Texas Memorial Museum

Exhibits: Hall of Geology and Paleontology

Onion Creek Mosasaur
Mosasaurus maximus

Near the end of the Age of Dinosaurs, at a time known to geologists as the Late Cretaceous, huge seagoing relatives of the lizards swam the shallow seas that then covered 40% of present day North America. These were mosasaurs (MOSE-uh-sawrs), predatory, aggressive creatures which were probably the closest approach to the mythical "sea serpent" that ever existed. Mosasaurs have been extinct for about 65 million years, but their bones are common fossils in some parts of the world. The Texas Natural Science Center is fortunate to have several fine mosasaur specimens. The most spectacular is the skeleton of the Onion Creek Mosasaur that is presently on display.

The Onion Creek Mosasaur belonged to one of the larger species of mosasaurs, and one that lived only a short time before the last mosasaurs went extinct. With whale-like flippers instead of feet, and a large, flattened tail, these giant creatures probably swam with a snake-like motion, using the tail as a propeller and rudder, and the flippers as stabilizers . Their long slender bodies probably made for great speed and agility.

Discovered in 1934 by The University of Texas at Austin geology students Clyde Ikins (shown above) and John P. Smith, the Onion Creek Mosasaur is 30 feet long, about 12 feet of which are tail. The head is 4 feet 8 inches long, and the jaws, when fully opened, have a gape of about 3 feet. The lower jaw is loosely hinged to the skull with a moveable joint on each side just behind the teeth. This loose joint likely permitted the animal to swallow large prey, much as some living snakes do.