Any of a group of large carnivorous dinosaurs that included Allosaurus and other related dinosaurs. Carnosaurs were one subgroup of the large, bipedal, flesh-eating theropod dinosaurs. (Another theropod group was the ceolurosaurs, which included the tyrannosaurs.) Carnosaurs were massive animals with short necks, large skulls, and wide, gaping mouths equipped with formidable teeth. Like all theropods, they walked on two legs. The carnosaurs seem to have appeared in the late Jurassic Period (about 150 million years ago) and become extinct at the end of the Cretaceous Period (65 million years ago).