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Sinognathus gracilis skull
Skull of Sinognathus gracilis (after Young 1959 fig.1)
Sinognathus is a cynodont, a therapsid group ancestral to mammals, recovered from the Upper Ermaying deposits in Shanxi Province in northern China, which dates to the Early Triassic period. The Upper Ermaying deposits, explored by C.C. Young (1959) among others, revealed an assemblage of vertebrates named the Sinokannemeyeria fauna. This is thought to correlate with the South African Cynognathus Zone, the latest of the Beaufort Group faunal assemblage zones, dating from ca. 249-245 mya.
Sinognathus gracilis belongs to the family Cynognathidae, and is regarded as similar to Cynognathus from South Africa. Sun (1980), however, notes that, while the South African cynodont Cynognathus is a relatively large individual with a skull that closely resembles that of a dog, displaying long and narrow post canine teeth, Sinognathus from northern China has a more complex maxilla or upper jaw area. This is illustrated in this figure of the skull of Sinognathus gracilis, showing its maxilla or upper jaw with an overlying bone element called a surmaxilla (Young 1959).
References:
Sun, Ailing 1980. Late Permian and Triassic Terrestial Tetrapods of North China. Vertebrata PalAsiatica Vol XVIII, No. 2, pp. 100-110.
Young, C.C., 1959. Note on the first Cynodont from the Sinokannemeyeria fauna in Shansi, China. Vertebrata PalAsiatica. Vol. 1, No. 1, pp. 124-131.
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