Allosaurus fragilis (Jurassic, 140 million years) was a large theropod with a length of up to 12 meters, and can be recognized by sharp claws on hands and feet and sharp, serrated teeth. The skull shows evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be swallowed. A famous fossil bed can be found in the Cleveland Lloyd Quarry in Utah. This fossil bed contains over 10.000 bones of mostly allosaurus. It is still a mystery how the remnants of so many allosaures can be found in one place, because normally the ratio of fossils of carnivorous animals over fossils of plant eaters is very small. Findings like these can be explained by pack hunting, although this is difficult to prove.
The skeleton of allosaurus and of all theropods shows birdlike features like fragile, hollow bones.