Mosasauroidea

Mosasaurs Temporal range: Late Cretaceous, 92–66 Ma PreЄ Є O S D C P T J K Pg N
Mounted skeleton of a plioplatecarpine (Plesioplatecarpus planifrons), Rocky Mountain Dinosaur Resource Center
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Clade:	Platynota
Superfamily:	†Mosasauroidea Gervais, 1853
Subgroups
†Aigialosaurus †Mosasauridae Gervais, 1853 †Halisaurinae †Mosasaurinae †Russellosaurina †Carsosaurus †Haasiasaurus †Komensaurus †Plioplatecarpinae †Tylosaurinae

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 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 pliosaurs, 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.

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow inland seas prevalent during the Late Cretaceous Period. Mosasaurs were so well adapted to this environment that they gave birth to live young, rather than returning to the shore to lay eggs as sea turtles do.

The smallest-known mosasaur was Dallasaurus turneri, which was less than 1 metre (3.3 ft) long. Larger mosasaurs were more typical, with many species growing longer than 4 metres (13 ft). Mosasaurus hoffmannii, the largest known species may have reached up to 17 metres (56 ft) in length. Currently, the largest publicly exhibited mosasaur skeleton in the world is on display at the Canadian Fossil Discovery Centre in Morden, Manitoba. The specimen, nicknamed "Bruce", is just over 13 metres (43 ft) long.