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ASPECTS of the CRANIAL MORPHOLOGY of the THEROCEPHALIAN Moschorhlnus (REPTILIA: THERAPSIDA)

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ASPECTS of the CRANIAL MORPHOLOGY of the THEROCEPHALIAN Moschorhlnus (REPTILIA: THERAPSIDA) ASPECTS OF THE CRANIAL MORPHOLOGY OF THE THEROCEPHALIAN Moschorhlnus (REPTILIA: THERAPSIDA) Jacobus Francois Durand A thesis submitted to the Faculty of Science, University of the Witwaters.-and, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg 1989 ERRATA p ill, line 11 For "alhough" read "although". p 11 "The dorsal part of the pterygoid contacts the foot of the epiptexygoid doreally" should read "The dorsal part of the pterygoid contacts the ventral surface of the foot of the epipterygoid". VP 6 , 7 "within the jugal arch" should read "medial to the jugal arch". PP 6 , 25, 26, 52, "temporal fossa" should read "temporal fenestra". 129 p 82 "ventro-lateral flange of the parietal" should read "latero-ventral flange of the parietal". pp 9 , 62, 65, 65, "processus aecendene of the epipterygoid" should read 105, 150, 151, 172 "££0088808 Mcendena". pp 125, 124, 128, "Jollie (1962)" should read "Jollie (197?)". 150, 151 p p 103, 161 "Hopsoa" should read "Hopcsa". Add to References BOOMSTRA, L.D. 19)8. On a Soutn African mamal-like reptile Baurla oynops. Palaeobioloairq 6 t 164-183. OVER, R. 1876. Description of the Reptiliia. of South Africa in the collection of the British Museum". 1-2 London $ British Museum. ii ABSTRACT A sound understanding of the morphology of the Therocephal1 a Is essential to our understanding of the reptile-mammal transition. In this thesis the anatony of the posterior half o the Moschorhinus skull Is described in detail. This study revealed many aspects overlooked or misinterpreted by othtr authors. Two Moschorhinus skulls were studied externally. Several misinter­ pretations concerning the anatomy of the skull were discovered in the literature, it was therefore deemed necessary to redescribe the external morphology of the skull of Moschorhinus. The skulls were subsequently sectioned with a rock-cutting saw and he matrix filling the endocranium of each was prepared out in order to study the interiors. This study yielded vital informa­ tion concerning the morphology of the endocranium of Moschorhinus which was previously unknown Moreover, this is the first de­ tailed description of the complete braincase of a tnerocephalian. The position of certain cartilaginous and membranous structures, which would have been present in life, is discussed. This new information also made it possible for the first time to recon­ struct the ur,ossified side wall of the endocranium and to deter­ mine the lateral limits of the brain and associated features if a therocephalian. Endocasts of the araincases were made and with he help of these, the morphology of the inner ear and certain m parts of the brain as well as the position of certain cranial nerves and bloodvessels could be determined. These features are described and compared with those of other therapsids. The morpholon. of the inner ear is compared to that of gorgonopsians and cynodonts. The provable morphology of the side wall of the endocranium, brain and associated structures are compared with those of extant reptiles. The position of the cranial bloodves­ sels Is compared with that rf cynodonts and extant reptiles and a new theory concerning the evolutionary development of these bloodvessels from the primitive reptile level to the cynodont level is proposed. It was found that alhough many mammal-like * features are present in the therocephalian skull, the morphology of the braincase, cranial bloodvessels, brain and associated structures were essentially typically reptilian. In the light of this new information concerning the anatomy of the posterior half of the skull and associated soft structures of Hoschorhinus. the taxonomic position of this genus relative to the other Therocephalia is discussed. iv DECIMATION I declare that this thesis is my own unaided work. It is being submitted for the degree of Doctor rf Philosophy in the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other University. line of Candidate) 3Q & day of rM d& aC . 19M. ACKNOWLEDGEMENTS I wish to thank Or C.E. Sow and Prof J.V. Kftchfitf for their advice and guidance. I would also like to thank my family and especially ny wife, Juanita, for their continuous support and patience. 1 am also grateful for the Wits University Senior Bursary received In 2985 and 1986. Vi CONTENTS Page ABSTRACT .................................... il DECLARATION .................................. 1v ACKNOWLEDGEMENTS .............................. v TABLE OF CONTENTS .............................. vl L,S. OF FIGURES ............................... vlii Chapter 1. INTRMMICTION .............................. ! 2. MATERIALS AND METHODS ....................... 3 3. EXTERNAL MORPHOLOGY OF THE SKULL ....... 6 Epipterygoid ............................ 7 Pterygoid .............................. 10 Prootic ................................ i4 Opisthotic .............................. 21 Squamosal ......................... 25 Supraoccipital and Interparietal .............. 29 Parietal . 31 Exoccipltal ............................. 34 Basioccl^ital ........................... 3s vll Basi sphenoid and Parasphenofd ............... 37 4. ENOOCRAMIUM .............................. 40 Parietal ............................... 42 frontal ................................ 45 Supraoccipltal . 47 Prootic ................................ 48 Oplsthotic .............................. 54 Exocctpltal ............................. 57 Baslocclpital ........................... 59 Eplpterygoid ............................ 60 Pterygoid .............................. 64 BasI sphenoid and Parasphenold ............... 68 5. DISCUSSION 5.1 Exterior of the posterior half of the skull ___ 74 5.2 Orbitotemporal region .................. 80 5.3 Posterior part of theendocranlum .......... 91 5.4 Cranial nerves ........................ 104 5.5 Inner ear ............................ Ill 5.6 Cnnlal bloodvessels .................. 122 6. CONCLUSIONS ............................... 148 LIST Of REFERENCES ............................. 154 LIST OF ABBREVIATIONS ........................... 156 FIGURES LIST OF FIGURES RECONSTRUCTIONS 1. Moschorhlnus kltchlngi. Dorsal view. 2. Moschorhlnus kltchlnol. Ventral view. 3. Moschorhlnus kltchlnol. Lateral view. 4. Detail of left temporal region. 5. Moschorhlnus kltchlnol. Detail of left fenestra oval Is and surrounding bones. 6. Occipital view. 7. Maschr.ch.inus. kitchinai- Sagittal section showing medial view of the left side wall of the posterior part of the endocra- nlum. 8. Moschorhlnus Jsttchinqi. Horizontal section showing Internal view of the posterior part of the endocranlal roof. 9. Moschorhlnus kltchlnol. Horizontal section showing view of the posterior part of the endocranlal floor. 10. Lateral view of the left tempo U region with reconstructed membranous and cartilaginous elements. 11. Moschorhlnus kltchlnol. Lateral view of reconstructed endocast. 12 Hoschorhlnus Mtchinqi. Medial view of the left otic region. 13. Moschorhlnus Mtchinql. Medial view of reconstructed left inner ear (the vestibulocochlear nerve (VII), endolymphatic duct and sac are not figured). ix 14. Hoschorhinus fcitchingi. 'ateral view of reconstructed left inner ear (the portion of the perilymphatic cistern overlying the sacculus is not figured). 15. Hoschorhinus kitchinoi. Lateral view of the left temporal region with reconstructed major veins. 16. Hoschorhinus kitchinoi. Lateral view of the left temporal region with reconstructed trigeminal and facial rami and major arteries. 17. Mss horhinus kitchinoi. Internal view of the aosterlor part of the endocranial roof with reconstructed major veins. 18. Hoschorhinus kitchinoi. Internal view of the posterior part of the endocranial floor with reconstructed major bloodves­ sels. 19. Hoschorhinus kitchinoi. Diagrammatic reconstruction of the evolution of the major cranial veins from primitive reptile level to cynodonc level. PLATES 1. Hoschorhinus kitchinoi (BP/1/2788). Dorsal view. 2. Hoschorhinus kitchinoi (BP/1/2788). Ventral view. 3. Hoschorhinus kitchinoi (BP/1/2788). Lateral view. 4. Hoschorhinus kitchinoi (BP/1/4636). Dorsal view. 5. Hoschorhinus kitchinoi (BP/1/4636). Ventral view. 6. Hoschorhinus kitchinoi (BP/1/4636). Lateral view. 7. HKChorkinw; kitchinoi (b P / i/463S). Dorso-lateral left temporal region. 8. Hoschorhinus kitchinui (BP/1/4636). Occipital view. 9. Hoschorhinus kitchinoi (BP/1/4636). Anterior view of poste­ rior part of the skull X 10. Moscftorhlnus Xitchinoi (BP/1/4636). Sagittal section showing medial view of the left side wall of the posterior part of the endocra.' cm. 11. H o ichorhinos kltchlngi (BP/1/4636). Ventral view of the posterior part of the endocran<al roof. 12. Hoschorhinus kitchlnal (BP/1/4636). Dorsal view of the posterior part of the endocranial floor. 13. Hoschorhinus kltchlngi (BP/1/2788). Horizontal section showing ventral view of the posterior part of the endocranial roof and dorsal part of the right ptarygo-paroccipital foramen. 14. Hoschorhinus kltchlngi (BP/1/2788). Horizontal section showing dorsal view of the posterior part of the endocranial floor, the ventral part of the right pterygo-paroccipital foramen and the right paroccipital fossa. 15. Hoschorhinus hitching I (BP/1/4636). Right lateral view of the endocast of the posterior part of the endocranium. 16. Hoschorhinus kitchinoi (BP/1/4636). Dorsal view of the endocast of the posterior part of the endocranium. 17. Hoschorhinus kltchlngi (BP/1/4636). Ventral view of the
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