Sinosaurosphargis yunguiensis (Li, Rieppel, Wu, Zhao and Wang 2011) Anisian, Middle Triassic, ~230 mya, ~60 cm in length was originally considred a possible turtle ancestor because the dorsal ribs were broadened to such an extent that the each one touched its neighbors and the torso was covered in bony osteoderms. Here Sinosaurosphargis nests outside the base of the Sauropterygia. Derived from a sister toAdelosaurus and Claudiosaurus. Sinosaurosphargis was a sister to Largocephalosaurus and Atopodentatus. Sinosaurosphargis represents the last of its lineage. It was not related to turtles, such as Odontochelys and Proganochelys, but resembled them overall through convergence.
Distinct from Claudiosaurus, the skull of Sinosaurosphargis was longer with a smaller naris raised to the top of the rostrum. The maxilla was larger with a broad ascending process. The lacrimal was smaller. The squamosal contacted the jugal. The postfrontal and postorbital were fused together. The parietals were fused. The teeth were convex onthe cheek side and concave on the tongue side. The upper temporal fenestrae were described as closed. Here they are reported as reduced but not closed.
The number of cervicals appears to be fewer than six. The cervical series was shorter than the skull. Each dorsal vertebrae included an elongated transverse process and a broad flat rib. The enlarged gastralia were also expanded similarly.
The scapula was not fused to the coracoid. The interclavicle was a broad T-shape. The humerus was strongly curved distally and was twice the length of the reduced but robust ulna. The unguals were reduced to nubs.