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.Gastralia (hanging belly ribs) are thin, fragile ribs that helped support and protect the internal organs (like the lungs) in the middle area of the body. These ribs were not attached to the backbone; they were attached to the skin in the belly area. An Apatosaurus vertebra was found with Allosaurus tooth marks etched into it, evidence of an ancient Allosaurus attack.Allosaurus was a huge carnivore, a meat eater equipped with sharp, pointed teeth in large, powerful jaws - it was the biggest meat-eater in its habitat. This theropod also had long, sharp clawed hands. Allosaurus probably ate large, plant-eating dinosaurs, like Stegosaurus.Allosaurus was a large, fierce predator that could kill medium-sized sauropods (or sick or injured large sauropods like Apatosaurus) and many others of its contemporaries. An Apatosaurus (a large sauropod) vertebra was found with Allosaurus tooth marks on it. Allosaurus may also have been a scavenger. Allosaurus may have faced competition from the meat-eating Ceratosaurus.Allosaurus may have hunted in groups. In groups, Allosaurus could ambush even the very large sauropods (like Diplodocus and Camarasaurus). It probably also preyed upon stegosaurs and iguanodonts. Allosaurus was the most abundant predator in late Jurassic North America.Allosaurus was a carnosaur, whose intelligence (as measured by its relative brain to body weight, or EQ) was high among the dinosaurs.
Allosaurus walked on two muscular legs. Allosaurus' leg length was about about 1.38 m; its stride length (distance between footprints) was about 2.72 m. Allosaurus' femur (thigh bone) was about 30 inches (77 cm) long.There has been some discussion on whether or not the massive, short-armed theropods (like T. rex, Giganotosaurus, 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).Allosaurus was the biggest meat-eater during the late Jurassic period, about 154 to 144 million years ago. 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 Portugal, Europe. Apatodon may in fact be Allosaurus.