Perhaps the best known of fossil sea reptiles are the fish-lizards, the ichthyosaurs. The best are known from fossils in Jurassic rocks, but their history9 reaches back into Triassic times. There are several distinct early shapes of ichthyosaurs, before the classic dolphin-like appearance was standardized.
Some are eel-like and others are enormous and whale-shaped.
Although Cyntbospondylus is formally regarded as part of the shastasaurid group of primitive ichthyosaurs, recent studies suggest that it may be more primitive than originally thought – maybe too primitive to be regarded as an ichthyosaur. Indeed, in appearance it does not seem to have the physical features, such as the dorsal fin and fish-like tail, which are so distinctive of the later members of the group. Cymbospondylus is the state fossil of Nevada.
Features Cymbospondylus is more eef-shaped than the other ichthyosaurs, with a narrow body and a long flexible tail that takes up about half the length of the animal. The legs have already evolved into paddles but these were probably used more for stabilization, while the swimming action was produced by undulations of the body. The head is quite small in relation to the body but is quite typical of the ichthyosaurs, with the long snout and the small, sharp fish-catching teeth already present.