The Allosaurus was a gigantic, carnivorous hunter over twelve metres tall. It walked on its hind limbs, had long, sharp saw-like teeth and two horns above its eyes. Standing more than five metres high and weighing more than a tonne, the Allosaurus was the largest carnivore of its time. It had a unique skeleton. Instead of having ribs that were attached to other bones in its body, this dinosaur had ribs that were attached to its skin. The bones in its back were bulky and heavy. Although it had short arms, its front feet were armed with sharp claws which it could use to catch its victims. The Allosaurus often hunted in groups, which made it easier to catch its prey. The Allosaurus was an intelligent, aggressive predator with a lifespan of up to twenty years.