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Join date : 2016-10-07
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PostSubject: Allosaurus   Thu Oct 27, 2016 2:40 pm

Allosaurus



Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Infraorder: †Carnosauria
Family: †Allosauridae
Genus: †Allosaurus
Species: A. fragilis, A. europaeus, A. lucasi, A. amplus

Allosaurus (IPA: /ˌæləˈsɔɹəs/) was a large (up to 9.7 m long) bipedal carnivorous dinosaur. The name Allosaurus comes from the Greek allos/αλλος, meaning 'strange' or 'different' and saurus/σαυρος, meaning 'lizard' or 'reptile'.[1] It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery. Allosaurus was the most common large predator in the Morrison Formation of 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 may have been potential prey.

Description

Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. Its most distinctive feature was a pair of blunt horns, just above and in front of the eyes. Although short in comparison to the hindlimbs, the forelimbs were massive and bore large, eagle-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 swallowed. The skeleton of Allosaurus, like other theropods, displayed bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs.

Allosaurus fragilis had an average length of 7-9 meters (~30 feet), with the largest definitive Allosaurus specimen (AMNH 680) measuring 9.7 m (32 ft). Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera. The closely related genus Saurophaganax (OMNH 1708) reached 10.9 m (36 ft) in length, and has sometimes been included in the genus Allosaurus as Allosaurus maximus, though recent studies lend support to the idea that it does belong in a seperate genus. Another specimen, once assigned to the genus Epanterias (AMNH 5767), may have measured 12.1 m in length. Epanterias may be a species of Allosaurus or Saurophaganax.

Finds

Allosaurus is the most common theropod in the vast tract of dinosaur-bearing rock in the American Southwest known as the Morrison Formation. Remains have been recovered in Montana, Wyoming, South Dakota, Colorado, Oklahoma, New Mexico and Utah, in the United States. There have also been finds in Portugal. Allosaurus shared the Jurassic landscape with several other theropods, including Ceratosaurus and the massive Torvosaurus.


A famous fossil bed can be found in the Cleveland Lloyd Dinosaur Quarry in Utah. This fossil bed contains over 10,000 bones, mostly of Allosaurus, intermixed with the remains of other dinosaurs, such as Stegosaurus and Ceratosaurus. It is still a mystery how the remnants of so many animals can be found in one place. The ratio of fossils of carnivorous animals over fossils of plant eaters is normally very small. Findings like these can be explained by pack hunting, although this is difficult to prove. Another possibility is that the Cleveland Lloyd site formed a 'predator trap', similar to the La Brea Tar Pits, that caused large numbers of predators to become mired in an inescapable sediment.

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