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AL - oh - SAW - rus
Name Means: "Other lizard"
Abundant remains of Allosaurus have been found in the late Jurassic Morrison Formation of the western United States. In many ways this was the quintessential large theropod. It had a deep skull and jaws filled with flattened, serrated teeth. The jaws were capable of bending outward in the middle, thus enlarging the mouth. The head was perched on a slender but strong neck. The dinosaur's forelimbs were heavily muscled and ended in powerful, three-fingered grasping hands with enormous claws. Its hind-limbs were massively constructed to support the animal's weight but were proportioned for rapid movement. Allosaurus stood on only the middle three of its five toes.
This formidable predator was probably one of the major threats to any ornithopods, stegosaurs, or sauropods that lived near it. An earlier name for Allosaurus-Antrodemus or the "nightmare dragon" -reflects its predatory dominance. Most specimens of Allosaurus are less than 26 feet (8 m) long, but some larger ones, including "Big Al," which is on display at the University of Wyoming, are close to 40 feet (12 m)- and scientists think that Big Al was still immature when it died.
Allosaurus belonged to the allosauroids, a group that peaked in the late Jurassic and early Cretaceous and was found in most parts of the world. This group includes Giganotosaurus, Carcharodontosaurus, and Sinraptor. By the late Cretaceous, however, other large theropods such as the tyrannosaurids and abelisaurids had replaced the allosauroids in most places.