A comparative study of the morphology of the braincase and associated structures of early Therocephalia (Amniota: therapsida)

Firm, Lyndsey (1994)

Thesis (M. Sc.) -- University of Stellenbosch, 1994.

Thesis

ENGLISH ABSTRACT: The early Therocephalia lies at the base of the line of mammal-like reptiles which eventually gave rise to mammals. The phylogenetic position of this taxon is therefore of great value in establishing mammalian ancestry and the description of the braincase forms a vital part of this research. However, a valid description of the early therocephalian braincase is still lacking. The aim of this study is to describe the braincase of the early Therocephalia in an effort to fill this hiatus and provide additional morphological information which may be utilized in future phylogenetical analysis. The primary study is based on serial sections of Glanosuchus macrops. This study was aided by reconstructions produced firstly, by means of two computer programs, secondly Pusey's reconstruction techniques and thirdly, building a wax model. These techniques, except for the grinding of the fossil, constitute the practical part of this study. The constituent bones of the braincase are individually described, with emphasis on the internal structure and foramina. The internal structure of the braincase is then discussed completely, especially the structure of the inner ear, and compared to other relevant therapsid groups. A postulate concerning the shape of the early therocephalian brain, based on a cranial cast derived from the serial sections is presented. Possible activity rates and metabolic tempo are deduced from the proposed structure of the brain. Keywords: Early therocephalian, braincase, inner ear, brain reconstruction.

AFRIKAANSE OPSOMMING: Die vroee Therocephalia le aan die basis van die lyn van soogdieragtige-reptiele wat oorsprong gegee het aan die soogdiere. Die filogenetiese posisie van hierdie takson is dus van groot belang in die bepaling van die voorouers van soogdiere. Die beskrywing van die breinkas vorm 'n noodsaaklike onderafdeling van hierdie navorsing. Desondanks die belang van hierdie tax on is 'n beskrywing van die breinkas van die vroee Therocephalia nog steeds afwesig. Die doel van hierdie studie is dus om die breinkas van die vroee Therocephalia te beskryf in 'n poging om hierdie gaping te vul en addisionele morphologiese data te voorsien wat in toekomstige filogenetiese analieses gebruik kan word. Die primere gedeelte van hierdie studie is gebaseer op serie snitte van Glanosuchus macrops. Aan die hand van hierdie snitte, is die breinkas met behulp van verskeie rekonstruksietegnieke, naamlik rekenaarpakette, Pusey se grafiese rekonstruksietegniek en 'n wasmodel gerekonstrueer. Al hierdie tegnieke, behalwe die slyp van die snitte, behels die praktiese gedeelte van hierdie studie. Met behulp van hierdie rekonstruksies is 'n gedetailleerde studie van die breinkas gemaak. Die bene van die breinkas word individueel bespreek met die klem op inteme struktuur en foramina. Die inteme struktuur van die breinkas word volledig bespreek met spesiale v~rwysing na die strukture van die binne oor en vergelyk met ander groepe binne die Therapsida. Die vorm van die brein van die vroee Therocephalia word gepostuleer op grond van 'n af gietsel van die breinholte gebaseer op die snitte van die breinkas. Verdere postulate behels afleidings rakende die aktiwiteitstempo en metabolisme. Sleutelwoorde: Vroee therocephalieer, breinkas, binneoor, breinrekonstruksie.

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