The Tyrannosaurus Rex possessed an astounding bite force with an estimated 3,630 kilograms of force, equivalent to the weight of three small cars.

This bite force was aided in T-Rex and other large predatory dinosaurs by an intriguing evolutionary modification to the skull, in which the eye socket – called the orbital bone – became elliptical or keyhole-shaped instead of circular, according to a study released Thursday.

The study used computer simulations to show that a skull with a circular eye socket was more vulnerable to high stresses during biting, but the modified shapes seen in large carnivorous dinosaurs greatly reduced these stresses and facilitated strong bite forces without compromise the integrity of the skull.

“The skull and lower jaw must withstand large biting forces and loads during feeding,” explains paleontologist Stephan Lautenschlager, from the University of Birmingham (England), author of the research published in the journal Communications Biology.

“This can be achieved by having a stronger skull – more bone – or by channeling the stresses and deformations that occur in a way that reduces loads. This is achieved with non-circular orbits,” he added.

Lautenschlager examined the eye socket shape of 410 extinct species, including 230 dinosaurs and some of their reptilian cousins, such as the crocodilian lineage and the flying reptiles called pterosaurs. The group of theropods, bipedal creatures that included all carnivorous dinosaurs, was especially interesting.

It turned out that once a theropod species reached a skull length of a meter or more, the shape of its eye sockets became elliptical or keyhole-shaped.

This evolutionary change occurred independently in various groups of theropods around the world over time, according to the study. In their youth, large carnivores had circular eye sockets, and the shape change occurred as the animal matured into adulthood.