Ceratosaurus

ceratosaurus
Ceratosaurus (Wikimedia Commons).

Name:

Ceratosaurus (Greek for "horned lizard"); pronounced seh-RAT-oh-SORE-us

Habitat:

Swamps of southern North America

Historical Period:

Late Jurassic (150-145 million years ago)

Size and Weight:

About 15 feet long and one ton

Diet:

Meat, fish and reptiles

Distinguishing Characteristics:

Row of bony plates on back; small horns on head; sharp teeth; bipedal posture

 

About Ceratosaurus

Ceratosaurus is one of those Jurassic dinosaurs that gives paleontologists fits: although it bore a distinct resemblance to other large theropods of its day (notably Allosaurus, the most common predatory dinosaur of late Jurassic North America, and the comically short-armed Carnotaurus of South America), it also possessed some distinct anatomical quirks--such as the line of bony plates along its back and the modest "horn" on its snout--that weren't shared by any other meat-eaters.

For this reason, Ceratosaurus is usually assigned to its own infraorder, the Ceratosauria, and dinosaurs that resemble it are technically classified as "ceratosaurs." There is one generally accepted species of Ceratosaurus, C nasicornis; two other species erected in 2000, C. magnicornis and C. dentisulcatus, are more controversial.

Whatever its place in the theropod family tree, it's clear that Ceratosaurus was a fierce carnivore, gobbling up pretty much any living thing it happened across--including fish, aquatic reptiles, and both herbivorous and carnivorous dinosaurs (the marine component of its diet can be inferred from the fact that Ceratosaurus had a more flexible and crocodile-like tail than other carnivores, which presumably allowed it to swim with greater agility). Compared to the apex predators of late Jurassic North America, though, Ceratosaurus was fairly small (measuring only about 15 feet from head to tail and weighing no more than two tons), meaning it couldn't have hoped to win a standoff with a full-grown Allosaurus over, say, the carcass of a deceased Stegosaurus.

(Interestingly, many dinosaur fossils have been discovered bearing Ceratosaurus tooth marks!)

One of the most misunderstood features of Ceratosaurus is its nasal "horn," which was actually more of a rounded bump, and nothing to compare with, say, the sharp, tapered horns of Triceratops. The famous American paleontologist Othniel C. Marsh, who named this dinosaur on the basis of remains discovered in Colorado and Utah, considered the horn an offensive weapon, but the more likely explanation is that this growth was a sexually selected characteristic--that is, Ceratosaurus males with more prominent horns had precedence when mating with females.

Assuming it was thickly lined with blood vessels, the bump may even have been brightly colored during mating season, making Ceratosaurus the Jurassic equivalent of Rudolph the Red-Nosed Reindeer!