Ichthyosauria (ichthyosaurs; class Reptilia, subclass Ichthyopterygia) An order of so-called ‘fish lizards’, whose first members date from the Triassic and were primitive in type. Mixosaurus atavaus, possibly the earliest of the mixosaurs, the first of the ichthyosaurs, is recorded from the Triassic of Germany. Unlike Ichthyosaurus, the mixosaur tail lacked the strong development of the fish-type of caudal fin. The typical, shark-like form, Ichthyosaurus, appeared in the Jurassic, when the group in general was especially common. Ichthyosaurs disappeared before the end of the Cretaceous.

Ichthyosauria (class Reptilia, subclass Ichthyopterygia) Order of so-called ‘fish lizards’, and the only order in the subclass, the first members of the group date from the Triassic and were primitive in type. The typical, shark-like form, Ichthyosaurus, appeared in the Jurassic, when the group in general was especially common. Ichthyosaurs disappeared before the end of the Cretaceous.