Allosaurus was a big, carnivorous dinosaur, meaning that it ate meat. It was the largest carnivore in North America during the late Jurassic period. Allosaurus was about 38 feet long and 16 feet tall. It weighed about 3 tons. That’s larger than a school bus! There were lots and lots of Allosaurus during the late Jurassic period. In fact there were more Allosaurus than any other predator in North America. Allosaurus was a bipedal dinosaur. It walked on two powerful legs and had a strong, S-shaped neck. On its head were two small horns and bony ridges. It also had knobs and ridges over its eyes. It used its small arms to grab things. It had three-fingered hands with six-inch claws. It had large, powerful jaws with long, sharp, teeth. Its teeth were serrated like a saw and up to four inches long.
The name Allosaurus means “different lizard”. It got its name because of its unusual vertebrae, which are bones in its back and neck. No other dinosaur was built quite the same way. Most dinosaurs have gastralia that come out of the backbone. Gastralia are ribs that hang over a dinosaur’s belly. They are thin and fragile, but help protect a dinosaur’s insides, like its heart and lungs. In the Allosaurus, these bones were growing from the skin in its belly instead. Allosaurus was a fierce hunter and probably ate large, plant-eating dinosaurs, like Stegosaurus and Iguanodon. It may also have been a scavenger, meaning that it ate leftovers from other dinosaurs’ dinners. But it was probably not a very fast runner. Big bipedal dinosaurs were so heavy that if they fell they could really hurt themselves.
Paleontologists studying Allosaurus have found many skeletons with broken ribs and cracked shoulder bones. When we look at these bones with an X-ray, we can see that they healed soon after they were broken. This probably means that Allosaurus fell often while running: it crushed its bones under its own great weight! The first whole Allosaurus skeleton was discovered in 1883, in Colorado, North America. Over 60 Allosaurus fossils have been found in the same region. They were often found together at the same site. Because of this we believe that Allosaurus may have hunted in groups.