Pliosaurs , on the other hand, generally had a short neck and a relatively large head. The limbs were also very large and modified into well developed, paddles which were the main means of propulsion. Recent studies of plesiosaur paddles have shown that, instead of being pulled back and forth like oars on a rowboat, they were 'flapped' up and down much like the wings of a bird or the paddles of a turtle. The plesiosaur, in effect, 'flew' through the water like a modern penguin. Plesiosaurs ate fish, small ammonites and other invertebrates .
Many specimens have gastroliths or stomach stones in their abdomens.
There is still some controversy about whether or not they laid eggs, but evidence found in South Dakota and Kansas seems to point toward plesiosaurs giving live birth like ichthyosaurs and mosasaurs. It is hard to imagine a forty-foot plesiosaur struggling up on a beach to lay eggs like a sea turtle. Copyright by and used with permission of Kenneth Carpenter. Click on the thumbnails, left and right, for additional views of this skull. A 'flesh on the bones' reconstruction of the head of Styxosaurus snowii , Mike Everhart, 1999.