| Utatsusaurus Temporal range: Early Triassic |
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|---|---|
| life restoration of Utatsusaurus hataii | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sauropsida |
| Superorder: | Ichthyopterygia |
| Family: | Utatsusauridae McGowan & Motani, 2003 |
| Genus: | Utatsusaurus |
| Binomial name | |
| Utatsusaurus hataii Shikama, Kamei & Murata, 1978 |
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Utatsusaurus is the earliest-known form of an ichthyopterygian (the group of marine reptiles that includes the ichthyosaurs), which lived in the early Triassic period (c. 245-250 millions years ago). Unlike the more advanced ichthyosaurs, Utatsusaurus has no dorsal fin and has a broad skull that tapers slowly toward the snout. For the size of the skull, the teeth are rather small, and arranged in a primitive groove. Utatsusaurus had small fins, with four toes instead of the usual five found in primitive ichthyosaurs. The tail had a long low fin, suggesting that the animal swam by undulation, rather than using its paddles and tail. Feeding on a diet of fish, Utatsusaurus reached a length of three meters (nine feet). Utatsusaurus has been found in Japan and Canada.
Ryosuke Motani from the University of California, Berkeley and Nachio Minoura from Hokkaido University re-examined the fossils of Utatsusaurus in 1998 using computer imagery to reverse the distortion of the original skeleton. They found that Utatsusaurus was closely related to the lizard-like diapsid reptiles such as Petrolacosaurus, making ichthyopterygians a distant relative to lizards, snakes and crocodiles.