A New Theory: Was Tyrannosaurus Nocturnal?

One of the greatest debates in paleontology centers around how Tyrannosaurus acquired its food. Some believe that Tyrannosaurus was an active, albeit solitary, hunter, sneaking up on prey until it was close enough to deliver a killing blow. Others believe that Tyrannosaurus was a pack hunter, utilizing more agile juveniles to chase unsuspecting prey straight into the jaws of waiting adults. There are even those who believe Tyrannosaurus was a pure scavenger, waiting patiently for its prey to die or for other carnivores to make a kill then laying claim to the carcass.

I have never found any of these theories to be convincing. With an average length of 12 meters and weight of seven tonnes, it would have been awfully difficult for an adult Tyrannosaurus to sneak up on potential prey in the middle of day ⁽¹⁾⁽³⁾. The pack hunting idea, while progressive and my personal favourite, loses credibility when you realize that the juvenile dinosaurs have to grow up at some point, leaving the adult dinosaurs in a vulnerable state for a large chunk of their lives. Then there is the scavenger theory, which can be discarded quickly as none of nature’s top predators exclusively scavenge.

With these theories leaving me unsatisfied, I began to wonder if there was an unconsidered theory to explain Tyrannosaurus’ hunting methods. Then it struck me: what if Tyrannosaurus was nocturnal? As I will outline in this article, a nocturnal lifestyle can be inferred by a variety of traits present on both Tyrannosaurus and other animals, both in the present and the past. In fact, the ability to see in the dark may have allowed for Tyrannosaurus to outcompete other large predators of the Mesozoic, thus allowing it to become the most infamous and terrifying predatory dinosaur of all time.

Exhibit #1: What Big Eyes You Have!

It is quite possible that Tyrannosaurus had the most advanced sense of vision amongst terrestrial animals⁽²⁾. The eyes of Tyrannosaurus face forwards, allowing them to perceive objects using binocular vision. Binocular vision means that Tyrannosaurus could see in three dimensions and perceive depth on an advanced level, allowing it to judge the precise distance and motions of prey with tremendous efficiency. Advanced binocular vision is a staple of predatory birds like hawks and owls, which can spot their prey from a tremendous distance and track its movements while staying in motion. Having binocular vision coupled alongside large eyes (larger eyes means better eyesight) would have made the vision of Tyrannosaurus impeccably precise. So precise that it may have been over 13x better than ours, making any hope of avoiding predation by standing still impossible ⁽²⁾.

Did advanced vision allow Tyrannosaurus to see in the dark? Probably. By comparing the eyes of Tyrannosaurus to close relatives like ostriches and alligators, researchers have revealed that Tyrannosaurus could see in the dark with increased precision ⁽²⁾. This night-vision would have been akin to that of an owl, allowing Tyrannosaurus to spot and track the movement of potential prey despite low amounts of light ⁽²⁾. The ability to spot and track prey in the dark gives this theory substantial weight and opens the possibility of Tyrannosaurs being nocturnal.

Exhibit #2: A Prehistoric Bloodhound.

In addition to an excellent sense of vision, Tyrannosaurus also had a fantastic sense of smell. The olfactory bulbs (portion of the brain dedicated to scent) of Tyrannosaurus were highly developed and were the largest proportionate to body size amongst all dinosaurs ⁽¹⁾. A heightened sense of smell would have assisted Tyrannosaurus in locating potential prey from long distances, making both hunting and scavenging far easier. Having a strong sense of smell would be particularly beneficial at night, where distinguishing the location of potential prey and threats would become far easier. The combination of extraordinary vision and smell allowed for Tyrannosaurus to track its prey at night with ease in spite of the darkness surrounding it.

Ehibit #3: How Slow Can You Go?

Tyrannosaurus wasn’t exactly a roadrunner. To be fair, no terrestrial animal that weighs over 7 tonnes could ever hope to be; but it goes without saying that Tyrannosaurus probably couldn’t catch a jeep. While speed is hard to calculate for animals that have been dead for over 65 million years, paleontologists have put in the research regardless. By scaling-up the muscle mass of a chicken to a realistic figure, paleontologists have estimated that the max speed of Tyrannosaurus lied between 15-35 kilometres per hour (10-22 miles per hour) ⁽³⁾. While the upper speed estimates are certainly fast, they weren’t as fast as prey like Edmontosaurus or Ornithomimus. With outrunning some prey impossible, Tyrannosaurus likely used a far more efficient means of attack: ambush.

This is where nocturnality may have come in handy for Tyrannosaurus. As previously mentioned, ambushing prey during daylight may have been difficult for a predator as large as Tyrannosaurus. However, the issues posed by size are mitigated by the low visibility of night. Prey like Triceratops and Ankylosaurus probably didn’t have the best sense of vision regardless of time, making them both increasingly vulnerable to attack at night. If your prey has difficulty differentiating you from trees or shrubs, wouldn’t that be the ideal time to strike? Nocturnality would have allowed for Tyrannosaurus to ambush potential prey with increased effectiveness, allowing it to kill prey before they knew what hit them.

Exhibit #4: When in Doubt, Look at the Present!

Presently, dozens of large carnivorous species are at least partially nocturnal. A few include wolves, tigers, leopards, lions, hyenas and snakes, the majority of which are top predators in their respective ecosystems. The closest living relatives of Tyrannosaurus, the birds and the crocodiles, have nocturnal species that are predatory. With this in mind, it isn’t too far-fetched to say Tyrannosaurus was nocturnal at least on occasion. Other dinosaurs, namely Troodon and Velociraptor, have been confirmed to be nocturnal ⁽⁴⁾; so, is it really that hard to envision Tyrannosaurus as a killer of the evening?

Will we Ever Know for Certain?

While my theory is all well and good, further research is required. Paleontologists were able to determine that Velociraptor was nocturnal because its scleral ring, the bones that form the eye, was fossilized and thus could be analyzed ⁽⁴⁾. At the time of writing, I have no knowledge of a Tyrannosaurid that has been discovered with its scleral rings in place and thus, the superb night vision of Tyrannosaurus cannot be confirmed. Additionally, even if Tyrannosaurus could see in the dark it is impossible to say whether it utilized this ability to hunt; after all, it’s hard to assess sleep patterns of an animal that has been dead for 65 million years.

Works Cited:

I do not Take Credit for any Images Found in This Article.

Night’s sky courtesy of The Independent, found here

Tyrannosaurus ambush courtesy of James Gurney, found here

Tyrannosaurus stare down courtesy of Universal Pictures, found here

Sue Silhouette courtesy of The Field Museum, found here

1. Brusatte, Stephen. The Rise and Fall of the Dinosaurs: a New History of a Lost World. William Morrow, an Imprint of HarperCollins Publishers, 2019.
2. Stevens, Kent A. “Binocular Vision in Theropod Dinosaurs.” Journal of Vertebrate Paleontology, vol. 26, no. 2, 2006, pp. 321–330., doi:10.1671/0272-4634(2006)26[321:bvitd]2.0.co;2.  
3. Benton, M. J. Dinosaurs Rediscovered: the Scientific Revolution in Paleontology. Thames & Hudson, 2020.
4. Schmitz, L., and R. Motani. “Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology.” Science, vol. 332, no. 6030, 2011, pp. 705–708., doi:10.1126/science.1200043.