Allosaurus is one of the most famous large carnivorous dinosaurs, occupying the top of the food chain in late Jurassic terrestrial ecosystems. Its model species, the fragile Allosaurus, was created by the great American paleontologist Osnil in the 20th century Marsh described the naming in 1877. They are also the most abundant and widely distributed predators discovered in the Late Jurassic period. Adult Allosaurus can grow up to 9 meters in length, with a few individuals believed to reach up to 12 meters. Although not as robust as the Tyrannosaurus rex, the body proportions of the Allosaurus are more symmetrical, with more developed forelimbs, making it appear more agile. The number of specimens is also much larger than that of Tyrannosaurus rex.