Title
Morphology and systematics of the Northern Dvina cynodonts (Reptilia, Therapsida; Upper Permian)
Publication Date
11-12-1968
Series Number
126
Abstract
The materials on the North Dvina cynodonts, Dvinia prima and "Permocynodon sushkini", are redescribed. These cynodonts have a complete secondary palate, an interpterygoid vacuity of the therocephalian type, a medioventral contact between the basipterygoid processes, and an additional mandibular articulation between the surangular and quadratojugal. In addition, I have found an impression of the external auditory meatus, which has a structure of the tritylodont type but runs to the region of the external quadrate condyle and is closely connected with the grooves for the veins in the occipital part of the skull. The problem of the position of the tympanum in theriodonts is discussed, and the opinion about the attachment of the tympanum to the medial quadrate condyle is criticized. Another very unusual feature is the structure of the lower "molars" of Dvinia, which are described for the first time in the present article; these "molars" have up to 22 additional cusps on the crown and differ sharply both from the upper "molars" of the same animal and, in general, from the "molars" of all previously known theriodonts. Dvinia's "molars", which are transversely widened, did not occlude; the lower "molars" lay interior to the upper and pressed the food against the secondary palate. t is shown that three Northern Dvina specimens that were described as two separate species actually belong to the same species, Dvinia prima. The morphological peculiarities of this Northern Dvina cynodont justify its being set apart in a separate family Dviniidae related to the Procynosuchidae — the extremely primitive cynodonts of South Africa.