Allosaurus fragilis

Allosaurus is one of the best known therapods  of the Mesozoic era because of  the sheer amount of fossil material collected, mainly from the late Jurassic Morrison formation. More than ten thousand bones of Allosaurus were uncovered at the Cleveland-Lloyd quarry in central Utah, representing many individuals from different size ranges and age classes. 

It is not known why so many Allosaurs died together. Perhaps it was some sort of predator trap such as that found at Rancho La  Brea.  Packs of Allosaurs may have been drawn to dying sauropods, the bones of which are found alongside the numerous predator remains at Cleveland -Lloyd. But the number of saurapod remains was nowhere near that of the Allosaur remains, which is unusual given the normal predator to prey ratios for terrestrial vertebrate faunas: the hunters are always less numerous than the hunted.

An active and powerful predator, adult Allosaurs averaged about 30 feet in length, though they may have grown throughout their lives provided they were able to survive well into adulthood at all. Remains of huge Allosaurs such as Epanterias and Saurophaganax are known from deposits of later age than the Morrison formation. These could be distinct species or just huge examples of Allosaurus. But the fossil evidence is incomplete, especially concerning Saurophaganax, so the taxonomic affinities are still in question