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Onion Creek Mosasaur

Mosasaurus maximus

Mosasaur skull

Near the end of the Cretaceous Period, 90-66 million years ago, huge relatives of lizards and snakes swam the shallow sea that covered 40% of present-day North America. These were mosasaurs (MOSE-uh-sawrs), marine reptiles that were the top predators in their ancient environment. They preyed on fish, ammonites, and even other marine reptiles! Mosasaurs have been extinct for about 66 million years, but their fossilized bones and teeth have been found in many parts of Texas. TMM is fortunate to have several fine mosasaur specimens, including the spectacular Onion Creek Mosasaur.

Photo of W. Clyde IkinsW. Clyde Ikins with the Onion Creek Mosasaur that he
and John P. Smith discovered in 1935.

The Onion Creek Mosasaur, Mosasaurus maximus, is among the largest 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 long, laterally flattened tail, the Onion Creek Mosasaur swam with a snake-like motion, using its powerful tail to propel its body through the water. Discovered in 1935 by The University of Texas at Austin geology students W. Clyde Ikins (in photo) and John P. Smith, the Onion Creek Mosasaur is 30 feet long, about 12 feet of which are tail. Excavated by a team of UT geologists and paleontologists, the skeleton first went on display in Gregory Gymnasium in 1936 at the University Centennial Exposition. After exhibition in TMM's Great Hall from 1965-1989, it was remounted into a more natural pose in the Hall of Geology and Paleontology, where you can view it today.