Plesiosaurus, as found at Lyme Regis, Dorset. From Lydekker's The Royal Natural History, 1893. Plesiosaurs were large, carnivorous aquatic reptiles. They look like a turtle with a snake threaded through its body, though they lacked a shell. They first appeared in the late Triassic period and thrived until the K-T extinction at the end of the Cretaceous. Despite being large Mesozoic reptiles, they were not a type of dinosaur. It is occasionally claimed that plesiosaurs are not extinct, although the scientific evidence for this belief is disputed; the modern sightings that are occasionally reported are usually explained as basking shark carcasses or hoaxes. 固opFoto / Fortean