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Roger Weller, geology instructor

by April Aloisio
Historical Geology
Spring 2007

Mosasaurs-The Largest Lizards







The Mosasaur comes from a family of large reptiles with lizard-like features with the official name of Mosasauridae. Mosasaur fossils were found around the upper Cretaceous rock. This lizard-like creature lived on earth about 65 million years ago. The mosasaur was not a dinosaur, it was a sea-dwelling creature. This large reptile was a carnivore that ate smaller mosasaurs, fish, shellfish, and other small sea organisms. Paleontologists also said that these creatures fed on oversized Portheus Molossus, which weighed up to eight hundred pounds. It was an extremely fast swimmer because of its four paddle like fins and its tremendously elongated body. This reptile had a long head, a short neck, and massive jaws with incredibly sharp teeth. Some of the fossils found today illustrate how enormous this creature really was. This reptile had seven vertebrae just to hold their neck together, even thought they body was extremely long. The individual vertebrae had a ball and socket expression, which allowed the mosasaur to move their body like a snake in a sideways motion.



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             In the picture above this fossil measured approximately 44 feet long by 8 feet wide and the skill is about 6 feet in length with teeth the size of a Tyrannosaurus rex’s set of teeth. Mosasaur fossils are found in North America and all other continents except for Antarctica and Australia. The most common place mosasaurs are found in the Niobrara Chalk of Kansas, in northwestern Europe in the Netherlands, and in the English Chalk. 




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             Around the Mesozoic flood was when the mosasaur lived, as they swam in the seas in North America and other places looking for food and trying to survive. This reptile was well adapted to warm shallow waters called epicontinental seas.  An epicontinental sea was a large body of salt water that lies between continents, just like the picture shown above. However, their habitat evolved from the land, then returned to their aquatic life in the sea. In these seas the mosasaur would also give birth to their young in shallow waters. These reptiles would give birth to their adolescent in the sea waters instead of laying eggs on the shore.





             In 1780, a workman discovered a petrified fossil skull in a chalk sandstone quarry by the Meuse River, under the Pietersburg Mount near the town of Maastricht.


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             The town of Maastricht is located in the Netherlands between Belgium and Germany. Since the workers had no thoughts to what species the skull belonged to they brought the fossil to a well known fossil hunter by the named of Doctor C. K. Hoffman. Dr. Hoffman knew that this fossil was a remarkable find and an expensive piece as well. So he then wanted to seize the fossil skull before the land owner found out about it. Eventually, the land owner found out and took Dr. Hoffman to court. His name was Canon Goddin, and later won the case in court. This fossil was fancied by a large number of people. When the French were at war with this town, the General in Command wanted the soldiers to leave Cannon Goddin’s property alone, and Mr. Goddin believed that there was a reason for the Generals command. Therefore he withheld the location of the fossil.  To Cannon Goddin’s amazement the French army presented him an offer for the specimen.  The offer was said to have been six hundred bottles of wine. Though to Cannon Goddin’s surprise the soldiers found the fossil skull and took it to Paris. The fossil inquired a few different names, such as a “breathing fish” then as “the Great Lizard of the Meuse”. However, the fossil was not described as a Mosasaur until 1822. Then it received its official Latin name, named after the Meuse River  which is “Mosasurus” until 1829.




                          Oxford University Museum of Natural History


             The mosasur reptile lived a short while with other reptiles such as the Plotosaurus, Tyosaurus, and the Clidastes. These massive reptiles had exceptionally similar body structures and became extinct during the late Cretaceous. Nevertheless, the mosasur was one of the most important marine carnivores living during this time. Good thing they not alive today or are they?




Fenton , Carroll, and Mildred Fenton. The Fossil Book. Garden City: Doubleday & Company, INC., 1958.

Walker, Cyril, and David Ward. Fossils. New York: Dorling Kindersley, INC., 1992.