Dryosaurus was discovered and named by the world famous paleontologist Othniel Charles Marsh.
Living during the Late Jurassic period, Dryosaurus is one of the first Ornithopods to have evolved. Ornithopod means bird-footed dinosaur, which refers to the fact that the hind feet of this dinosaurs was very similar to those of modern birds. Many scientists today believe that birds actually evolved from dinosaurs.
Another feature that Dryosaurus had in common with modern birds was its beak. It used this beak to cut vegetation, which it then chewed using teeth located near its cheeks.
Dryosaurus had three digits, or toes, on its hind feet, and five on its much shorter front feet. Its bone structure suggests that it was a very fast runner. Using its stiff long tail as a counter-weight, Dryosaurus could have darted from side to side quickly, avoiding predators. This speed was probably its only defense against being eaten.