Allosaurus << `al` uh SAWR uhs >> was a large, meat-eating dinosaur that lived about 150 million years ago. Allosaurus lived in what is now the western United States, including Colorado, Utah, and Wyoming. It grew about 30 feet (9 meters) long, stood about 7 feet (2 meters) high at the hips, and weighed about 2 short tons (1.8 metric tons).
The head of Allosaurus was 3 feet (0.9 meter) long. Its jaws had about 70 teeth, each 3 inches (8 centimeters) long with jagged edges for slicing flesh. Holes in the skull lightened the weight of the dinosaur’s large head. A pair of distinctive low, bony bumps rose in front of the eyes. The short front legs had three strong, curved claws on each hand. The hind feet were birdlike, with three toes pointing forward and a small inner toe pointing backward. Allosaurus walked on two legs with its body parallel to the ground and held its long tail out behind for balance. The animal could rear up to a height of 12 feet (3.7 meters) or more.
Allosaurus preyed on other dinosaurs. Unlike other meat-eating dinosaurs, such as Ceratosaurus, that lived at the same time, Allosaurus had powerful arms and hands with large claws. These would have allowed it to use its arms while attacking prey. Many dinosaurs, including Apatosaurus, Diplodocus, and Stegosaurus, were much larger than Allosaurus. It may have attacked only the weaker ones, such as the young or the sick. It may also have eaten dinosaurs that had already died.
Fossilized bones of Allosaurus were first discovered in 1869 in Colorado. The dinosaur was initially given the name Antrodemus by scientists. The American paleontologist Othniel Charles Marsh examined the fossils and published a description in 1877. He gave this dinosaur the name Allosaurus. The names come from the Greek words meaning “different lizard.” Utah designated Allosaurus as the official state fossil in 1988.
