Plesiosaurs shared the seas with the mosasaurs during Cretaceous times. They too were reptiles descended from land-dwelling ancestors. A plesiosaur has been described as "a snake, threaded through the body of a turtle", however it did not have a shell. Unlike the mosasaur, plesiosaurs may have been surface feeders. They were not as quick and maneuverable in the water as the mosasaur because of a smaller, less muscular tail, and less flexible flippers. They propelled themselves through the water by means of their four large flippers, in a manner much like underwater flight. Like the mosasaur, they were carnivorous, air-breathing and scaly-skinned. It is likely they bore live young. Because their jaws were designed for tearing and not chewing, plesiosaurs swallowed rocks to grind their food.We call hese rocks gastroliths or stomach stones.

There are two major types of plesiosaur. One of these types is the Elasmosaurus. It had an enormous neck composed of more than 70 vertebrae. It's skull is small in comparison to the rest of its body, and it had numerous needle-sharp teeth. The elasmosaurs were specialized for rapid maneuvering by twisting and turning. Their long necks enabled them to easily feed on fish near the surface.

The Pliosaur, or short-necked plesiosaur had only 20 vertebrae in its neck and had a large head. In some forms the head may account for up to one-quarter its total length. Its large teeth were designed better for eating cephalopods of deeper waters than for eating surface fish. They were compact, streamlined creatures, built for power and sustained speed, unlike the slower Elasmosaur.

During the Jurassic Period, plesiosaurs were common. They were less numerous during the Cretaceous Period, when the mosasaurs appeared in the world's oceans. Plesiosaur remains are not found as often as mosasaurs in Manitoba.

The Canadian Fossil Discovery Centre recently acquired a new fossil display.  A fully reconstructed plesiosaur skeleton was created for the Centre by Prehistoric Animal Structures of East Coulee, Alberta, a firm that specialized in musem quality display mounts.  The specimen, a short necked plesiosaur called Trinacromerum, was excavated in 1972 and was nearly 100% complete.

The mounted skeleton is a complete reproduction of the originall fossils.  This new display was the first of its kind of the CFDC.

Click photo to enlarge.