Earliest evidence of Inostrancevia in the southern hemisphere: new data from the Usili Formation of Tanzania

ABSTRACT

Gorgonopsia is an iconic group of saber-toothed, carnivorous therapsids. They have a rich fossil record in the Karoo Basin of South Africa, but are also relatively common components of coeval Malawian, Tanzanian, Zambian, and Russian assemblages. Phylogenetic analyses have demonstrated that African gorgonopsians form a monophyletic subclade distinct from their Russian relatives, which all fall out near the root of the cladogram, thus suggesting a northern hemisphere origin for the clade as a whole. Surprisingly, recent research has demonstrated that a species of Inostrancevia, a genus previously recorded solely in Russia, occurs in the upper Daptocephalus Assemblage Zone of the Karoo Basin, perhaps the result of immigration following the demise of endemic rubidgeine gorgonopsians in the lower subzone of that unit. Here we describe a large, isolated gorgonopsian premaxilla from a bone-rich, conglomeratic interval at the base of the Usili Formation of Tanzania’s Ruhuhu Basin. Based on its stratigraphic position and fossil content, this unit likely correlates with the Cistecephalus Assemblage Zone. The premaxilla can be confidently referred to the genus Inostrancevia on the basis of its four incisors, a feature unique to Inostrancevia among gorgonopsians. In contrast to the disjunct distribution of inostranceviines and rubidgeines in the uppermost Permian of South Africa, the Tanzanian Inostrancevia likely overlapped with large-bodied rubidgeines such as Dinogorgon and Rubidgea.

DISCLOSURE STATEMENT

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

ACKNOWLEDGMENTS

Fieldwork in southern Tanzania that led to the collection of NMT RB380 was supported by National Geographic 7787-05 (to CAS) and NSF DBI-0306158 and the Grainger Foundation (to K. Angielczyk), with continuing research supported by NSF EAR1337569 (to CAS). We thank the 2007 field team, which included M. Abdalla, K. Angielczyk, S. Nesbitt, R. Smith, A. Tibaijuka, and L. Tsuji. We also thank C. Saanane (University of Dar es Salaam) as well as L. Nampunju and A. Tibaijuka (Antiquities Division, Ministry of Natural Resources and Tourism) for assistance in arranging and carrying out this project. Finally, we acknowledge B. Crowley, G. Livingston, and K. Abrams (Burke Museum) for preparation of the specimen and C. Shin for the illustration in Figure 2B. Special thanks go to K. Angielczyk for updating the dicynodont occurrence data in Table 1 and to C. Kammerer and an anonymous reviewer for their assistance on the manuscript.

AUTHOR CONTRIBUTIONS

CAS designed the project. Both authors gathered data as well as drafted and edited the manuscript.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are openly available in Morphosource at https://doi.org/10.17602/M2/M553598, media ID 000553598.