Gorgonops and Endothiodon (Synapsida: Therapsida) from the Madumabisa Mudstone Formation: evidence of a previously unreported tetrapod biozone in the Mid-Zambezi Basin of southern Zambia

ABSTRACT

Fossils referable to the gorgonopsian Gorgonops sp. and to the dicynodont Endothiodon sp. are described from the Permian Madumabisa Mudstone Formation of the Mid-Zambezi Basin of southern Zambia. Specimens of the former taxon conform to recent diagnoses of the genus (e.g., five postcanine teeth, transverse flange of the pterygoid backswept, postorbital bar rugose and moderately expanded), but differ slightly from South African material in some respects (e.g., reduced dentition on the transverse flange of the pterygoid). Fossils of the latter are less complete, but show diagnostic features such as a dentary with numerous teeth, a ventral boss, and a shallow posterior dentary sulcus, oval palatine pads, and a narrow intertemporal region of the skull, although a species-level identification is not currently possible. Although the relevant fossils were never described, a vertebrate fossil assemblage including Endothiodon was previously reported from the Madumabisa Mudstone Formation in northern Zimbabwe (i.e., K5d), suggesting that this biozone was relatively broadly distributed across the Mid-Zambezi Basin. The Mid-Zambezi Basin of southern Zambia was previously demonstrated to host Guadalupian Tapinocephalus Assemblage Zone-equivalent strata, with rhinesuchids, burnetiamorphs, tapinocephalids, and dicynodonts recognized. The recognition of Lopingian Endothiodon Assemblage Zone-age rocks expands the stratigraphic range of vertebrate-bearing horizons in southern Zambia.

ACKNOWLEDGMENTS

Our research in Zambia has been supported by the National Geographic Society (CRE 8571-088 to S. Steyer, CRE 8961-11 to C.A.S.), with additional support from The Grainger Foundation and the Field Museum/IDP, Inc. African Partner’s Program (to K.D.A.) and NSF EAR-1337569 (to C.A.S.) and EAR-1337291 (to K.D.A. and S. Nesbitt). We thank K. Mwamulowe and J. Museba (NHCC) for assistance in arranging and carrying out the fieldwork. In addition, N. Barbolini, C. Beightol, A. Goulding, J. Museba, S. Nesbitt, R. Smith, S. Steyer, N. Tabor, and S. Tolan were part of the field teams in 2012 and 2014 and helped to collect the fossils discussed here. Preparation was skillfully performed by K. Abrams, S. Egberts, A. Shinya, and C. Van Beek. Finally, we thank M. Day, C. Kammerer, and B. Rubidge for their helpful reviews and J. Fröbisch for his editorial assistance.

AUTHOR CONTRIBUTIONS

CAS designed the project. CAS, KDA, and AM gathered and analyzed the data, and all three wrote and edited the manuscript.

DISCLOSURE STATEMENT

No potential conflict of interest was declared by the author(s).