Could T. Rex Really Only See You If You Moved?

Boogeyman13, 'Hunting in a storm,' via Flickr

“Don’t move! He can’t see us if we don’t move.” An iconic scene in an iconic movie- Dr. Alan Grant saves the pair from being a T-Rex’s next meal by staying frozen still since, apparently, their vision is based on movement (let’s just forget about the fact that the dino would definitely have been able to smell them). We know it’s a film, but is there actually any truth to this? Let’s find out.

University of Oregon researcher Professor Kent Stevens began a project called “DinoMorph” in 1993 (the same year as Jurassic Park was released, funnily enough) which set out to generate digital models of various theropod dinosaurs, including the infamous Tyrannosaurus rex and Velociraptors (which, by the way, were actually much smaller than the film depicted, and had feathers). Theropods were bipedal, flesh-eating dinosaurs with short forelimbs. 

The idea of the project was to recreate the visualizations of these animals. After collaborating with other researchers in the field, Stevens was able to map the binocular fields of view and depth perceptions of the dinosaurs using scale models of their heads.

To do this, Stevens effectively turned a technique used to measure and assess visual fields, called perimetry, inside out. This novel technique, called inverse perimetry, involved the use of taxidermic eyes, a laser and a glass plate which together allowed Stevens to estimate whether a particular object would be visible at various elevations. The wider the binocular range (the area that can be viewed by both eyes at one time), the better the depth perception and ability to distinguish objects.

At the same time, he also investigated the vision of several modern relatives of the T. rex for comparison- the alligator, ostrich and eagle. The vision of these extant animals is specialized for different settings- alligators have good night vision, eagles have incredible daytime vision and ostriches are somewhere in between with some night vision and good daytime vision.

Even without this extensive investigation, the first tell-tale sign that the T. rex had good vision comes from the fact that this dinosaur had front-facing eyes set in a narrow skull. This means that there would have been an overlap in the fields of vision from the individual eyes, bestowing the animal with decent depth perception. Then there is the fact that each eyeball was around the size of a softball.

In support of the implications of these basic observations, Stevens found that the T. rex’s binocular range was 55 degrees which is actually greater than that of a hawk, which is of course renowned for its remarkable vision. Furthermore, he found that the other theropods investigated in the study also had binocular ranges similar to that of modern raptorial birds (carnivorous, predatory birds).

Further investigation revealed that the T. rex may have had visual clarity up to 13 times greater than a human! That’s pretty impressive. He even worked out that some objects could remain reasonably clear for up to 6 kilometers.

T. rex had pretty darn awesome vision, and unfortunately Dr. Grant wouldn’t have stood a chance being a mere three feet away from its nostrils. To add to this, they also had a brilliant sense of smell as indicated by the presence of a massive olfactory bulb (the brain region involved in processing smells). Oh, and those teeny tiny front limbs would have meant that if the dinosaur had fallen whilst running, it would probably have never been able to get up, so it’s very unlikely that it would have chased that car.

Header image "Hunting in a storm," by Boogeyman13, via Flickr, used in accordance with CC BY-NC-ND 2.0

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