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Completeness of the Dinosaur Fossil Record: Disentangling Geological and Anthropogenic Biases

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Completeness of the Dinosaur Fossil Record: Disentangling Geological and Anthropogenic Biases COMPLETENESS OF THE DINOSAUR FOSSIL RECORD: DISENTANGLING GEOLOGICAL AND ANTHROPOGENIC BIASES by DANIEL DAVID CASHMORE A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY September 2019 School of Geography, Earth and Environmental Sciences, College of Life and Environmental Sciences, University of Birmingham University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Non-avian dinosaurs were a highly successful clade of terrestrial tetrapods that dominated Mesozoic ecosystems. Their public and scientific popularity makes them one of most intensely researched and understood fossil groups. Key to our understanding of their evolutionary history are interpretations of their changing diversity through geological time. However, spatiotemporal changes in fossil specimen completeness, diagnostic quality, and sampling availabil- ity can bias our understanding of a group’s fossil record. Methods quantifying the level of skeletal and phylogenetic information available for a fossil group have previously been used to assess potential bias. In this thesis, these meth- ods are used to critically assess the saurischian dinosaur fossil record, includ- ing an examination of changes in specimen completeness through research time. Novel metrics are presented that quantify the diagnostic quality of fos- sil specimens and assemblages. Results suggest that recent changes in our un- derstanding of the dinosaur fossil record mostly derive from taxonomic and stratigraphic revisions. The completeness of the sauropodomorph fossil record is temporally segregated, whereas the theropod record is heavily spatially and environmentally biased, plus shows signs of taphonomic and taxonomic identi- fication bias towards particular subgroups. These results represent a significant contribution to better understanding the nature of the dinosaur fossil record. An exploration in Time And Relative Dimensions In Space Acknowledgements I am deeply indebted to Richard Butler, firstly for giving me the opportunity to fulfill a dream of being a palaeontological researcher, but also for his incredible levels of support and guidance throughout the entire PhD project. His tireless efforts and commitment towards not only me but to the rest of his students are greatly appreciated. I also like to thank my internal co-supervisor Ivan Sansom, my academic supervisor James Wheeley, my co-author Susannah Maidment, and special thanks to my external co-supervisors Philip Mannion and Paul Upchurch for their exceptional guidance with the project. I would also like to thank Roger Close for his guidance with many methodological issues. I thank the European Research Council and the European Union’s Horizon 2020 research and innovation programme 2014–2018 (ERC Starting Grant) for funding my PhD project. I would like express my special appreciation of all of the postgraduates and staff in the Earth Sciences department, University of Birmingham, and the staff of the Lapworth Museum of Geology. There are too many names to mention but I thank you for all for being a positive part of my life for the last four years. Special mention should go to Gretchel Coldicott and Aruna Mistry too whom I felt I could always turn to for departmental issues. I must however especially thank my office mates, friends and colleagues in the Palaeobiol- ogy research group. To Emma Dunne, my PhD twin, for whom I have shared this journey and has provided amazing support and a constant source of inspiration. To Andy Jones, Pedro Godoy and Juan Benito Moreno who have been my palaeo-brothers and fantastic humans, I am incred- ibly grateful for the fun times we had and the support you gave. To Gemma Benevento, I am very thankful for her incredible understanding and support by allowing me to usurp her home in the final months of write-up before handing in my thesis. I would like to thank my family, Kim, Paul, Richard and my cats Tinkerbell, Alfie and Jesse, for keeping me (relatively) sane and for being my outlet back to reality. I also thank my friends, Eleanor Rathbone and James Pynegar (JP), whom have been incredibly supportive even after I became a recluse. Finally, I need to thank my girlfriend Emily, to whom I owe too much. I cannot express the level of gratitude I have for the unwavering love, support and patience she has shown me over the course of the last three years. She has single-handedly dragged me through some tough times and I thank her from the bottom of my heart. Table of contents 1. Introduction 1 1.1. Approaches to assessing the completeness of the fossil record 2 1.1.1. Relative completeness 3 1.1.2. Specimen completeness 4 1.2. Sampling bias 6 1.3. Dinosauria 7 1.4. Objectives 9 2. Skeletal Completeness Of The Non-Avian Theropod Dinosaur Fossil 11 Record 2.1. Introduction 11 2.2. Methodology 12 2.2.1. Completeness metrics 12 2.2.2. Dataset 16 2.2.3. Theropod completeness subdivisions 17 2.2.4. Temporal correlations 19 2.2.5. Non-temporal comparisons 21 2.2.6. Statistical tests 21 2.3. Results 23 2.3.1. Theropod completeness through time 23 2.3.2. Correlations with theropod taxonomic richness through time 25 2.3.3. Lagerstätten 25 2.3.4. Correlations with sampling proxies and sea level 26 2.3.5. Comparison to other tetrapod fossil records 28 2.3.6. Theropod subgroups and body size 32 2.3.7. Geographical completeness 34 2.3.8. Sedimentary and depositional setting 36 2.4. Discussion 37 2.4.1. Comparative completeness 37 2.4.2. Depositional biases 41 2.4.3. Biological and ecological biases 44 2.4.4. Sampling biases 49 2.4.5. Lagerstätten influence 53 2.4.6. Impact on evolutionary understanding 54 2.5. Conclusions 56 3. Ten more years of Discovery: revisiting the quality of the sauropodo- 59 morph dinosaur fossil record 3.1. Introduction 59 3.2. Materials and Methods 60 3.2.1. Completeness Metrics 60 3.2.2. Data 61 3.2.2.1. Geological Time Series 64 3.2.2.2. Historical Species Accumulation and Time Series 65 3.2.3. Statistical Tests 65 3.2.4. Analyses 67 3.2.4.1. Temporal Correlations 67 3.2.4.2. Non-temporal Comparisons 67 3.3. Results 68 3.3.1. Historical sampling changes 68 3.3.1.1. Species accumulation and changes in historical 68 completeness 3.3.1.2. Changes to geological completeness and diversity 69 curves through historical time 3.3.2. Current understanding of the sauropodomorph fossil record 72 3.3.2.1. Sauropodomorph completeness through geological 72 time 3.3.2.2. Correlations with taxonomic diversity through time 74 3.3.2.3. Comparisons with other tetrapod fossil records 74 3.3.2.4. Geographical completeness 76 3.3.2.5. Environmental completeness 79 3.3.2.6. Taxonomic subgroup, phylogenetic and body size 80 completeness 3.4. Discussion 82 3.4.1. Changes in our understanding of the sauropodomorph fossil 82 record 3.4.2. Impact of changes on understanding sauropodomorph evo- 85 lution 3.4.3. Explaining the current completeness of the sauropodomorph 86 record 3.4.3.1. Comparative completeness 86 3.4.3.2. Sampling bias 87 3.4.3.3. Climatic biases 91 3.4.3.4. Sea level and environmental bias 92 3.4.3.5. Taxonomic and biological bias 95 3.4.3.6. Specimen collection bias 102 3.5. Conclusions 104 4. Taxonomic identification bias of theropod dinosaurs: preservation po- 107 tential and diagnosability 4.1. Introduction 107 4.2. Methodology 108 4.2.1. Metrics 108 4.2.1.1. Diagnostic likelihood metric 108 4.2.1.2. Completeness metrics 112 4.2.2. Datasets 112 4.2.3. Global subdivisions and analyses 115 4.2.3.1. Non-temporal 115 4.2.3.2. Temporal 117 4.2.4. Localised case study: Morrison Formation 117 4.2.5. Statistical tests and plotting 119 4.3. Results 119 4.3.1. Preservation likelihood and taxonomic diagnoses 119 4.3.2. Taphonomic preservation sequence 124 4.3.3. Temporal changes 129 4.3.4. Geological formations 132 4.3.5. Local study: Morrison Formation 133 4.4. Discussion 134 4.4.1. Preservation likelihood, identifiable characters and natural 134 bias 4.4.2. Preservation likelihood, identifiable characters and human 138 bias 4.4.3. Localised differential diagnosability 139 4.4.4. Impact on evolutionary understanding 143 4.4.5. Diagnosability and fossil completeness 144 4.4.6. Limitations and application of diagnosability metrics 145 ` 4.4.7. Implications for theropod research 147 4.5. Conclusions 149 5. Summary and Perspectives 151 5.1. Conclusions 151 5.2. Comparisons to other completeness studies 153 5.3. Future directions 155 References 159 Appendices 204 Appendix A 205 Appendix B 229 Appendix C 244 Contribution statements Chapter 2: This chapter is a modified version of a manuscript published in Palaeontology, with the following citation: CASHMORE, D. D. and BUTLER, R. J. 2019. Skeletal completeness of the non- avian theropod dinosaur fossil record. Palaeontology. doi:10.1111/pala.12436 Online version can be accessed here: https://onlinelibrary.wiley.com/doi/full/10.1111/ pala.12436 My contribution to this manuscript involved conducting all parts of the research, includ- ing data collection, analysis and interpretation of results, as well production of the manuscript.
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