Cryptosaurus

Cryptosaurus (meaning "hidden lizard") is a dubious genus of dinosaur known from a partial femur from the Late Jurassic of England. The sole species is Cryptosaurus eumerus.
The femur was found by the geologist Lucas Ewbank and donated by him to the Woodwardian Museum at Cambridge in 1869. "Cryptosaurus" was the same year named by British paleontologist Harry Seeley; the type species is "Cryptosaurus eumerus". The genus name is derived from Greek "kryptos", "hidden", a reference to the rarity of the find. The specific name means "well-formed thigh" in Greek, a reference to the stout build of the bone. The description of 1869, part of a catalogue of the Cambridge University collection, was rather minimal, consisting of the single sentence "On Shelf g is temporarily placed the femur of a Dinosaur from the Oxford Clay, Cryptosaurus eumerus". From this it is sometimes concluded that the name remained a "nomen nudum" until a full description by Seeley in 1875.
The holotype, CAMSM J.46882, was discovered in the "Great Gransden brick pit", in strata of the Ampthill Clay Formation (Oxford Clay), dating from the upper Oxfordian. The right femur is about 33 centimetres long and has a thick shaft. It belonged to an adult or at least subadult individual, meaning that the species was rather small.
Seeley thought that "Cryptosaurus" was a relative of "Iguanodon", the first such discovered from the Oxford Clay — hence the generic name. Friedrich von Huene classified it in the Camptosauridae in 1909. The work of Peter Galton however, showed that "Cryptosaurus" is an ankylosaurian of unknown affinities. Today it is commonly considered to be a "nomen dubium" because of the limited remains.
"Cryptosaurus" was for a long time known as Cryptodraco, which is an unnecessary replacement name. In 1889, Richard Lydekker renamed "Cryptosaurus" as he believed the name "Cryptosaurus" was already previously in use for another animal ("Cystosaurus" Geoffroy, described in 1832). This was in error, a mistake originally caused by a wrong spelling of "Cystosaurus" in the French "Bibliothèque universelle des sciences, belles-lettres, et arts", and the name "Cryptosaurus" has precedence.