Enaliosaurians (Gr.Enaliosaurians 0600478 marine, andEnaliosaurians 0600479 a lizard), an order of fossil marine reptiles, found in the liassic, triassic, and cretaceous epochs. They unite characters which appear at first sight incompatible, having the vertebrae of fishes, the teeth of crocodilians, the body of lizards, the paddles of cetaceans or marine turtles, and some have a long snake-like neck. Many of these aquatic saurians attained a large size, and from their voracity must have been the terror of the waters of the secondary epoch, after the disappearance of the great sauroid fishes of the carboniferous period. Pictet considers them as coming nearest to the saurians, though so different from any existing types as to require the establishment of a new order, whose principal characters are biconcave vertebras, wider than long, with laminae feebly united to the bodies; conical teeth, without cavity at their base, implanted in short deep-seated alveoli; and four short, flattened limbs, whose fingers are formed by discoidal bones disposed like those of cetaceans. They have been divided into two groups, whose characters correspond also to their geological position.

The ichthyosaurians (including the ichthyosaurus and plesiosaurus) have well developed crania, with small fossae and cavities; these have been found in the Jurassic and cretaceous strata. The other group, the simosaurians (including nothosaurus, simosaurus, &c), have the cranium with very large temporal fossa) and orbital and nasal cavities; they are found only in the triassic strata. The first two genera are the best known, and the most common in the strata of England and Germany; the ichthyosaurus must have attained a length of 25 ft., and the plesiosaurus of more than 12, and both presented forms most unlike those of any existing animals, though admirably adapted to the circumstances in which they lived. (See Ichthyosaurus, and Plesiosaurus.)