Paleontologyany fishlike marine reptile of the extinct order Ichthyosauria, ranging from 4 to 40 ft. (1.2 to 12 m) in length and having a round, tapering body, a large head, four paddlelike flippers, and a vertical caudal fin.
see ichthyosaurus 1820–30
ich′thy•o•sau′ri•an, adj., n. ich′thy•o•sau′roid, adj.