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	Dvinia suschkini skull Skull of Dvinia suschkini with labelled bones (after Amalitsky 1922)
	Dvinia is a Late Permian cynodont ("dog-tooth") therapsid named for the Dvinia River near Arkhangelsk, Russia. It was found in Upper Tatarian deposits (258-255 mya) on the Dvinia River examined by Amilitsky (1922).  Dvinia was a small to medium-sized carnivore with large upper canines. Discovered by Amalitsky, and initially studied by P.P. Sushkin in 1927, Dvinia was more completely defined by Tatarinov (1968) who placed it in the Procynosuchoid superfamily, and because of its distinct anatomy, within its own family, Dviniidae. Dvinia is considered close to several South African forms from the Late Permian and Early Triassic, including Trithelodontia (Broom), Gomphognathus, Trirachodon, and Diademodon. Dvinia, whose skull length was 7-10 cm, had an enlarged brain, with various changes occuring in the floor of the braincase and in the region of the middle ear which have led it to be considered as a possible ancestor of early mammals.  The stapes or columella (the reptilian middle ear ossicle) was recognized as a cartiligenous feature by Tatarinov (1968). Sushkin (1927) had also noted features of the middle ear region of Permocynodon, a taxa closely related to Dvinia, which Tatarinov (1968) later redefned as the same species. These otic features included a contact between the stapes and the paraoccipital process, and the presence of an opening called the foramen stapediale. Besides changes in the middle ear, Dvinia has advanced or transitional features  in double set of both reptilian and mammalian jaw hinges. The dentary bone was now the major bone of the lower jaw. The other jaw bones that had been present in early reptiles were reduced to a complex of smaller bones near the jaw hinge. The single occipital condyle was split into two surfaces.  Dvinia also had cheek teeth with tiny cusps, and large temporal fenestra.               References Amalitzky, V. P.  1922. Diagnoses of the new forms of vertebrates and plants from the upper Permian of North Dvina. Bulletin of the Russian Academy of Sciences, St. Petersburg 16 (6), pp.329–340. Tatarinov, L.P.  1968. Morphology and Systematics of the Northern Dvinia Cynodonts (Reptilia, Synapsida; Upper Permian).  Yale University Postilla 126.     .
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