Plesiosaurus is a genus of extinct marine reptiles that lived during the Mesozoic Era, specifically the Jurassic period, approximately 201-66 million years ago. These creatures belonged to a group called plesiosaurs, characterized by their long necks, streamlined bodies, and paddle-like limbs adapted for swimming. Plesiosaurus had a relatively small head with sharp teeth and likely fed on fish and other small aquatic animals. Fossil specimens of Plesiosaurus have been found in various parts of the world, including Europe, North America, and South America. They are iconic representations of ancient marine life and have captured the imagination of scientists and the public alike.