A reinterpretation of the Upper Triassic ichthyosaur Shonisaurus

Shonisaurus, from the Upper Triassic (Carnian) of Nevada, is represented by some 40 individuals. However, many comprise only a few elements, and not o ne of the skeletons is complete. Furthermore, preservation is often poor, s o information is limited. Reaching lengths of up to 15 m, possibly slightly more, Shonisaurus was about the size of a Gray Whale. The only other ichth yosaur of comparable size was a little known and unnamed ichthyosaur from t he English Lower Jurassic, which may have reached 15 m (McGowan, 1996). Sho nisaurus was long-bodied, with about 60 presacral vertebrae. Some of the ce ntra, at about the level of the 97th vertebra, are wedge-shaped, indicating a tailbend. However, their cambers are small, and their combined angle of deflection is only about 5 degrees, which hardly constitutes a tailbend. Th e paired fins were long and slender, with no more than three major digits i n each, possibly only two. Contrary to previous descriptions, the emarginations on the free margins of many of the fin elements were probably preaxial rather than postaxial, as in all other ichthyosaurs. The coracoid does not have a hooked process dist ally, and is therefore much like that of Shastasaurus. The teeth are set in individual sockets, as previously described. Three species have been descr ibed, but S. popularis is here considered the only valid species.