NEW MATERIAL OF XINJIANGCHELYS (REPTILIA, TESTUDINES) FROM THE LATE JURASSIC QIGU FORMATION (SHISHUGOU GROUP) OF THE PINGFENGSHAN LOCALITY, JUNGGAR BASIN, XINJIANG

The Late Jurassic Qigu Formation of the Shishugou Group in the Pingfengshan locality contains a vertebrate fauna dominated by two taxa of turtles, both members of the genus Xinjiangchelys. One of these, Xinjiangchelys latimarginalis (Young and Chow, 1953), is well represented by a series of specimens. The second is specifically indeterminate and is represented by only a single fragmentary specimen but is distinctive in having a long narrow plastral lobe. Derived features of Xinjiangchelys that separate it from Plesiochelys include the presence of a loose connection between the plastron and carapace, with pegs on the plastron fitting in sockets on the peripherals; the extension of the pleural-marginal sulcus onto costals one to five; the dorsal thickening of the lateral edges of peripherals two to seven; the highly expanded seventh to eleventh peripherals; the extension of the anal scute to the hypoplastron - xiphiplastron suture or onto the hypoplastron; a reduction in length of the first dorsal rib; and the presence of a sinusoidal midline sulcus. The first five of these features are shared with Early Cretaceous turtles from Asia generally referred to the '' Macrobaenidae, '' indicating that Xinjiangchelys is more closely related to this group than is Plesiochelys.