Taxonomic revision of tapinocephalid dinocephalians-the key to understand Middle Permian biodiversity

GUVEN, S; RUBIDGE, B.S.; ABDALA, F.

Bristol

Conferencia; 69th Meeting of the Society of Vertebrate Paleontology; 2009

SOCIETY OF VERTEBRATE PALEONTOLOGY

The dinocephalian subfamily Tapinocephalidae was the dominant and most successful herbivorous therapsid group of the Middle to early Late (?) Permian, but for all their early success it appears that dinocephalians became extinct by the start of the Late Permian. Tapinocephalids are most abundantly known from the Eodicynodon and Tapinocephalus assemblage zones of the Beaufort Group in South Africa, with fourteen genera currently recognized. Taxonomically less diverse tapinocephalid faunas are also known from Russia and Zimbabwe. Tapinocephalids are characterized by having moderate to excessive cranial pachyostosis, reduced temporal openings, intermeshing incisor teeth with a talon and crushing heel, heels on the postcanine teeth, and an anterior shift in the position of the jaw hinge. Recent biostratigraphic studies have emphasized the relatively large number of genera of tapinocephalid dinocephalian when compared with the number of genera of all the other major groups of herbivorous therapsids in any particular biozone of the Beaufort Group. This suggests that too many tapinocephalid genera may currently be recognized form the Lower Beaufort of South Africa and that a taxonomic re-appraisal is necessary. A major obstacle to such a study is that most of the tapinocephalid holotypes are based on very fragmentary material making comparison between different specimens difficult. Preliminary assessment suggests that some of these holotypes are based on juvenile specimens, and there are indications of sexual dimorphism as well. Accordingly it appears that of the fifteen currently recognized genera only eight may be valid. Because dinocephalians are a significant component of middle Permian tetrapod biodiversity, it is essential to fully understand the range of variation within different tapinocephalid genera.