Displayed at Quarry Exhibit Hall in Dinosaur National Monument, this Allosaurus fragilis skeleton is cast from bones of the Jurassic Period (149 million years ago) dug from the Cleveland-Lloyed Quarry in east-central Utah, USA. Allosaurus was the most common predatory animal in the Morrison Formation's ancient ecosystem. The theropod (meaning "beast-footed") dinosaurs are a diverse group of bipedal saurischian ("lizard-hipped") dinosaurs. Therapods include the largest carnivores ever to have walked the earth. Not all dinosaurs are extinct, since birds are actually the descendants of small nonflying theropods.