ICHTHYOSATJRITS, ik'thretesa'rus ( NP1). Lat.. from Gk. lx06r, iclithyR, fish craiipot, sauros, lizard). An extinct genus of fish-like reptiles found in the :Mesozoic rocks of Europe and North .tnierica. The ichthyosaurs among reptiles are analogous to the whales among mam mm als. and they have many points of resemblance to these. Their bodies were round and tapering, heads large. with long snouts and very short reeks, limbs reduced to paddles, and they had a broad. vertical fin on the tail and a triangular lin at the middle of the bark. The body was covered with thin. smooth skin and 110 traces of dermal plates have heel' diseovered. The jaws were armed with a large number of sharp. conical teeth that have a complicated internal structure similar to that of the teeth of Lahyrinthodonts or Stegocephalia. The eyes are surrounded by circles of sclerotic hones, and there is a large pineal foramen on top of the skull between the eyes. The vertehrm are biconcave, and the pelvic arch is separated from the vertebral column, for there is no sacrum. In size they ranged from 4 to 40 feet, and they must have swarmed in im mense numbers in some portions of tin European seas, especially during Liassic time, for their remains have been found in abundance in de posits of that age at Lyme Regis, England, and in Wurttemberg, Germany. That they were pre daceous animals and fed largely on fish, is evi denced by the fish fragments found within their coprolites and also within the abdominal cavity of some skeletons. Some ichthyosaurs were vivip
arous. for specimens obtained in the Wtirttem berg quarries show several small embryonic skeletons contained in the abdominal cavities of the adults. About thirty-five species of Ieh thyosaurus are known, and they have been found in the Mesozoic deposits of Europe, the East In dies, Australia. New Zealand. and South Amer ica. Allied genera are Mixosaurus, of small size from the Trias, and Oplithalmosaurus, a tooth less ichthyosaur from the Upper Jurassic and Lower Cretaceous. A single representative, Bap tanodon, is found in the North American Juras sic, .and is very close to Ophthalmosaurus. The ichthyosaurs and their allies, together with the Sauropterygia, comprising the plesiosaurs and allied forms, were formerly included in an order Enaliosauria, which is not now recognized.
BIBLIOGRAPHY. Woodward, Outlines of VerBibliography. Woodward, Outlines of Ver- tebrate Paleontology for Students of Zoology (Cambridge, IS9S) ; Owen, Monograph of the Fossil Reptiles of the Liassic Formation. Part III., lehthyopterygia (London, ISS1) Fraas. Die lehthyosu der siiddeutschen Trios mind Jura-.lblagerungen (Tubingen. 1S91) ; Nicholson and Lydekker. Manual of Paleontology, vol. ii. (Edinburgh and London, 1SS9). See REPTILE.