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Ceratosaurus, Late JurassicMorrison Formation, Colorado · named 1884
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Ceratosaurus

seh-RAT-oh-SORE-us

"horned lizard"

Lived
155 to 143 million years ago, Late Jurassic
Diet
Carnivore
Length
about 6 m (20 ft)
Group
Theropods
Found in
United States, Portugal and Tanzania
Named by
Marsh 1884

Size comparison

To scale

Where its fossils were found

The evidence

Today

26 finds

150 million years ago

Map: C. R. Scotese, PALEOMAP

Also reported from Uruguay.

Habitat

Its Morrison habitat included river floodplains with conifers, ferns and horsetails. Stegosaurus, Diplodocus and Apatosaurus lived in the same region.

Field notes

About Ceratosaurus

What it was like

Ceratosaurus was a mid-sized meat-eating dinosaur that grew to about 6 meters (20 feet) long. It is best known for a tall, blade-like horn on its snout and a smaller horn above each eye, along with deep, powerful jaws lined with long, blade-shaped teeth.

A row of small bony plates ran down the middle of its neck, back, and tail. Its arms were short but still had four clawed fingers. The snout horn was probably too fragile for fighting and more likely served as a display feature to attract mates or signal to rivals.

Its world

Ceratosaurus lived from about 155 to 143 million years ago, spanning the Late Jurassic and Early Cretaceous, in what is now the United States, Portugal, and Tanzania, with possible remains also reported from Uruguay. In the United States, fossils have been found in Colorado, Wyoming, Utah, and Oklahoma.

It shared its world with other large predators, including Torvosaurus and Allosaurus, and with plant eaters such as Stegosaurus, Brachiosaurus, and Diplodocus.

How it was found

Marsh named Ceratosaurus in 1884, based on a nearly complete skeleton. Around 26 finds are now known, though only a handful are as complete as the first. Ceratosaurus gives its name to Ceratosauria, a wider group of theropods, and its closer relatives include Genyodectes and Saltriovenator.

Field gallery

More views of Ceratosaurus

Scenes reconstructed from the available fossil evidence.

Ceratosaurus in its habitat, photo 1

1 of 7

Lived alongside

Found in the same rock formations

A rock formation can hold fossils laid down millions of years apart, so not every animal here met Ceratosaurus.

The evidence

The science behind Ceratosaurus

Which parts of the picture come from its own bones, and which come from its relatives.

From its own fossils

  • A nearly complete skeleton shows a deep skull, long blade-shaped teeth, a narrow snout horn and smaller horns above the eyes.
  • Its short hands had four fingers, with the outermost greatly reduced.
  • Small bony plates preserved with the skeleton formed a row along the middle of the back.

Borrowed from relatives

  • Most of the body is known from its own bones.
  • Lips and scaly skin are inferred by comparison with other theropods, including Carnotaurus.

Still unknown

  • Its color.
  • How the horns changed as it grew.
  • The full arrangement of its bony skin plates.

Often drawn wrong

  • The snout horn was a narrow blade, rather than a thick rhinoceros-like cone.
  • The palms faced inward, rather than downward.
  • A tall sail or several rows of large back spikes replace its small bony plates with invented structures.

Discovery timeline

  1. 1884Named itMarsh
  2. 2003Fossil sitesAntunes & Mateus
  3. 2008Family treeCarrano & Sampson
  4. 2016Full descriptionCarrano & Choiniere
  5. 2025Growing upSombathy, O'Connor & D'Emic

Key papers

The research behind what we know of Ceratosaurus

Close relatives

Other members of Ceratosauria

Sources: Wikidata