In 1876, Samuel Wendell Williston in Albany County, Wyoming discovered the remains of small euornithopods. In 1878, Professor Othniel Charles Marsh named these as a new species of "Laosaurus", "Laosaurus altus". The specific name "altus", meaning "tall" in Latin, refers to it being larger than "Laosaurus celer". In 1894, Marsh made the taxon a separate genus, "Dryosaurus". The generic name is derived from the Greek δρῦς, "drys", "tree, oak", referring to a presumed forest-dwelling life mode. Later it was often assumed to have been named after an oak-leaf shape of its cheek teeth, which, however, is absent. The type species remains "Laosaurus altus", the "combinatio nova" is "Dryosaurus altus".