Mosasaur Facts

Mosasaurs are an extinct group of marine reptiles, and depending on the particular species, varied from about 10 feet (3 meters) in length, up to a maximum of 57 feet (17.5 meters). These reptiles lived during the latter part of the Cretaceous period of the Mesozoic Era (from about 96 million years ago to about 65 million years ago), and spent their entire lives at sea. Mosasaurs were carnivores eating fish, sea urchins, turtles, and shellfish. Although they lived at the same time as many of the dinosaurs, and like the dinosaurs became extinct during the Cretaceous-Tertiary mass extinction, Mosasaurs were not dinosaurs, but lepidosaurs (the same taxonomic group which includes lizards, snakes and sphenodonts such as the tuatara).

The evolution of Mosasaurs is quite an interesting topic of speculation and debate. Many similarities have been observed between Mosasaur anatomy and that of monitor lizards, and it is thought that Mosasaurs may have evolved from aigialosaurs, which were semi-aquatic lizards of the early Cretaceous period, and are themselves believed to be related to monitor lizards.

Another possibility is that Mosasaurs may share a common ancestor with snakes - both animals have very similar jaws and reduced limbs. The idea of a Mosasaur-snake link of this type was first proposed by Edward Drinker Cope way back in 1869. In the 1990s fossils were found showing early snakes with vestigial limbs living in marine environments, and which was consistent with this hypothesis. More recently however some other early snake fossils have been found, and these seem to show early snakes living a burrowing lifestyle in a terrestrial environment.