Utatsusaurus
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 life restoration of Utatsusaurus hataii
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Extinct (fossil)
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| Utatsusaurus hataii Shikama, Kamei & Murata, 1978 |
Utatsusaurus is the earliest-known form of an ichthyopterygian (the group of marine reptiles that includes the ichthyosaurs), inhabiting the Scythian stage of the middle Triassic period. Unlike the more advanced icthyosaurs, 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 3 meters (10 feet).
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 diaspid reptiles such as Petrolacosaurus, making ichthyopterygians a distant relative to lizards and snakes. This study challenged the older theory that ichthyopterygians developed from swimming amphibians and were a distinctly different genus of reptile.
[edit] References
Dixon, Dougal. "The Complete Book of Dinosaurs." Hermes House, 2006.
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