The comparative and functional cranial morphology of the early Therocephalia (Amniota: Therapsida)

Thesis (D.Phil)—Stellenbosch University, 1987.

AFRIKAANSE OPSOMMING: Die skedelmorfologie van die vroeë Therocephalia word bespreek op historiese, anatomies-vergelykende en taksonomiese grondslag. Daar word aangetoon dat die familienaam Scylacosauridae voorrang geniet bo die algemeen aanvaarde naam Pristerognathidae en dat ander historiese familiename binne die Therocephalia, te wete Alopecodontidae en Ictidosauridae ongeldig is en gevolglik binne die parameters van die enkele familie Scylacosauridae resorteer. Nuwe eksemplare het ook aan die lig gebring dat 'n digotomie binne die vroee Therocephalia bestaan en dat 'n tweede takson, gebaseer op 'n groot aantal anatomiese kenmerke, gevolglik uitgeken kan word. Die familienaam Lycosuchidae is beskikbaar vir hierdie takson. Al die geldige taksa wat voorheen in die Pristerognathidae, Lycosuchidae, Alopecodontidae en Ictidosauridae gegroepeer is, resorteer dus binne hierdie twee groepe. 'n Groot aantal taksa bestaan in die literatuur as gevolg van swak gepreserveerde eksemplare wat verkeerd geidentifiseer is. 'n Besondere poging is dus aangewend om al die eksemplare op 'n meer objektiewe grondslag te beoordeel. As gevolg hiervan het die aantal geldige taksa drasties afgeneem. Die Lycosuchidae word verteenwoordig deur die enkele takson Lycosuchus en die Scylacosauridae deur Scylacosaurus, Pristerognathus, Pardosuchus, Ictidosaurus, Glanosuchus en Alopecodon. Kladistiese analise van die afkomskenmerke toon dat die Scylacosauridae nader verwant aan die res van die Therocephalia is as aan die Lycosuchidae. Die Lycosuchidae word dus beskou as die sustergroep van die Scylacosauridae + die res van die Therocephalia. Numeriese en alfabetiese lyste van al die eksemplare wat ooit in die bostaande families geplaas is, word verskaf. Elke eksemplaar word uitvoerig bespreek en fotografies gedokumenteer met behulp van stereofotos in 'n poging om die evaluering daarvan so objektief as moontlik te maak en om die leser wat nie die eksemplare eerstehands kon inspekteer nie, te help.

ENGLISH ABSTRACT: The cranial morphology of the early Therocephalia is discussed on a historical, comparative and a taxonomic basis. It is shown that the family name Scylacosauridae has precedence over the generally used name Pristerognathidae and that other historical therocephalian family names viz. Alopecodontidae and Ictidosauridae fall within the parametres of the Scylacosauridae and are consequently invalid. In addition, new material has shown that a dichotomy exists within the early Therocephalia and a second taxon, based on a large number of anatomical features, can consequently be identified. The family name Lycosuchidae is available for this taxon. Into these two groups are incorporated all the valid taxa previously placed in the Pristerognathidae, Lycosuchidae, Alopecodontidae and Ictidosauridae. Because a large number of taxa exist in the literature as the result of poor specimens wrongly identified, a particular attempt was made to assess all the material on a more objective basis. As a result the number of valid taxa has been drastically reduced. The Lycosuchidae is represented by the single taxon Lycosuchus and the Scylacosauridae by Scylacosaurus, Pristerognathus, Pardosuchns, Ictidosaurus, Glanosuchus and Alopecodon. Cladistic analysis of the derived characters indicate that the Scylacosauridae is more closely related to the rest of the Therocephalia than to the Lycosuchidae. The Lycosuchidae is therefore the sister group of the Scylacosauridae + rest of the Therocephalia. Numerical and alphabetical lists of all specimens ever included in the above families are supplied. Each specimen is extensively discussed and photographically documented by means of stereo photographs in an effort to increase the objectivity of the assessment and to assist those readers whom may not have had the oppurtunity to inspect all the specimens at first hand.

Doctoral