This, the earliest-known ichthyosaur, was found in 1982 in Japan, but it was not until a study of the skeleton was published in 1998 that is significance as the most primitive of the group was noted.
Like most primitive ichthyosaurs it swam by undulations of its body rather than by sweeps of the tail, and it probably inhabited the shallow waters of the continental shelf.
The skull is rather broad and tapers gradually towards the snout, unlike the narrow jaws of most other ichthyosaurs. The teeth are small for the size of the skull and arranged in a groove - a primitive feature. Its paddles are small and unusually, the hindlimb is bigger than the forelimb. The paddle is made up of four fingers, unlike the usual five found in other ichthyosaurs. Its undulating swimming action is shown by the large number of very thin narrow vertebrae, making for a very flexible body.