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Tyrannosaurus (/ t ɪ ˌ r æ n ə ˈ s ɔː r ə s, t aɪ-/) [a] is a genus of large theropod dinosaur. The type species Tyrannosaurus rex (rex meaning 'king' in Latin), often shortened to T. rex or colloquially T-Rex, is one of the best represented theropods.
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- Overview
- Form and function
- Skull and dentition
- Other skeletal features
- Prey
- Fossil evidence
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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 din...
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 th...
The species also had a massive skull—with the size of most specimens reaching up to 1.3 meters (about 4.3 feet) long. (The longest known T. rex skull is “Maximus,” an exceptional specimen spanning 2 meters [6.6 feet] long). The skull bones of large specimens are often several centimeters thick and are strongly braced to each other, which suggests a resistance to the forces of biting, both inflicted upon and received from other tyrannosaurs. Engineering models, in fact, show that the bite force of T. rex would have been capable of easily ripping through the roof of an automobile, as portrayed in the 1993 motion picture Jurassic Park. The huge mouth contained some 60 teeth that could protrude as far as 15 cm (6 inches). The crowns of the teeth were shed and regrown frequently (every 250 days or so, estimated on the basis of microscopic lines visible within the teeth). Serrations of the teeth bear deep pocketlike recesses in which bacteria may have flourished to provide an infectious bite.
The front teeth are small and U-shaped. The side teeth are large, and in adults they become even larger, fewer in number, and D-shaped in cross section rather than daggerlike as in most theropods, or flesh-eating dinosaurs. In juveniles the teeth are laterally compressed and serrated front and back, like those of other theropods. In mature individuals, however, the teeth fall neatly into three general classes: upper front teeth, upper side teeth, and lower jaw teeth.
In contrast to the powerful jaws and legs, the forelimbs of tyrannosaurs were very small (less than the length of the shoulder blade), and in some forms the hands were reduced to only two digits. Although a mechanical reconstruction suggests that the musculature of the arms of T. rex and some other large tyrannosaurs could have lifted about 180 kg (400 pounds), the hands would not have been able to reach the mouth or grasp prey. The hind limb bones appear massive but are lightly constructed: the thickness of the bone wall is only about 20 percent of the bones’ diameter—a ratio approaching that of many birds.
Determining the sex of individual dinosaurs from fossil remains continues to be a challenging task for paleontologists; however, techniques applied to the study of modern birds have helped scientists discover the sex of some T. rex skeletons. During the reproductive cycles of female birds, a layer of bone (medullary bone) is often deposited on the inner wall of the long bones. This process has been recognized in some fossils of tyrannosaurs (and of a few other dinosaurs), indicating that these specimens are female. Counts of the annual growth rings that are laid down in the long bones from early growth stages to adulthood show that T. rex effectively reached full size in less than 20 years.
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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).
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.
Learn about the largest and best-known predatory dinosaur that lived in the Cretaceous Period. Find out how its size, bite, teeth, and sex are studied and debated by paleontologists.
- John P. Rafferty
Apr 1, 2014 · “Tyrannosaurus” is Greek for “tyrant lizard,” and “rex” means “king” in Latin. So, Tyrannosaurus rex was “King of the Tyrant Lizards.” When and where did T. rex live? T. rex lived about 66–68 million years ago during the Cretaceous Period in the western United States, including Montana and Wyoming. What was the world like ...
- Bob Strauss
- Not the Biggest Meat-Eating Dinosaur. 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.
- Arms Not as Tiny as Once Thought. 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.
- Very Bad Breath. 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.
- Females Bigger Than Males. 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.
Learn about the "king of the tyrant lizards," a ferocious carnivore that dominated the Cretaceous period. Discover how T. rex lived, hunted, grew, and met its end in a mass extinction event.
- 4 min
- Amy McKeever
Almost everything about Tyrannosaurus rex indicates the enormous power of one of the largest theropod dinosaurs that ever existed. The first skeleton of Tyrannosaurus rex was discovered in 1902 in Hell Creek, Montana, by the Museum's famous fossil hunter Barnum Brown.
Apr 1, 2024 · The mighty Tyrannosaurus rex is arguably the most iconic dinosaur that ever lived.
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