WASHINGTON • You might call the Jurassic Period meat-eating dinosaur, the Allosaurus, the ultimate big mouth.
A new study analysing dinosaur jaw musculature found that this fearsome hunter that prowled North America about 150 million years ago was able to crank open its jaws between 79 and 92 degrees, wider than a right angle.
With a skull length of about 90cm, that means a jaw gape of more than 80cm, a terrifying threat to the plant-eating dinosaurs stalked by the Allosaurus, a beast more than 10m long.
Its maximum jaw gape angle was larger than that of the Tyrannosaurus rex (T. rex), an even bigger carnivore that roamed North America about 66 million years ago. The T. rex could open its jaws 63.5 to 80 degrees.
"Swift ambush predators such as Allosaurus had the largest jaw gape among the studied dinosaur species, which is consistent with the requirement for a predator hunting larger prey," said paleontologist Stephan Lautenschlager of Britain's University of Bristol.
"Tyrannosaurus, in comparison, was able to exert continuous muscle force during different gape angles, which would be necessary for an animal biting through thick flesh and crushing bones."
The study, published yesterday in the journal Royal Society Open Science, examined three species: meat-eaters Allosaurus fragilis and T. rex and herbivore Erlikosaurus andrewsi. All belong to the group of two-legged dinosaurs called theropods.
The Erlikosaurus was a strange pot-bellied dinosaur with scythe-like hand claws. It reached about 6m long and lived about 90 million years ago in Central Asia. Its maximum jaw gape reached 43.5 to 49 degrees.
Dr Lautenschlager said the Allosaurus and T. rex most likely used their maximum jaw gape only rarely, "probably only in cases when large prey had to be captured". Their optimal gape angle was 28 degrees.
The T. rex boasted a large, massively built skull with dagger-like teeth. The Allosaurus possessed a more gracile skull, with curved, serrated teeth. The Erlikosaurus had a slender and narrow skull, a beak-like snout tip and leaf-shaped teeth.