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The South African Mesozoic: Advances in Our Understanding of the Evolution, Palaeobiogeography, and Palaeoecology of Sauropodomorph Dinosaurs

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The South African Mesozoic: Advances in Our Understanding of the Evolution, Palaeobiogeography, and Palaeoecology of Sauropodomorph Dinosaurs The South African Mesozoic: Advances in our understanding of the evolution, palaeobiogeography, and palaeoecology of sauropodomorph dinosaurs Blair W. McPhee A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016 i I declare that the vast majority of this thesis is my own, unaided work. It is being submitted for the Degree of Doctor of Philosophy at the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination at any other University. As this thesis is primarily comprised of multiple-authored published papers, the contributions of each co-author are stated clearly within section five of the introduction. ________23rd______day of ________May___________2016____________at_____Wits________ ii ABSTRACT The Palaeontological record of South Africa is remarkable in that it preserves the two major temporal transitions of the Mesozoic: The Triassic–Jurassic boundary (the Elliot Formation) and the earliest depositional stages of the Cretaceous (the Kirkwood Formation). Work within the Elliot Formation has reiterated the importance of this horizon for our understanding of the early evolution and subsequent radiation/diversification of basal sauropodomorph dinosaurs. Moreover, inextricably contained within this radiation is the early evolution of the columnar-limbed, long necked sauropods, the largest terrestrial animals to have ever evolved. The Elliot Formation therefore imparts vital information on the genesis of the group that would become the dominant dinosaurian herbivores throughout most of the Mesozoic. However, several outstanding issues obscure a full understanding of this important radiation. Of primary concern is the complicated taxonomy of the sauropodomorphs of the Upper Triassic lower Elliot Formation and a lack of current consensus as to what precisely constitutes a true sauropod. The latter issue is further complicated by a lack of well-preserved sauropod material prior to the Toarcian. The discovery of new, associated material from both the lower and upper Elliot Formation has direct relevance to both of these concerns. Specifically, although the genus Eucnemesaurus is supported in the current analysis, the bauplan diversity of lower Elliot Sauropodomorpha remains relatively conservative save for the stocky pedal architecture of Blikanasaurus and the autapomorphically robust morphology of a newly rediscovered ilium that is potentially referable to it. Within the upper Elliot Formation, a recently discovered highly apomorphic bone-bed is diagnosed as a new species of sauropod that, in addition to placing the earliest unequivocal sauropods within the basal rocks of the Jurassic, suggests the underlying ecological factors driving the divergence of the derived sauropodan bauplan. In addition to new information provided by the Elliot Formation, two decades’ worth of collecting from the Early Cretaceous Kirkwood Formation affords a long overdue insight into the sauropod fauna occupying southern Gondwana at the outset of the Cretaceous. The surprising diversity of forms recognized from the Kirkwood suggests that the taxonomic decline of Sauropoda previously inferred for the earliest Cretaceous is a product of sampling bias compounded by a generally poor fossil record. However, a lack of absolute dates for the Kirkwood Formation means that the plethora of “Jurassic-type” specimens is potentially explicable via their being contemporaneous with similar Late Jurassic faunas of eastern Africa and North America. iii ACKNOWLEDGEMENTS This thesis is the product of the ongoing friendship, support, and assistance of a great many people. Foremost amongst them, I would like to thank my supervisor Jonah Choiniere for insightful commentary and advice, timely edits, generosity in facilitating a great many aspects of this project, and his unchanging open-door policy. Sincere thanks also go to Bruce Rubidge for his appreciable assistance in making a kiwi expat solvent in the otherwise merciless funding waters of the RSA. I extend warm thanks to my lab-mates Kimi Chapell, Kathleen Dollman, Katherine Clayton, and Casey Staunton for good company both in and out of the field. With respect to the latter, I would also like to acknowledge the welcome company of Matt Baron, Simon Wills, Paul Barrett, Serjoscha Evers, David Ford, and Roger Benson. Lara Sciscio and Emese Bordy, thanks for keeping the Elliot classy. Closer to home, the ongoing unconditional support of my parents, Alf and Glenda McPhee, is the real aether that makes ventures such as this possible. Natasha Phillips, I’m not sure how I’ll figure out how to repay your fathomless love, support, and patience (other than, obviously, in kind). But I’ll figure it out. The friendship of Aurore Val, Mike Day, Vincent Fernandez, Matt Caruana (okay mainly your Playstation), Fernando Abdala, Ashley Hinton, Pia Viglietti, Edward Cavanagh, Sam Challis, Alice Mullen, Ben Collins, Jerome Reynard and Gerrit Dusseldorp is a constant and vital source of distraction and encouragement. Finally, a very sincere Thank You is due Adam Yates, who has graciously allowed me to take the lead in a number of otherwise spoken-for and/or half-started projects. iv CONTENTS DECLARATION …………………………………………………………………………………………………………………………. ii ABSTRACT……………………………………………………………………………………………………………………………….. iii ACKNOWLEDGEMENTS……………………………………………………………………………………………………………. iv 1. Introduction ..…………………………………………………………………………………………………......... 1 2. Recent advances in sauropodomorph phylogenetics ……………………………………………… 3 3. The current state of sauropodomorph palaeogeobiography ………………………………….. 6 4. Geological and palaeontological context of the dinosaur-bearing strata of South Africa ..……………………………………………………………….. 11 4.1. The Elliot Formation ..…………………………………………………………………………………. 11 4.1.1. Sauropodomorpha within the Elliot Formation ..………………………………….. 14 4.2. The Kirkwood Formation ……………………………………………………………………………. 16 5. Aims of the current thesis and declaration of personal contribution ……………………… 17 STUDY ONE: A second species of Eucnemesaurus van Hoepen, 1920 (Dinosauria, Sauropodomorpha): new information on the diversity and evolution of the sauropodomorph fauna of South Africa’s lower Elliot Formation (latest Triassic). Journal of Vertebrate Paleontology. STUDY TWO: A new basal sauropod from the pre-Toarcian Jurassic of South Africa: evidence of niche-partitioning at the sauropodomorph–sauropod boundary? Scientific Reports. STUDY THREE: High diversity in the sauropod dinosaur fauna of the Lower Cretaceous v Kirkwood Formation of South Africa: Implications for the Jurassic– Cretaceous transition. Cretaceous Research. STUDY FOUR: A hyper-robust sauropodomorph dinosaur ilium from the Upper Triassic–Lower Jurassic Elliot Formation of South Africa: Implications for the functional diversity of basal Sauropodomorpha. Submitted for review to the Journal of African Earth Sciences. 6. Key findings and future work ……………………………………………………………………………… 20 6.1. Eucnemesaurus ………………………………………………………………………………………. 20 6.2. Pulanesaura ……………………………………………………………………………………………. 22 6.3. Kirkwood sauropods ………………………………………………………………………………. 24 6.4. A hyper-robust ilium ………………………………………………………………………………. 27 7. Synthesis and concluding remarks ………………………………………………………………………. 28 8. References ………………………………………………………………………………………………………….. 30 vi 1. INTRODUCTION As per the palaeobiologist’s favoured inaugural line when introducing any analysis of the group, sauropodomorph dinosaurs include the largest terrestrial animals to have ever evolved. Although derived (i.e., neosauropod) members of the group have been studied extensively since first being recognised as gigantic, long-necked saurians in the 1870’s (Marsh, 1878), basal sauropodomorphs (‘prosauropods’) have tended to be overlooked by comparison. This is potentially an artefact of the outdated notion that basal sauropodomorphs were relatively morphologically homogeneous compared to more well- known dinosaurian groups, as well as early systematic hypotheses that ‘Prosauropoda’ and Sauropoda formed mutually exclusive sister-taxa, and hence the former was cladistically removed from the evolutionary history of the latter. However, an influx of interest over the past decade has settled on something of a consensus that the traditional ‘prosauropod’ assemblage is – at least to a degree – paraphyletic with respect to Sauropoda. The primary upshot of this development is the appreciation that sauropod origins can be traced back to the large array of “semi-bipedal” forms that represented the dominant dinosaurian herbivores of the Late Triassic and earliest Jurassic. 1 With respect to the terrestrial context, this time period is perhaps best captured by the purple–red mudstones of the Elliot Formation of South Africa. Furthermore, within the Algoa Basin of South Africa’s Eastern Cape, the Kirkwood Formation preserves an abundance of fragmentary dinosaur remains that provide information on one of the poorest sampled periods of the Mesozoic – the earliest Cretaceous. Drawing on new fossil material collected over recent years from both the Elliot and Kirkwood formations, this thesis aims to extend our knowledge of both the early evolutionary history of Sauropodomorpha, as well as this under-studied latter period of the group’s history – a time in which sauropod dinosaurs were previously thought to have undergone a dramatic drop in taxonomic diversity. Representing at least two new
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