A new specimen of Promoschorhynchus (Therapsida: Therocephalia: Akidnognathidae) from the Lower Triassic of South Africa and its implications for theriodont survivorship across the Permo-Triassic boundary

ABSTRACT

The anatomy of a new subadult specimen of eutherocephalian therapsid, attributed to Promoschorhynchus cf. P. platyrhinus, is described from lowermost Triassic Lystrosaurus Assemblage Zone strata in the main Karoo Basin of South Africa. The specimen preserves information previously unknown in the genus, including details of the posterior region of the skull and intertemporal region, and a partial (though disarticulated) postcranial skeleton. A cladistic analysis of 32 therapsid taxa, including 24 Permo-Triassic therocephalian genera, and 121 craniodental and postcranial characters supports the specimen's placement within the Permian akidnognathid genus Promoschorhynchus (making it the youngest documented occurrence of this taxon) within a monophyletic Therocephalia. Inclusion of new postcranial characters strengthens support of the therocephalian clade. The new record of Promoschorhynchus offers insights into the diversity of eutheriodonts across the Permo-Triassic boundary (PTB) in the Karoo Basin. In contrast to cynodonts, therocephalians exhibited decreased rates of cladogenesis across the PTB, with several Triassic lineages having roots in the Late Permian rather than representing earliest Triassic radiations.

ACKNOWLEDGMENTS

Jude Swales illustrated the specimen (Fig. 3). Hedi Stummer performed initial preparation, and Bruce Crowley helped with final preparation of the specimen. Christian Kammerer and Fernando Abdala provided important discussions of therocephalian taxonomy, and Jennifer Botha-Brink offered additional discussion and comparative material. Greg Wilson and Lauren Berg gave comments on early versions of the manuscript. We thank Randall Irmis, Christian Kammerer, and an anonymous reviewer for improving the content of the final manuscript. This study was supported by the University of Washington Department of Biology Snyder Award and the Society of Vertebrate Paleontology Richard Estes Award to A.K.H., the National Science Foundation (ANT-0838762) to C.A.S., and the National Research Foundation to R.M.H.S.

Handling Editor: Randall Irmis.