Allosaurus grew from 30–35 feet, with large specimens growing to 39 feet—roughly the same size as some large Tyrannosaurus—with a skull 3 feet in length filled with dozens of sharp, serrated teeth. It was a "typical" theropod dinosaur, bipedal with strong, long legs and a long thick tail. It's arms were long, though short in proportion to its legs and powerful, ending in three clawed fingers. It also had three primary toes, with a fourth vestigial "dewclaw". It also possessed a pair of horns above the eyes, varying in size between individual Allosaurus. The horns were extensions of the skull covered by keratin to protect the bone and blood vessels. Their function is believed to be used for combat between individual Allosaurus or as sunglasses to protect eyes from sunlight.