Arctops umulunshi, sp. nov. (Therapsida: Gorgonopsia) from the upper Madumabisa Mudstone Formation of Zambia, with new information on gorgonopsian postcranial anatomy

The fossil record of Zambian gorgonopsians includes reports from the Madumabisa Mudstone Formation in both the Mid-Zambezi and Luangwa basins. Despite a longer history of collection, previous reports of gorgonopsians from the Luangwa Basin have been restricted to taxonomic lists, with little in the way of voucher specimens or diagnostic features referenced. Here we introduce Arctops umulunshi, sp. nov., the type of which comprises a nearly complete skull and lower jaws, as well as a large portion of the appendicular skeleton and several vertebrae. The skull is robust and broad-snouted, with three maxillary postcanine teeth, a median vomerine ridge that is displaced anteriorly relative to the lateral ridges, and three teeth on the pterygoid transverse flange surrounded by raised rim of bone. Limb proportions suggest a stocky, strongly built carnivore and potentially diagnostic postcranial features include: atlas intercentrum substantially wider than atlas pleurocentrum, at least one accessory ectepicondylar foramen, and ungual phalanx of pedal digit five very reduced. Our phylogenetic analysis finds Smilesaurus as most closely related to A. willistoni + A. umulunshi, with Lycaenops as the immediate outgroup. These three genera are the sister taxon to a large clade including rubidgeines + Arctognathus. Despite less intensive sampling, the upper Madumabisa Mudstone Formation hosts a gorgonopsian diversity approaching that of coeval South African strata, with most of the same genera represented. Continued detailed anatomical work will further refine the tetrapod biogeography of southern Pangea as well as shed light on ecomorphological differences permitting niche partitioning among coexisting gorgonopsian species.