Recent analyses of fossil jaw muscles of the dinosaur Allosaurus shows that the jaw could be opened at an angle between 79 and 92 degrees.
The dinosaur could, therefore, open its mouth wider than the right angle.
This can be compared to Tyrannosaurus Rex that was able to open its jaw between 64 and 80 degrees.
This means that the Allosaurus, which lived in North America some 150 million years ago and which had a head of nearly a meter (3,3 feet) long, had an 80 centimeter (2,6 feet) wide gape.
The British researchers that made the discovery says that the Allosaurus wide gape simply made it possible to eat larger prey.
Estimating cranial musculoskeletal constraints in theropod dinosaurs