Allosaurus, which after TRex is one of the best-known dinosaurs was a genus of large theropod dinosaur that lived 155 to 145 million years ago, in the late Jurassic period. The name Allosaurus means "different lizard" .

Allosaurus was a large bipedal predator with a large skull, equipped with dozens of large, sharp teeth.  Remains suggest it could have reached over 12 meters (39 ft).

The majority  of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania.  Some palaeontologists  believe Allosaurus may have had  cooperative social behaviour, and hunted in packs.