Xinpusaurus kohi (Yin et al. 2000, Jiang et al. 2004) Late Triassic ~210 mya, ~1.5 m in length, is a basal thalattosauriform. Derived from Stereosternum and the basal ichthyopterygids, Hupehsuchus and Utatsusaurus, Xinpusaurus phylogenetically preceded Askeptosaurus.
Overall larger than and distinct from the larger Stereosternum, the skull of Xinpusaurus had a straight rostral margin and a kinked jawline. The jugal included an elongated quadtratojugal process, but there was no quadtratojugal. The upper temporal fenestra was reduced to a slit. The mandible was shorter than the rostrum with no teeth at the sharp tip. A sharp coronoid process appeared beneath the posterior jugal.
The cervicals were shortened, as in Utatsusaurus. The dorsal vertebrae and ribs increased to 35. The caudals also increased in number and decreased in length. The anterior chevrons were very deep, but reduced in the first third of the tail.
The forelimbs were not larger than the hindlimbs. The humerus tapered distally. The ulna tapered proximally. The fingers were gracile with digits III and IV by far the longest.
The femur tapered distally. The pedal digits were close to subequal, as in Hupehsuchus.