Plesiosaurus dolichodeirus marine reptile, fossil skull. This is the head and neck of this plesiosaur, a type of marine reptile. It dates from the Lower Jurassic, and was found in Lyme Regis, Dorset, UK. This specimen is the first articulated plesiosaur ever found, and one of the most celebrated discoveries made by Mary Anning. It is part of the collections held at the Natural History Museum, London, UK.