According to new research, large dinosaur predators, such as Tyrannosaurus rex, evolved different shapes of eye sockets to better deal with high bite forces.
While in many animals, including most dinosaurs, the eye socket is just a circular hole in the skull housing the eyeball, this is very different in large carnivores.
A new study reveals how the unusual elliptical, or oval eye sockets found in the skulls of these predators, could have evolved to help the skull absorb impact as they pounced on prey. This research, by scientists at the University of Birmingham, was published today (August 11, 2022) in Communications Biology.
Dr. Stephan Lautenschlager, Senior Lecturer for Palaeobiology at the 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.”
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.
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.