Shonisaurus
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Shonisaurus Temporal range: Late Triassic, 215 Ma |
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| Restored skull | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Ichthyosauria |
| Family: | †Shonisauridae |
| Genus: |
†Shonisaurus Camp, 1976 |
| Species: | †S. popularis |
| Binomial name | |
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Shonisaurus popularis Camp, 1976 |
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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 215 million years ago.
Shonisaurus lived during the Norian stage of the late Triassic period. S. popularis measured around 15 metres (49 ft) long. A second species from British Columbia was named Shonisaurus sikanniensis in 2004. S. sikkanniensis was one of the largest marine reptiles of all time, measuring 21 metres (69 ft). However, phylogenetic studies later showed S. sikanniensis to be a species of Shastasaurus rather than Shonisaurus. A new study, of the year 2013, reassert 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.
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