The feeding style of the dinosaurs and what they ate was largely influenced by their jaws and how wide they could open them. A Bristol University study shows how the carnivorous Tyrannosaurus and Allosaurus beat the herbivore Erlikosaurus.

The carnivore theropods could open their mouths wide up almost to a 90-degree angle with the Allosaurus a bit ahead in the race.

Using digital models and computer analyses, the study by Bristol's School of Earth Sciences looked at the muscle strain during jaw opening of a diverse group of two-legged dinosaurs with different dietary habits - meat-eating Allosaurus fragilis, Tyrannosaurus rex and herbivore Erlikosaurus andrewsi. The species were also compared to living relatives like crocodiles and birds for maximal jaw gape and muscle strain.

The Jurassic period Allosaurus that roamed the North American plains million of years ago could open their jaws to anywhere between 79 and 92 degrees or more than 80cm. This is consistent with the requirement of a swift ambush predator which sought large prey.

T rex which was an even bigger carnivore could manage between 63 and 80 degrees. The herbivorous Erlikosaurus was limited to a 45-degree gape. T rex however could produce sustained muscle force for various jaw angles required to bite and crush its prey.

"All muscles, including those used for closing and opening the jaw, can only stretch a certain amount before they tear. This considerably limits how wide an animal can open its jaws and therefore how and on what it can feed," said paleontologist Stephen Lautenschlager.

Tyrannosaurus boasted a large, massively built skull with dagger-like teeth. Allosaurus possessed a more slender skull and had curved, serrated teeth. Pot-bellied Erlikosaurus had a slender and narrow skull, a beak-like snout tip and leaf-shaped teeth and lived in Central Asia, writes Reuters.

Optimal and maximal jaw gapes for the three dinosaurs in the new study: Allosaurus fragilis, Tyrannosaurus rex and Erlikosaurus andrewsi Stephan Lautenschlager