Abstract
AbstractThe turtle fauna of the Middle Jurassic Xiashaximiao Formation in the Sichuan Basin and the type series ofChengyuchelys baenoidesYoung & Chow, 1953 are revised. By the absence of a mesoplastron and other shell characters, both the holotype and paratype ofChengyuchelys baenoidesbelong to the family Xinjiangchelyidae and come probably from the Upper Jurassic Shangshaximiao Formation. The Middle Jurassic turtle assemblage of the Sichuan Basin is composed of two entities: the Bashuchelyidae fam. nov. (Bashuchelysgen. nov.,Chuannanchelysgen. nov.) andProtoxinjiangchelysgen. nov. on the one hand, andSichuanchelyson the other hand, with the former as the dominant group. Bashuchelyids and xinjiangchelyids are closely related to one another, whileSichuanchelysis more primitive and has no shared apomorphic features with bashuchelyids. The whole assemblage appears to be endemic to the Sichuan Basin at genus level and distinct from the Late Jurassic turtle fauna of the same basin in its relict nature and absence of the Polycryptodira.
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