Ceratosaurus was named in 1884 by the eminent American paleontologist Othniel Charles Marsh of Yale University. Marsh based his description on an almost complete skeleton from Colorado. In reference to its most distinctive feature, Marsh named it Ceratosaurus, meaning ‘horned lizard’, and gave it the species name C. nasicornis, meaning ‘ornamental nose’. Today, Ceratosaurus is known from at least five individuals, including a nearly complete mature adult skeleton and a young skeleton.
Most Ceratosaurus fossils come from the 150-million-year-old Morrison Formation in Colorado and Utah, USA. Three other species of Ceratosaurus have been named, including C. dentisulcatus, from Utah and Portugal; and C. magnicornis, from Colorado. However, some paleontologists regard these species as invalid. Instead, they suggest that these slightly different species are really variants of C. nasicornis, possibly due to changes in the skeleton that occurred as the animals matured. The third species, C. roechlingi, was described in 1925 from Tanzania, Africa, but this probably represents a different type of dinosaur related to Ceratosaurus.
Ceratosaurus’ striking nasal horn may have looked vicious, but it was compressed from side to side and was actually rather delicate. It was probably used for show, not as a weapon, and may have been colorful. Ceratosaurus is unique among theropod dinosaurs because it is the only one with rows of small bony plates preserved along its neck and back. These would have given it a grizzled appearance in life, and a very tough skin.
Ceratosaurus lived alongside the larger predator Allosaurus and therefore probably occupied a different ecological niche and had a different hunting strategy. Maybe Ceratosaurus preferred a diet of small prey.