MOSASAURIA, an order of marine reptiles of the Upper Cretaceous Period, typical of the reptilian subclass Pythonomorpha. They were of world-wide distribution and their remains occur so plentifully in the western United States as well as in the Old World that their structure is thoroughly known. They were large predaceous marine lizards, resembling the modern monitors in many features, but reach ing in many species the size of crocodiles larger in some cases, but no skeletons are known indicating a greater length than 45 feet. They had four limbs with all the bones well developed but enclosed in a mitten of flesh and skin, forming paddles, which, with their great tails, must have made them powerful and agile swimmers. "Their cup-and-ball vertebra indi cate great flexibility of the body, their sharp teeth denote ability to capture slippery prey, and the structure of the lower jaw shows that they probably ate in a hurry and swallowed their food entire. . . . In the mosasaurs, as in the cormorants, among birds, there is a sort of joint in each half of the lower jaw, which i permits it to bow outward when open; . . .
if the reader will extend his arms at full length, the palms touching, and then bend his elbows outward, he will get a very good idea of the action of a mosasaur's jaws— Lucas. The mosasaurs were of three types, namely, Tylo murmur, resembling gavials, with a long slender beak or exension of the snout beyond the teeth, and long paddles strengthened with numerous phalanges; Platecarpinee, short headed, very long-tailed reptiles, including Platecarpus, Prognathosaurus, Brochysourns and some other genera; and Mosasaurince. The last were the typical mosasaurs, apparently the most completely marine and powerful and per fected of the race. The two genera are Mosasaurus and Clidases. None survived the close of the Cretaceous. Consult Zittell-East man,