Dan Varner

The stomach stones or gastroliths found in the plesiosaurs made it possible for them to swallow their food whole, letting the gastrolith grind the food. The stones may also have served as ballast or weight for deep diving.

The skeletal remains of plesiosaurs are rare. Late Cretaceous plesiosaurs can be
classified into three main groups

    the long-necked Elasmosaurs
    the giant-headed Pliosaurs
   the short-necked Polycotylids.
Dan Varner