Cryptosaurus (meaning "hidden lizard") is a dubious genus of dinosaur known from a partial femur from the Late Jurassic of England. Cryptosaurus was named by British paleontologist Harry Seeley in 1869; the type species is Cryptosaurus eumerus. Cryptosaurus is considered today to be an ankylosaurian of unknown affinities.
Cryptosaurus is sometimes 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 1833). This was in error, and the name Cryptosaurus has precedence.