MOSASAUR

family of extinct aquatic lizards closely related to the present-day Oriental and African monitor lizards. They attained a high degree of adaptation to the marine environment and became distributed around the world during Cretaceous time (from 144 to 66.4 million years ago). The mosasaurs competed with other marine reptilesthe plesiosaurs and ichthyosaursfor food, which consisted largely of ammonites, fish, and cuttlefish. Many of the Late Cretaceous forms were large animals, exceeding 9 metres (30 feet) in length; but the most common ones were no larger than most of the porpoises of today. The mosasaurs had snakelike bodies with large skulls and long snouts. Fore and hind limbs were modified as paddles, having shorter limb bones and more numerous finger and toe bones than their precursors. The tail region of the body was long, and its end was slightly downcurved in a manner similar to that of the early ichthyosaurs. The backbone consisted of more than 100 vertebrae. The construction of the skull was very similar to that of the modern monitors. The jaws bore many conical, slightly recurved teeth set in individual sockets. The jawbones are noteworthy in that they were jointed near mid-length, as in some of the advanced monitors, and connected in front by ligaments only. This arrangement enabled the animals not only to open the mouth by lowering the mandible but also to extend the lower jaws sideways while feeding on large prey.