Allosaurus fragilis was one of the first large meat-eating dinosaurs discovered and named in North America. Bones now regarded as probably Allosaurus remains were described in 1870 under the name of ’Antrodemus’. However, the first definitive bones of Allosaurus were found in Cañon City, Colorado, and described in 1877 by the eminent American paleontologist, Othniel Charles Marsh of Yale university. Since then, the fossilized remains of at least 60 Allosaurus individuals have been found and described from across the USA, including some complete skeletons.
Allosaurus is the most common theropod dinosaur in a series of rocks called the Morrison Formation. This rock formation was deposited during the Jurassic, about 150 million years ago, and is exposed in many states across the country. Allosaurus is known from the Morrison Formation of Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah and Wyoming. A slightly different species of Allosaurus has also been uncovered in Portugal, Europe, and was given the name A. europaeus in 2006.
The American species, Allosaurus fragilis lived alongside a diverse fauna of other well-known dinosaurs from the Morrison Formation, including the plated Stegosaurus, and the long-necked Apatosaurus, two plant-eating dinosaurs it may have hunted.