ALLOSAURUS

formerly Antrodemus, genus of large carnivorous dinosaurs found as fossils in Late Jurassic to Early Cretaceous rocks of North America, Africa, and Australia (the Jurassic Period preceded the Cretaceous Period and ended 144 million years ago). Allosaurus weighed 2 tons and grew to 10.5 m (35 feet) in length (although fossil records indicate some could have reached 12 m ), half of which consisted of a well-developed tail that probably functioned as a counterbalance for the body. Allosaurus, a biped, had very strong hind limbs and a massive pelvis with strong anteriorly and posteriorly directed projections. The forelimbs, much smaller than the hind limbs and probably used for grasping, had three fingers ending in sharp claws. The skull was very large in relation to the compact body and was lightened by the presence of several large openings. The powerful jaws had large pointed teeth and were very flexible, allowing the animal to take large bites out of its prey. It is likely that Allosaurus preyed upon the medium-sized dinosaurs, especially the ornithopod forms and their relatives. It is possible that Allosaurus was also a scavenger, feeding upon carcasses of dead or dying animals. It may have hunted in groups.