Shonisaurus  Shonisaurus is a genus of ichthyosaur. At least 37 incomplete fossil specimens of the marine reptile have been found in the Luning Formation of Nevada, USA. This formation dates to the late Carnian age of the late Triassic period, about 237-227 million years ago. "Shonisaurus" lived during the Carnian stage of the late Triassic period. "S. popularis" measured around long. A second species from British Columbia was named "Shonisaurus sikanniensis" in 2004. "S. sikanniensis" was one of the largest marine reptiles of all time, measuring . However, phylogenetic studies later showed "S. sikanniensis" to be a species of "Shastasaurus" rather than "Shonisaurus". A new study published in 2013 reasserted the original classification, finding it more closely related 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 (about 210 million years ago). "Shonisaurus" had a long snout, and its flippers were much longer and narrower than in other ichthyosaurs. While "Shonisaurus" was initially reported to have had socketed teeth (rather than teeth set in a groove as in more advanced forms), these were present only at the jaw tips, and only in the very smallest, juvenile specimens. All of these features suggest that "Shonisaurus" may be a relatively specialised offshoot of the main ichthyosaur evolutionary line. It was historically depicted with a rather rotund body, but studies of its body shape since the early 1990s have shown that the body was much more slender than traditionally thought. "S. popularis" had a relatively deep body compared with related marine reptiles. "Shonisaurus" was also traditionally depicted with a dorsal fin, a feature found in more advanced ichthyosaurs. However, other shastasaurids likely lacked dorsal fins, and there is no evidence to support the presence of such a fin in "Shonisaurus". The upper fluke of the tail was probably also much less developed than flukes found in later species. Fossils of "Shonisaurus" were first found in a large deposit in Nevada in 1920. Thirty years later, they were excavated, uncovering the remains of 37 very large ichthyosaurs.