Large dinosaurs had keyhole-shaped eye sockets for stronger bites - study

Dinosaurs like the Tyrannosaurus rex (T-rex) possess strange keyhole-shaped eye sockets. This study suggests that the shape let it develop such a powerful bite.

 The skull of the dinosaur Tyrannosaurus rex (T-rex). These predators had incredible eyesight but a strange keyhole-shaped eye socket (Illustrative). (photo credit: PIXABAY)
The skull of the dinosaur Tyrannosaurus rex (T-rex). These predators had incredible eyesight but a strange keyhole-shaped eye socket (Illustrative).
(photo credit: PIXABAY)

Many large carnivorous dinosaurs, such as the Tyrannosaurus rex (T-rex), were able to take such powerful bites out of their prey thanks to the development of a different type of eye socket, according to a recent study.

The findings shed light on the reason for the strange shape of large predatory dinosaur eye sockets.

The study was published in the peer-reviewed academic journal Communications Biology.

"Don't move. Its eyesight is based on movement."

Jurassic Park, falsely claiming T-rexes had poor eyesight

Dinosaurs and vision: T-rex eyesight was not based on movement

The eye sockets on some dinosaurs like the T-rex are shaped rather curiously. Unlike other eyes, which usually have a more circular shape, these eye sockets were elliptical, resembling something more akin to a keyhole or a figure eight.

 The T-rex dinosaur is seen in a prehistoric jungle in this artistic illustration. (credit: PIXABAY) The T-rex dinosaur is seen in a prehistoric jungle in this artistic illustration. (credit: PIXABAY)

Now, this is strange for a number of reasons.

A circular-shaped eye socket is something that is often assumed by scientists because its shape would usually match the shape and size of the eyeball itself.

In addition, the size of the eye also usually has some degree of correlation to the size of the head itself.

But this is where things get weird. After all, take a look at the eye socket of a T-rex. It's very small, considering the massive size of its head. 

But despite this, there is also the role of vision to consider.

Now, despite the famous line in Jurassic Park that a T-rex's "eyesight is based on movement," which implies poor vision, this is actually very false. In fact, T-rexes had excellent vision, being very sharp and likely able to gauge distances of prey.

Overall, despite scientists noting that it likely moved at a speed comparable to human walking speed, it is estimated that a T-rex's powerful eyesight was actually superior to that of modern-day hawks.

Having said that, this shape of eye socket poses its own problems. By not matching the size and shape of the eyeball, the T-rex's eyes would have less room, posing its own limitations. 

So why are its eye sockets in this strange shape? What purpose did this keyhole-shaped eye socket serve?

Dinosaurs need stronger eyes for stronger bites

Well, that is what this study, authored solely by the University of Birmingham's Dr. Stephan Lautenschlager, sought to answer. And it turns out, the reason may not have so much to do with the strength of eyesight as much as the strength of its biting.

Lautenschlager analyzed the shape of eye sockets of hundreds of different dinosaurs and other animals. Through this, he made computer simulations and stress tests to try and figure out its utility and what reason this eye socket shape could have formed. And the answer seems to be biting. 

Circular eye sockets were still very common among dinosaurs. Specifically, they could still be seen among herbivores or smaller carnivores - including younger T-rexes.

The difference between the herbivores and smaller carnivores with the larger carnivorous dinosaurs seems to be the need for bite force. These larger predators would need an incredibly powerful bite, but this can come with consequences for the eyes.

As Lautenschlager discovered, these circular-shaped eye sockets may have a link to the surrounding bones being deformed during biting due to stress. And with a powerful bite like a T-rex's, that stress would be much stronger. And for a large predator who might rely on senses like eyesight to hunt prey, protecting one's eyes was of the utmost importance.

But this keyhole-shaped eye socket seemed to be much better for this, with the shape keeping the stress from being focused on a single area and causing harm, rather dissipating it throughout the skull itself.

But that isn't the only benefit that this shape of eye socket might have had.

Specifically, Lautenschlager noted that circular eye sockets might take up too much space in the skull, limiting the amount of room for jaw muscles. This, in turn, would certainly reflect on how strong the force of the bite would be.

So in other words, this eye socket serves to both allow for a stronger bite and to absorb the stress of these bites.

In addition, it also may have been cost-efficient. The amount of energy and resources that would have been needed for circular eye sockets would have a high cost, as the T-rex would require some 700% more eye volume in order to have complete circular orbit. Evolving the eyeballs and eye sockets needed just simply wouldn't have been worth it.

As for how all of this happened, it is likely that both the bite strength and the eye socket shape likely evolved in tandem. In turn, this combination is what led to dinosaurs like the T-rex having such a powerful bite.