Ceratosaurus nasicornis was a carnivorous theropod dinosaur that lived in the Late Jurassic, approximately 161 to 146 million years ago. Ceratosaurus was a large predator, approximately 6 m long and weighing 600 kg. C. nasicornis has a very distinctive appearance, with a large head, small arms, horn-like ridges above each eye, and a nose horn. It preyed upon a variety of large dinosaurs, such as Stegosaurus, but competed with the even larger predatorAllosaurus(1). Unlike other theropod dinosaurs,C. nasicornishad an armored back, with four rows of small armor plates running down its spine (2).
Ceratosaurus nasicornis lived approximately 161 to 146 million years ago in the Late Jurassic. Specimens have been found in Colorado and Utah in the Morrison formation. During this time period, the habitat thatC. nasicornisinhabited was semiarid, with forests and floodplain prairies. There was a short wet season, but otherwise the climate was fairly dry.C. nasicorniswas a predatory dinosaur and fed on larger species, such as sauropods and stegosaurs.C. nasicorniswas not the only predator in this habitat. Allosaurus and Torvosaurus also lived in this environment and may have competed withC. nasicornisfor resources and prey (1). Though Allosaurus was the larger dinosaur,C. nasicornishad some advantages.C. nasicornishad a deep tail, similar to a crocodile. This could have been used to helpC. nasicornisswim and exploit more environments than Allosaurus (2).
Ceratosaurus nasicornis was the only species in the Ceratosaurus genus until the year 2000. There are now three Ceratosaurus species recognized, though questions have been raised on the taxonomic identity of the later two (1). Ceratosaurus magnicornis is so similar toC. nasicornisthat some paleontologists think that they are the same species (2). Ceratosaurus dentisulcatus is much larger thanC. nasicornis, but it is possible that it may simply have been an older individual, and therefore larger than previous specimens (1).
C. nasicornisand all other Ceratosaurus species are part of the Ceratosauria group. This group is defined as all dinosaurs that are more closely related to Ceratosaurus than to birds. Ceratosaurus evolved fairly early in Ceratosauria. Recent analysis has showed Ceratosaurus to be closely related to Genyodectes, another theropod dinosaur (3).
Ceratosaurus nasicornis was a carnivore. It had large bladed teeth and it probably preyed upon large dinosaurs such as sauropods and stegosaurs. Its small arms were likely ineffective as weapons. Instead,C. nasicornisattacked using its teeth, inflicting slashing bite wounds. It was an ambush predator, relying on stealth to capture prey rather than pursuit (1).
Originally, paleontologists believed that the nose horn of Ceratosaurus nasicornis was used as a weapon both in defense and offense (1). This explanation is no longer considered accurate. It is possible thatC. nasicorniscould have used its nose horn in combat among other ceratosaurs, competing for breeding rights like male deer butting heads and locking antlers (2). Others suggest that the nose horn may have only been used for display purposes. If this was the case, the horn may have been brightly colored (3).
