Aspects of the cranial morphology of the therocephalian Moschorhinus (Reptilia : Therapsida)

Abstract :

A sound understanding of the morphology of the Therocephalia is essential to our understanding of the reptile-mammal transition. In this thesis the anatomy of the posterior half of the Moschorhinus skull is described in detail. This study revealed many aspects overlooked or misinterpreted by other 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 the 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 therocephalian.

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 unossified side-wall of the endocranium and to deter- mine the lateral limits of the brain and associated features of a therocephalian. Endocasts of the braincases were made and with the help of these, the morphology of the inner ear and certain 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 morphology of the inner ear is compared to that of gorgonopsians and cynodonts. The probable 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 of 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 al hough 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 Moschorhinus, the taxonomic position of this genus relative to the other Therocephalia is discussed.

 

Details

Author Durand JF
URL http://hdl.handle.net/20.500.11892/106487
Date Accessioned 2016-09-22T11:14:19Z
Date Available 2016-09-22T11:14:19Z
Date Created
Identifier URL 1989
Language English
Subject
Subject 2
Alternative Title
Degree Type Doctoral degree
Degree Description  PhD