Mosasaur, << MOH suh sawr, >> is an extinct marine reptile. Mosasaurs lived from about 100 million to 65 million years ago. There were many species (kinds) of mosasaurs. The first mosasaur fossils were found in the late 1700’s in an underground limestone mine near the Meuse River in the Netherlands.
Mosasaurs evolved (developed over time) from ancestors that lived on land. Early mosasaurs looked much like modern monitor lizards. They lived mostly on land but spent much time in the water. Later mosasaurs became adapted to life in the water. These mosasaurs swam by pushing themselves through the water with their powerful tails. They had finlike limbs for steering and streamlined bodies. Most early mosasaurs measured less than 6 feet (2 meters) long. Some later species reached more than 40 feet (12 meters) long.
Mosasaurs were predators and fed mainly on small to medium-sized fish and squidlike animals. Some species were capable of eating almost anything that they encountered, including sharks and other mosasaurs. Additionally, a mosasaur had two sets of teeth, an outer row in the jaws and an inner row in the back of the mouth. The animal continuously shed and replaced its teeth, ensuring an effective bite. Like modern whales, mosasaurs had to surface periodically to breathe air. Mosasaurs gave birth to live young underwater.
Mosasaurs quickly spread throughout the seas of the world. They became the most common fossil marine reptiles of the end of the Mesozoic Era, the time during which the dinosaurs lived. Although mosasaurs and dinosaurs lived at the same time, they are not closely related to each other. Mosasaurs became extinct around the same time as did the dinosaurs.
