Allosaurus was a large bipedal predator with a large skull, equipped with dozens of large, sharp teeth. It averaged 8.5 meters (28 ft) in length, though fragmentary remains suggest it could have reached over 12 meters (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long, heavy tail.
Allosaurus fragilis, the best-known species, had an average length of 8.5 meters (28 ft), with the largest definitive Allosaurus specimen estimated at 9.7 meters long (32 ft), and an estimated weight of 2.3 metric tons (2.5 short tons).
The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size.
Allosaurus is a genus of large theropod dinosaur that lived 155 to 145 million years ago, in the late Jurassic period in the Kimmeridgian and Tithonian, in what is now North America and Europe.