A review of the Mesozoic turtles of the Junggar Basin (Xinjiang, Northwest China) and the paleobiogeography of Jurassic to Early Cretaceous Asian testudinates

Middle Jurassic to Early Cretaceous sediments exposed in the Junggar Basin have yielded a rich turtle assemblage. Jurassic taxa include the purportedly basal turtle Sichuanchelys sp. and at least six basal eucryptodires, which are currently united in the likely paraphyletic taxon "Xinjiangchelyidae." Early Cretaceous assemblages, by contrast, include a single "xinjiangchelyid" and a single potential pantrionychian, but are otherwise dominated by more derived eucryptodires, currently grouped in the paraphyletic taxon "Sinemydidae"/"Macrobaenidae." Comparison of the Junggar turtle assemblage with those of coeval Asian localities reveals that Jurassic turtle assemblages were rather homogenous throughout the Jurassic, but split in the Early Cretaceous. In particular, the Early Cretaceous Junggar turtle assemblage resembles those of other northern Chinese provinces, Mongolia and the Lake Baikal region of Russia in their retention of rather basal turtles, whereas all other Asian localities are dominated by more derived eucryptodires, particularly pantrionychians. This chasm may be the result of biogeographic, ecological and climatic conditions, where dry conditions in isolated inland basins created an ephemeral lake habitat optimal for basal eucryptodires, whereas the river environments typical of the surrounding coastal areas were favourable for more derived eucryptodires. © Senckenberg, Gesellschaft für Naturforschung and Springer 2010.