Fossils of Allosaurus have been found in both North American and Portugal. It is in fact one of the most abundant large predators in the Morrison Formation, an area that is home to many fossils in the US.
Allosaurus hunted other big predators, but probably not the very largest. Paleontologists have found fossil evidence that it hunted Stegosaurus and other large dinosaurs.
Scientist believe that this frightening predator may have been able to run as fast as 30-55 km/h. By comparison, the fastest humans in the world can run at a speed of about 45 km/h.