Ceratosaurus also meaning 'horned lizard', has a large blade-like horn on the snout (which gives refrence to its name.), and a pair of hornlets over the eyes. The Ceartosaurus was a large predatory dinosaur from the Late Jurassic Period, found in the Morrison Formation of North America, in Tanzania and Portugal. This species of dinosaur was characterized by the large jaws with blade-like teeth, along with its horns. The forelimbs were very short yet built to be powerful. The bones of the sacrum were fused and the pelvic bones were fused together. A row of small osteoderms was present down the center of its back.

The Ceratosaurus is known to have two further species which were described in 2000. Both are more powerfully build, more derived, and appear in slightly younger rocks. It is said that the Allosaurus and the Ceratosaurus competed for prey. Although the Ceratosaurus had a longer, more flexible body, with a deep tail shaped like that of a crocodilian and was suggested to be a better swimmer then the Allosaurus. A study also suggests that sometimes adults and juveniles ate togeter. This evidence of course is very debatable. Ceratosaurus tooth marks are very common on large, terrestrial dinosaur prey fossils. Another common theory is that Ceratosaurus preyed primarily on Dryosaurus, Camptosaurus, and other ornithopoda, since it was likely a lone hunter and incapable as such of bringing down adult sauropods.