Unlike many herbivores of its time, Dryosaurus altus was not very large. Standing four feet high at the hips and growing up to 11 feet in length, Dryosaurus may have weighed only 200 pounds. But this bipedal dinosaur was fast. It had long, powerful hind legs that carried it through the Late Jurassic wilderness, providing its primary defense against predators.
With a name that means “tall oak tree lizard,” Dryosaurus had short front limbs and a long tail that may have been used as a counterbalance. It had a beak for cropping vegetation and was most likely an efficient chewer, with strong teeth and a hinged jaw. This hinge allowed the herbivore to slide its upper and lower jaws past one another as it chewed, an unusually advanced feeding adaptation for this time period.
One of the oldest known members of the dinosaur group Ornithopoda, Dryosaurus fossils have been found in the western United States and possibly eastern Africa (though some paleontologists think the African fossils belong instead to a close relative called Dysalotosaurus). The specimen on display at Carnegie Museum of Natural History was discovered in 1910 by Earl Douglass and his field crew in the Morrison Formation at what is now Dinosaur National Monument in Utah.