Allosaurus Jurassic Dinosaur


Phylum Chordata, Class Sauropsida, Superorder Dinosauria, Order Saurischia, Suborder Theropoda, Infraorder Carnosauria, Family Allosauridae

Geological Time: Upper Jurassic, Kimmeridgian and Tithonian stages (~150 m.y.a.)

Size: up to about 40 feet long

Stratigraphy: Western United States, Canada and Australia

Allosaurus skullAllosaurus was a large bipedal carnivorous dinosaur measuring up to 12 m (39 ft) long. It was named 'different lizard' because its vertebrae were different from those of all other dinosaurs. It was the most common large predator in what is now North America, 155 to 145 million years ago, in the late Jurassic period. It shared the landscape with several genera of giant sauropods such as Apatosaurus, Diplodocus and Camarasaurus, as well as other herbivores such as Stegosaurus and Camptosaurus, all of which Allosaurus may have preyed upon. The fossil remains of smaller species resembling Allosaurus and dating from the Early Cretaceous of North America, Australia and Japan supports the hypothsis that it survived the mass extinction at the end of the Jurassic, some 144 mya.

Allosaurus, a typical large theropod, sported a massive skull on a short neck, a long tail, and markedly reduced forelimbs. Its most differentiating characteristic was a pair of blunted horns just above and in front of the eyes. Although short in comparison to the hindlimbs, the forelimbs were massive and bore large, tallon-like claws. The skull showed evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be engorged. The skeleton of Allosaurus, also like other theropods, had bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs. Allosaurus is the most common theropod coming from the Morrison Formation, a huge formation in the American Southwest. Allosaurus fossils have been found in Montana, Wyoming, South Dakota, Colorado, Oklahoma, New Mexico and Utah, in the United States.

click fossil pictures to enlarge

Allosaurus fragilis

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