Distinctive emydopoid dicynodont (Therapsida, Anomodontia) mandibles from the Permian Ruhuhu and Usili formations (Songea Group), Ruhuhu Basin, Tanzania
Angielczyk et al
Dicynodont therapsids were discovered in the Permian Usili Formation (Ruhuhu Basin, Tanzania) in the 1930s and in the Permian Ruhuhu Formation in the 1960s, with further collections being made in 2007, 2008, and 2012. Here we describe two fragmentary mandibles that represent a new morphotype of emydopoid dicynodont. One specimen was collected in the middle fossiliferous horizon of the Ruhuhu Formation, and the other originated in the overlying Usili Formation. Three synapomorphies support the placement of these specimens in the emydopoid subclade Kingoriidae: mandibular fenestra occluded by the dentary; curved ridge that follows the profile of the symphysis present on the edge between the anterior and lateral surfaces of the dentary; and posterior dentary sulcus absent. The specimens may represent a new dicynodont species, a previously known species for which mandibular material was unknown, or an intraspecific variant of Dicynodontoides nowacki. Regardless of which of these options is correct, the specimens constitute the first taxon with a stratigraphic range extending from the likely middle Permian middle fossiliferous horizon of the Ruhuhu Formation into the late Permian Usili Formation. They also improve our understanding of the middle Ruhuhu tetrapod fauna, which previously consisted only of Endothiodon tolani.