Mosasaurs are the largest known lizards ever to have lived. They lived 144 million to 65 million years ago in the shallow sea that covered most of Kansas during the late Cretaceous period. Mosasaurs are distant relatives of the lizards that you might find today in your backyard.

Mosasaurs were so completely adapted to life in the sea that their limbs had evolved into paddles. Although they breathed air, they probably never came onto the land, even to lay eggs as many sea-going reptiles, such as sea turtles, do. Mosasaurs probably gave birth to live young in the water, as other marine reptiles did.