Plesiosaurus is a genus of swimming reptile known as a plesiosaur. Although, fossils were first known in England, they have been found all over Europe, Asia, Africa, South America, and New Zealand. Many species have been named in the genus. However, they are now classified as new plesiosaur species such as Hydrorion, and Microcleidus. It had a long neck, and a turtle shaped body. It grew about 11 ft long.