Tyrannosaurus Rex: Facts About T. Rex, King of the Dinosaurs

Aside from being one of the largest of the known carnivorous dinosaurs, Tyrannosaurus rexT. rex for short — is the dinosaur that has arguably gotten the most media exposure. He had a starring role in the "Jurassic Park" movies and has a renowned exhibit at the American Museum of Natural History.

The name Tyrannosaurus rex is derived from the Greek. Broken down into three parts —  "tyranno," meaning tyrant; "saurus," meaning lizard; and "rex" meaning "king" — the name means "king of the tyrant lizards." Henry Fairfield Osborn, president of the American Museum of Natural History, named Tyrannosaurus rex in 1905.

T. rex was a member of the Tyrannosauroidea family of huge predators with small arms and two-fingered hands. Other Tyrannosaurids included Albertosaurus, Alectrosaurus, Alioramus, Chingkankousaurus, Daspletosaurus, Eotyrannus, Gorgosaurus, Nanotyrannus, Prodeinodon and Tarbosaurus.

Artwork by Scott Hartman reveals the bone structure of T. rex.
Artwork by Scott Hartman reveals the bone structure of T. rex.
Credit: © Scott Hartman / All rights reserved

Based on their examination of fossils, paleontologists estimate that T. rex was 15 feet to 20 feet tall (4.6 meters to 6 meters) and about 40 feet (12 m) from head to toe. Recent measurements show that T. rex weighed as much as 9 tons (about 8,164 kg). While no complete skeleton has ever been unearthed, scientists estimate that T. rex had about 200 bones, roughly the same number as humans.

T. rex had a lizard-like appearance with strong thighs and a powerful tail that enabled it to move quickly. T. rex may have run at speeds of up to 15 mph (24 kph) when pursuing prey even though it weighed 5 tons to 7 tons.

This is the skull of the most complete Tyrannosaurus rex ever found. The Black Hills Institute of Geological Research in Hill City, South Dakota excavated it. This picture was taken on Nov. 10, 2003 at the Smithsonian National Museum of Natural History.
Credit: © 2003 Calvin J. Hamilton

T. rex left footprints 1.55 feet long (46 cm), although its feet were much longer — about 3.3 feet (1 m) — as T. rex, like other dinosaurs, walked on its toes. It had a stride length of 12 feet to 15 feet (3.7 m to 4.6 m).

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. The real work of dispensing with its prey was left to the dinosaur’s massive 5-foot-long (1.5 m) thick skull — which it used to bore into his kill — its 4-foot-long (1.2 m) jaw that could easily crush bones— and a mouth full of serrated teeth that were continually replaced. Scientists believe that T. rex could consume up to 500 pounds (230 kg) in one bite.

What did T. rex eat?

T. rex was a huge carnivore and primarily ate herbivore dinosaurs, including the Edmontosaurus and the Triceratops. They acquired their food through scavenging and hunting. T. rex was also not above enjoying another T. rex for dinner; if two T. rexes fought to the death the winner would eat the loser.

Scientists theorize that unlike carnivores of today, T. rexes did not hunt in packs but rather were solo hunters. There is a debate as to whether the dinosaur relied solely on live prey or would it feast on already-dead food as well.


When and where T. rex lived

T. rex fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 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.

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 30 specimens of T. rex have been identified, some of which are nearly complete skeletons and at least one skeleton included soft tissue and proteins. [Image Gallery: The Life of T. Rex]

Fossils of different Tyrannosaurus species have been found in Montana, Texas, Utah and Wyoming, as well as Canada (Alberta and Saskatchewan) and Mongolia in east Asia. One T. rex footprint was also discovered in New Mexico.

The first T. rex fossil was discovered in the Montana portion of the Hell Creek Formation by fossil hunter Barnum Brown in 1902.

Brown found a total of five Tyrannosaurus partial skeletons. His first find was sold to the Carnegie Museum of Natural History in Pittsburgh. His fourth and largest discovery, also from Hell Creek, is on display in the American Museum of Natural History in New York.

In 1998, a juvenile T. rex was found in the western South Dakota portion of Hell Creek Formation. Called Tinker or Kid rex, the skeleton was about 70 percent intact when it was discovered and it is estimated to have been 5 and 6 years old at the time of its death. Tinker is the nickname of Ron Frithiof, an Austin, Texas, real estate developer turned dinosaur hunter, who unearthed the fossil. This teenage T. rex was about two-thirds the size of an adult but only about one-quarter of an adult's weight.

In 2000, Jack and Celeste Horner, Bob Harmon, Larry Boychuk and Greg Wilson found five T. rex fossils on federal land near the Fort Peck Reservoir in Montana. This was the first time more than one T. rex was found in a single area.

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


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