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Description
Dvinia is an extinct genus of cynodonts found in the Salarevo Formation of Sokolki on the Northern Dvina River near Kotlas in Arkhangelsk Oblast, Russia. It is the only known member of the family Dviniidae. Its fossil remains date from the Late Permian and were found with Inostrancevia, Scutosaurus and Vivaxosaurus.
Dvinia was a small omnivore possessing a large temporal opening typical of advanced therapsids, with a thin postorbital bar separating the eye from the muscle attachment. As a cynodont, it was closely related to mammals. The dentition consisted of a set of small incisors followed by 2 canines and 10-14 postcanines.
The study of the skull of the Late Permian cynodont Dvinia prima Amalitzky, 1922 shows a combination of the general primitive skull design with the development of a number of “advanced” features (expansion of the temporal fenestra, development of the parietal crest, and closed pineal foramen, unusual structure of the premaxilla, complicated postcanines, and reduction of the angular wing). Dvinia prima is treated as a specialized omnivore and assigned to the family Dviniidae of the superfamily Thrinaxodontoidea.
The external surface of the facial lamina of the maxilla projects laterally in the region of the alveolus of the upper canine and is concave posterior to it, where a large oval depression with a smooth surface is located. This depression is treated as a probable location of a glandular field. The surface of the projecting part is covered with weak pits similar to the pits in this region of, for example, therocephals; these are possibly traces of large bulbs of vibrissae and their blood lacunae. However, a network of small vascular foramina and anastomotic grooves connecting them is not seen here, but this area contains two large foramina; one is just anterior to the fossa of the “gland” and the second is somewhat lower. The palatine laminae of the maxillae bypass laterally a narrow and long incisor foramen and, close to the level of the anterior buccal teeth, come in contact at the medial line, adjoining posteriorly the laminae of the palatines. Naturally, it is hardly probable that these evolutionary trends of primitive cynodonts represent reconstruction of true phyla; they likely display stages of morphological changes. For example, Dvinia was probably endemic to Eastern Europe and could have been formed independently (of primitive forms, suchas Sludica). The presence of parallelisms in the development of primitive cynodonts is undoubted (see, for example, Kemp, 1979). Certainly, this complex evolutionary picture is connected with the primary adaptive radiation of cynodonts at the end of the Permian– beginning of the Triassic, when the group which evolved from small primitive Middle Permian entomophages occupied all accessible econiches by the minimaly morphologically changed derivatives of both predatory and phytophagous directions.
Dvinia was a small omnivore possessing a large temporal opening typical of advanced therapsids, with a thin postorbital bar separating the eye from the muscle attachment. As a cynodont, it was closely related to mammals. The dentition consisted of a set of small incisors followed by 2 canines and 10-14 postcanines.
The study of the skull of the Late Permian cynodont Dvinia prima Amalitzky, 1922 shows a combination of the general primitive skull design with the development of a number of “advanced” features (expansion of the temporal fenestra, development of the parietal crest, and closed pineal foramen, unusual structure of the premaxilla, complicated postcanines, and reduction of the angular wing). Dvinia prima is treated as a specialized omnivore and assigned to the family Dviniidae of the superfamily Thrinaxodontoidea.
The external surface of the facial lamina of the maxilla projects laterally in the region of the alveolus of the upper canine and is concave posterior to it, where a large oval depression with a smooth surface is located. This depression is treated as a probable location of a glandular field. The surface of the projecting part is covered with weak pits similar to the pits in this region of, for example, therocephals; these are possibly traces of large bulbs of vibrissae and their blood lacunae. However, a network of small vascular foramina and anastomotic grooves connecting them is not seen here, but this area contains two large foramina; one is just anterior to the fossa of the “gland” and the second is somewhat lower. The palatine laminae of the maxillae bypass laterally a narrow and long incisor foramen and, close to the level of the anterior buccal teeth, come in contact at the medial line, adjoining posteriorly the laminae of the palatines. Naturally, it is hardly probable that these evolutionary trends of primitive cynodonts represent reconstruction of true phyla; they likely display stages of morphological changes. For example, Dvinia was probably endemic to Eastern Europe and could have been formed independently (of primitive forms, suchas Sludica). The presence of parallelisms in the development of primitive cynodonts is undoubted (see, for example, Kemp, 1979). Certainly, this complex evolutionary picture is connected with the primary adaptive radiation of cynodonts at the end of the Permian– beginning of the Triassic, when the group which evolved from small primitive Middle Permian entomophages occupied all accessible econiches by the minimaly morphologically changed derivatives of both predatory and phytophagous directions.
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