Large meat-eating dinosaurs like T Rex traded big eyes for stronger bite, study suggests

Large predatory dinosaurs like the mighty Tyrannosaurus rex developed different eye socket shapes to deal with higher bite forces, according to a new study.

While the eye socket is just a circular hole in the skull housing the eyeball in many animals, scientists, including those from the University of Birmingham in the UK, say this is very different in large carnivores, including dinosaur predators like the T rex.

The new research, published on Thursday in the journal Communications Biology, suggests that the unusual elliptical or oval eye sockets found in the skulls of these dinosaur predators could have evolved to help the skull absorb impact as they pounced on prey.

In the study, scientists, including Stephan Lautenschlager from the University of Birmingham, looked at the shape of the eye sockets of over 400 different dinosaurs and closely-related species like crocodiles.

They used computer simulations and stress analysis to test what purpose these unusual eye socket shapes could have served.

Based on the analysis, researchers say while a skull with a circular eye socket was more prone to high stress during biting, if these were replaced with other eye socket shapes, stress was considerably reduced.

Such different eye socket shapes allowed top predators like the Tyrannosaurus rex to evolve high bite forces without compromising skull stability, scientists suspect.

Researchers also found that most plant-eating species and juvenile individuals retained a circular eye socket. Only large predator dinosaurs adopted other shapes like elliptical, keyhole-shaped, or figure-of-eight-shaped eye sockets.

“The results show that only some dinosaurs had eye sockets that were elliptical or keyhole-shaped. However, all of those were large, carnivorous dinosaurs with skull lengths of 1m (3.3 ft) or more,” Dr Lautenschlager said in a statement.

“In these species, just the upper part of the eye socket was actually occupied by the eyeball. This also led to a relative reduction of eye size compared with skull size,” he added.

Researchers suspect evolving narrower eye sockets may have reduced the space available for eyeballs within these large dinosaur skulls while increasing the space available for jaw muscles and “enhancing the robustness of their skulls.”

They say this adaptation may have helped them bite more powerfully at the expense of accommodating larger eyes.

Scientists also analysed what would have happened if the eye size had increased at the same rate as skull length.

In such a case, they say the eyes of Tyrannosaurus rex would have been up to 30cm in diameter and weighed nearly 20kg.