Mosasaurs (from Latin Mosa meaning the ‘Meuse river’, and Greek σαύρος sauros meaning ‘lizard’) are an extinct group of large marine reptiles. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards[1] known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and decline of plesiosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-T event at the end of the Cretaceous period, approximately 66 million years ago..They are extinct marine reptiles that are believed to be distantly related to monitor lizards such as the Komodo Dragon. Based on recent evidence, however, it may be that they were even more closely related to snakes than monitor lizards. The discovery and study of mosasaurs near Maastricht in Europe in the late 1700s and some of the first mosasaur remains were collected by Professor Benjamin Mudge and Dr. George M. Sternberg more than 130 years ago. A few years later, in a series of scientific expeditions sponsored by O. C. Marsh and Yale University, hundreds of specimens were collected. As a group, the fossilized remains of mosasaurs had been found all over the world.