Ancient Species of the Genus Dvinosaurus (temnospondyli, Dvinosauria) from the Permian Sundyr Tetrapod Assemblage of Eastern Europe

The oldest species of the genus Dvinosaurus Amalitzky, 1921—Dvinosaurus gubini sp. nov.—is described from the Sundyr-1 reference locality of the Sundyr faunal assemblage of Eastern Europe (Upper Permian, Upper Severodvinian, Suchonica vladimiri Assemblage Zone) based on abundant bone material. The diagnostic criteria for the new species are its smaller size compared to other dvinosaurs, the narrowest skull, a short and wide zygomatic bone, and the parasphenoid body with a wider base of the cultriform process, which is well ossified with the basisphenoid; a strongly curved dentary with a well-defined symphysial crest extending downward from the labial side of the symphysial surface and, in some cases, with a single symphysial tusk, a large angle (135°–152°) between the clavicular plate and dorsal process of the clavicle, narrow areas of the interclavicle for insertion of the clavicles, and a narrow entepicondylus of the humerus. The small size, narrow skull, single symphysial tusk, and hypocentrum morphology make the new form similar to the basal Dvinosauria, in particular, to ancestral Trimerorhachidae.