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

[摘要] ENGLISH ABSTRACT:The early Therocephalia lies at the base of the line of mammal-like reptiles whicheventually gave rise to mammals. The phylogenetic position of this taxon is therefore ofgreat value in establishing mammalian ancestry and the description of the braincaseforms a vital part of this research. However, a valid description of the earlytherocephalian braincase is still lacking. The aim of this study is to describe thebraincase of the early Therocephalia in an effort to fill this hiatus and provideadditional morphological information which may be utilized in future phylogeneticalanalysis.The primary study is based on serial sections of Glanosuchus macrops. This study wasaided by reconstructions produced firstly, by means of two computer programs,secondly Pusey's reconstruction techniques and thirdly, building a wax model. Thesetechniques, except for the grinding of the fossil, constitute the practical part of thisstudy.The constituent bones of the braincase are individually described, with emphasis on theinternal structure and foramina. The internal structure of the braincase is then discussedcompletely, especially the structure of the inner ear, and compared to other relevanttherapsid groups. A postulate concerning the shape of the early therocephalian brain,based on a cranial cast derived from the serial sections is presented. Possible activityrates and metabolic tempo are deduced from the proposed structure of the brain.Keywords: Early therocephalian, braincase, inner ear, brain reconstruction.

[发布机构] Stellenbosch University