Callovosaurus (meaning "Callovian lizard") is a genus of iguanodontian dinosaur known from most of a left thigh bone discovered in Middle Jurassic-age rocks of England.

First noting its distinctiveness in a review of English hypsilophodontids,[4] he then gave the species the new genus Callovosaurus in 1980, which he placed in Camptosauridae.

[5] While considered a dubious iguanodontian in several reviews, which refer to it as "Camptosaurus" leedsi,[6][7] Jose Ignacio Ruiz-Omeñaca and coauthors have proposed that Callovosaurus is a valid genus, and the oldest known dryosaurid.

[1] Callovosaurus was found in the lower Oxford Clay, which has yielded a diverse reptile assemblage: ichthyosaurs, plesiosaurs, crocodyliforms, pterosaurs, sauropod dinosaurs, the stegosaurids Loricatosaurus and Lexovisaurus, and the armoured dinosaur Sarcolestes.

[1][8] These rocks were once thought to be somewhat younger, from the Oxfordian of the Late Jurassic, but they are now known to be middle Callovian in age.