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Field Notes

Name Means: "Horned lizard"
Length: 20 feet (6 m)
Diet: Carnivore (Meat-Eater)
Time: Late Jurassic
Location: North America

Ceratosaurus gets its name from the blunt horn at the end of its snout. It is the best known of several theropods that had such a horn. Ceratosaurus also had two other short, thin horns, one over each eye.

We do not know for certain which function these three horns served. They may have worked as social signaling devices, allowing individual Ceratosaurus to recognize each other across the floodplains on which they lived. They may also have distinguished male and female animals, but as we have only a few specimens of this dinosaur, we do not know if the sexes had differently shaped horns. The horns do not seem large enough to have played a role in defense.

Ceratosaurus is known mainly from the late Jurassic Morrison Formation of the western United States. The Morrison Formation is famous for its incredible diversity of sauropods (including Apatosaurus and Brachiosaurus) as well as for the more common theropod Allosaurus. Teeth gathered from the Tendaguru Formation of Tanzania, which is roughly the same age as the Morrison, may represent a very large species of Ceratosaurus. This, however, has not yet been firmly established.

Throughout most of the 20th century, paleontologists grouped all large theropod dinosaurs, including Ceratosaurus, under the heading "carnosaurs." Smaller theropods were classed as "coelurosaurs." Beginning in the 1980s, however, scientists began to pay much greater attention to evolutionary relationships when classifying dinosaurs. Scientists now think that Ceratosaurus was only distantly related to most other large theropods, such as Allosaurus and Tyrannosaurus. It was probably more closely related to the smaller-bodied coelophysoids and to the Abelisauridae (including Abelisaurus) - an intriguing group that lived throughout the Southern Hemisphere during the Cretaceous period.

Ceratosaurus certainly demonstrates the danger in classifying dinosaurs solely on the basis of size, as large body size evolved numerous times within the theropods.

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