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T O O T H R E P L A C E M E N T P A T T E R N S I N E U T H E R I O D O N T I A ( S Y N A P S I D A , T H E R P A S I D A ) F R O M T H E S O U T H A F R I C A N K A R O O S U P E R G R O U P by Luke Allan Norton Thesis Submitted in fulfilment of the requirements for the degree Doctor of Philosophy in Palaeontology to the Faculty of Science, University of the Witwatersrand, Johannesburg, South Africa Supervisors: Prof. Fernando Abdala, Prof. Bruce S. Rubidge & Dr Jennifer Botha April 2020 I declare that 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. _______________________ Luke Allan Norton 24th day of April 2020 in Johannesburg, South Africa ii ABSTRACT This is the first comprehensive study, using micro-computed tomography, of eutheriodont tooth replacement patterns through ontogeny in therocephalians (Lycosuchus and Bauria) and cynodonts (Cynosaurus and Galesaurus). Comparison of tooth replacement patterns of the incisors, canines and postcanines revealed that this varied the most in the postcanines, followed by the canines. The incisor replacement pattern is conservative, with all four taxa exhibiting alternating replacement. Lycosuchidae retain the basal synapsid condition of two maxillary canine loci, whereas Bauria and the epicynodonts Cynosaurus and Galesaurus have only a single maxillary canine. Maxillary canine replacement occurred several times through ontogeny in the two epicynodonts with cessation of canine replacement coinciding with attainment of skeletal maturity. This differs from the condition previously reported for the epicynodont Thrinaxodon, in which canine replacement continued well into adulthood. In contrast, there is no evidence of canine replacement in Bauria. Alternating postcanine replacement occurs in Lycosuchus, Cynosaurus, and Galesaurus, with the pattern of Cynosaurus more closely resembling that previously described in Thrinaxodon. In Cynosaurus, replacement waves move along the jaw from front-to-back in multiples of two in the mandible, and three in the maxilla. It is hypothesised that the first maxillary postcanine locus became dormant after two replacements, causing a distal shift in the postcanine series. Conversely, Galesaurus, does not exhibit cessation of replacement and the first iii maxillary postcanine is replaced even in the largest specimens. Additional teeth are added distally to the postcanine series in Galesaurus, such that larger specimens have more postcanine teeth. Only one Bauria specimen manifests postcanine replacement, suggesting that reduction in replacement activity is an adaptation to maintain precise occlusion. As each of the study taxa exhibit different replacement patterns, especially with regard to the postcanines, this study highlights a previously unrecognised diversity in tooth replacement patterns amongst the Eutheriodontia. iv “Because of their hardness the teeth are the most generally and perfectly preserved of all fossilized organs; hence they are the especial guides and friends of the palæontologist in his peculiar field of work from imperfect evidence.” —H.F. Osborn (1907), Evolution of Mammalian Molar Teeth, p. 1 “In paleontology, increasing knowledge leads to triumphant loss of clarity.” —A.S. Romer (1961), Synapsid Evolution and Dentition, p. 33 v In memory of my grandmother, Cynthia Harriet Briedenham 5 January 1938 – 9 October 2014 my son, Michael Tomas Norton 13 May 2017 – 1 July 2017 and my father, Anthony George Norton 23 November 1955 – 19 November 2019 M E M E N T O M O R I vi ACKNOWLEDGEMENTS Many people have contributed to this research. Foremost, I am indebted to my supervisors Prof. Fernando Abdala, Prof. Bruce Rubidge, and Dr Jennifer Botha for their guidance, critical analysis, and patience during the course of this research. I would like to thank Dr Bernhard Zipfel and Sifelani Jirah (Evolutionary Studies Institute), Dr Jennifer Botha and Elize Butler (National Museum), Sheena Kaal, Prof. Roger Smith and Zaituna Erasmus (Iziko: South African Museum), Dr Juri van den Heever (Stellenbosch University), Dr Billy de Klerk (Albany Museum), and the Rubidge Family (Rubidge Collection) for allowing specimens in their care to be taken on loan and scanned. Thank you to Dr Kuda Jakata, Dr Kris Carlson and Dr Tea Jashashvili for the scanning (and sometimes re-scanning) of specimens. Dr Julien Benoit is thanked for sharing his extensive collection μCT data for comparative purposes. I would also like to thank Marc Van den Brandt for sharing his knowledge of Cynosaurus, Dr Sandra Jasinoski for her discussions on Galesaurus and general cynodont biology, as well as for sharing her cranial measurement data. Dr Mike Day, Dr Hilary Ketchum, Tannis Davidson, Dr Robert Asher, and Dr Adam Huttenlocker are thanked for their assistance in locating and identifying several of the therocephalian specimens previously studied by K.A. Kermack. vii Thank you to Dr Adam Huttenlocker, Dr Sandra Jasinoski, and Dr Aaron LeBlanc for their input and corrections to this thesis, which have greatly improved the end product. I am very grateful to the National Research Foundation (NRF) for their generous financial support received through a Professional Development Programme bursary. To my wife Marisa, thank you for your unwavering support during the good times and the bad. To my daughter Jade, thank you for being the happy little person that you are. To my parents, Anthony and Shirley, thank you for your continued support and encouragement throughout my academic career. Finally, to my brother Gwylum, thanks for always making sure there are a couple of beers waiting in the fridge for when I come home to Cape Town. viii TABLE OF CONTENTS ABSTRACT ........................................................................................................... iii ACKNOWLEDGEMENTS .................................................................................. vii TABLE OF CONTENTS ....................................................................................... ix LIST OF FIGURES .............................................................................................. xv LIST OF TABLES ............................................................................................. xviii ABBREVIATIONS ............................................................................................. xix Institutional Abbreviations ............................................................................... xix Anatomical Abbreviations ................................................................................ xx THESIS LAYOUT ............................................................................................... xxi List of papers produced for the Ph.D. .............................................................. xxi Other papers published during Ph.D. registration ........................................... xxii 1 INTRODUCTION .......................................................................................... 1 1.1 Synapsida .................................................................................................. 5 1.2 Basal synapsids (“Pelycosauria”) ............................................................. 8 1.3 Therapsida ................................................................................................ 9 1.4 Gorgonopsia ........................................................................................... 10 1.5 Eutheriodontia ........................................................................................ 12 1.5.1 Therocephalia .................................................................................. 13 1.5.2 Cynodontia ...................................................................................... 16 2 MATERIALS AND METHODS .................................................................. 22 2.1 Material .................................................................................................. 22 2.2 Micro-computed tomography scanning .................................................. 23 2.3 Segmentation workflow ......................................................................... 23 2.4 Photography ............................................................................................ 24 2.5 Figure preparation .................................................................................. 24 ix 2.5.1 Symbols and colours ....................................................................... 24 2.6 Terminology ........................................................................................... 26 2.6.1 Tooth types ...................................................................................... 26 2.6.2 Orientation....................................................................................... 26 2.6.3 Number of tooth replacement generations ...................................... 28 3 RE-EVALUATION OF TOOTH REPLACEMENT PATTERNS OF THE LYCOSUCHIDAE (THERAPSIDA, THEROCEPHALIA) USING MICRO- COMPUTED TOMOGRAPHY............................................................................ 29 3.1 Abstract .................................................................................................. 30 3.2 Introduction ............................................................................................ 31 3.3 Materials and methods ...........................................................................
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