To prove their point they scaled up a chicken to the size of T. rex and found the giant chicken probably would not have been able to stand.

Researchers now believe that tyrannosaurs spent almost all of their time on Earth as small, flighty predators like Raptorex.

But in the past year half a dozen new tyrannosaur species have been described, and during the past decade the known diversity of tyrannosaurs has more than doubled.

They now believe super-carnivores, such as tyrannosaurus rex and velociraptor - the two stars of the Jurassic Park movies - were the exception rather than the rule.

Deeper—or shorter—snouts may have evolved in concert with a more powerful bite and smaller forearms in tyrannosauroids in western North America and Asia, which were connected during the Cretaceous.