Dryosaurus ("Oak Lizard") is a genus of ornithopod dinosaur which lived during the late Jurassic period (160-140 MYA) in what is now North America and Africa.
Dryosaurus lived during the Middle to Late Jurassic Period from 176-145 million years ago. Dryosaurus was first discovered by Samuel Wendell Williston in 1876.
Dryosaurus stood 5 feet tall, measured 10-14 feet long, and weighed 170-200 pounds, a rather large member of its family in comparison with the average sized species that is related to it.
Dryosaurus also had a horny beak and cheek teeth as well as a long neck, long, slender legs and a long, stiff tail. A quick and agile runner with strong legs, Dryosaurus used its stiff tail as a counterbalance. Its arms, however, with five fingers on each hand, were short.
Like many dinosaurs, especially one like them such as Othnielia and Leaellynasaura, Dryosaurus lived in huge groups in both open lands and forests. Whenever the herd was feeding, one adult, the Sentry, kept watch.
It was still a small, swift herbivorous dinosaur under the threat of predation at all time, and so its main defence, was to simply outrun its attackers with bolts of lightening fast speed. A slightly larger relative of Othnielia, Dryosaurus relied on lightning fast speed to survive. Even large predators like Allosaurus could not possibly run down such swift prey like these.