Plesiosaurus is an extinct genus of plesiosaur that lived during the Early Jurassic. Plesiosaurus is known from its long neck, short tail, blunt body and four tail fins. Plesiosaurus swam through the shallow reefs and ate fish as it passed by. Plesiosaurus studies show that its neck could only go from side to side without breaking and that it had a tail fluke like other pliosaurs. Plesiosaurus swam by coasting around corners and using its flippers as paddles. Plesiosaurus moved each pair of flippers at the same time, but staggered the strokes (front pair up, back pair down).