Allosaurus sp.
[A. amplexus, A. atrox, A. ferox, A. fragilis, A. lucaris, A. medius, A. sibiricus, A. tendagurensis]



Genus Name: Allosaurus
Meaning: Different lizard
Named by: O. Marsh, 1883
Length: 38 ft (12 m)
Diet: Meat
Walk: Bipedal
Time: Late Jurassic, 154-144 million years ago
Location: W. North America, Australia
Classification: Theropod                   

Allosaurus was named in 1877 by paleontologist Othniel C. Marsh. The first virtually complete Allosaurus skeleton was discovered by rancher M. P. Felch in 1883, in Colorado, USA.

Over 60 Allosaurus fossils have been found, mostly in the Morrisson Formation in Colorado, USA, but also in other locations in western North America and one possible find in Australia. Allosaurus fossils may have also been found in Africa and Austrialia.  Apatodon may in fact be Allosaurus.

Allosaurus could kill medium-sized sauropods (or sick or injured large sauropods like Apatosaurus) and many others of its contemporaries. An Apatosaurus vertebra was found with Allosaurus tooth marks on it. Allosaurus may also have been a scavenger. Allosaurus was a powerful predator that walked on two powerful legs, had a strong, S-shaped neck, and had vertebrae that were different from those of other dinosaurs (hence its name, the "different lizard"). It had a massive tail, a bulky body, and heavy bones. Its arms were short and had three-fingered hands with sharp claws that were up to 6 inches (15 cm) long.

Allosaurus was up to 38 feet long (12 m) and 16.5 feet tall (5 m). It weighed about 1400 kg. It had a 3 feet long (90 cm) skull with two short brow-horns and bony knobs and ridges above its eyes and on the top of the head. It had large, powerful jaws with long, sharp, serrated teeth 2 to 4 inches (5 to 10 cm) long. The different species of Allosaurus varied in weight. Allosaurus fragilis, A. atrox, and A. ferox weighed about 1.1 to 1.9 tons (1 tonne to 1.7 tonnes); A. amplexus was much heavier and weighed about 2.7 to 5.5 tons (3 tonnes to 5 tonnes).

There has been some discussion on whether or not the massive, short-armed theropods (like T.rex, Gigantosuarus, Albertosaurus, and Allosaurus) could run very fast because if they fell, their short arms would not break their fall and they would be badly injured (James Farlow, 1995). This meant that these large theropods were slow, lumbering animals.  Dr. Bruce Rothschild, of the Arthritis Center of Northeast Ohio, has found evidence of 14 fractured ribs in an Allosaurus that reflect healed injuries that were probably received in falls. These were most likely bellyflops that happened while running (as reported in the April 16, 1998, New Scientist). An X-ray analysis of the Allosaurus fossil indicated that the Allosaurus ribs near the scapula (the shoulder bone) were cracked and had healed. The Allosaurus was capable of recovering after many severe forward tumbles that probably occurred while it was running. So the suggestion that perhaps the large short-armed theropods were not capable of running because they couldn't recover after a fall apparently wasn't so, at least for Allosaurus - this Allosaurus did recover many times after bad tumbles.

Allosaurus was very common and the biggest meat-eater in North America during the late Jurrassic period (about 154 to 144 million years ago). It may have faced competition from the meat-eating Ceratosaurus.