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 36 feet (11 meters) long, stood about 7 feet (2 meters) high at the hips, and weighed about 2 short tons (1.8 metric tons).