Science

Large dinosaur predators – like T. rex – evolved different orbital shapes to allow for more powerful bites

Illustration of Tyrannosaurus rex Dinosaur
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Illustration of Tyrannosaurus rex dinosaur

New research shows that large dinosaur predators evolved different orbital shapes to better deal with high bite forces.

According to new research, large dinosaur predators, such as tyrannosaur, developed different shapes of eye sockets to better deal with high biting forces.

While in many animals, including most dinosaurs, the eye socket is just a circular hole in the skull that houses the eyeball, this is very different in large carnivores.

A new study shows how the unusual elliptical, or oval, eye sockets found in the skulls of these predators may have evolved to help the skull absorb impact when they lunge at prey. This research by scientists at the University of Birminghamwas published today (11 August 2022) in communication biology.

Tyrannosaurus rex eye sockets

Tyrannosaurus rex skull and life reconstruction with original orbit and eye (left) and hypothetical reconstruction with circular orbit and enlarged eye (right). Credit: Dr. Stephan Lautenschlager, University of Birmingham

DR. Stephan Lautenschlager, private lecturer for paleobiology at the[{” attribute=””>University of Birmingham and author of the new study, analyzed the shape of the eye sockets of ca. 500 different dinosaurs and related species.

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

Hypothetical Dinosaur Skulls Computer Simulations

Computer simulations of hypothetical dinosaur skulls. Colors indicate skull stress. High stresses occur in the skull with a round eye socket (top), lower stresses in a skull with a keyhole-shaped eye socket (bottom). Credit: Dr. Stephan Lautenschlager, University of Birmingham

Dr. Lautenschlager tested what purpose these unusual eye socket shapes could have by using computer simulations and stress analysis.

The results demonstrated that a skull with a circular eye socket was more prone to high stresses during biting. However, if these were replaced with other eye socket shapes stresses were significantly reduced. This allowed top predators, including Tyrannosaurus rex, to evolve high bite forces without compromising skull stability.

The study also showed that most plant-eating species and juvenile individuals retained a circular eye socket. Only large carnivores adopted other morphologies, such as elliptical, keyhole-shaped, or figure-of-eight-shaped eye sockets.

Different Dinosaur Skulls

Skulls of different dinosaurs showing variation in eye socket shape (stippled outline). Credit: Dr. Stephan Lautenschlager, University of Birmingham

Dr. Lautenschlager added: “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.”

The researchers also investigated what would have happened if eye size had increased at the same rate as skull length. In such a case, the eyes of Tyrannosaurus rex would have been up to 30 cm (12 inches) in diameter and weighed nearly 20 kg (44 pounds). This is instead of an estimated 13 cm (5 inches) and 2 kg (4.4 pounds).

Reference: “Functional and ecomorphological evolution of orbit shape in mesozoic archosaurs is driven by body size and diet” by Stephan Lautenschlager, 11 August 2022, Communications Biology.
DOI: 10.1038/s42003-022-03706-0

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