Tyrannosaurus rex | Description, Dinosaur, & Facts (2024)

Tyrannosaurus rex, (Tyrannosaurus rex), species of predatory dinosaurs that lived during the end of the Cretaceous Period (about 66 million years ago) known from fossils found in the United States and Canada dating to between about 80 million and 66 million years ago. Tyrannosaurus rex is the best-known and largest member of a group of theropod dinosaurs called tyrannosaurs; its scientific name is Latin for “king of the tyrant lizards.”

Since 1902 paleontologists have recognized the T. rex as the only formal member of the genus Tyrannosaurus. This classification remained largely unchallenged until 2022, when some paleontologists suggested on the basis of variation in femurs and teeth among T. rex specimens that T. rex should be separated into three species (T. rex, T. imperator, and T. regina); however, this division is controversial. Moreover, the results of a separate analysis performed in 2024 of a partial skull and lower jaw, which were assigned to T. rex initially, suggested that these fossils belonged to a new species which the study’s authors called T. mcraeensis.

Form and function

T. rex was large and walked on powerfully developed hind limbs, which, scientists estimate, could have enabled the animal to run 32 km (20 miles) per hour for short distances. If T. rex had stood upright, it would have been more than 6.5 meters (21 feet) tall, but its usual posture was horizontal, with the body carried parallel to the ground and the tail held off the ground as a counterbalance. In this position a large adult, weighing 4,000 to 7,000 kg (about 9,000 to 15,000 pounds), could measure more than 12 meters (about 39 feet) long. The largest T. rex specimens known are “Sue”—which was discovered in South Dakota in 1990 and measures 12.8 meters (42 feet) long—and “Scotty”—which was found in Eastend, Saskatchewan, in 1991 and whose length and weight were estimated at 13 meters (42.7 feet) long and 8,870 kg (19,555 pounds), respectively.

Prey

Gut contents and coprolites (fossilized feces) of tyrannosaurs, as well as remains of other dinosaurs preserved with tyrannosaurid bite marks, show that tyrannosaurs were voracious predators that could easily bite through skulls, pelvises, and limbs of other dinosaurs. In addition to having the capacity to hunt large prey, T. rex also may have been a scavenger, feeding upon dead animals. Bite marks found on the bones of other tyrannosaurs, especially T. rex, have been interpreted by some scientists as evidence of cannibalism.

Some paleontologists note that tyrannosaur forelimbs and claws could have been used to strike out and slash at prey during close encounters, or they could have played a part in social displays or as pelvic claspers that males used during mating. Others argue that large forelimbs would have been a disadvantage when several tyrannosaurs came together to feed on a carcass. Although pack hunting among tyrannosaurs has not been proven conclusively, small forelimbs may have evolved to keep these appendages out of the way of snapping jaws, ultimately making the tyrannosaur less vulnerable to serious injury (which could have led to amputation, blood loss, infection, and death).

Fossil evidence

Most fossils of T. rex are found in western North America, especially at the Hell Creek Formation of Garfield county, Montana, and adjacent areas of the United States. Some specimens have been found at other sites, including the Lance Formation in Wyoming, South Dakota’s Cheyenne River Sioux reservation, and the Frenchman Formation in Saskatchewan. The species is thought to have evolved in North America, but some paleontologists suggest—based on morphological similarities between T. rex and its slightly older close relatives from Asia, Tarbosaurus and Zhuchengtyrannus—that the species may have migrated to North America from Asia across a temporary land bridge between the continents some 67 million years ago.

Before 1980 all knowledge of T. rex was based on only four skeletons, none very complete. The Latin name was given to the first specimen by American paleontologist Henry Fairfield Osborn in 1905 and was based on partial specimens collected from the Hell Creek Formation by renowned fossil hunter Barnum Brown. Since 1980 more than two dozen other specimens of T. rex have been discovered in western North America, some nearly complete; however, some are in private collections and are therefore lost to science and education. Two of the best specimens, consisting of almost complete adult skeletons, were unearthed in 1990. One, the 85-percent-complete “Wankel” T. rex, is on display at the Museum of the Rockies in Bozeman, Montana, and the other, the 90-percent-complete “Sue,” is displayed at the Field Museum in Chicago.

Other T. rex specimens are mounted at other natural history museums in North America, such as the Denver Natural History Museum, the University of California Museum of Paleontology in Berkeley, the Natural History Museum of Los Angeles County, and the Royal Tyrrell Museum in Drumheller, Alberta, near Dinosaur Provincial Park. In 2000 five T. rex specimens were discovered in the Hell Creek Formation. Several are now on display at the Museum of the Rockies; one of them, the “B-rex,” preserves soft tissues and also medullary bone that indicate the specimen was female. The soft tissues preserve transparent, flexible, hollow blood vessels that contain small round microstructures highly reminiscent of the structure of red blood cells.