"Utatsusaurus" is one of the most primitive (basal) types of ichthyosaur. It has transitional features between its ancestral land-dwelling forms and the more derived ichthyosaurs. Unlike the more advanced ichthyosaurs, "Utatsusaurus" has no dorsal fin and has a broad skull. The snout gently tapers, compared to the more rounded one of more derived ichthyopterygians. The tail had a long low fin, quite different from the tail shape of later forms. This suggests that the animal swam by undulation, waving its body to & fro, rather than using its paddles and tail.