Plesiosaurs were fascinating marine reptiles that lived during the time of the dinosaurs, specifically in the Mesozoic Era. They are known for their long necks, small heads, and large bodies, which made them unique among prehistoric creatures. Plesiosaurs swam gracefully in the oceans, using their four flippers to propel themselves through the water. These creatures were not dinosaurs, but they shared the same era and environment. Plesiosaurs primarily fed on fish and other marine animals, using their sharp teeth to catch prey. Their distinctive shape and size have made them popular in movies and books, often depicted as mysterious sea monsters from the past.