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Bound By Blissett Bookbinders 020 8992 3965 Skull evolution and functional morphology in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria) Marc E. H. Jones Department of Anatomy and Developmental Biology University College London 2006 - 1 - UMI Number: U591750 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U591750 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 The tuatara, Sphenodon, is the sole extant representative of the Rhynchocephalia, a group of diapsid reptiles that were extremely widespread during the Mesozoic. Traditionally, Sphenodon was considered to be ••primitive’', and its fossil relatives are frequently disregarded as conservative. However, a detailed review shows that the group was diverse in terms of both morphology and lifestyle. In particular, it demonstrates a range of different tooth morphologies and arrangements. Geometric morphometric analysis shows that differences between the skull shape of different taxa is related to feeding (e.g. muscle volume, jaw joint position). Derived taxa possess stouter teeth, an increase in space for adductor musculature, a larger skull size and in turn a greater potential bite force. A surv ey of suture morphology rev eals that by comparison to basal taxa ( Diphydontosaurus, Gephyrosaurus), derived taxa (e.g. Clevosaurus, Sphenodon) have more complicated sutures including extensive overlaps. These observ ations correspond with research indicating that sutures are important for controlling and reducing stresses within the skull. Variation in sutures is also found between different derived taxa. For example in Clevosaurus the most complex sutures are found in the palate; by contrast in Sphenodon, the most complex sutures surround the postfrontal bones. These differences are probably related to the extent and distribution of forces experienced by the skull. A contributing factor is the different mode of shearing mechanism employed by each taxon: a precise orthal scissor-like cut in Clevosaurus and a prooral rip in Sphenodon, each of which required a specific muscle arrangement. The Rhynchocephalia as a whole demonstrate a progressive evolutionary trend in their diet toward larger and harder food items; this allowed at least one clade to become herbivorous. This to some extent echoes Sphenodon ontogeny. The rhynchocephalian skull is highly integrated; suture complexity increased in parallel with increasing complexity of feeding apparatus. Key Words: skull design, functional morphology, bite force, jaws, teeth, palaeoecology ACKNOWLEDGEMENTS I am indebted to Professor Susan E. Evans (UCL, for institutional abbreviations please see Section 10) for her invaluable superv ision, support and patience during this work. l;or financial support 1 would like to thank the BBSRC which paid for three years tuition fees and living costs. Amphibia Tree which paid for flights to Texas, the Bogue Fellowship which funded subsidence costs and a CT scan whilst visiting the University of Texas, Austin. The Graduate School also contributed to travel and subsistence costs to two Symposium of Vertebrate Palaeontology meetings (Denver 2004 and Mesa 2005). East but not least 1 thank my parents and especially my long-suffering girlfriend Kate Bird (UCLan) for assistance with subsistence and accommodation in the closing months. For access to museums and university collections I thank Dr Helen Chatterjee/Jo Hatton- Simon Levey/Jask Ashby/Corinna Washbrook (all UCLGMZ), Dr Colin McCarthy (NHM), Ray Symonds/Professor Jenny Clack (both UMZC), Raymond Coory (NMNZ), Sandra Chapman/Dr Angela C. Milner (both NHM), Dr Andrew R. Milner (BCUI/NHM), Jeremy Adams (BMB), Dr Malgosia Nowak-Kemp/Lisa Conyers (both OMNH), Lyndon K. Murray/Dr Chris Bell (both UTA), Logan lvy/Dr Kenneth Carpenter (both DMNH), Dr Luis Chiappe/Dr Sam McLeod (both LACM), Professor Li Jin Ling (IVPP), and staff of the Digimorph website (UTA). Advice from Wendy Birch (UCL) was extremely valuable for disarticulating Sphenodon skull specimen DGPC1. For discussions, correspondence and assistance in obtaining references there are many people to thank including Professor Susan E. Evans (UCL), Dr Chris Bell (UTA), Dr Don Henderson (RTMP), Dr Paul M. Barrett (NHM), Dr Kris Lappin (CPP), Dr Colin G. Barras (NHM), Gabe Bever (UTA), Dr Wolfgang Kathe, Dr Nick C. Fraser (VMNH), Dr Andrew R. Milner (BCUL/NHM), Dr Marcello Ruta (UB), Dr Paul Upchurch, (UCL), Dr Alison Cree (UONZ), Jason Head (SI), Robin L. Whatley (UCSB), Dr Pete Grindrod (UCL), Dr Ian Jenkins, Dr Daniele Serdoz (UCL), Professor Keith Thompson (ANS/OMNH) and Professor David W. Krause (SB). Tamsin Rothery (RPMMU) graciously shared with me unpublished data from her thesis on pleurosaurs including an unpublished reconstruction o f 'Acrostturus' in lateral view. Similarly, Sebastian Apesteguia (ArgMNH) supplied an unpublished image of Priosphenodon in dorsal view. Fom Kemp (OMNH) provided unpublished drawings of Clevosaurus -3- hudsoni drawn by Jeanne Evans in the 1970s. Also Raymond Coory (NMNZ) and Gregory J. Watkins-Colwell (YPM) both supplied photos of Sphenodon material in their care. I:or guidance and training with the Scanning Electron Microscope I thank Mark Turmaine (UCL). For repeated help with morphometics I would also like to thank Sandra Martclli, Brian Ruth, and Nick Jones (all UCL). For assistance with manipulation of CT data I thank Dr Jessie Maisano, Dr Matt Colbert, Amy Balanhoff and Gabe Bever (all UTA). For advice and help regarding images I thank Jane Penjiky, and Dr Pete Grindrod. For drawing my attention to the potential of a tlatbed scanner I am indebted to Professor Alan Boyde (QMUL), and Dr Tim Arnett (UCL). I thank Sadiqua Khan and Steve Townend (both UCL) for the use of their colour printer. For reading proofs and editing I thank Gwylim Jones, Kate Bird (UCLan) and in particular Professor Susan E. Evans (UCL). In memory of Brian Ruth (UCL), Martin O'Regan (NMGW) and Hannah Sheard (UCL). DECLARATION OF ORIGINALITY 1 Marc Emyr Huw Jones confirm that the work presented in this thesis is my own. CONTENTS ACKNOWLEDGEMENTS 3 DECLARATION OF ORIGINALITY 4 CONTENTS 5 1 INTRODUCTION 8 1.1 TUATARA 8 1.1.1 General background 8 1.1.2 'Living fossil' status 10 1.1.3 Sphenodon skull morphology 11 1.2 FOSSIL TAXA 14 1.2.1 General introduction 14 1.2.2 The best known taxa 23 1.2.3 Other taxa 24 1.3 A REVIEW OF PHYLOGENETIC SYSTEM A'TICS 32 1.3.1 Historical perspective 32 1.3.2 Lepidosauria (Rhynchocephalia-Squamata) 33 1.3.3 Rhynchocephalia 34 1.3.4 W ithin Rhynchocephalia 35 1.3.5 Summary 44 1.4 AIMS AND OBJECTIVES 46 2 THE FEEDING MECHANISMS OF RHYNCHOCEPHALLANS 48 2.1 INTRODUCTION TO FEEDING MECHANISMS 48 2.1.1 Descriptions of tooth morphology in the best known taxa 48 2.1.2 Functional analogues 54 2.1.3 heeding strategy 55 2.1.4 Food reduction and processing 57 2.1.5 Diet 59 2.1.6 Mechanical properties of food 63 2.1.7 Teeth 64 2.1.8 Secondary bone 97 2.1.9 Tower jaws 99 2.1.10 Jaw movement 102 2.2 TOOTH BAS!: DIMENSIONS 108 2.2.1 Methods and materials 109 2.2.2 Results 116 2.2.3 Discussion 133 2.3 SUMMARY 137 3 RHYNC'HOCEPHALIAN SKULL EVOLUTION 138 3.1 INTRODUCTION 138 3.1.1 Variation