Tyrannosaurus

Tyrannosaurus is a genus of large theropod dinosaur. The type species Tyrannosaurus rex (rex means 'king' in Latin), often shortened to T. rex or nicknamed T-Rex, is one of the best represented theropods. It lived throughout what is now western North America, on what was then an island continent known as Laramidia. If you search for "T. rex," you will land on this article. Other uses are listed on a separate page, T. rex (disambiguation).

Tyrannosaurus had a much wider range than other tyrannosaurids. Fossils have been found in a variety of geological formations that have been dated to the late Maastrichtian age of the late Cretaceous period, 69 to 66 million years ago. Some isolated specimens may show an earlier origin in the middle Campanian age. It was one of the last known members of the tyrannosaurids and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore, meaning it walked on two legs and ate meat. It had a massive skull balanced by a long, heavy tail. Its forelimbs were short but unusually powerful for their size, and they had two clawed digits. Although some other theropods might have rivaled or exceeded it in size, Tyrannosaurus is still among the largest known land predators. Its estimated bite force was the largest among all land animals. It was most likely an apex predator, hunting hadrosaurs, young armored plant-eaters like ceratopsians and ankylosaurs, and possibly sauropods. For a long time, scientists debated whether it was a hunter or a pure scavenger, but most paleontology experts today accept that it was a predator.

Some specimens of Tyrannosaurus rex are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. Because so many fossils have been found, scientists have been able to study many parts of the animal's life, including its biomechanics. Its feeding habits, physiology, and possible speed are still subjects of debate. Tyrannosaurus has been one of the best-known dinosaurs since the early 20th century. Its fossils are popular attractions in museums, and it has appeared in media like Jurassic Park.

History of research

See also: Specimens of Tyrannosaurus

A tooth from what is now known to be a Tyrannosaurus rex was found in July 1874 on South Table Mountain (Colorado) by Peter T. Dotson, a student of Jarvis Hall, working under Arthur Lakes near Golden, Colorado. The rock layer was part of the Denver Formation. In the early 1890s, John Bell Hatcher collected bones in eastern Wyoming. These were first thought to belong to the large species Ornithomimus grandis, now called Deinodon, but are now considered T. rex remains. In 1892, Edward Drinker Cope found two bones from a large dinosaur. He first thought they came from a ceratopsid dinosaur. Henry Fairfield Osborn later saw that they matched T. rex. In 2000, the Black Hills Institute found about 10% of a Tyrannosaurus skeleton. Scientists still debated which name should be used under the International Code of Zoological Nomenclature, the set of rules for naming animals.

Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of T. rex in eastern Wyoming in 1900. In 1902, he found another partial skeleton in the Hell Creek Formation in Montana, with about 34 fossil bones. Brown wrote that he had "never seen anything like it from the Cretaceous." Osborn, the museum's president, named this second skeleton T. rex in 1905. The name comes from the Greek words for "tyrant" and "lizard," and the Latin word rex means "king." The full binomial means "King Tyrant Lizard." In 1941, the type specimen was sold to the Carnegie Museum of Natural History, and the original Dynamosaurus material is kept by the Natural History Museum in London. From the 1910s to the end of the 1950s, Barnum's finds were the only known Tyrannosaurus specimens, because the Great Depression and wars kept many scientists out of the field.

Interest returned in the 1960s, and 42 skeletons were recovered from western North America. In 1967, a skeleton named "MOR 008" was found, and its rebuilt skull is shown at the Museum of the Rockies. The 1990s brought many finds, including two of the most complete skeletons, Sue and Stan. Sue Hendrickson discovered the most complete and largest skeleton in the Hell Creek Formation on August 12, 1990. It was later bought by the Field Museum of Natural History. Stan, found in 1992, is the second most complete skeleton. Bucky, found in 1998, is the first Tyrannosaurus known to have preserved a furcula, or wishbone, and it is displayed at The Children's Museum of Indianapolis.

In 2000, crews led by Jack Horner discovered five Tyrannosaurus skeletons near the Fort Peck Reservoir. In 2001, a crew from the Burpee Museum of Natural History found Jane, a half-complete young skeleton. It was first thought to be a pygmy tyrannosaur called Nanotyrannus, but was later seen as a young T. rex. The dig for a skeleton called "Wyrex" in 2004 became the first live online Tyrannosaurus excavation. In 2006, Montana State University revealed the largest Tyrannosaurus skull found so far, from MOR 008, which measured 152 centimetres (5 feet) long.

Description

T. rex was one of the largest land meat-eaters of all time. One of its largest and most complete specimens, Sue (FMNH PR2081), measured 12.3–12.8 m (40–42 ft) long and stood 3.66–3.96 m (12.0–13.0 ft) tall at the hips. The most recent studies estimate its body mass at about 8.4–9.22 t (8.27–9.07 long tons; 9.26–10.16 short tons). A specimen nicknamed Scotty (RSM P2523.8), kept at the Royal Saskatchewan Museum, is reported to be 13 m (43 ft) long. Using a method based on the circumference of the thigh bone, Scotty was estimated to be the largest known specimen, at 8.87 t (8.73 long tons; 9.78 short tons). Not every adult was this big. Past estimates of average adult mass have varied widely, from as low as 4.5 t to more than 7.2 t, while most modern estimates fall between 5.4 and 8.0 t. A 2024 study found little evidence that size differed between male and female individuals.

The largest known skulls measure up to 1.52 m (5 ft 0 in) long. Large fenestrae (openings) in the skull reduced its weight, as in all meat-eating theropods. Unlike other large non-tyrannosaurid theropods, its skull was extremely wide at the back but had a narrow snout, which gave it unusually good binocular vision. The skull bones were massive, and the nasals and some other bones were fused together. Many were pneumatized, containing a "honeycomb" of tiny air spaces that made them lighter. These features helped give tyrannosaurids an increasingly powerful bite. The teeth showed marked heterodonty, or differences in shape. The premaxillary teeth at the front of the upper jaw were incisiform, with chisel-like tips, while the back teeth were robust and widely spaced. The lower jaw's front dentary bone held thirteen teeth. The skeleton had a short, deep neck with an S-shaped curve, built to support the massive head. The vertebral column had ten neck vertebrae, thirteen back vertebrae, and five fused sacral vertebrae, with many tail vertebrae. Air-filled spaces in the bones, created by air sacs, lightened the skeleton. The shoulder girdle was longer than the whole forelimb, and it included a coracoid, a small furcula, and possibly cartilage in the breast bones. The forelimbs were very short, with a short but robust humerus, an ulna and radius much shorter than the upper arm bone, and only two clawed fingers. The pelvis was large, with a very long and high ilium, a pubic bone, and a slender ischium. The hindlimbs were among the longest in proportion to body size of any theropod. The metatarsus in the foot was "arctometatarsalian," meaning the third metatarsal was pinched near the ankle. Many bones were hollowed out, which reduced weight without losing much strength.

Classification

Tyrannosaurus is the main example, or type, of the family Tyrannosauridae, which sits inside the superfamily Tyrannosauroidea. Scientists use it as the standard for deciding whether other species belong in this group. Other close relatives include Daspletosaurus, from North America, and Tarbosaurus, from Asia. Some scientists have sometimes treated these as the same as Tyrannosaurus. Tyrannosaurs were once thought to come from large earlier dinosaurs like megalosaurs and carnosaurs, but they are now grouped with the generally smaller coelurosaurs. They started out small, and at least some grew larger by the Early Cretaceous.

Many studies have found that Tarbosaurus bataar is the sister taxon of T. rex, meaning the two are closely related. The discovery of Lythronax suggests that Tarbosaurus and Tyrannosaurus are close relatives. A 2016 study also suggested that Tyrannosaurus may have come from Asia. Scientists still disagree about many species names. Some have been proposed and then questioned by other experts, and some researchers think Nanotyrannus may be a young T. rex.

Main article: Nanotyrannus

Paleobiology

Feathered dinosaur · Physiology of dinosaurs · Feeding behavior of Tyrannosaurus

Fossils of young Tyrannosaurus rex have helped scientists learn how the animal grew. The smallest juvenile specimen is estimated to have weighed only about 30 kg (66 lb), while the largest adults, such as Sue, probably weighed about 5,650 kg (12,460 lb). Growth was slow at first, then sped up around age 14, when a young T. rex could gain about 600 kg (1,300 lb) a year for four years. Growth slowed again at about 18 years of age. Over half of the known T. rex specimens appear to have died within six years of reaching adulthood. Scientists have studied the skin, arms, posture, speed, and senses of Tyrannosaurus, though many questions remain. Its skin was probably mostly covered in scales, and feathers, if present, may have been limited to the upper body. Its arms were very small but had large muscle attachments, so they may have helped hold struggling prey. It was probably not a fast runner, and its senses of smell and sight were strong. Most scientists think it was an active predator that also scavenged, although Jack Horner has argued it was mainly a scavenger. Its bite was likely the most powerful of any land animal that has lived.

Scientists once thought Tyrannosaurus stood upright like a tripod, but by 1970 they had realized this pose was incorrect. Modern models show it with its body nearly parallel to the ground and its tail balancing its head. Its behavior is less certain. Philip J. Currie suggested it may have hunted in packs, but this idea has not been widely accepted. There is no direct evidence that Tyrannosaurus raised its young, though it may have protected and fed them, as its living relatives, birds and crocodiles, often do.

Hell Creek Formation

Paleoecology

Tyrannosaurus lived at the end of the Late Cretaceous, during the Lancian faunal stage (Maastrichtian age). It ranged from Canada in the north to at least New Mexico in the south of Laramidia. Many notable remains have been found in the Hell Creek Formation, where the area was maritime to subtropical, with a warm, humid climate. Plants there were mostly angiosperms, along with trees like dawn redwood (Metasequoia). Other animals found there included the ceratopsians Leptoceratops, Torosaurus, and Triceratops, the hadrosaurid Edmontosaurus annectens, the parksosaurid Thescelosaurus, the ankylosaurs Ankylosaurus and Denversaurus, the pachycephalosaurs Pachycephalosaurus, Platytholus and Sphaerotholus, the paravian theropods Acheroraptor and Pectinodon, other maniraptoran theropods Anzu, Eoneophron, Trierarchuncus and ornithomimids, the tyrannosauroid Nanotyrannus, and the azhdarchid pterosaur Infernodrakon.

Tyrannosaurus remains have also been found in the Lance Formation of Wyoming, which is thought to have been a bayou area similar to today's Gulf Coast. Its animals were very similar to those of Hell Creek, though Struthiomimus replaced its relative Ornithomimus, and the small ceratopsian Leptoceratops also lived there. In the south, remains from the North Horn Formation of Utah show Tyrannosaurus rex living alongside the titanosaur Utetitan, the ceratopsid Torosaurus, and some troodontids and hadrosaurids. Tyrannosaurus mcraeensis from the McRae Group of New Mexico lived with the ceratopsid Sierraceratops and possibly Alamosaurus. Possible Tyrannosaurus remains have also been found in the Javelina Formation of Texas, where the pterosaurs Quetzalcoatlus and Wellnhopterus were found too. This southern area is thought to have been semi-arid inland plains, after the Western Interior Seaway retreated as global sea levels fell. Tyrannosaurus may also have lived in Mexico's Lomas Coloradas Formation in Sonora, where six teeth appear to match those of Tyrannosaurus, suggesting its range may have been wider than thought. Some scientists think tyrannosaurs may have started in Asia and migrated to North America before the end of the Cretaceous period. Studies published in 2021 by Charles Marshall et al. estimated that about 20,000 adult Tyrannosaurus lived at any given time, though computer estimates ranged from 1,300 to 328,000, and the authors think the true number was probably higher. Over the whole existence of the genus, about 2.5 billion animals are estimated to have lived.

Cultural significance

Tyrannosaurus is the most widely known dinosaur in popular culture. Science writer Riley Black says that no animal gets our attention quite like Tyrannosaurus rex. Since this dinosaur was officially named in 1905, it has stood as the ultimate dinosaur. Paleontologist David Hone notes that Tyrannosaurus models and skeleton displays are popular in museums. He writes that films like Jurassic Park and King Kong "would not have been the same without it."

T. rex is the only dinosaur that most people know by its full scientific name (binomial name). The short form T. rex has also become widely used.