Plesiosaurus was a large marine sauroptergyian reptile that lived in the Jurassic Period. Distinguished by a small head, long slender neck, and two pairs of large paddles (fins). Plesiosaurs ate Belemnites (squid-like creatures) and fish. These predators gave live birth in open water. Roughly twice the size of a grown man, half their length was neck! Check out our teeth selection, which changes with new items found in our travels.