In new research, Dr. Stephan Lautenschlager from the University of Birmingham analyzed the shape of the eye sockets in 410 specimens of dinosaurs and related species.
“The results show that only some dinosaurs had eye sockets that were elliptical or keyhole-shaped,” Dr. Lautenschlager said.
“However, all of those were large, carnivorous dinosaurs with skull lengths of 1 m (3.3 feet) or more.”
Dr. Lautenschlager compared the eye sockets of 410 fossilized specimens from the Mesozoic Era, including dinosaurs and their close relatives such as crocodiles.
The researcher found that most species, particularly herbivores, had circular eye sockets.
However, large carnivores with skulls longer than 1 m often had elliptical or keyhole-shaped eye sockets as adults, although they tended to have circular sockets as juveniles.
More ancient species tended to have more circular eye sockets than more recent species, with large theropods having more keyhole-shaped eye sockets than their ancestors.
These observations suggest that larger carnivorous species evolved keyhole-shaped eye sockets over time but that they developed this shape as adults, not juveniles.
To study the impact of eye socket shape on skull structure and function, Dr. Lautenschlager compared the forces that a theoretical model reptile skull with five different eye socket shapes was subjected to during biting simulations.
He also compared the maximum eyeball sizes that could be accommodated by model skulls of Tyrannosaurus rex with either a circular or keyhole shaped socket.
Keyhole-shaped eye sockets deformed less during biting compared to circular sockets, and helped to reduce the stress that skulls were subjected to by distributing forces along stronger parts of the skull behind the eye socket.
However, the Tyrannosaurus rex model with a circular eye socket could accommodate an eyeball with a volume seven times larger than the model with the keyhole-shaped socket.
“Evolving narrower eye sockets may have reduced the space available for eyeballs within theropod skulls while increasing the space available for jaw muscles and enhancing the robustness of their skulls,” Dr. Lautenschlager said.
“This may have helped them bite more powerfully at the expense of accommodating larger eyes, which previous research has proposed can improve visual perception.”
The research is described in a paper in the journal Communications Biology.
S. Lautenschlager. 2022. Functional and ecomorphological evolution of orbit shape in Mesozoic archosaurs is driven by body size and diet. Commun Biol 5, 754; doi: 10.1038/s42003-022-03706-0
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