Allosaurus (meaning "different lizard") is an extinct genus of large theropod dinosaur from Europe and North America. Allosaurus was one of the most common predators of the Late Jurassic period and among the most dangerous. Like most theropod dinosaurs, its jaws were filled with sharp serrated teeth shaped like blades. Computer studies suggest that Allosaurus attacked by using its upper jaw like a machete to hack at its victim, then it used its lower jaw to bite out a slice of meat, although recent studies have proven this unlikely. In terms of size, it was the second-largest theropod of its era; only the likes of the megalosaurid Torvosaurus (10-11 meters or 33-36 feet with 4-5 tons of weight behind it). It averaged around 8.5 meters long (28 feet) and around 3 meters (10 feet) tall. However fragmentary remains suggest larger lengths of 11 to 12 meters (36-39 feet). Allosaurs top speed is estimated at 19 to 34 mph. It is thought that when hunting in groups they lacked "pack" cohesion. Fossils discovered are often riddled with broken bones, that later healed.