Dinosaur with an amazing gape
August 17, 2022 - Studies of jaw musculature of Jurassic Period meat-eating dinosaurs have revealed that Allosaurus fragilis could open its jaws wider than the king of the dinosaurs, Tyrannosaurus rex.
A. fragilis roamed North America about 150 million years ago and could crank open its jaws to an angle of 79 degrees. Its maximum jaw gape angle was more extensive than T. rex, which prowled about 66 million years ago.
However, T. rex could attack with awe-inspiring force, with the colossal carnivore’s bone-crunching bite estimated at 3.6 tonnes. By comparison, Allosaurus had a bite force of around 365kg -- the same as a modern-day lion.
This bite strength was aided in T. rex and A. fragilis by an intriguing evolutionary modification in the skull, with the eye socket, or orbital bone, becoming elliptical or keyhole-shaped rather than circular, according to a study published in Communications Biology.
The researchers found that juveniles of these big meat-eaters had circular eye sockets, with the change in shape unfolding as the animal matured into adulthood.
“Only some dinosaurs had eye sockets that were elliptical or keyhole-shaped. However, all of those were large, carnivorous dinosaurs with skull lengths of one metre or more,” said palaeontologist Dr Stephan Lautenschlager of the University of Birmingham in Britain.
“Tyrannosaurus 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.”
Lautenschlager said A. fragilis and T. rex most likely used their maximum jaw gape rarely. Their optimal gape angle was 28 degrees.
The orbital modification yielded narrower eye sockets. While this may have limited the size of the eyes, it increased the space available for jaw muscles and added to skull robustness, Lautenschlager said.
- Dinosaurs evolved different eye socket shapes to allow stronger bites (University of Birmingham)
- Functional and ecomorphological evolution of orbit shape in mesozoic archosaurs is driven by body size and diet (Communications Biology)
- Allosaurus fragilis: When Your Bark is Bigger Than Your Bite (Darwin’s Door)
- Allosaurus fragilis (Utah State University)