CERATOSAURUS

genus of large carnivorous dinosaurs found as fossils in Late Jurassic rocks (144 to 163 million years old) of North America. Ceratosaurus was similar to, and perhaps closely related to, Allosaurus (q.v.). Ceratosaurus, however, although weighing up to 2 tons, was slightly smaller than Allosaurus, bore a distinctive horn on its snout and a row of bony plates down the middle of its back, and had four clawed fingers rather than three.