Ceratosaurus (Greek for "horned lizard"); pronounced seh-RAT-oh-SORE-us
Swamps of southern North America
Late Jurassic (150-145 million years ago)
Size and Weight:
About 15 feet long and 1 ton
Meat, fish and reptiles
Row of bony plates on back; small horns on head; sharp teeth
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 Jurassic North America, and the comically short-armed Carnotaurus), it also possessed some anatomical quirks--such as the line of bony plates along its back--that weren't shared by any other meat-eaters. For this reason, Ceratosaurus is usually assigned to its own infraorder, ceratosauria, and dinosaurs that resemble it are classified as "ceratosaurs."
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 part of its diet can be inferred from the fact that Ceratosaurus had a more flexible tail than other carnivores, allowing it to swim with greater agility). Compared to the apex predators of its ecosystem, though, Ceratosaurus was fairly small (only about 15 feet from head to tail and one ton), meaning it couldn't have hoped to win a standoff with a full-grown Allosaurus over, say, the carcass of a deceased Stegosaurus.
One of the most misunderstood features of Ceratosaurus is its nasal "horn," which was actually more of a rounded bump. The famous paleontologist Othniel C. Marsh, who named this dinosaur, considered the horn an offensive weapon, but the more likely explanation is that the horn was a sexually selected characteristic--that is, Ceratosaurus males with more prominent horns had precedence when mating with females. The bump may even have been brightly colored during mating season, making Ceratosaurus the Jurassic equivalent of Rudolph the red-nosed reindeer!