Life is all about compromise, and this seems to be a notion that even Tyrannosaurus rex couldn’t escape. New research has suggested that these fierce predators’ eyes shrunk as their bitey jaws got massive. Ancestors of T. rex evolving to have narrower eyes may have paved the way for later models to bite more powerfully, giving rise to the large, predatory dinosaurs we’ve come to know as theropods.
Research into the eye sockets of 410 fossilized reptile specimens led to this conclusion, which was published in the journal Communications Biology. The ancient reptiles hailed from the Mesozoic, between 252 and 66 million years ago, ending with that pesky meteor strike that saw the end of the Age of the Dinosaurs.
Gazing into their eye holes revealed to study author Dr Stephan Lautenschlager that there were certain trends among dinosaur and ancient reptile eyes. Herbivores had circular eye sockets, as did the juveniles of certain predatory species.
Adult predators, however, seemed to develop keyhole-shape eye sockets, which house the tiny eyes as we see on T. rex (which complement its tiny arms). Circular eyes were also more common in early Mesozoic species whose later ancestors were more likely to have smaller, less circular eyes.
To try and understand the driver of this ocular trend, Lautenschlager used a theoretical model to simulate what forces different eye shapes were exposed to, given jaw size. The simulations revealed that the keyhole-shaped eyes of species like T. rex deformed less under the pressure of a bite compared to the circular sockets of herbivores and earlier species.
Getting your gnashers around a plump Triceratops is only really worth it if you don’t pop your eyeballs in the process, after all. Keyhole sockets it seems were a good investment for predatory animals, but they came at a cost.
Further models looked at how different eye socket shapes could accommodate differently sized eyeballs in a T. rex skull. They showed that by switching to an ocular socket shape the skull could accommodate an eyeball seven times the size of one that slotted comfortably into the keyhole-shaped sockets.
That’s a lot of ball for your socket – but again, questionable in its value if you risk squishing your turgid sight organs every time you have a meal. While bigger eyes are believed to have equaled better vision for the animals, it's arguably a good compromise when you grow so large that even your targets are big.
It’s possible, then, that the evolution of T. rex ancestors gradually swapped out circular sockets and big eyes so that they could become more efficient carnivorous predators. Doing so gave them a more robust jaw which exerted pressure across the length of the skull so that later species could go to town on giant prey without a second thought for their ophthalmic health.
Good for them.