About
Ceratosaurus was a medium-sized dinosaur instantly recognizable by the prominent horn on its snout and the two smaller horns above its eyes. This striking predator roamed the floodplains and river valleys of Late Jurassic North America alongside giants like Allosaurus and the massive sauropods that made up much of the available prey. Unlike its larger contemporary Allosaurus, Ceratosaurus retained several primitive features, including a more flexible tail and a row of small bony running down its back—a trait rarely seen in large theropods.
The genus was first described in 1884 by the legendary American paleontologist Othniel Charles Marsh, based on a remarkably complete skeleton discovered in Garden Park, Colorado. This specimen, found in the famous Morrison Formation, gave scientists an unusually detailed picture of this unusual predator. The nearly complete nature of the made Ceratosaurus one of the best-understood theropods of the 19th century.
Ceratosaurus possessed a deep, narrow skull with blade-like teeth that were proportionally longer than those of Allosaurus, suggesting it may have specialized in different prey or hunting strategies. Some paleontologists have proposed it may have been more aquatic in its habits, possibly hunting fish and smaller prey near waterways, though it was certainly capable of taking larger game. Its relatively short but powerful arms bore four fingers, another primitive trait compared to the three-fingered hands of later theropods.
Despite being less common in the fossil record than Allosaurus, Ceratosaurus has been found in both North America and Europe, indicating these continents were still connected or easily traversable during the Late Jurassic. Its distinctive appearance has made it a popular subject in dinosaur media, though it often plays second fiddle to its more famous contemporaries.
Explore the anatomy
5 featuresA striking horn sat right on the snout, made of a bony core covered in keratin (the same stuff as your fingernails) — so in life it looked even bigger than the fossil shows. Scientists think it was probably for showing off or fighting rivals, since it seems too fragile to use as a weapon against prey.
Those teeth were long, flat, and serrated like steak knives — very different from the cone-shaped teeth of its neighbor Allosaurus. Some scientists think these slicing chompers were perfect for catching fish or tearing into soft-bodied prey.
A row of small, oval bony plates ran down the middle of the back — a rare feature almost no other large meat-eating dinosaurs had. These little shields are a clue that Ceratosaurus kept some ancient features that later theropods lost over time.
While most famous theropods like Allosaurus had three fingers, Ceratosaurus held onto a tiny fourth finger on each hand. This extra digit is a hint that it belonged to an older branch of the meat-eater family tree — one that split off before the line that eventually led to birds.
The tail was unusually tall and flexible, with a cross-section shaped almost like a crocodile's. Some paleontologists think this powerful tail helped Ceratosaurus swim through rivers, sweeping side to side like a giant paddle — though we can't say for sure without more evidence.
Where fossils were found
Morrison Formation
Colorado, Utah, Wyoming, Montana +6 more · United States
149.2–143.1 million years ago(6.1m year span)
Where Ceratosaurus Roamed
During the Late Jurassic, *Ceratosaurus nasicornis* roamed the semi-arid floodplains and river channels of what is now the Morrison Formation in western North America, a vast alluvial basin stretching across the ancient supercontinent Laurasia. This dynamic landscape featured seasonal wetlands, conifer-dotted savannas, and meandering rivers that supported a rich ecosystem of giant sauropods, stegosaurs, and competing theropod predators beneath warm, subtropical skies.
Keep exploring the vault
Diplodocus
Diplodocus carnegii
Ceratosaurus coexisted with Diplodocus in the Morrison Formation.
Stegosaurus
Stegosaurus stenops
Both species occur in the Morrison Formation.
Allosaurus
Allosaurus fragilis
Both large theropod predators from the Morrison Formation, competing for similar prey.
Carnotaurus
Carnotaurus sastrei
Both are ceratosaurian theropods with distinctive cranial ornamentation (nasal horn in Ceratosaurus, paired brow horns in Carnotaurus).
Brachiosaurus
Brachiosaurus altithorax
Both inhabited the Morrison Formation ecosystem.
Compsognathus
Compsognathus longipes
Ceratosaurus was a medium-sized Late Jurassic theropod predator that would have been capable of preying on small dinosaurs like Compsognathus.