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Allosaurus fragilis ( Jurassic, 140 million years) was a large theropod carnivorous dinosaur with a length of up to 12 meters. Allosaurus is a classic big theropod: a big skull on a short neck, a long tail, and reduced forelimbs. Its most distinctive feature is a pair of blunt horns just above and in front of the eyes. Although short in comparison to the hindlimbs, the forelimbs are massive and bear large, eagle-like claws. The skull shows evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be swallowed. A famous fossil bed can be found in the Cleveland Lloyd Quarry in Utah, USA. This fossil bed contains over 10,000 bones, mostly of Allosaurus, with other things like Stegosaurus and Ceratosaurus thrown in. It is still a mystery how the remnants of so many animals can be found in one place: normally the ratio of fossils of carnivorous animals over fossils of plant eaters is very small. Findings like these can be explained by pack hunting, although this is difficult to prove. Allosaurus is the most common theropod in the huge section of dinosaur-bearing rock known as the Morrison Formation. Curiously, Allosaurus shared the Jurassic landscape with several other theropods, including Ceratosaurus and the massive Torvosaurus . It is unclear how many species of Allosaurus there were. The material from the Cleveland-Lloyd Allosaurus is much smaller and more lightly built than Brigham Young Univerity's Dry Mesa huge, robust Allosaurus. Fossils resembling Allosaurus have been described from Portugal.Allosauruss closest relative is probably the Lower Cretaceous Acrocanthosaurus.
The skeleton of allosaurus and of all theropods shows birdlike features like fragile, hollow bones.
Allosaurus is the official state fossil of Utah.
Dinosaurs
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