ICHTHYORNIS, ik-thi-oenIs, a genus of fossil carinate birds constituting an order Ich thyornithes and family Ichthyornithidte. They were about the size of, and presumably had much the habits and appearance of, rather large gulls, but they had extremely large heads, and both mandibles of the long pointed beak were studded with sharp, backward pointing, snake-like teeth, each set in a distinct socket. These sea-birds fished in the great inland sea which during the Cretaceous Age covered so much of the present western half of the United cephalopods (squids). The members of this order," remarks Zittel, "differ conspicuously from all living reptiles and are distinguished chiefly by their fish-like form of body, paddle shaped limbs with numerous oval or polygonal phalanges, large head with elongated rostrum, short arnphiccelous vertebra, and naked integu ment.* They had no dermal armament like crocodiles, but the snout was prolonged, nar row like that of a gavial or a dolphin, the teeth were acutely conical, crocodile-like and thickly set in a groove without separate sockets; as many as 400 have been counted in a single mouth. The eyes were surrounded by a circle of wedge-shaped sclerotic plates. That they breathed air is plain from the absence of branchial arches, the shape of the hyoid bones, and other evidences of pulmonary respiration; and their viviparous habit is demonstrated by several well-preserved skeletons embracing em bryonic remains in the abdominal cavity,— as many as seven young in one case. As re
gards external form and adaptation to a marine existence, the ichthyosaurus as widely from other reptiles as whales do from land mammals, and occupy as isolated a posi tion.* Their composite character is most puz zling to the phylogenist, and nothing is cer tainly known as to their origin or descent, ex cept that they certainly were modified from terrestrial ancestors. The only family is Ich thyosauride, which existed from the Lias to the Cretaceous periods, and contains the small sized and primitive genus Mixosaurus, the typ ical and exclusively Old World genus lchthy °saurus, Baptanodon (q.v.), and Shastasaurus, the last two being American in their distribu tion and recovered from the upper Jura and Trias rocks of Wyoming, Nevada and northern California. Consult Zittel-Eastmann, 'Text book of Pabeontology,' (Vol.II, New York 1902); Gadow, 'Amphibia and Reptiles> (Lon don 1901).