Tyrannosaurus Rex: King of the Dinosaurs

One of the largest known carnivorous dinosaurs, Tyrannosaurus rexT. rex, for short — is also arguably the most iconic. With a star turn in the "Jurassic Park" franchise and a renowned exhibit at the American Museum of Natural History in New York City among many other pop culture moments, T. rex maintains a reputation as king of the dinosaurs.

In fact, the animal's name means "king of the tyrant lizards". "Tyranno" means tyrant in Greek; "saurus" means lizard in Greek; and "rex" translates to "king" in Latin. In 1905, Henry Fairfield Osborn, president of the American Museum of Natural History at the time, officially dubbed the species Tyrannosaurus rex.

T. rex was a member of the Tyrannosauroidea family of huge predatory dinosaurs with small arms and two-fingered hands. Aside from Tyrannosaurs, other Tyrannosaurid genera include Albertosaurus, Alectrosaurus, Alioramus, Chingkankousaurus, Daspletosaurus, Eotyrannus, Gorgosaurus, Nanotyrannus (a controversial genus that experts say is likely an adolescent T. rex), Prodeinodon, Tarbosaurus and Zhuchengtyrannus.

T. rex fossils are found in western North America, from Alberta to Texas. But it's possible that T. rex was an invasive species from Asia, according to a 2016 study published in Scientific Reports. An analysis of T. rex's skeletal features showed that the dinosaur king was more similar to two Tyrannosaurs in Asia, Tarbosaurus and Zhuchengtyrannus, than it was to North American Tyrannosaurs, the researchers told Live Science. The animals may have crossed over about 67 million years ago when the seaway between Asia and North America receded.

However, the finding is still preliminary, and other experts maintain that T. rex evolved in North America, the researchers acknowledged.

Sue the T. rex had an awful infection when she died.

T. rex fossils reveal that the animals could grow to 40 feet (12.2 m) in length. (Image credit: Kirstin Brink)

How big was T. rex?

The most complete T. rex skeleton ever found was nicknamed Sue after its discoverer, paleontologist Sue Hendrickson. Measurements of Sue suggest T. rex was one of the largest carnivorous dinosaurs to ever live, coming in at up to 13 feet (4 meters) tall at the hips (the beast's highest point since it did not stand erect) and 40 feet (12.3 m) long. A recent analysis of Sue, published in 2011 in the journal PLOS ONE, shows T. rex weighed as much as 9 tons (about 8,160 kilograms).

In 2019, researchers published the discovery of another T. rex fossil, nicknamed "Scotty," that edged out Sue as the most massive of its kind, likely weighing in at 19,555 lbs. (8,870 kilograms) in life. Scotty also likely lived longer than many of its fellows, outlasting Sue's 28 years to live to the ripe old (for a Tyrannosaurus) age of 30.

T. rex had strong thighs and a powerful tail, which counterbalanced its large head (Sue's skull is 5 feet, or 1.5 m, long) and allowed it to move quickly. The 2011 study, which also modeled T. rex's muscle distribution and center of mass, suggests the giant could run 10 to 25 mph (17 to 40 km/h), as previous studies had estimated.

Its two-fingered forearms were puny, making it unlikely that T. rex could use them to kill or even get a meal to its mouth. However, it's possible that T. rex had such tiny arms because of its powerful bite, according to research from Michael Habib, an assistant professor of clinical cell and neurobiology at the University of Southern California and a research associate at the Dinosaur Institute at the Natural History Museum of Los Angeles County.

The "king of dinosaurs" needed thick neck muscles to hold up its large skull and power its forceful bite. Neck and arms muscles compete for space in the shoulder, and it appears that the neck muscles edged out the arm muscles in T. rex's case, according to Habib's research. Moreover, long arms can be broken, are vulnerable to disease, and take energy to maintain, so having short arms may have been beneficial to the king in the long run, Habib's research shows. 

The real work of dispensing with its prey was left to the dinosaur's massive and thick skull. T. rex had the strongest bite of any land animal that ever lived, according to a 2012 study in the journal Biology Letters. The dinosaur's bite could exert up to 12,814 pounds-force (57,000 Newtons), which is roughly equivalent to the force of a medium-size elephant sitting down.

Artwork by Scott Hartman reveals the bone structure of T. rex. (Image credit: © Scott Hartman / All rights reserved)

T. rex had a mouth full of serrated teeth; the largest tooth of any carnivorous dinosaur ever found was 12 inches (30 centimeters) long. But not all of the dinosaur's teeth served the same function, according to a 2012 study in the Canadian Journal of Earth Sciences. Specifically, the dinosaur's front teeth gripped and pulled; its side teeth tore flesh, and its back teeth diced chunks of meat and forced food into the throat. Importantly, T. rex's teeth were wide and somewhat dull (rather than being flat and daggerlike), allowing the teeth to withstand the forces exerted by struggling prey, the study found.

T. rex may be big, but its predecessors were small. The first tyrannosaurs, which were human- to horse-size, originated about 170 million years ago during the mid-Jurassic. Though lacking in stature, these little tyrannosaurs had advanced brains and advanced sensory perceptions, including hearing, a 2016 study detailed in the journal Proceedings of the National Academy of Sciences revealed. The finding, on a newfound mid-Cretaceous tyrannosaur named Timurlengia euotica, suggests that the advanced brains tyrannosaurs developed while they were still small helped them become apex predators once they grew to T. rex's size. 

Teenage T. rex were more lightly built and faster than the much larger, lumbering, bone-crushing adults they would grow into.

Teenage T. rex were more lightly built and faster than the much larger, lumbering, bone-crushing adults they would grow into. (Image credit: Julius T. Csotonyi)

What did T. rex eat?

T. rex was a huge carnivore and primarily ate herbivorous dinosaurs, including Edmontosaurus and Triceratops. The predator acquired its food through scavenging and hunting, grew incredibly fast and ate hundreds of pounds at a time, said University of Kansas paleontologist David Burnham.

"T. rex was probably opportunistic and may have fed on carcasses, but that is not a very abundant or consistent food source," Burnham told Live Science. "T. rex had a hard life. They had to go out and kill for food when they were hungry."

For many years, the evidence that T. rex actually hunted for its meals was circumstantial and included such things as bones with bite marks, teeth near carcasses and foot tracks suggesting pursuits, Burnham said. But in a 2013 study in the journal Proceedings of the National Academy of Science, Burnham and his colleagues unveiled direct evidence of T. rex's predatory nature: T. rex tooth embedded in a duckbill dinosaur's tailbone, which healed over the tooth (meaning the duckbill got away).

"We found the smoking gun!" Burnham said. "With this discovery, we now know the monster in our dreams is real."

T. rex was also not above enjoying another T. rex for dinner, according to a 2010 analysis published in PLOS ONE of T. rex bones with deep gashes created by T. rex teeth. However, it's not clear if the cannibalistic dinosaurs fought to the death or merely ate the carcasses of their own kind.

Scientists are unsure whether T. rex hunted alone or in packs. In 2014, researchers found dinosaur track marks in the foothills of the Canadian Rockies in British Columbia — out of the seven tracks, three belonged to Tyrannosaurids, most likely AlbertosaurusGorgosaurus or Daspletosaurus. The study, published in PLOS ONE, suggests that T. rex's relatives, at least, hunted in packs.

When and where did T. rex live?

T. rex fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous period, which lasted from 67 million to 65 million years ago, toward the end of the Mesozoic Era. It was among the last of the non-avian dinosaurs to exist prior to the Cretaceous-Paleogene extinction event, which wiped out the dinosaurs.

More mobile than many other land-based dinosaurs, T. rex roamed throughout what is now western North America, at the time an island continent identified as Laramidia. More than 50 skeletons of T. rex have been unearthed, according to National Geographic. Some of these remains are nearly complete skeletons, and at least one skeleton included soft tissue and proteins. [Image Gallery: The Life of T. Rex]

Fossil hunter Barnum Brown discovered the first partial skeleton of a T. rex in the Montana portion of the Hell Creek Formation in 1902. He later sold this specimen to the Carnegie Museum of Natural History in Pittsburgh. Another T. rex fossil discovery of his, also from Hell Creek, is on display in the American Museum of Natural History in New York.

In 2007, scientists unearthed what may be a T. rex footprint in Hell Creek, and described their discovery in the journal Palaios. If the track did indeed belong to T. rex, it would be only the second confirmed T. rex footprint ever discovered, the first being a footprint discovered in New Mexico in 1993.

Kim Ann Zimmermann and Live Science senior writer Laura Geggel contributed to this article. It was updated again on April 20, 2021 by Live Science Reference Editor Vicky Stein.

Learn about T. rex's massive teeth, bones, habitat and other dinosaur secrets. (Image credit: Ross Toro, Livescience contributor)

More dinosaurs

Time periods

Precambrian: Facts About the Beginning of Time

Paleozoic Era: Facts & Information

Mesozoic Era: Age of the Dinosaurs

Cenozoic Era: Facts About Climate, Animals & Plants

Additional resources

Joseph Castro
Live Science Contributor
Joseph Bennington-Castro is a Hawaii-based contributing writer for Live Science and Space.com. He holds a master's degree in science journalism from New York University, and a bachelor's degree in physics from the University of Hawaii. His work covers all areas of science, from the quirky mating behaviors of different animals, to the drug and alcohol habits of ancient cultures, to new advances in solar cell technology. On a more personal note, Joseph has had a near-obsession with video games for as long as he can remember, and is probably playing a game at this very moment.