8 Facts About the Fearsome T. Rex

tan t-rex skull and neck showing bared teeth

David Monniaux / Wikimedia Commons / CC BY-SA 3.0

The Tyrannosaurus rex is undoubtedly the most famous of the dinosaurs. Having roamed present-day western North America 65 million years ago, it was feared by its contemporary creatures and future admirers alike.

But what makes the T. rex so famous? Well, it's not named "king" (rex) for nothing. As a fierce carnivore and massive specimen, it earned its figurative crown. But did you know that T. rexes had highly sensitive faces, or that they were as smart as a modern chimpanzee? Here are some facts about T. rexes that may surprise you.

1. T. Rexes Were Made for Hunting

artwork of a Tyrannosaurus rex running after smaller dinosaur with mouth open
Science Photo Library, Mark Garlick / Getty Images

T. rexes were vicious carnivores. Though the belief that they were the largest dinosaur predator has been disproven, there is no denying that they were ferocious, effective hunters. In fact, their bodies were designed for it.

At 40 feet long and 12 feet high, the T. rex had the advantage of size when going after prey. Also, their mouths were home to serrated teeth the size of bananas, though one discovered tooth was a massive 12 inches long. Perhaps most important to the T. rex was its impressive bite force, which could crunch through bone effortlessly. A 2019 study found that this ability was due largely to the rigidity of the T. rex's skull, which helped convey the full force of its giant jaw muscles into its teeth.

2. T. Rexes' Brains Helped Them Evolve

T. rexes had brain to match their brawn — twice as much, actually. This dinosaur's brain was double the size of most of its peers'. And while brain size and intelligence are only weakly correlated, its encephalization quotient — a scientific measure used to roughly compare the intelligence of different animals — indicates that T. rexes were quite smart. They were likely intellectually on par with modern chimpanzees, which is more intelligent than dogs and cats.

It was that mind, as opposed to muscle, that allowed the T. rex to evolve into the super predator we know. Fossils indicate that it was originally a tiny creature, and it may have eaten its way up the food chain by utilizing its superior wits.

3. Their Senses Were Razor-Sharp

With those big brains came highly tuned senses, including smell, hearing, and sight. T. rexes had unusually large olfactory regions for a dinosaur, meaning its sense of smell was particularly strong. This helped the creature successfully track and hunt prey at night.

T. rexes also had a keen sense of hearing. The cochlea, a part of the inner ear, was exceptionally long. This suggests an ability to pick up sounds from extremely low frequencies.

Finally, with eyes the size of oranges, the T. rex had an equally impressive sense of sight. The eyes were set high on the dinosaur's head, improving its sight for long distances. They were also placed wide apart, which enhances depth perception.

4. They Could Not Run

They may have been big and strong, but T. rexes weren't fast. Though there were once thoughts that the T. rex's large, muscled legs could help it run faster than a horse, later research suggests that this aspect of the dinosaur's unique physiology actually held it back.

According to one 2017 study, any speed beyond a walking gait "would apply greater loads to the skeleton than it would have been able to withstand." In other words, running would put so much pressure on a T. rex's legs that they would probably break.

5. T. Rexes Were Sensitive Lovers

In the face of its terrifying reputation, it's easy to overlook the T. rex's surprisingly sensual side. Scientists discovered that tyrannosaurids, the family that T. rexes belonged to, had especially sensitive areas of the face that were perforated by nerve openings; their snouts were more sensitive to touch than human fingertips.

One area where this sensitivity may have been utilized was in courtship. Researches reported that "tyrannosaurids might have rubbed their sensitive faces together as a vital part of pre-copulatory play."

6. Their Small Arms May Have Been Useful

silhouette of t-rex sculpture at sunset, showing profile with large head and small, short arms
Jacobs Stock Photography Ltd / Getty Images

Perhaps just as famous as the T. rex's powerful bite are its disproportionately small arms. They don't appear to have been useful — they may not have been long enough for the dinosaur to even touch its own face.

Scientists are still unsure of the exact reason for the tiny arms, but there are theories. One is that the arms were used more for hugging than reaching out. They may have been able to rotate their palms upward, which could mean holding prey close to its chest (and crushing it).

Another theory is that they were useful for young dinosaurs in hunting before their jaws grew strong, and they simply remained on the body as the T. rex grew to have other means of catching prey.

7. They Had Built-In Air Conditioners

Just as humans sweat, many animals have anatomical systems for maintaining body temperature — including T. rexes. The species had two large holes in the roof of its skull called dorsotemporal fenestra. These holes were long thought to hold muscles related to jaw movements, but by looking to the skull of the alligator, a comparable reptile, researchers suspect differently.

The holes, which are present in both the T. rex and alligator skulls, seem to be part of a cross-current circulatory system that contained blood vessels. They likely acted as a kind of internal thermostat to help the cold-blooded creatures warm up and cool down when necessary, based on its environment.

8. T. Rexes Were Loving Parents

Courtship wasn't the only time T. rexes utilized their sensitive noses; they also helped with parenting. T. rexes used their faces to ensure that fragile eggs were moved around gently. Meanwhile, the dinosaur's keen sense of smell helped to sniff out the ideal place for a nest to lay those carefully transported eggs.

It's possible that T. rex parents were protective of their young as well. There is a surprising lack of juveniles in the fossil record. This could mean a number of things, and one of the theories is that most young T. rexes lived long enough to reach adulthood, which would have meant parental help and guidance.