New discoveries from the Sinokannemeyeria-Shansisuchus Assemblage Zone: 2. A new species of Nothogomphodon (Therapsida: Therocephalia) from the Ermaying Formation of Shanxi, China

A new therocephalian specimen collected from the upper part of the Ermaying Formation of Liulin, Shanxi, China is named as Nothogomphodon sanjiaoensis sp. nov. This new species is differentiated from the type species Nothogomphodon danilovi by the following characters: dentary lower margin uneven; canine base is ovate rather than rounded; distinct diastema present between canine and first postcanine; absence of accessory cutting cusps on posterior border of the postcanines. Nothogomphodon has a postcanine morphology that resembles that of sectorial toothed basal cynodonts, which is the only evidence of therocephalians having developed this kind of complex sectorial dentition. Faunal analysis between the Russian Eryosuchus fauna and the Chinese Sinokannemeyeria-Shansisuchus Assemblage indicates that only Nothogomphodon is common to both faunas, whereas there is no common genus shared between the Chinese Ermaying and Karamayi formations. Therocephalians were present at a moderate level of diversity in Middle Triassic faunas from Laurasia, whereas nonmammaliaform cynodonts are only represented by two taxa. Conversely, in Gondwana cynodonts experienced an explosion in diversity in the Middle Triassic with the evolution of Gomphodontia, while therocephalians were scarcely represented in faunas of this age.