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Systematics and Evolutionary History of Proterosuchian Archosauriforms

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Systematics and Evolutionary History of Proterosuchian Archosauriforms Systematics and evolutionary history of proterosuchian archosauriforms by Martin D. Ezcurra A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Supervisor: Dr Richard J. Butler Co-supervisor: Dr Ivan Sansom School of Geography, Earth and Environmental Sciences University of Birmingham March 2015 1 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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. 250 million years ago… “Life found the way” Alan Grant paraphrasing Ian Malcom (Jurassic Park, 1993) …to survive and bloom again From right to left: Richard J. Butler, Roland B. Sookias and Martín D. Ezcurra with a complete skull of a not-fully-grown Erythrosuchus africanus (BP/1/5207). Johannesburg, South Africa (May 2014). 2 Table of contents Abstract 8 Chapter 1 – Introduction 10 Chapter 2 − The Permian archosauromorph record 15 2.1. Background 15 2.2. Review of the Permian saurian record 17 2.2.1. “Younginiformes” 17 2.2.2. Other putative Permian lepidosauromorph records 18 2.2.3. Permian records of Archosauromorpha 21 2.2.3.1. Protorosaurus speneri 22 2.2.3.2. Eorasaurus olsoni 25 2.2.3.3. Archosaurus rossicus 35 2.2.3.4. Putative proterosuchian from the late Permian of South Africa 39 2.2.3.5. Specimens identified as either varanopid “pelycosaurs” or basal archosauromorphs from the Permo-Triassic of Uruguay. 47 2.2.3.6. “Problematic reptile” from the late Permian of Tanzania 48 2.3. Discussion 55 2.3.1. Timing of the crocodile-lizard (or bird-lizard) divergence and recommendations for molecular calibrations 55 2.3.2. Ghost lineages and archosauriform divergence 58 2.3.3. Palaeobiogeography 60 Chapter 3 − Taxonomy of proterosuchid specimens from the earliest Triassic of South Africa 62 3.1. Background 62 3.2. Taxonomic history of the South African Lystrosaurus AZ proterosuchids 63 3 3.3. Materials and methods 69 3.3.1. Studied specimens 69 3.3.2. Quantitative analyses 71 3.4. Results 74 3.4.1. Qualitative results 74 3.4.1.1. Redescription of the holotype of Proterosuchus fergusi (SAM-PK-591) 74 3.4.1.2. Differences between the holotype of Proterosuchus alexanderi comb. nov. (NMQR 1484) and other South African proterosuchid specimens 74 3.4.1.3. Differences between the holotype of Proterosuchus goweri sp. nov.(NMQR 880) and other South African proterosuchids 83 3.4.1.4. Other differences among South African proterosuchid specimens 87 3.4.2. Quantitative results 92 3.4.3. Systematic Palaeontology 96 3.5. Discussion 113 Chapter 4 − Post-hatchling cranial ontogeny of Proterosuchus fergusi 116 4.1. Background 116 4.2. Materials and methods 117 4.2.1. Studied specimens and available ontogenetic series 117 4.2.2. Qualitative analysis 121 4.2.3. Quantitative analysis: allometric regressions 122 4.2.4. Quantitative analysis: ontogram 123 4.2.5. Bivariate plots, thin plate spline analysis and general statistics 125 4.3. Results 125 4 4.3.1. Qualitative analysis 125 4.3.2. Quantitative analysis 130 4.3.2.1. Allometric regressions 133 4.3.2.2. Ontogram 138 4.4. Discussion 141 4.4.1. Comparisons with previous studies 141 4.4.2. Sequence of somatic maturity in Proterosuchus fergusi 144 4.4.3. Allometric growth patterns in Proterosuchus fergusi and possible palaeoecological implications 147 4.4.4. Implications for early archosauromorph evolution 148 Chapter 5 − Phylogenetic relationships of basal archosauriforms 153 5.1. Background 153 5.2. Historical background of the phylogenetic relationships of “Proterosuchia” 154 5.3. Materials and methods 164 5.3.1. Objectives and taxonomic sample 164 5.3.2. Taxa with problematic hypodigms 168 5.3.3. Synonymous species and modified hypodigms 171 5.3.4. Character sampling and scorings 179 5.3.5. Alternative analyses 184 5.3.6. Tree search, strict reduced consensus and tree support calculation methodologies 186 5.4. Results 190 5.5. Discussion 205 5.5.1. The non-monophyly of “Prolacertiformes” 205 5 5.5.2. The taxonomic content and monophyly of Proterosuchidae 216 5.5.3. The taxonomic content and monophyly of Erythrosuchidae 227 5.5.4. The phylogenetic positions of Euparkeria and Proterochampsidae 233 5.5.5. The phylogenetic position of Doswelliidae 245 5.5.6. The phylogenetic position of Phytosauria 248 5.5.7. Macroevolutionary implications 255 Conclusions 262 Acknowledgements 268 References 271 Appendix 1 333 Appendix 2 336 Appendix 3 364 Appendix 4 366 Appendix 5 367 Appendix 6 371 Appendix 7 386 Appendix 8 396 Appendix 9 513 Appendix 10 534 6 Acknowledgement of collaborative work Chapters 1 to 4 have been already published in collaboration with colleagues (Chapter 1: Ezcurra et al., 2013; Chapter 2: Ezcurra et al., 2014; Chapter 3: Ezcurra and Butler, 2015a; Chapter 4: Ezcurra and Butler, 2015b). In all cases, I designed or co-designed the research projects, conducted the research (i.e. collected, analysed and interpreted data), and wrote up the results. I was lead author on all of the resultant publications. My collaborators contributed to funding and designing the research projects, and provided comments and feedback on interpretations and drafts of manuscripts. Chapter 5 was conducted solely by me. I estimate that >95% of this thesis is my own work. 7 Abstract The vertebrate clade Archosauromorpha comprises archosaurs (e.g. dinosaurs, birds, crocodilians) and several morphologically disparate Permian and Triassic taxa (e.g. tanystropheids, rhynchosaurs, proterosuchids, erythrosuchids, proterochampsians). The evolutionary history of archosauromorphs is of particular interest because it includes the origins of two of the best-known and most distinctive extant tetrapod groups: crocodylians and birds. Substantial previous research efforts have been focused on the crown group Archosauria, and by contrast the origin and early evolutionary radiation of archosauromorphs is relatively poorly understood. This incomplete understanding stems from the poor anatomical knowledge currently available for most of the early species of the clade and the paucity of detailed systematic work conducted in recent decades. In this thesis, the anatomy, taxonomy and systematics of the Permo-Triassic non-archosaur archosauromorphs are revised, with special emphasis on the proterosuchian archosauriforms. A revision of the Permian archosauromorph record indicates that only four Permian species are known (Protorosaurus speneri, Eorasaurus olsoni, Archosaurus rossicus, Aenigmastropheus parringtoni gen. et sp. nov.), which have a wider palaeobiogeographic distribution than previously appreciated. Following re-examination of proterosuchid taxa in collections worldwide, it is here concluded that there are three valid proterosuchid species in the Lystrosaurus Assemblage Zone of South Africa (Proterosuchus fergusi, Proterosuchus goweri sp. nov, Proterosuchus alexanderi comb. nov.). This result indicates a greater species richness of earliest Triassic archosauriforms than previously appreciated, but also that archosauriform morphological disparity remained low in this time interval. Qualitative and quantitative analyses of cranial ontogenetic 8 variation in Proterosuchus fergusi found that the skull of this species became proportionally taller, the infratemporal fenestra larger, and the teeth more isodont and numerous but with smaller crowns through ontogeny. The skulls of juvenile specimens of Proterosuchus fergusi closely resemble those of adults of the more basal archosauromorph Prolacerta broomi, whereas adult specimens of Proterosuchus resemble adults of more derived archosauriforms (e.g. erythrosuchids, Euparkeria capensis). This observation underpins the novel hypothesis that ontogenetic modification events (e.g. heterochrony) may have been key drivers of the evolution of the general shape of the skull at the base of Archosauriformes. The most comprehensive quantitative phylogenetic analysis to date focused on non- archosaurian archosauromorphs recovered a polyphyletic “Prolacertiformes” and restricted the taxonomic content of Proterosuchidae to only six species that occur immediately either side of the Permo-Triassic boundary. Erythrosuchidae was recovered as monophyletic and composed of eight nominal species, and Euparkeria capensis was found as the sister-taxon of the clade that includes proterochampsians (doswelliids + proterochampsids) and archosaurs. Phytosaurs were recovered within the crown-group Archosauria, as the most basal pseudosuchians. The results obtained here suggest that the evolutionary history of the archosauriforms during the Early Triassic can be subdivided into a first phase characterized by the short-lived “disaster- clade” Proterosuchidae and a second phase that witnessed the initial morphological and probably palaeoecological diversification of the group. A third phase in archosauriform evolution is documented by the diversification of the group into multiple ecomorphotypes during the Middle to Late Triassic. 9 Chapter 1: Introduction The vertebrate clade Archosauromorpha comprises archosaurs (e.g. dinosaurs, birds, crocodylians) and several morphologically disparate Permian
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