P.L., and Mortensen, J.K., 2000b, A U-PB and 40Ar/39Ar time scale for the Jurassic: Canadian Journal of Earth Sciences, v. 37, p. 923-944. Panella, G., and MacClintock, C., 1968, Biological and environmental rhythms reflected in molluscan shell growth: Journal of Paleontology, v. 42, p. 64-79. Parrish, J.T., 1992, Jurassic climate and oceanography of the Pacific region, in Westermann, G.E.G., ed., The Jurassic of the Circum-Pacific: Oxford, Oxford University Press, p. 365-379. Parrish, J.T., 1993, Climate of the supercontinent Pangea: Journal of Geology, v. 101, p. 215-233. Parrish, J.T., and Curtis, R.L., 1982, Atmospheric circulation, upwelling and organic-rich rocks in the Mesozoic and Cenozoic eras: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 40, p. 31-66. Pedersen, K.R., and Lund, J.J., 1980, Palynology of the plant-bearing Rhaetian to Hettangian Kap Stewart Formation, Scoresby Sund, East Greenland: Review of Palaeobotany and Palynology, v. 32, p. 1-69. Perkins, B.F., 1974, Paleoecology of a rudist reef complex in the Comanche Cretaceous Glen Rose Limestone of central Texas: Geoscience and Man, v. 8, p. 131-173. Ponsler, H.E., 1977, The geology and mineral deposits of the Garfield District, Mineral County, Nevada [unpublished master's thesis], University of Nevada, Reno, 73 p. Posenato, R., Masetti, D., and Loriga Broglio, C., 2000,1 banchi a bivalvi del Giurassico inferiore (Piattaforma di Trento): Dinamica deposizionale, modalita di insediamento e sviluppo: Accademia Nazionale Sciences, Lettres, Arti di Modena, Collana di Studi, Crisi biologiche, radiazioni adattative e dinamica delle piattaforme carbonatiche, v. 20, p. 211-214. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 240 Poulsen, C.J., Barron, E.J., Johnson, C.C., and Fawcett, P., 1999, Links between major climatic factors and regional oceanic circulation in the mid-Cretaceous, in Barrera, E., and Johnson, C.C., eds., Evolution of the Cretaceous ocean- climate system, Special Paper, Volume 332: Denver, CO, Geological Society of America, p. 73-89. Purchon, R.D., 1959, A phylogenetic classification of the Lamellibranchia with special reference ot the Protobranchia: Proceedings of the Malacological Society o f London, v. 33, p. 224-230. Raup, D.M., and Boyajian, G.E., 1988, Patterns of generic extinction in the fossil record: Paleobiology, v. 14, p. 109-125. Raup, D.W., and Sepkoski, J.J., 1982, Mass extinctions in the marine fossil record: Science, v. 215, p. 1501-1503. Reis, O., 1903, Uber Lithiotiden: Jahrbuch der Kaiserlich-Koniglichen Geologischen Reichsanstalt, v. XVII. Retallack, G.J., 2001, A 300 million-year record of atmospheric carbon dioxide from fossil plant cuticles: Nature, v. 411. Rey, J., Andreo, J., Garcia-Hernandez, M., Martm-Algarra, A., and Vera, J.A., 1990, The Liassic "Lithiotis” facies north of Velez Rubio (Subbetic Zone): Revista de la Sociedad Geologica de Espana, v. 3, p. 199-212. Roberts, C.M., McClean, C.J., Veron, J.E.N., Hawkins, J.P., Allen, G.R., McAllister, D.E., Mittermeier, C.G., Schueler, F.W., Spalding, M., Wells, F., Vynne, C., and Werner, T.B., 2002, Marine biodiversity hotspots and conservation priorities for tropical reefs: Science, v. 295, p. 1280-1284. Rollier, L., 1914, Fossiles nouveaux ou peu connus des terraines secondaires (mesozoiques) du Jura et des contres environmentes: Memoires de la Societe Paleontolgique de la Suisse, v. 40, p. 321-440. Romanek, C.S., and Grossman, E.L., 1989, Stable isotope profiles of Tridacna maxima as environmental indicators: Palaios, v. 4, p. 402-413. Romanek, C.S., Jones, D.S., Williams, D.F., Krantz, D.E., and Radtke, R.L., 1987, Stable isotopic investigation of physiological and environmental changes recorded in shell carbonate from the giant clam, Tridacna maxima: Marine Biology, v. 94, p. 385-393. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 241 Sackett, W.M., and Moore, W.S., 1966, Isotopic variations of dissolved inorganic carbon: Chemical Geology, v. 1, p. 323-328. Savazzi, E., 1996, Preserved ligament in the Jurassic bivalve Lithiotis: Adaptive and evolutionary significance: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 120, p. 281-289. Schettino, A., and Scotese, C.R., 2001, New internet software aids paleomagnetic analysis and plate tectonic reconstructions, Eos, v. 82 (http://www.itis- molinari.mi.it/Intro-Reconstr.html) Schubert, J.K., and Bottjer, D.J., 1992, Early Triassic stromatolites as post-mass extinction disaster forms: Geology, v. 20, p. 883-886. Scotese, C., and Golonka, J., 1992, PALEOMAP paleogeographic atlas: Arlington, TX, University of Texas, 114 p. Scott, R.W., 1995, Global environmental controls on Cretaceous reefal ecosystems: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 119, p. 187-199. Seilacher, A., 1972, Divaricate patterns in pelecypod shells: Lethaia, v. 5, p. 325- 343. Seilacher, A., 1973, Frabricational noise in adaptive morphology: Systematic Zoology, v. 22, p. 451-465. Seilacher, A., 1984, Constructional morphology of bivalves: evolutionary pathways in primary versus secondary soft-bottom dwellers: Palaeontology, v. 27, p. 207-237. Seilacher, A., 1990, Aberrations in bivalve evolution related to photo- and chemosymbiosis: Historical Biology, v. 3, p. 289-311. Septfontaine, M., 1984, Biozonation (a l'aide des foraminiferes imperfores) de la plate-forme interne carbonatee liasique du Haut Atlas (Maroc): Revue de Micropaleontologie, v. 27, p. 209-229. Septfontaine, M., 1986, Milieux de depots et foraminiferes (Lituolides) de la plate- forme carbonatee du Lias moyen au Maroc: Revue de Micropaleontologie, v. 28, p. 265-289. Silberling, N.J., 1959, Pre-Tertiary stratigraphy and Upper Triassic paleontology of the Union District, Shoshone Mountains, Nevada: Reston, VA, USGS, 67 p. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 242 Silberling, N.J., Jones, D.L., Blake, M.C., Jr., and Howell, D.G., 1984, Lithotectonic terrane map of the western conterminous states, in Silberling, N.J., ed., Lithotectonic terrane maps of the northern Cordillera, U. S. Geological Survey Open-File Report 84-523, p. 43. Simkiss, K., 1964, Phosphates as crystal poisons of calcification: Biological Reviews, v. 39, p. 487-505. Siung, A.M., 1980, Studies on the biology of Isognomon alatus Gmelin (Bivalvia: Isognomonidae) with notes on its potential as a commercial species: Bulletin of Marine Science, v. 30, p. 90-101. Sorokin, Y.I., 1990, Aspects of trophic relations, productivity and energy balance in coral-reef ecosystems, in Dubinsky, Z., ed., Coral Reefs: Ecosystems of the World, Volume 25: Amsterdam, Elsevier, p. 401-408. Soussi, M., and Ben Ismail, M.H., 2000, Platform collapse and pelagic seamount facies; Jurassic development of central Tunisia: Sedimentary Geology, v. 133, p. 93-113. Stanley, G.D., Jr., 1988, The history of early Mesozoic Reef Communities: A Three- Step Process: Palaios, v. 3, p. 170-183. Stanley, G.D., Jr., 1994, What happened to reef ecosystems during the Triassic- Jurassic interval?, Coral reefs, in the past, present and future: Conference proceedings, Luxembourg, International Society for Reef Studies, p. 113. Stanley, G.D., Jr., and Beauvais, L., 1994, Corals from and Early Jurassic coral reef in British Columbia: Refuge on an oceanic island reef: Lethaia, v. 27, p. 35- 47. Stanley, G.D., Jr., and Fautin, D.G., 2001, The origins of modem corals: Science, v. 291, p. 1913-1914. Stanley, G. D., Jr., and Swart, P.K., 1995, Evolution of the coral-zooxanthellate symbiosis during the Triassic: a geochemical approach: Paleobiology, v. 21, p. 179-199. Stanley, K.O., 1971, Tectonic and sedimentologic history of lower Jurassic Sunrise and Dunlap formations, west-central Nevada: The American Association of Petroleum Geologists Bulletin, v. 55, p. 454-477. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 243 Stanley, S.M., 1972, Functional morphology and evolution of byssally attached bivalve mollusks: Journal of Paleontology, v. 46, p. 165-212. Stanley, S.M., 1999, The myth of the diversity plateau: High extinction rates, not ecological saturation stifled the diversification of Paleozoic marine life, Geological Society of America Annual Meeting: Denver, CO, Geological Society o f America, p. 336. Stasek, C.R., 1963, Synopsis and discussion o f the association of ctenidia and labial palps in the bivalved Mollusca: The Veliger, v. 6, p. 91-97. Steams, C.E., 1962, Geology of the Eastern Part of Mount Jura, California [unpublished master's, thesis], University of Oregon 75 pgs. Steuber, T., 1996, Stable isotope sclerchronology of rudist bivalves: Growth rates and Late Cretaceous seasonality: Geology, v. 24, p. 315-318. Stoddart, D.R., 1969, Ecology and morphology of recent coral reefs: Biological reviews o f the Cambridge Philosophical Society, v. 44, p. 433-489. Surge, D., Lohmann, K.C., and Dettman, D.L., 2001, Controls on isotopic chemistry of the American oyster, Crassostrea virginica; implications for growth patterns: Palaeogeogrpahy, Palaeoclimatology, Palaeoecology, v. 172, p. 283- 296. Swanson, R.G., 1981, Sample Examination Manual, Shell Oil Company, Exploration Training, Methods in Exploration Series: Tulsa, OK, American Association of Petroleum Geologists, 123 p. Swofford, D., 1998, PAUP®: Sunderland, MA, Sinauer Associates. Tanaka, N., Monaghan, M.C., and Rye, D.M., 1986, Contribution of metabolic carbon to mollusc and barnacle shell carbonate: Nature, v. 320, p. 520-523. Tanner, L.H., Hubert, J.F., Coffey, B.P., and Mclnemey, D.P., 2001, Stability of atmospheric C 02 levels across the Triassic-Jurassic boundary: Nature, v. 411, p. 675-677. Tausch, L., 1890, Zur Kenntniss der Fauna der "Grauen Kalke": Abhandlungen der Kaiserlich-Koniglichen Geologischen Reichsanstalt, v. 42, p. 1-42. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 244 Taylor, D.G., Smith, P.L., Laws, R.A., and Guex, J., 1983, The stratigraphy and biofacies trends of the lower Mesozoic Gabbs and Sunrise formations, west- central Nevada: Canadian Journal o f Earth Sciences, v. 20, p. 1598-1608. Taylor, J.D., Kennedy, W.J., and Hall, A., 1969, The shell structure and mineralogy of the Bivalvia, Introduction, Nuculacea-Trigonacea: Bulletin of the British Museum of Natural History, Zoology Supplement, p. 1-125. Thayer, C.W., 1979, Biological bulldozers and the evolution of marine benthic communities: Science, v. 203, p. 458-461. Tripp, B.W., and Farrington, J.W., 1985, Using sentinel organisms to monitor chemical changes in the coastal zone: Progress or paralysis, in Society, T.C., ed., Gambling with the shore: Proceedings of the Ninth Annual Conference of the Coastal Society: Atlantic City, New Jersey, The Coastal Society, p. 195-209. Tucker, M.E., 1969, The field description of sedimentary rocks: Milton Keynes, U.K., Open University Press, 112 p. Vakhrameev, V.A., 1982, Main features of phytogeography of the globe in Jurassic and Early Cretaceous time: Journal of Paleontology, v. 2, p. 122-133. Veevers, J.J., 1989, Middle/Late Triassic (230 ±5 Ma) singularity in the stratigraphic and magmatic history of the Pangean margin: Geology, v. 17, p. 787-787. Vogel, K., 1975, Endosymbiotic algae inrudists: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 17. Walker, R.G., and Plint, A.G., 1992, Wave- and storm-dominated shallow marine systems, in Walker, R.G., and James, N.P., eds., Facies Models: Response to Sea Level Change: St. Johns's, Newfoundland, Canada, Geological Association of Canada, p. 219-238. Waller, T.R., 1978, Morphology, morphoclines and a new classification of the Pteriomorphia (Mollusca: Bivalvia): Philosophical Transactions of the Royal Society of London, B., v. 284, p. 345-365. Waller, T.R., 1990, The evolution of ligament systems in the Bivalvia, in Morton, B., ed., The Bivalvia-Proceedings of a Memorial Symposium in Honour of Sir Charles Maurice Yonge, Edinburgh, 1986: Hong Kong, Hong Kong University Press, p. 49-71. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 245 Waller, T.R., 1998, Origin of the molluscan class Bivalvia and a phylogeny of major groups, in Johnston, P.A., and Haggart, JW., eds., Bivalves: An Eon of Evolution: Calgary, Alberta, University of Calgary Press, p. 1-46. Warme, J., 1988, Jurassic carbonate facies of the central and eastern High Atlas Rift, Morocco, in Jacobshagen, V.H., ed., The Atlas System of Morocco: Studies on its Geodynamic Evolution, Lecture Notes in Earth Sciences: Berlin, Springer-Verlag, p. 169-199. Wefer, G., and Killingley, J.S., 1980, Growth histories of strombid snails from Bermuda recorded in their lsO and 1 3 C profiles: Marine Biology, v. 60, p. 129-135. Wesley, A., 1965, The fossil flora of the grey limestones of Veneto, northern Italy and its relationships to the other European floras of similar age: The Palaeobotanist, v. 14, p. 124-130. Westermann, G.E.G., 1993, Global bio-events in mid-Jurassic ammonites controlled by seaways, in House, M.R., ed., The Ammonoidea: Environment, Ecology and Evolutionary Change, Systematic Association Special Volume 47, p. 187-226. Wetterauer, R.H., 1977, The Mina Deflection; a new interpretation based on the history of the Lower Jurassic Dunlap Formation, western Nevada [unpublished dissertation], Northwestern University, Evanston, IL. 185 pgs. Wood, R., 1993, Nutrients, Predation and the History of Reef-Building: Palaios, v. 8, p. 526-543. Wood, R., 1999, Reef Evolution: Oxford, Oxford University Press, 414 p. Yapp, C.J., and Poths, H., 1996, Carbon isotopes in continental weathering environments and variations in ancient atmospheric C02 pressure: Earth and Planetary Science Letters, v. 137, p. 71-82. Yonge, C.M., 1936, Mode of life, feeding, digestion and symbiosis with zooxanthellae in the Tridacnidae: Scientific Reports, Great Barrier Reef Expedition, 1928-1929, v. 1, p. 283-321. Yonge, C.M., 1953, The monomyarian condition in the Lamellibranchia: Transactions of the Royal Society of Edinburgh, v. 42, p. 443-478. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 246 Yonge, C.M., 1968, Form and habit in species of Malleus (including the "hammer oysters") with comparative observations on Isognomon isognomon: Biological Bulletin, v. 135, p. 378-405. Zampieri, D., Zorzin, R., and Sorbini, L., 1993, Carta Geologica de Lessini Centro- Occidentali tra la Valpantena e la Val d'lllasi: Memorie del Museo Civico di Storia Naturale di Verona (II Serie) Sezione Scienze della Terra. Zempolich, W.G., 1993, The drowning succession in Jurassic carbonates of the Venetian Alps, Italy: A record of supercontinent breakup, gradual eustatic rise and eutrophication of shallow-water environments, in Loucks, R.G., and Sarg, J.F., eds., Carbonate Sequence Stratigraphy: Tulsa, American Association of Petroleum Geologists, p. 545. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 247 A P P E N D IX A Phylogenetic Character Codes for Bivalve Families and “Lithiotis” Facies Bivalves after Waller (1998) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1 AB-1 2 AB-1 3 AB-1 4 A B-1 5 A B -1 D escription Gill structure A brfrontal gill cilia protobranchiate, no-reflected 1 reflected filam entous, either fiiibranchiate or eulam ellibranchiate unevenly distributed or absent Pattern o fla te ra l ciliated cells on gill filam ents stiffening structures in cilia o f the eulaterofrontal cirri o f sills hinge teeth uniform ly distributed on abrfrontal surfaces lateral ciliated cell tract w ide, consisting cell tract narrow er, w ith cells rectangular and o f cells in an indefinite arrangem ent arranged in definite row s .2 •• • 9 3 S © * i ja r £ J s e a < j < 3 e» 1 1 I I I 11111 eo a. a. 1111111 1 1 1 1 11111 110 1 1 1 1 1 I I 1 1 1 1 1 I 1 1 I 1 absent m odified taxodont plan present 6 AB-2 Fibrous ligam ent um burrid-like dental ontogeny w ith elongate, shallow ly inclined prim ary teeth and sockets characterizing early grow th stages m ainly opisthodetic, continuous w ith the adult fibrous ligam ent discontinuous w ith early post I I I 1111111 1 1 i 1 ! 1 1 1 1 0 1 11111 1 1 1 1 7 A B -2 8 AB-2 9 AB-2 10 AB-2 C ross-sectional shape o f the rectum Stom ach type A uricles o f heart A dductor m uscles (Y onge, 1953) early post-larval resilium rounded T ype -IV o fP u rc h o n ( 1959) Separate from one another dim yarian, w ith anterior and posterior m uscles o f approxim ately equal size Pigm ented eye spots close to the absent prim ordia o f the gills in veliger larvae (C ragg, 1996, p. 376) larval resilium w ith original opisthodetic system replaced by duplivincular or m ultivincular system s flattened Type -III auricles intercom m unicating anisom yarian, w ith anterior adductor sm aller than posterior o r m onom yarian w ith anterior adductor absent in adult stage present 0,1 1 1 1 1 1 1 0,1 0,1 0,1 11111 1 1 I 1 1 0,1 1 1 1 1 1 1 J- t- 11 1 1 ? ? 9 9 1 1 1 1 1 1 1 1 1 1 0 1 I i 1 i I 1 1 I 0 1 1 i 1 1 1 1 I 1 1 1 I 1 1 1 i 1 1 1 1 1 1 1 1 1 0 11 1 1 11 0 1 1 1 1 1 1 0 I 7 7 9 ? ? 0 1 ? 7 ? ? ? 0 1 9 7 ? ? ? 0,1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 ? ? ? 7 7 12 A B -3 Pseudonym phae absent present 0,1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ? ? ? 7 7 13 A B-3 m antle fusion absent fusion o f inner m antle folds betw een the exhalant and inhalant apertures 0,1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 7 7 7 7 14 A B -3 branchial septum connecting gills to m antle in fused region betw een exhalant and inhalant absent present apertures 0,1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ? ? 7 7 7 15 A B -3 anterior extent o f dem ibranchs inner and outer dem ibranchs equal in anterior ends o f outer dem ibranchs shorter than o f the gill anterior extent those o f inner dem ibranchs 0,1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ? 7 ? ? ? 16 A B -4 O pisthodetic dorsal ligam ent (W aller, 1990) present absent, replaced by duplivincular, m ultivincular, or alivincular ligam ent system s 0,1 0 1 1 I I 1 1 1 1 1 1 1 1 1 1 0 1 1 1 I 1 1 17 A B -4 Laterofrontal gill cilia (A tkins, m acrociliobranchiate m icrociliobranchiatc 1938) 0.1 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 ? ? 7 7 7 18 A B-4 A ssociation o f anterior gill filam ents and labial palps (Stasek, 1963) C ategory I C ategory HI 0,1 0 1 I I 1 i 1 1 I 1 I 1 1 1 I 0 1 7 9 7 7 ? 19 AB-5 H in ec teeth cvrtodontoid plan arcoid plan 0,1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 20 A B -5 com pound photocreccptore on absent present outer fold o f m antle 0,1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 ! A B -5 shell m icrostructure inner layers nacreous inner layers m ainly crossed lam ellar 0.1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 22 A B-5 shell tubules absent o r restricted to early shell o r to present throughout the area w ithin the pailial line inner shell layers and penetrating the shell to the inner surface o f the 0 periostracum 0,1 0 I 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 23 AB-6 foot norm al, non-reversed reversed 0,1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4^ 00 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 24 AB-6 25 AB-6 26 A B -6 27 A B -6 28 A B -7 29 AB-8 30 AB-8 31 AB-8 32 AB-8 D escription tentacles photoreceptors on m antle m argin lips sim ple iieam ent system C alcitic regular colum nar prism atic shell structure anterior shell lobe anterior adductor pallial line crossed lam ellar aragonitic m icrostruciures 0 1 sim ple lobate extensions o f m antle edge, com plex tentacles w ith bands o f cells secreting ooorlv extensible D rcdatorrenellants absent eyes on inner fold, w ithout lens eyes present on inner fold, w ith lens and w ith retina and with retina not inverted inverted hypertrophied, free, o r fused, lim ed type o f B ernard ( 1972) duplivincular absent or m inor presence in outer shell layers present present continuous present in association w ith nacreous aragonite J = II s a o -« 3 o © s , £ * S J ! < S -3 fibrous alivincular com prising outer shell layers, at least on right valve absent absent anterior, discontinuous crossed lam ellar aragonitic m icrostructures absent, inner shell layers com pletely nacreous 33 AB-9 Shell sym m etry 34 A B -iO Bvssal openine 35 A B -10 Sym m etry o f paired abdom inal sym m etrical sense organs 36 A B -5 1 Ligam ent system valves equal in convexity absent 37 A B- 12 Position o f posterior pedal retractor scar relative to nostcrinr adductor scar 38 A B -12 Extent o f m arginal fringe o f regular colum nar prism atic calcite 39 A B -12 pallial line 40 A B -12 ligam ent system 41 A B -13 42 A B -13 43 A B -13 fibrous resilium Shell shape duplicvincular dorsal side o f a rounded adductor scar narrow present duplivincular triangular and com m only alivincular pterioid, inequivalved post-larval stage W aste canals on m antle (Y onge, absent 1953) 44 A B-13 Preoral unpaired pallial gland absent opening in the inhalant cham ber (Y onge, 1953) 45 A B -13 P osterior pallial organ in absent exhalant cham ber (Y onge, 19531 46 A B -13 Tentacles on m iddle fold o f absent m antle (Y onge, 1953) inequivalved (usually left valve m ore convex in early ontogeny) present asym m etrical, w ith the left reduced relative to the right alivincular o r m ultivincular w ith resilifers unevenly spaced and ventrnlly expanding throughout ontosenv inset o f the anterior, concave face o f a crescent posterior adductor scar very broad m arkedly discontinuous to obsolete, the pallial m antel retractor m uscles converge on relatively few attachm ent points on the shell alivincular o r m ultivincular ligam ent w ith resilifers evenly spaced and rem aining parallel-sided through m ost o f ontogeny posterior elongated nearly the entire length o f the posterior dorsal m argin pinnoid eqiuivalved in post-larval stage present present present present « ss .s cn cu o- sL S 1 §■ 0,1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 7 7 7 7 0,1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 7 > 7 0,1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 0,1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 1 0 0 0.1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 0.1 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 } 0 0 1 } } 0,1 0 0 0 0 0 I 1 1 1 1 1 1 1 1 1 0 1 7 7 7 7 ? 0,1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0,1 G 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 i 1 1 0 1 1 0,1 0 0 0 0 0 0 0 1 I 0 0 0 0 0 0 0 1 0 0 0 i I 0,1 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 1 1 1 1 1 } 0,1 0 0 0 0 0 0 0 i 1 0 0 0 0 0 0 0 1 1 1 0 1 1 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 7 7 7 7 7 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 7 7 7 7 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 7 7 7 7 7 0,1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 7 7 V 7 ’ ? to -1^ \o Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ■E 2 S - f i .2 .r o U £ 47 AB-13 48 AB-14 49 AB-15 50 AB-15 51 A B-15 52 AB-15 D escrip tio n S econdary anterior and posterior absent m antle retractor attachm ents (Y onge, 1953) anal flan (Y onee, 1968) byssal opening in early ontogeny o f dissoconch •S s R O i .5 6 E < 2 J < s e. « .a a. 3 g ® o ® 3 = u e -2 3 £ -3 <J £ S * s. ^ 3 I ‘ S . -5 present tentacles o f m iddle fold o f m antle posterior pedal retractors nacreous aragonite absent o r sm all prom inent a shallow sinus in the m argin o f th e right sharp notch in the right valve setting o ff the right valve or both valves not setting o ff the anterior auricle from the disk anterior auricles sharply from disk not strongly differentiated and extensible strongly differentiated and extensible 0.1 0,1 present on both right and left sides w ith right posterior pedal retractor greatly reduced or only m inor asym m etry absent com prising m iddle and inner shell layers trend tow ard replacem ent o f nacre by other aragonitic structures in the m iddle and inner shell layers 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 1 ? ? ? ?? 0 0 1 0 0 1 0 0 1 53 AB-15 calcitic m icrostructures regular colum nar prism atic trend tow ard thinning, asym m etry o r disappearance o f regular colum nar prism atic calcite outer layers and tow ard increasing dom inance o f o th er calcitic m icrostructures including foliate calcite 0,1 0 0 0 0 0 0 0 0 0 1 0,1 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 54 A B -15 cyrtodontid-pterineid-type present reduced to a single elongate lam ellar tooth nearly dentition parallel to the hinge line on each side o f the beak 0,1 0 0 0 0 0 0 0&1 0 0 1 1 1 1 0 0 0 0 0 0 0 55 A B -I6 byssal notch triangular to rounded, not accom panied deep curved, accom panied by trend tow ard 0 bv a reduced auricle reduction in site o f anterior auricle 0,1 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 56 A B -16 calcitic m icrostructure com m only prom inent in outer calcitic shell layers and com m only com prising crossfoliated m icrostructure com m only prom inent in outer calcitic shell layers and com m only parts o f m iddle an inner shell layers com prising parts o f m iddle and inner shell layers 0,1 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 57 A B -17 neobranch absent present 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 7 7 7 58 AB-17 ontogenetic loss o f foot does not occur o r occurs late in ontogeny occurs im m ediately after settlem ent 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 ? 7 7 59 A B -17 gill structure filibranchiate eulam ellibranchate w ith a sim ilar grade o f fusion betw een filam ents and gill lam ellae in both O streidac and G ryphaeidae 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 60 A B -17 posterior palliobranchial fusion absent present 0,1 0 0 0 0 0 0 0 0 0 0 i 1 0 0 0 0 0 0 0 0 0 0 61 A B -17 postanal notch and track in absent w ell-developed prodissoconch-11 shell 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 7 7 ? 7 62 A B-17 cem entation absent o r bv right valve cem ented bv left valve 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 63 A B-17 shell m ineralogy and m icrostructure o f inner shell com pletely o r partially aragonitic, the aragonitic portion either nacreous or com pletely calcitic ostracum consisting o f lathic or foliated calcite; nacre and crossed aragonitic layers crossed lam ellar structures absent 0,1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 64 A B-17 chom ata absent present 0.1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 7 7 65 A B -18 accessory heart in the neobranch absent present 0,1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 ? ? ? 7 66 A B -18 relationship o f rectum to the penetrating the pericardium and rectum bypassing pericardium on its dorsal side pericardium ventricle 0,1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 ? 7 7 7 67 A B-19 byssal opening open notch in right valve nearly closed o r closed centralized foram ent w ith a sutural groove connecting the foram ent to the anterodorsai m argin o f the shell 0,1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 1110 0'????? 1 1 I 0 0 0 0 0 0 0 1110 0 0 0 0 0 to o Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. •S « O •3 © V u ■ g « © •? '5 •§ 5. 3 U S E 68 AB-19 D escription ligam ent system I 1 S S g -5 . „ o S -S s s e >- .S .2 o-Soo-c<fl-a 3 s s « r S’ £ £ ! I 1 I I U I I I •* } tj ^ 5 § norm al external alivincular internalized overarched alivincular system incorporating the anterior and posterior lam ellar ligam ents, supported on a raised support on the right valve 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o r 0 0 0 69 AB-19 right posterior pedal retractor sm aller than posterior adductor and larger than posterior adductor and w ell separated adjacent to its dorsal side from it 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 70 AB-19 byssys non-caleified calcified except in E nigm onia, w here byssus is secondarily absent 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 71 A B -19 pericardium present w ith ventricle penetrated by absent w ith rectum bypassing ventricle on its dorsal rectum side 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ? 7 ? 72 AB-20 resilium containing densely packed aragonitic fibers throughout, w ithout extensive non-m ineraiized organic core w ith fibrous lateral parts, developed m ainly ventral to the hinge line developm ent ventral to the hinge line 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 73 AB-20 eyes on m iddle m antle fold absent o r o f a low grade developm ent w ell-developed eyes w ith a reversed double retina 0 .1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 7 7 ? 74 AB-21 hinge dentition heteroconchid (3a/2/ 3b core hom ology) present absent Y onge ( 1963) 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 75 AB-21 ligam ent nvm phae absent present 0,1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 ? 7 ? 76 intercalations betw een ligam ent absent present 0 0 0 0 0 0 grooves 0,1 0 0 0 0 0 0 0 .1 0 0 0 0 1 i 0 1 0 77 strong discordancy absent present 0 ,1 0 0 0 0 0 0 0,1 0.1 0 0 0 0 0 0,1 1 1 to L h A P P E N D IX B Bivalve Stable Isotope Data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 253 from umbo) 5i3C (% « PDB) 5 1 3 C precision 5 lsO (%o PDB) 5 lsO precision Crassostrea gigas 1 0 .3 8 6 0 .0 0 6 - 0 .3 9 5 0 .0 0 3 Crassostrea gigas 1 - 0 .1 4 9 0 .0 0 7 - 0 .9 6 3 0 .0 1 6 Crassostrea gigas 2 - 3 .7 5 7 0 .0 0 5 - 6 .3 3 5 0 .0 0 3 Crassostrea gigas 3 - 0 .1 7 1 0 .0 0 4 - 0 .5 9 6 0 .0 0 9 Crassostrea gigas 4 0 .3 3 7 0 .0 0 3 - 1 .7 6 5 0 .0 1 4 Crassostrea gigas 5 - 1 .0 0 6 0 .0 0 8 - 2 .9 0 5 0 .0 1 7 Crassostrea gigas 6 0 .1 9 3 0 .0 0 3 - 1 .0 1 6 0 .0 0 8 Crassostrea gigas 6 0 .1 5 8 0 .0 0 9 - 1 .0 8 9 0 .0 1 8 Crassostrea gigas 7 - 0 .0 6 6 0 .0 0 6 - 0 .0 4 1 0 .0 1 8 Crassostrea gigas 8 0 .1 5 8 0 .0 1 1 - 0 .2 4 8 0 .0 1 1 Crassostrea gigas 9 0 .3 0 9 0 .0 0 9 - 0 .4 1 3 0 .0 2 3 Crassostrea gigas 1 0 - 0 .5 0 6 0 .0 0 5 - 1 .4 2 0 0 .0 1 6 Crassostrea gigas 1 1 - 1 .2 4 6 0 .0 0 7 - 2 .6 6 1 0 .0 1 1 Crassostrea gigas 1 1 - 1 .3 6 9 0 .0 0 4 - 3 .0 4 2 0 .0 1 1 Crassostrea gigas 1 2 - 2 .3 9 7 0 .0 0 9 - 4 .1 6 5 0 .0 0 6 Crassostrea gigas 1 4 - 0 .9 1 7 0 .0 1 1 - 1 .6 8 7 0 .0 1 5 Crassostrea gigas 1 5 - 2 .1 2 4 0 .0 1 9 - 2 .5 7 4 0 .0 3 1 Crassostrea gigas 1 6 - 4 .1 6 2 0 .0 0 4 - 4 .9 2 3 0 .0 0 9 Crassostrea gigas 1 7 - 2 .1 5 9 0 .0 1 3 - 3 .2 2 7 0 .0 0 6 Crassostrea gigas 1 8 - 0 .5 3 0 0 .0 0 7 - 2 .0 3 8 0 .0 1 2 Crassostrea gigas 1 9 - 1 .2 2 4 0 .0 0 3 - 1 .7 4 9 0 .0 0 8 Crassostrea gigas 2 0 - 0 .0 2 6 0 .0 0 5 - 0 .1 9 6 0 .0 0 9 Crassostrea gigas 2 1 - 1 .0 7 7 0 .0 1 2 - 1 .7 8 3 0 .0 2 5 Crassostrea gigas 2 2 - 2 .0 2 7 0 .0 0 6 - 3 .5 3 2 0 .0 1 7 Crassostrea gigas 2 4 - 0 .0 5 1 0 .0 0 4 - 0 .8 4 5 0 .0 0 3 Crassostrea gigas 2 5 0 .3 5 6 0 .0 0 4 - 0 .2 9 5 0 .0 1 9 Crassostrea gigas 2 6 0 .0 9 6 0 .0 1 1 - 1 .0 3 2 0 .0 0 9 Crassostrea gigas 2 7 - 0 .1 0 0 0 .0 0 4 - 1 .5 4 8 0 .0 1 5 Crassostrea gigas 2 8 - 0 .4 7 2 0 .0 1 2 - 2 .2 9 7 0 .0 1 2 Crassostrea gigas 2 9 0 .3 0 3 0 .0 0 7 - 0 .1 8 7 0 .0 2 7 Lithioperna scutata 1 - 1 .5 9 1 0 .0 0 2 -4 .7 4 3 0 .0 0 8 Lithioperna scutata 2 -2 .2 2 4 0 .0 0 2 -2 .3 5 6 0 .0 0 6 Lithioperna scutata 3 - 2 .7 0 3 0 .0 0 4 -2 .7 7 2 0 .0 1 1 Lithioperna scutata 4 - 2 .6 4 1 0 .0 0 3 -2 .7 0 6 0 .0 0 9 Lithioperna scutata 5 - 2 .4 0 3 0 .0 0 3 -2 .2 8 8 0 .0 0 2 Lithioperna scutata 6 -2 .5 1 3 0 .0 0 3 -2 .4 7 0 0 .0 0 6 Lithioperna scutata 7 -2 .7 3 4 0 .0 0 4 -2 .7 8 9 0 .0 0 3 Lithioperna scutata 8 - 2 .9 7 1 0 .0 0 2 - 3 .1 6 1 0 .0 0 5 Lithioperna scutata 9 - 2 .8 9 9 0 .0 0 2 - 3 .0 1 1 0 .0 0 6 Lithioperna scutata 1 0 - 2 .9 3 2 0 .0 0 4 -3 .4 5 7 0 .0 0 6 Lithioperna scutata 1 1 - 2 .3 8 8 0 .0 0 4 -2 .6 9 0 0 .0 0 5 Lithioperna scutata 1 2 - 2 .1 9 3 0 .0 0 2 -2 .6 6 0 0 .0 0 6 Lithioperna scutata 1 3 - 1 .8 6 2 0 .0 0 2 -2 .4 9 9 0 .0 1 3 Lithioperna scutata 1 4 - 2 .2 8 3 0 .0 0 4 -2 .7 6 7 0 .0 0 2 Lithioperna scutata 1 5 - 1 .7 8 6 0 .0 0 2 - 1 .4 1 1 0 .0 0 8 Lithioperna scutata 1 6 - 1 .9 1 5 0 .0 0 2 -2 .2 1 9 0 .0 0 6 Lithioperna scutata 1 7 - 1 .7 3 9 0 .0 0 5 -2 .0 1 7 0 .0 0 6 Lithioperna scutata 1 8 -1 .8 3 2 0 .0 0 5 -2 .3 5 8 0 .0 1 0 Lithioperna scutata 1 9 - 1 .9 8 3 0 .0 0 2 -2 .5 5 6 0 .0 1 1 Lithioperna scutata 2 0 - 1 .9 4 5 0 .0 0 5 -2 .3 0 7 0 .0 1 0 Lithioperna scutata 2 1 - 2 .4 2 3 0 .0 0 4 -2 .6 9 9 0 .0 0 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. shell from umbo) Sl3 C(%oPDB) 5I 3 C precision 5,80 (% o PDB) 5,80 precision Lithioperna scutata 22 -2 .7 1 2 0.004 -2 .8 7 2 0.006 Lithioperna scutata 23 -2.743 0.003 -2 .7 6 5 0.007 Lithioperna scutata 24 -2 .7 4 7 0.004 -2 .7 7 6 0.006 Lithioperna scutata 25 -2 .8 6 9 0.002 -2 .8 3 1 0.003 Lithioperna scutata 26 -2.653 0.003 -2 .6 3 8 0.005 Lithioperna scutata 27 -2 .6 1 7 0.002 -2 .6 8 6 0.004 Lithioperna scutata 28 -2.450 0.004 -2 .5 3 5 0.003 Lithioperna scutata 29 -2 .7 4 6 0.004 -2 .8 7 2 0.005 Lithioperna scutata 30 -2 .7 5 9 0.003 -2.901 0.007 Lithioperna scutata 31 -2 .3 6 9 0.004 -2 .8 0 7 0.003 Lithioperna scutata 32 -2 .4 3 7 0.005 -2 .8 3 3 0.002 Lithioperna scutata 33 -2.418 0.002 -2 .8 4 0 0.004 Lithioperna scutata 34 -2.306 0.002 -2 .6 8 9 0.005 Lithioperna scutata 35 -2.282 0.005 -2 .7 7 5 0.009 Lithioperna scutata 36 -2.221 0.003 -2.701 0.006 Lithioperna scutata 38 -2 .6 0 6 0.005 -2 .5 3 3 0.005 Lithioperna scutata 39 -2 .2 6 9 0.006 -2 .7 2 7 0.009 Lithioperna scutata 40 -2 .9 0 9 0.001 -3 .3 0 9 0.007 Lithioperna scutata 41 -2.921 0.003 -3 .3 8 5 0.009 Lithioperna scutata 42 -2 .3 3 2 0.005 -2.581 0.006 Lithioperna scutata 43 -2 .5 4 9 0.005 -2.801 0.007 Lithioperna scutata 44 -2.571 0.005 -2 .6 0 5 0.004 Lithioperna scutata 45 -2 .5 1 9 0.007 -2 .6 3 3 0.004 Lithioperna scutata 46 -2.227 0.004 -2 .7 6 2 0.010 Lithioperna scutata 47 -2.177 0.004 -2 .6 8 9 0.008 Lithioperna scutata 48 -2.656 0.005 -4 .0 0 5 0.004 Lithioperna scutata 49 -2 .3 3 7 0.006 -3 .0 3 3 0.008 Lithioperna scutata 50 -2.003 0.004 -2 .7 4 9 0.011 Lithioperna scutata 51 -2.569 0.006 -3 .1 1 7 0.006 Lithioperna scutata 52 -2.662 0.003 -2 .9 9 8 0.004 Lithioperna scutata 53 -2.413 0.001 -2 .4 6 3 0.009 Lithioperna scutata 53 -2 .3 8 9 0.003 -2 .4 1 6 0.010 Lithioperna scutata 54 -2.362 0.003 -2 .5 4 5 0.006 Lithioperna scutata 54 -2.332 0.006 -2 .4 5 4 0.010 Lithioperna scutata 55 -1.566 0.002 -1 .6 2 9 0.006 Lithioperna scutata 55 -1.613 0.002 -1 .7 2 5 0.004 Lithioperna scutata 56 -2.932 0.003 -3 .6 8 9 0.003 Lithioperna scutata 57 -2.742 0.004 -2 .8 4 6 0.007 Lithioperna scutata 58 -2.596 0.005 -2 .5 2 5 0.009 Lithioperna scutata 58 -2.562 0.003 -2 .4 6 2 0.005 Lithioperna scutata 59 -2.424 0.003 -2 .7 8 4 0.009 Lithioperna scutata 60 -2.415 0.005 -2.401 0.005 Lithioperna scutata 60 -2.438 0.005 -2.401 0.005 Lithioperna scutata 61 -2.448 0.002 -2 .4 5 6 0.005 Lithioperna scutata 62 -2.555 0.004 -2 .7 3 3 0.005 Lithioperna scutata 63 -2.494 0.006 -2 .5 5 5 0.009 Lithioperna scutata 64 -2.470 0.001 -2 .4 4 4 0.007 Lithioperna scutata 65 -2.367 0.003 -2 .2 3 9 0.007 Lithioperna scutata 66 -2.419 0.005 -2 .2 1 5 0.003 Lithioperna scutata 67 -2.525 0.002 -2 .8 0 8 0.007 Lithioperna scutata 68 -2.507 0.004 -2 .4 1 0 0.007 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 255 from umbo) ^i3 C (% o PDB) 5 I 3 C precision 8 I 8 0 (% o PDB) 8I 8 0 precision Lithioperna scutata 69 -2,396 0.002 -2.271 0.005 Lithioperna scutata 70 -2.693 0.003 -2 .7 3 6 0.007 Lithioperna scutata 71 -2.585 0.004 -3 .0 6 4 0.006 Lithioperna scutata 72 -2.628 0.005 -3 .0 1 7 0.003 Lithioperna scutata 73 -2 .5 4 2 0.007 -2 .7 0 4 0.010 Lithioperna scutata 74 -2.565 0.004 -2 .6 8 6 0.007 Lithioperna scutata 75 -2 .7 6 2 0.003 -3 .1 6 2 0.004 Lithioperna scutata 76 -2 .5 2 7 0.003 -2.791 0.009 Lithioperna scutata 77 -2 .0 7 0 0.004 -3 .9 1 6 0.007 Lithioperna scutata 78 -2 .6 3 0 0.005 -2 .8 8 0 0.006 Lithioperna scutata 79 -2 .6 1 0 0.005 -2 .7 5 8 0.010 Lithioperna scutata 80 -2 .6 9 2 0.003 -2 .9 8 2 0.009 Lithioperna scutata 81 -2 .6 2 9 0.003 -2 .8 8 4 0.007 Lithioperna scutata 82 -2 .1 2 4 0.006 -2 .3 5 7 0.004 Lithioperna scutata 83 -2 .4 5 4 0.003 -2.425 0.004 Lithioperna scutata 84 -2 .4 5 4 0.002 -2 .3 3 9 0.005 Lithioperna scutata 85 -2 .6 1 7 0.003 -2 .6 6 8 0.006 Lithioperna scutata 86 -2.381 0.003 -2 .3 8 4 0.003 Lithioperna scutata 87 -2.288 0.003 -2 .3 0 9 0.004 Lithioperna scutata 88 -1.782 0.003 -2 .0 3 0 0.007 Lithioperna scutata 89 -1 .6 9 0 0.003 -2.375 0.008 Lithioperna scutata 90 -2.558 0.004 -2 .8 4 0 0.003 Lithioperna scutata 91 -2 .5 0 4 0.005 -2 .7 4 6 0.006 Lithioperna scutata 92 -2 .6 6 7 0.007 -3 .2 2 4 0.008 Lithioperna scutata 93 -2.375 0.004 -2 .9 2 4 0.007 Lithioperna scutata 94 -2.675 0.004 -2 .9 6 9 0.006 Lithioperna scutata 95 -2.615 0.003 -2 .9 7 7 0.005 Lithioperna scutata 96 -2.775 0.006 -3 .3 9 2 0.006 Lithioperna scutata 97 -2 .9 3 2 0.004 -3.351 0.002 Lithioperna scutata 98 -2.658 0.004 -2 .7 7 9 0.003 Lithioperna scutata 99 -2.726 0.003 -2 .7 1 2 0.006 Lithioperna scutata 100 -2.831 0.006 -3.071 0.009 Lithioperna scutata 101 -2.767 0.004 -3 .0 7 8 0.006 Lithioperna scutata 102 -2.728 0.002 -2 .8 5 0 0.006 Lithioperna scutata 103 -2 .7 4 9 0.004 -2 .7 1 8 0.007 Lithioperna scutata 104 -2 .6 7 4 0.003 -2 .7 4 2 0.007 Lithioperna scutata 106 -2.574 0.004 -2 .4 8 5 0.009 Lithioperna scutata 107 -2 .5 1 0 0.003 -2 .5 7 4 0.006 Lithioperna scutata 108 -2.748 0.004 -2 .9 7 0 0.005 Cochlearites loppianus 1 3.582 0.01 -7 .5 7 8 0.009 Cochlearites loppianus 1 3.678 0.005 -7.491 0.009 Cochlearites loppianus 2 3.752 0 .0 0 9 -7 .8 6 9 0.014 Cochlearites loppianus 3 3.754 0.0 0 9 -7 .6 8 4 0.0 0 9 Cochlearites loppianus 4 3.7 5 9 0 .0 0 4 -7 .4 7 4 0.0 1 4 Cochlearites loppianus 4 3.655 0.011 -7 .2 6 4 0.018 Cochlearites loppianus 5 3.644 0.0 0 4 -7 .3 6 2 0.005 Cochlearites loppianus 6 3.743 0.003 -7.941 0.006 Cochlearites loppianus 6 3.715 0.0 0 8 -7 .8 9 6 0.012 Cochlearites loppianus 7 3.545 0.008 -7 .3 5 6 0.003 Cochlearites loppianus 8 3.493 0.0 0 2 -6 .9 4 9 0.012 Cochlearites loppianus 9 4.14 0.0 1 2 -6 .5 4 4 0.017 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 256 from umbo) 5 I 3 C (%oPDB) 5 1 3 C precision 6,80 (% o PDB) 8 I 8 0 precision Cochlearites loppianus 10 3.8 0 9 0 .0 0 4 -7 .5 7 0.016 Cochlearites loppianus 11 4.173 0 .0 1 7 -7 .0 1 9 0.0 0 7 Cochlearites loppianus 11 3.6 9 4 0.005 -7 .5 6 4 0.008 Cochlearites loppianus 12 3.738 0.011 -7 .7 5 4 0.013 Cochlearites loppianus 13 3.781 0.0 1 2 -7 .6 6 5 0.015 Cochlearites loppianus 14 3.8 0 2 0.003 -7 .6 7 0.0 0 4 Cochlearites loppianus 15 3.672 0.0 0 6 -7.355 0.013 Cochlearites loppianus 16 3.865 0 .0 0 2 -7 .4 6 0.013 Cochlearites loppianus 16 3.661 0.0 0 8 -7 .3 2 7 0.0 0 2 Cochlearites loppianus 17 3.652 0.01 -6.825 0.0 1 7 Cochlearites loppianus 18 3.804 0.0 0 7 -7 .7 4 9 0.01 Cochlearites loppianus 19 3.518 0.0 0 9 -6 .8 6 6 0.0 0 9 Cochlearites loppianus 20 3.525 0.01 -6 .8 5 4 0.011 Cochlearites loppianus 21 3.616 0.003 -7 .4 7 0.013 Cochlearites loppianus 22 3.5 4 4 0 .0 0 9 -6 .2 8 6 0.015 Cochlearites loppianus 22 3.53 0.005 -6 .3 8 4 0.013 Cochlearites loppianus 23 3.268 0.0 0 8 -5 .4 5 6 0.016 Cochlearites loppianus 24 3.496 0.0 0 8 -6.123 0.011 Cochlearites loppianus 25 3.806 0.0 0 2 -5.443 0.011 Cochlearites loppianus 26 3.618 0.0 0 6 -5 .9 9 9 0.0 1 4 Cochlearites loppianus 27 3.736 0.015 -6 .1 7 9 0.011 Cochlearites loppianus 28 3.923 0.0 0 4 -7 .4 3 7 0.007 Cochlearites loppianus 29 3.801 0 .0 0 6 -7 .5 4 6 0.015 Cochlearites loppianus 30 3.848 0 .0 0 7 -7.745 0.009 Cochlearites loppianus 31 3.94 0 .0 0 9 -8.091 0.01 Cochlearites loppianus 32 3.929 0 .0 0 6 -8 .0 2 4 0.011 Cochlearites loppianus 32 3.928 0 .0 0 6 -7 .9 9 6 0.0 0 4 Cochlearites loppianus 33 3.922 0.003 -8 .0 0 4 0.0 1 7 Cochlearites loppianus 34 3.715 0.011 -7.013 0.029 Cochlearites loppianus 35 3.56 0.005 -6 .6 9 4 0.005 Cochlearites loppianus 37 3.631 0 .0 0 9 -6 .7 8 9 0.0 2 2 Cochlearites loppianus 37 3.608 0.0 0 7 -6.821 0.004 Cochlearites loppianus 38 3.739 0 .0 0 9 -7 .7 8 2 0.013 Cochlearites loppianus 38 3.378 0 .0 0 9 -6.778 0.018 Cochlearites loppianus 39 3.772 0 .0 1 2 -6 .2 0 8 0.0 1 2 Cochlearites loppianus 40 3.417 0 .0 0 7 -6 .7 8 4 0.025 Cochlearites loppianus 41 3.376 0.0 0 7 -6 .8 9 7 0.003 Cochlearites loppianus 42 3.51 0.0 0 7 -6 .9 3 2 0.004 Cochlearites loppianus 43 3.377 0.005 -6.411 0.006 Cochlearites loppianus 44 3.596 0.01 -7 .0 8 4 0.008 Cochlearites loppianus 45 3.466 0 .0 0 4 -6 .8 6 7 0.013 Cochlearites loppianus 46 3.718 0.011 -7.443 0.025 Cochlearites loppianus 46 3.406 0.015 -6.941 0.009 Cochlearites loppianus 48 3.744 0 .0 0 7 -7 .4 7 7 0.015 Cochlearites loppianus 4 9 3.787 0.0 1 6 -7 .5 2 7 0.007 Cochlearites loppianus 50 3.587 0.0 0 6 -7.315 0.011 Cochlearites loppianus 50 3.561 0.005 -7 .2 1 9 0.02 Cochlearites loppianus 51 3.883 0 .0 0 4 -8 .1 3 9 0.008 Cochlearites loppianus 52 3.82 0.0 1 2 -7 .8 3 4 0.022 Cochlearites loppianus 53 4.13 0.0 0 4 -7.903 0.007 Cochlearites loppianus 54 3.773 0.003 -7 .7 9 8 0.011 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 257 from umbo) 5'3 C (%o PDB) 51 3 C precision 5 1 ! i O(%oPDB) 81 8 0 precision Cochlearites loppianus 55 3 .7 8 7 0.005 -7.925 0.027 Cochlearites loppianus 55 3.841 0.0 0 4 -7 .9 4 8 0.01 Cochlearites loppianus 56 3 .9 1 7 0.0 0 4 -7 .8 9 2 0.009 Cochlearites loppianus 57 3.87 0.008 -7.858 0.013 Cochlearites loppianus 58 3.84 0.0 0 6 -8 .0 3 4 0.019 Cochlearites loppianus 59 3.8 0.007 -7.541 0.006 Cochlearites loppianus 60 3.8 9 9 0.005 -7 .7 4 7 0.007 Cochlearites loppianus 60 3.895 0 .0 0 2 -7 .7 3 7 0.017 Cochlearites loppianus 61 4 .0 2 8 0.001 -7 .4 7 0.012 Cochlearites loppianus 62 3.9 1 6 0.01 -7.801 0.01 Cochlearites loppianus 63 3.89 0.0 0 9 -7 .8 4 8 0.014 Cochlearites loppianus 64 4.023 0.005 -7 .7 3 8 0.016 Cochlearites loppianus 65 3.915 0.0 0 4 -7 .6 6 9 0.013 Cochlearites loppianus 65 4.0 5 2 0 .0 0 4 -7 .3 0 9 0.008 Cochlearites loppianus 66 4.175 0.003 -7.703 0.001 Cochlearites loppianus 67 3.924 0.008 -7 .5 1 6 0.011 Cochlearites loppianus 68 3.967 0.007 -7.788 0.012 Cochlearites loppianus 69 3.942 0.008 -7.423 0.018 Cochlearites loppianus 70 4.011 0.007 -8 .1 6 9 0.005 Cochlearites loppianus 70 4.011 0.008 -8.135 0.009 Cochlearites loppianus 71 3.943 0.0 0 9 -8.053 0.013 Cochlearites loppianus 71 4 .0 0 2 0.0 0 7 -8.123 0.007 Cochlearites loppianus 72 3 .3 8 9 0.005 -5 .8 4 7 0.01 Cochlearites loppianus 7 2 3.847 0 .0 0 6 -7.601 0.011 Cochlearites loppianus 73 3.966 0 .0 0 7 -6 .8 8 8 0.02 Cochlearites loppianus 73 3.778 0.012 -7 .3 9 7 0.004 Cochlearites loppianus 74 4.0 2 5 0 .0 0 0 6 -8 .0 5 6 0.008 Cochlearites loppianus 74 3 .8 1 6 0.005 -7 .4 9 8 0.005 Cochlearites loppianus 75 3.842 0.0 0 4 -7.543 0.009 Cochlearites loppianus 76 3.5 2 4 0.0 0 9 -7.453 0.023 Cochlearites loppianus 76 3.725 0 .0 0 4 -7 .3 8 0.005 Cochlearites loppianus 77 3.96 0.0 0 4 -8 .0 1 4 0.012 Cochlearites loppianus 78 4 .2 0 6 0.01 -7 .5 8 6 0.013 Cochlearites loppianus 79 4.051 0.003 -8.261 0.005 Cochlearites loppianus 80 3.983 0.0 0 4 -2 .8 4 4 0.004 Cochlearites loppianus 81 4.2 2 2 0.005 -7.801 0.021 Cochlearites loppianus 81 3.9 3 7 0.005 -8 .1 2 0.01 Cochlearites loppianus 82 0.433 0.01 -1.665 0.011 Cochlearites loppianus 83 3.7 5 9 0.0 0 4 -7 .5 9 0.008 Cochlearites loppianus 84 3.591 0.0 0 9 -7.458 0.022 Cochlearites loppianus 85 3.488 0.005 -7 .7 3 6 0.011 Cochlearites loppianus 86 3.697 0.008 -7.68 0.006 Cochlearites loppianus 86 3.741 0.005 -6 .9 2 2 0.005 Cochlearites loppianus 86 3.726 0.005 -7 .5 9 6 0.014 Cochlearites loppianus 87 3.7 7 8 0 .0 1 6 -6.365 0.008 Cochlearites loppianus 88 3.208 0.0 0 4 -5 .1 0 4 0.014 Cochlearites loppianus 89 3 .6 4 4 0.01 -6 .7 2 7 0.01 Cochlearites loppianus 90 3.365 0 .0 1 2 -7 .0 8 9 0.019 Isongomon janus 1 4.125 0.01 -0.833 0.007 lsongomon janus 3 4 .47 0.005 -0 .3 0 9 0.012 Isongomon janus 4 4 .0 0 9 0.0 0 6 -0.268 0.007 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 258 from umbo) ^I 3 C (% o PDB) 5I 3 C precision 5 “0 (% o PDB) 8 1 8 0 precision Isongomon janus 5 3.846 0.011 -0 .0 1 4 0.0 0 4 Isongomon janus 6 3.6 3 4 0.0 0 6 -0 .2 4 9 0.01 Isongomon janus 7 2 .7 2 6 0.0 0 8 0.2 4 4 0.0 2 4 Isongomon janus 8 3.1 9 6 0.005 -0 .0 7 0.005 Isongomon janus 9 3.871 0.0 0 5 -0 .5 5 9 0.011 Isongomon janus 10 3.861 0.0 0 2 -0 .5 2 9 0.011 Isongomon janus 11 3.3 8 6 0.01 -0 .6 5 0.021 Isongomon janus 12 3.6 3 2 0.01 -0 .7 6 5 0 .0 0 7 Isongomon janus 13 3.7 2 9 0.0 0 7 -0 .6 0 3 0.008 Isongomon janus 14 3.313 0.0 0 9 -1.213 0 .0 1 7 Isongomon janus 15 3 .0 2 9 0.0 1 2 -0 .9 9 6 0.011 Isongomon janus 16 3 .4 7 2 0.0 1 7 -1.071 0 .0 1 2 Isongomon janus 17 3.003 0.015 -1.125 0.015 Isongomon janus 18 1.802 0.0 0 7 -1 .3 7 5 0.013 Isongomon janus 19 3.41 0.0 0 9 -1 .1 2 2 0.0 3 2 Isongomon janus 20 3.4 8 6 0.0 0 6 -1 .0 2 3 0.01 Isongomon janus 21 3.1 9 5 0.0 0 2 -1 .2 8 9 0.011 Isongomon janus 22 3.2 2 7 0 .0 1 2 -1.173 0 .0 3 9 Isongomon janus 23 3.2 7 9 0.0 0 4 -1.401 0.0 1 7 Isongomon janus 24 3 .1 6 9 0.006 -0 .9 8 8 0.005 Isongomon janus 25 3.671 0.005 -0 .7 2 4 0.008 Isongomon janus 26 2.611 0.005 -0.433 0.011 Isongomon janus 2 7 3.7 4 6 0.0 0 4 -0.751 0.01 Isongomon janus 28 3.543 0 .0 0 4 -0 .8 4 2 0.011 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Asset Metadata

Creator Fraser, Nicole Marie (author)

Core Title Early Jurassic reef eclipse: Paleoecology and sclerochronology of the "Lithiotis" facies bivalves

School Graduate School

Degree Doctor of Philosophy

Degree Program Earth Sciences

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

Tag geochemistry,OAI-PMH Harvest,paleoecology,paleontology

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Bottjer, David (committee chair), Bakus, Gerald (committee member), Douglas, Robert (committee member), Fischer, Alfred G. (committee member), Gorsline, Donn (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-249049

Unique identifier UC11334769

Identifier 3093763.pdf (filename),usctheses-c16-249049 (legacy record id)

Legacy Identifier 3093763.pdf

Dmrecord 249049

Document Type Dissertation

Rights Fraser, Nicole Marie

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 au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA