Ceratosaurus was a predatory dinosaur from the Upper Jurassic period, 156 to 145 million years ago.
It was first described by O.C. Marsh in 1884. It had a horn on its nose, and a pair of small horns above its eyes. Unusually, for a theropod, Ceratosaurus had armour: small osteoderms ran down the middle of its back.
The animal had deep jaws and long blade-like teeth. A nearly complete skeleton was discovered in Garden Park, Colorado, in rocks belonging to the Morrison Formation.
Other examples or close relatives have since been found.