10 Facts About Tyrannosaurus Rex

How Much Do You Know About This King of the Dinosaurs?

Tyrannosaurus rex is by far the most popular dinosaur, having spawned a huge number of books, movies, TV shows, and video games. What's truly amazing, though, is how much what was once assumed as fact about this carnivore has later been called into question and how much is still being discovered. Here are 10 facts known to be true:

01
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Not the Biggest Meat-Eating Dinosaur

An artist rendering of a <i>T-rex</i> showing a mouthful of teeth
An artist rending of a T-rex. The largest one named Scotty was discovered in Canada's Badlands. It's on display at the Royal Saskatchewan Museum in Canada. SCIEPRO / Getty Images

Most people assume that the North American Tyrannosaurus rex—at 40 feet from head to tail and seven to nine tons—was the biggest carnivorous dinosaur that ever lived. T. rex, however, was equaled or outclassed by not one but two dinosaurs: the South American Giganotosaurus, which weighed about nine tons, and the northern African Spinosaurus, which tipped the scales at 10 tons. These three theropods never had the chance to square off in combat, since they lived in different times and places, separated by millions of years and thousands of miles.

02
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Arms Not as Tiny as Once Thought

<i>Tyrannosaurus rex</i> and a comet
Some think that the small arms of T. rex were the right size for holding prey near their jaws.

Mark Garlick / Science Photo Library / Getty Images

One feature of Tyrannosaurus rex that everyone makes fun of is its arms, which seem disproportionately tiny compared to the rest of its massive body. T. rex's arms were over three feet long, however, and may have been capable of bench pressing 400 pounds each. In any event, T. rex didn't have the smallest arm-to-body ratio among carnivorous dinosaurs; that was the Carnotaurus, whose arms looked like tiny nubs. 

03
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Very Bad Breath

<i>Tyrannosaurs rex</i> skeleton partially covered in a white powdery sand
What is known about the four-foot jaws and mouth of Tyrannosaurus rex is it contained about 60 serrated teeth (some 12 inches long) ready for tearing meat—and its breath was most likely horrendous.

Mark Garlick / Science Photo Library / Getty Images

The dinosaurs of the Mesozoic Era obviously didn't brush their teeth or floss. Some experts think shards of rotten, bacteria-infested meat constantly lodged in its closely packed teeth gave Tyrannosaurus rex a "septic bite," which infected and eventually killed its wounded prey. This process likely would have taken days or weeks, by which time some other meat-eating dinosaur would have reaped the rewards.

04
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Females Bigger Than Males

An illustration of a <i>Tyrannosaurus rex</i> dinosaur and other prehistoric creatures around a watering hole
Scientists have trouble distinguishing whether a T-rex individual was male or female.

Roger Harris / SPL / Getty Images

There's a good reason to believe, based on fossils and the shapes of the hips, that the female T. rex outweighed the male by a few thousand pounds. The likely reason for this trait, known as sexual dimorphism, is that females had to lay clutches of T. rex-size eggs and were blessed by evolution with bigger hips. Or maybe females were more accomplished hunters than males, as is the case with modern female lions.

05
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Lived About 30 Years

Silhouette of a dinosaur sculpture at sunset in Moab, Utah
It’s believed that some dinosaurs lived to about 150 years old, while the life span of Tyrannosaurus rex was about 30 years. Dave and Les Jacobs / Getty Images

It's difficult to infer a dinosaur's life span from its fossils, but based on analysis of existing specimens, paleontologists speculate that Tyrannosaurus rex may have lived as long as 30 years. Because this dinosaur was atop the food chain, it would most likely have died from old age, disease, or hunger rather than attacks by fellow theropods, except when it was young and vulnerable. Some of the 50-ton titanosaurs that lived alongside T. rex might have had life spans of more than 100 years.

06
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Both Hunters and Scavengers

Artwork of a <i>Tyrannosaurus rex</i> hunting in the desert
Tyrannosaurus rex may have been both a hunter and scavenger.

Mark Garlick / Science Photo Library / Getty Images

For years, paleontologists argued about whether T. rex was a savage killer or an opportunistic scavenger—that is, did it hunt its food or tuck into the carcasses of dinosaurs already felled by old age or disease? Current thinking is that there's no reason Tyrannosaurus rex couldn't have done both, as would any carnivore that wanted to avoid starvation.

07
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Hatchlings Possibly Covered in Feathers

<i>Tyrannosaurus rex</i> dinosaur prowling in a marsh
An artist's rendering of an adult Tyrannosaurus rex. The hatchlings were much different—about the size of a turkey and thought to be covered in feathers.

AC Productions / Getty Images

It's accepted as fact that dinosaurs evolved into birds and that some carnivorous dinosaurs (especially raptors) were covered in feathers. Some paleontologists believe that all tyrannosaurs, including T. rex, were covered in feathers at some point during their lives, most likely when they hatched, a conclusion supported by the discovery of feathered Asian tyrannosaurs such as Dilong and the almost T. rex-size Yutyrannus.

08
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Preyed on Triceratops

A model of a <Tyrannosaurus rex</i> skull with open jaws
The debate continues on T. rex's diet, but many think that Triceratops was on the menu.

Leonello Calvetti / Science Photo Library / Getty Images

Imagine the matchup: a hungry, eight-ton Tyrannosaurus rex taking on a five-ton Triceratops, a not-inconceivable proposition since both dinosaurs lived in late Cretaceous North America. Granted, the average T. rex would have preferred to tackle a sick, juvenile, or newly hatched Triceratops, but if it was hungry enough, all bets were off.

09
of 10

Incredibly Powerful Bite

In a dark forest setting, a model of a <i>Tyrannosaurus rex</i> shows off its bright white teeth
Scientists continue to debate the amount of power T. rex had in its bite.

Roger Harris / Science Photo Library / Getty Images

In 1996, a team of Stanford University scientists examining a T. rex skull determined that it chomped on its prey with a force of 1,500 to 3,000 pounds per square inch, comparable to that of a modern alligator. More recent studies put that figure in the 5,000-pound range. (The average adult human can bite with a force of about 175 pounds.) T. rex's powerful jaws may have been capable of shearing off a ceratopsian's horns.

10
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Tyrant Lizard King

An artist's rending of a <i>T. rex< /i>
Paleontologists take into consideration the shape of hip bones as well as other body parts when naming, classifying, or grouping dinosaurs.

 Stocktrek Images / Getty Images

Henry Fairfield Osborn, a paleontologist and president of the American Museum of Natural History in New York City, selected the immortal name Tyrannosaurus rex in 1905. Tyrannosaurus is Greek for "tyrant lizard." Rex is Latin for "king," so T. rex became the "tyrant lizard king" or "king of the tyrant lizards."