Definition
A plesiosaur is a type of long-necked marine reptile that lived during the Mesozoic Era. Imagine a sea monster with a turtle-like body, paddle-like limbs, and an incredibly long neck. Plesiosaurs were well-adapted to swimming and hunting in the oceans. They used their long necks to ambush prey from a distance. Some plesiosaurs had small heads, while others had larger, crocodile-like heads. Plesiosaurs were formidable predators in their time.