Thaisaurus chonglakmanii (Mazin et al. 1991, Early or Middle Triassic) a basalmost ichthyopterygian that nests between Wumengosaurus and Shastasaurus pacificus. Perhaps the late appearance of Thaisaurus, long after its hypothetical genesis in the earliest Triassic has made this taxon less famous than it should be. Small sharp teeth lines the jaws. Like Stereosternum, and unlike Wumengosaurus, the cervical vertebrae were robust and approximately ten in number. Thaisaurus demonstrates that the front limbs developed into flippers before the hind limbs did. The tail was not the main swimming organ.

Xinminosaurus catactes (Jiang et al. 2008, Middle Triassic, GMPKU-P-1071) is another basal ichthyopterygian. Compared to the more basal Thaisaurus (above), the humerus was shorter, the hand was larger, the hind limbs were paddles. The teeth were large square shapes in this descendant of that as yet unknown ancestor with small sharp teeth. A slight bend to the tail is an early indication of a small tail fin, making it the main swimming orgain.

Jiang D, Motani R, Hao W, Schmitz L, Rieppel O, Sun, Sun Z 2008. New primitive ichthyosaurian (Reptilia, Diapsida) from the Middle Triassic of Panxian, Guizhou, southwestern China and its position in the Triassic biotic recovery. Progress in Natural Science 18 (10): 1315.

Mazin JM, Suteethorn V, Buffetaut E, Jaegaer JJ and Helmcke-Ingavat R. 1991.
Preliminary description of Thaisaurus chonglakmanii n. g. n. sp. a new ichthyopterygian
(Reptilia) from the Early Triassic of Thailand. C.-R. Seanc. Acad. Sci. Paris, Ser. II,
313: 1207–1212.

wiki/Xinminosaurus
wiki/Thaisaurus