mosasauria

from The Century Dictionary.

• noun A group of remarkably long-bodied marine reptiles, from the Cretaceous rocks of Europe and America.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (Paleon.) An order of large, extinct, marine reptiles, found in the Cretaceous rocks, especially in America. They were serpentlike in form and in having loosely articulated and dilatable jaws, with large recurved teeth, but they had paddlelike feet. Some of them were over fifty feet long. They are, essentially, fossil sea serpents with paddles. Called also Pythonomarpha, and Mosasauria.