Shastasaurus

popularis (green) and S. sikanniensis (red), a possible species of Shastasaurus'', compared with a human Shastasaurus lived during the late Triassic period. The type species, S. pacificus, is known from California, with the name Shastasaurus directly referencing Shasta County, Northern California, where the type specimen was found. S. pacificus was a medium-sized ichthyosaur, measuring over in length. A second possible species of Shastasaurus, S. sikanniensis, is known from the Pardonet Formation British Columbia, dating to the middle Norian age (about 210 million years ago). By comparison, S.sikanniensis was one of the largest known ichthyosaurs, similar in size to modern-day cetaceans, measuring up to in length and weighing . Shastasaurus was highly specialized, and differed considerably from other ichthyosaurs. It was very slender in profile. S. sikanniensis had a ribcage slightly less than deep despite a distance of over between its flippers. and since some species like Shonisaurus had robust sectorial teeth with gut contents of mollusk shells and vertebrates. It is unknown whether Shastasaurus had a dorsal fin; however, the smaller, more basal ichthyosaur Mixosaurus had one. The upper fluke of the tail was probably much less-developed than the shark-like tails found in later species. ==Species and synonyms==

The type species of Shastasaurus is S. pacificus, from the late Carnian of northern California. It is known only from fragmentary remains, which have led to the assumption that it was a 'normal' ichthyosaur in terms of proportions, especially skull proportions. Several species of long-snouted ichthyosaur were referred to Shastasaurus based on this misinterpretation, but are now placed in other genera (including Callawayia and Guizhouichthyosaurus). Elizabeth Nicholls and Makoto Manabe considered this species as a nomen dubium in 2000. Shastasaurus may include a second species, Shastasaurus liangae. It is known from several good specimens, and was originally placed in the separate genus Guanlingsaurus. Complete skulls show that it had an unusual short and toothless snout. S. pacificus probably also had a short snout, although its skull is incompletely known. In the 2019 study, S. sikanniensis was pertained within the genus Shastasaurus. In the 2021 analysis, S. sikanniensis forms a clade with Shonisaurus, indicating that it is closer to Shonisaurus than to Shastasaurus. Specimens belonging to S. sikanniensis have been found in the Pardonet Formation British Columbia, dating to the middle Norian age. 'Synonyms of S. / G. liangae:' Guanlingichthyosaurus liangae Wang et al., 2008 (lapsus calami) 'Synonyms of S. pacificus:' Shastasaurus alexandrae Merriam, 1902 Shastasaurus osmonti Merriam, 1902 ==See also==