T rex’s keyhole eye sockets helped its bite, research suggests

·3 min read
<span>Illustration: Eye Risk/Alamy</span>
Illustration: Eye Risk/Alamy

With a huge body, sharp claws, and dagger-like teeth, Tyrannosaurus rex would not have relied on looks to kill. But research suggests its eyes may have contributed to its bone-crushing bite.

A study has proposed the keyhole-shaped eye sockets of T rex may have helped to disperse stress across the skull of the fearsome predator as it chomped on its prey.

“They really had specialised eye socket shapes, which helped them deal with high bite forces,” said Dr Stephan Lautenschlager, a vertebrate palaeontologist at the University of Birmingham and author of the study.

But, he added, the benefit to skull stability may have come at a cost, noting the T rex had relatively small eyes for the size of its skull.

While Lautenschlager said that did not mean the T rex had bad eyesight, he said large eyes were associated with sharper sight.

“There’s a bit of a trade-off between better vision, larger eyes, but higher stresses in the skull because of [a circular eye socket],” he said.

Writing in the journal Communications Biology, Lautenschlager analysed the shape of the eye socket, or orbit, of 410 species that lived between 252m and 66m years ago, including dinosaurs, pterosaurs and the ancestors of crocodiles.

His results reveal that while most of the species had circular eye sockets, some had orbits that resembled a keyhole or a figure-of-eight.

“About two-thirds or three-quarters have the typical circular orbit and then the rest are deviating from that and doing something more extreme or more fancy,” said Lautenschlager.

Lautenschlager notes the keyhole or figure-of-eight orbits were generally found among meat-eaters with large skulls, in particular big carnivorous theropod dinosaurs such as Tyrannosaurus rex.

“There are a few groups within the theropods which have switched diet and adapted to a plant-eating or herbivorous diet. And those again have circular orbits,” said Lautenschlager. “So [orbit shape is] very closely linked to diet and size.”

Lautenschlager used a series of computer models to explore the ramifications of the different eye socket shapes, finding that a circular orbit is associated with greater deformation of the bones around the eye socket during biting, and that key-hole or figure-of-eight shaped orbits helped to distribute stresses across the skull so they were not concentrated at one point.

The study also proposes that circular orbits might limit the space for jaw muscles, and hence their volume, with Lautenschlager noting that could affect overall bite force.

Lautenschlager said it was likely the non-circular eye sockets and high bite forces evolved in parallel.

“Interestingly, you see that in juvenile T rex, they still have the perfectly circular or nearly circular orbits, because they didn’t produce that high bite forces presumably, or had slightly different diet, or different prey repertoire,” Lautenschlager added.

Prof Steve Brusatte, a palaeontologist and T rex expert at the University of Edinburgh, who was not involved in the work, welcomed the study.

“When you peer into the eyes of a T rex skull, the eye socket looks a little bit funny, kind of like a keyhole. And it seems small for an animal with a head the size of a bathtub,” he said.

“This innovative new study shows that the eyes of T rex were shaped not only by the need for keen vision, but also by the need to bite strongly,” said Brusatte.

“As weird as it seems, the eyes of T rex actually helped make it one of the strongest biters in Earth history.”