Tyrannosaurus

Tyrannosaurus (pronounced or ; meaning 'tyrant lizard', from Greek tyrannos meaning 'tyrant' and sauros meaning 'lizard'), also known colloquially as T. rex and 'The King of the Dinosaurs', was a giant carnivorous theropod dinosaur.

It existed in the Upper Maastrichtian, the last stage of the Cretaceous Period, 70–65 million years ago. As of 2005, 30 specimens have been found,In the Field, January-February 2005 issue, Field Museum of Natural History. including three complete skulls. Tyrannosaurus is now a prime subject of ongoing scientific research and popular culture, although there have been published reports of larger predatory dinosaurs (such as Giganotosaurus and Spinosaurus). It has been described as having the strongest bite force of all dinosaurs (~3000 lb).

One of the most interesting Tyrannosaurus finds is 'Sue', currently held at the Field Museum in Chicago, USA. Sue, named after the explorer Sue Hendrickson who found the skeleton in South Dakota in 1990, is the largest and most intact Tyrannosaurus skeleton ever found. Sue is estimated at being 90% complete and has greatly expanded human knowledge of the Tyrannosaurus. Guinness World Records Ltd. (2003). 2003 Guinness World Records. pg 90.

Characteristics

About 12-13 m (39-43 ft) in length, 5 m (16 ft) tall and estimated to have been from 4 tons to 8 tons in weight, Tyrannosaurus was one of the largest land carnivores of all time. Compared to other carnivorous dinosaurs, the skull of Tyrannosaurus is heavily adapted. Many of the bones are fused together, preventing movement between them. The bones themselves are much more massive than is typical of a theropod and the serrated teeth, far from being bladelike, are massive and oval in cross-section. Heavy tooth wear and the bite marks found on bones of other dinosaurs indicate that these teeth could bite into solid bone. Discovered teeth are often worn or broken at the tips, from heavy use but, unlike in mammals, they were continually grown, shed and replaced, throughout the life of the animal. The brain of Tyrannosaurus was long and close to cylindrical, probably placing this dinosaur among the most intelligent theropods, as measured by its brain to body mass ratio. The neck was short and muscular, to support the head. The two-fingered 'arms' of Tyrannosaurus were very small (perhaps making up for the weight of its enormous head) but they were very sturdy. They may have been used for grasping during mating, as aids in rising from a lying position or perhaps to pin meat against the body, while dragging a carcass, to prevent it from swinging around. The legs were relatively long and slender for an animal of its size. To compensate for its immense bulk, many of its bones were hollow. This considerably reduced the weight of the skeleton, while retaining much of the strength of the bones.

Paleobiology

As with all dinosaurs, much of the Tyrannosaurus biology, including lifespan, breeding behaviour, coloration, ecology and physiology, remains unknown. A site in Alberta has at least nine individuals of Albertosaurus (a closely related animal) of different ages preserved together but whether these animals lived together or simply died together is unclear.

Posture

For over 50 years, Tyrannosaurus had been depicted as a 'living tripod', with the body at 45 degrees or less from the vertical, with the tail dragging along the ground, acting as a balance for the legs. This concept dated from around 1906, when Osborn, who believed the creature stood upright, was preparing a Tyrannosaurus skeleton for display at the American Museum of Natural History, in New York. It stood this way for over half a century, until it was dismantled in 1992. The depictions in many paintings (such as the mural The Age Of Reptiles by Rudolph Zallinger in the Peabody Museum Of Natural History at Yale University) and in films continued in this manner until the 1990s, when films such as Jurassic Park showed Tyrannosaurus with its body approximately parallel to the ground.

Arms

When Tyrannosaurus was first discovered, the forelimbs were still unknown. For the initial mounted skeleton, as seen by the public, Osborn substituted three-fingered Allosaurus forelimbs. However, in 1914, Lambe demonstrated the closely-related Albertosaurus had two-fingered forelimbs. Complete Tyrannosaurus forelimbs were only found in 1989. The 'arms' are relatively tiny, at 1 metre (3 feet, 4 inches) long, yet very muscular. Their purpose is unknown. The muscle placement indicates a restricted range of movement but great strength; a Tyrannosaurus forelimb was strong enough to lift two grown men.Lambert, David. The Ultimate Dinosaur Book. New York: Dorling Kindersley. Judging from their size, relative to the animal as a whole, it is very unlikely that they took any part in locomotion or in saving the animal's balance, were it to have fallen. However, they are well-placed to hold prey still during feeding or to grip it while it was being dragged.

Feathers

It has been proposed that Tyrannosaurus and other theropod dinosaurs may have had feathers. Small coelurosaurs (a closely-related dinosaur group) from the Yixian Formation in Liaoning, China, have been discovered with either pennaceous feathers or fur-like 'protofeathers', which suggest the possibility that tyrannosaurids may also have borne feathers. In 2004, the primitive tyrannosauroid Dilong was discovered, from the same formation and showed evidence of long tail plumes. However, skin impressions from adult tyrannosaurs in Alberta and Mongolia appear to show the pebbly scales typical of other dinosaurs. This would be consistent with the creature's size as, at 8 tons, the warm-blooded tyrannosaur's heat dispersal would actually have been impeded by a covering of feathers. It is possible that Tyrannosaurus evolved to lose any feathers its ancestors may have had, as with the hair of the modern elephant and hippopotamus. It is quite possible though that young tyrannosaurs had a down coat of feathers to insulate them, which were simply shed as the dinosaur grew.

Feeding strategies

Most debate about Tyrannosaurus centers on its feeding patterns and locomotion. One paleontologist, noted hadrosaur expert Jack Horner, claims that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all.Horner, J.R. and Lessem, D. (1993). The Complete T. rex: How Stunning New Discoveries Are Changing Our Understanding of the World's Most Famous Dinosaur. New York: Simon & Schuster. Horner has only presented this in an official scientific context once, while mainly discussing it in his books and in the media. His hypothesis is based on the following: Tyrannosaurs have large olfactory bulbs and olfactory nerves (relative to their brain size). These suggest a highly developed sense of smell, allegedly used to sniff out carcasses over great distances. Tyrannosaur teeth could crush bone, a skill perhaps used to extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Since at least some of Tyrannosaurus's prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger (see more on this below).Horner, J.R., (1994). Steak knives, beady eyes, and tiny little arms (a portrait of Tyrannosaurus as a scavenger). The Paleontological Society Special Publication 7: 157-164.

Most scientists who have published on the subject since insist that Tyrannosaurus was both a predator and a scavenger, taking whatever meat it could acquire, depending on the opportunity that was presented.Farlow, J. O. and T. R. Holtz, Jr. 2002. The fossil record of predation in dinosaurs. pp. 251–266, in M. Kowalewski and P. H. Kelley (eds.), The Fossil Record of Predation. The Paleontological Society Papers 8. Modern carnivores are seldom strict predators or scavengers. Lions, for example, sometimes scavenge prey that hyenas have killed (and vice versa). Scavenging behavior depends upon prey availability, among many other factors.

Some evidence exists that suggests hunting behavior in Tyrannosaurus. The ocular cavities of Tyrannosaurs are positioned so that the eyes would point forward, giving the dinosaur binocular vision. A scavenger might not need the advanced depth perception that stereoscopic vision affords; in modern animals, binocular vision is found primarily in predators. Bite marks in other animals and even other tyrannosaur fossils suggest predatory behavior.

When examining Sue, paleontologist Peter Larson found a broken and healed fibula (calf bone) and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurus embedded in a neck vertebra. If correct, it might be strong evidence for aggressive behavior between tyrannosaurs but whether it would be competition for food and mates or active cannibalism is unclear. However, more recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict. In the Sue excavation site, an Edmontosaurus annectens skeleton was also found with healed tyrannosaur-inflicted scars on its tail. The fact that the scars seem to have healed suggests active predation instead of scavenging a previous kill. Another piece of evidence is a Triceratops found with a third of its horn missing and a tooth mark along a piece of frill. Again, these were inflicted by a tyrannosaur and they too appear healed.

For all intents and purposes, the 'scavenging debate' does not actually exist in any scientific context. However, there have been conflicting studies regarding the extent to which Tyrannosaurus could run and exactly how fast it might have been; speculation has suggested speeds up to 70 km/h (45 mph) or even more.

Some argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs remain a choice as top predators. In this light, scavenger hypothesis adherents have hypothesized that the size and power of tyrannosaurs allowed them to steal kills from smaller predators.

Locomotion

Scientists who think that Tyrannosaurus was able to run slowly point out that hollow Tyrannosaur bones and other features that would have lightened its body may have kept adult weight to a mere 5 tons or so, or that other animals like ostriches and horses with long, flexible legs are able to achieve high speeds, through slower but longer strides. Additionally, some have argued that Tyrannosaurus had relatively larger leg muscles than any animal alive today, which could have enabled fast running (40-70 km/h or 25-45 mph).

Some old studies of leg anatomy and living animals suggested that Tyrannosaurus could not run at all and merely walked. The ratio of femur (thigh bone) to tibia (shank bone) length (greater than 1, as in most large theropods) could indicate that Tyrannosaurus was a specialized walker, like modern elephants. In addition, it had tiny 'arms' that could not have stopped the dinosaur's fall, had it stumbled while running; standard estimates of Tyrannosaurus weight at 6 to 8 tons would produce a lethal impact force, should it have fallen. It should be noted, however, that giraffes have been known to gallop at 50 km/h (31 mph). At those speeds, the animal risks breaking a leg or worse, which can be fatal even when the accident occurs in a 'safe' environment, such as a zoo. If it could run, Tyrannosaurus may have been a risk-taker, in much the same way as animals alive today are. Yet estimates of leg bone strength in Tyrannosaurus show that its legs were little if any stronger than those of elephants, which are relatively limited in their top speed and don't ever become 'airborne', as would happen in running.

Walking proponents estimate the top speed of Tyrannosaurus at about 17 km/h (11 mph). This is still faster than the most likely prey species that co-existed with tyrannosaurs, the hadrosaurs and ceratopsians. Hutchinson, J. R. and Garcia, M. (2002). Tyrannosaurus was not a fast runner. Nature 415: 1018-1021 In addition, some predation advocates claim that tyrannosaur running speed is not important, since it may have been slow but better designed for speed than its probable prey or it may have used ambush tactics, to attack faster prey animals.

The most recent research on Tyrannosaurus locomotion does not specify how fast it may have run but admits that there is little capacity to narrow down speeds further than a range from 17 km/h (11 mph), which would be only walking or slow running, to 40 km/h (25 mph), which would be moderate-speed running. For example, a paper in NatureHutchinson, J. R. and Garcia, M. (2002). Tyrannosaurus was not a fast runner. Nature 415: 1018-1021 used a mathematical model (validated by applying it to a wide range of living animals) to gauge the leg muscle mass needed for fast running (over 25 mph). They found that proposed top speeds in excess of 40 km/h (25 mph) were unfeasible, because they would require very large leg muscles (more than approximately 40-86% of total body mass.) Even moderately fast speeds would have required large leg muscles. This discussion is difficult to resolve, as it is unknown how large the leg muscles were. If they were smaller, only ~11 mph walking/jogging might have been possible.

Environment

In the times of Tyrannosaurus, the area that is now North America had both familiar and strange elements. The soft-shelled turtles, crocodiles, pike (Esocidae), and gar (Lepisosteidae) alive at the time were quite similar to those living today. Frogs and monitor lizards were other familiar animals. Ferns, horsetails, palms, magnolias, southern beech, poplars, and shrubs were some of the dominant plants; grasses had evolved but were not yet widespread. Conifers such as sequoias, araucaria, pines, and cypresses were common. The North American T. rex probably lived in many different habitats, because of its broad range but many of the fossil sites in which it is commonly found appear to have been humid, subtropical forests. Birds with beaks were already in existence, including waterfowl. Other inhabitants of the landscape were less familiar. There were birds with teeth and some of the giant pterosaurs still thrived, such as Quetzalcoatlus, which had an estimated wingspan of 12 m. Other theropods included dromaeosaurids, troodontids, and Ornithomimus, all of which appear to have been less than 4 or 5 meters long. Herds of Triceratops, Torosaurus and duck-billed dinosaurs (hadrosaurs), such as Edmontosaurus, roamed the land. Other dinosaurian herbivores included armored Ankylosaurus, boneheaded Pachycephalosaurus and Stygimoloch and small ornithopods such as Bugenasaura and Thescelosaurus. Mammals (predominantly multituberculates and marsupials) were mostly small, shrew- to rat-sized nocturnal animals. Primitive primates may have been around (this issue is open to debate). Snakes had evolved by this time, very similar to some snakes today.

Tyrannosaurus is believed to have required extensive geographic feeding ranges. Theropods the size of Tyrannosaurus arose in response to the retreat of the Western Interior Seaway of North America, 69 million years ago, which would have increased the size of the feeding range.Scientific American, 290, no. 2, February 2004 pp. 23-24.

History

The first fossil specimen of Tyrannosaurus (a partial vertebra) was found by Edward Cope in 1892 (although this specimen was originally named Manospondylus gigas--see Classification below). Barnum Brown, assistant curator of the American Museum of Natural History, found the second Tyrannosaurus skeleton in Wyoming in 1900. This specimen was originally named Dynamosaurus imperiosus, in the same paper in which Tyrannosaurus rex was described. Had it not been for page order, Dynamosaurus would have become the official name. The original "Dynamosaurus" material resides in the collections of the Natural History Museum, London.

In total, Barnum Brown found five Tyrannosaurus partial skeletons. Brown collected his second Tyrannosaurus in 1902 and 1905 in Hell Creek, Montana. This is the holotype used to describe Tyrannosaurus rex Osborn, 1905. In 1941 it was sold to the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. Brown's fourth and largest find, also from Hell Creek, is on display in the American Museum of Natural History in New York.

Susan Hendrickson, amateur paleontologist, discovered the most complete (more than 90%) and largest Tyrannosaurus fossil skeleton currently known, in the Hell Creek Formation near Faith, South Dakota, on August 12, 1990. This Tyrannosaurus, now named "Sue" in her honor, became embroiled in a legal battle over its ownership. In 1997 this was settled in favor of Maurice Williams, the original land owner and the fossil collection was sold at auction for USD 7.6 million. It has now been reassembled and is currently exhibited at the Field Museum of Natural History. Based on a study of her fossilized bones, Sue died at 28 years of age, having reached her full size at 19 years of age. Researchers report that a subadult and a juvenile skeleton were found in the same quarry as Sue; this lends evidence to the possibility that tyrannosaurs ran in packs or other groups.

Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota, in the spring of 1987. After 30,000 hours of digging and preparing, a 65% complete skeleton emerged. Stan is currently on display in the Black Hills Museum of Natural History Exhibit in Hill City, South Dakota, after an extensive world tour. This tyrannosaur, too, was found to have many bone pathologies, including broken and healed ribs, a broken (and healed) neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth. Both Stan and Sue were examined by Peter Larson.

In 2001, a 50% complete skeleton of a juvenile Tyrannosaurus was discovered in the Hell Creek Formation in Montana, by a crew from the Burpee Museum of Natural History of Rockford, Illinois. Dubbed "Jane", the find was initially considered the first known skeleton of the pygmy tyrannosaurid Nanotyrannus but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus. It is the most complete and best preserved juvenile example known to date. Jane has been examined by Jack Horner, Pete Larson, Robert Bakker, Greg Erikson and several other renowned paleontologists, because of the uniqueness of her age. Jane is currently on exhibit at the Burpee Museum of Natural History in Rockford, Illinois.

In the March 2005 Science magazine, Mary Higby Schweitzer of North Carolina State University and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone, from a 68-million-year-old Tyrannosaurus. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation. Flexible, bifurcating blood vessels and fibrous but elastic bone matrix tissue were recognized. In addition, microstructures resembling blood cells were found inside the matrix and vessels. The structures bear resemblance to ostrich blood cells and vessels. However, since an unknown process distinct from normal fossilization seems to have preserved the material, the researchers are being careful not to claim that it is original material from the dinosaur. The presence of medullary bones in this specimen is also of interest.

If it turns out to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may merely be the result of people assuming preserved tissue was impossible, therefore simply not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.

In a press release on April 7th 2006, Montana State University revealed that it possessed the largest Tyrannosaurs skull yet discovered. Discovered in the 1960s and only recently reconstructed, the skull measures 59 inches long compared to the 55.4 inches of “Sue’s” skull, a difference of 6.5%.

Classification

In 2000, there was controversy regarding the validity of the name Tyrannosaurus. Bones unearthed in South Dakota in June of that year, clearly attributable to Tyrannosaurus rex, were part of a fragmentary fossil specimen that had previously been named Manospondylus gigas. According to the rules of International Commission on Zoological Nomenclature, the system that gives animals their Latin designation, Cope's 1892 name Manospondylus gigas should have priority, because his discovery came before Tyrannosaurus was first described by Osborn in 1905. However, in the ICZN 4th edition, which took effect on January 1 2000, Chapter 8, Article 35.5 stated that any such discovery made after 1999 does not cause the older name to replace the newer, prevailing name and that Tyrannosaurus is to be a nomen conservandum ("conserved name"). Therefore, regardless of the result of the discovery, the Tyrannosaurus name is still used by biologists today.

Currently, the only species universally recognized as belonging to the genus Tyrannosaurus is T. rex. Tarbosaurus, from Mongolia, is sometimes placed in the genus Tyrannosaurus as T. bataar, though most tyrannosaur researchers, such as Tom Holtz, find them to be more than distinct enough to warrant separate genera. Nonetheless, Tarbosaurus and Tyrannosaurus are very closely related and belong to the tribe Tyrannosaurini.

A large number of Tyrannosaur-like species have now been classified as either Tyrannosaurus rex or Tarbosaurus bataar, listed below:

T. amplus (Marsh, 1892) nomen dubium (originally Aublysodon) genus misassigned, now Aublysodon amplus
T. gigantus 1990 nudum "gigantic tyrant lizard" species misassigned, now Tyrannosaurus rex
T. imperiosus (Osborn, 1905) (originally Dynamosaurus) species misassigned, now Tyrannosaurus rex
T. lancensis (Gilmore, 1946) (originally Gorgosaurus) ?= Tyrannosaurus rex
T. megagracilis (Paul, 1988) (originally Albertosaurus) ?= Tyrannosaurus rex
T. stanwinstonorum Pickering, 1995 nomen nudum species misassigned, now Tyrannosaurus rex
T. bataar (Maleev, 1955) (originally Tarbosaurus) genus misassigned, now Tarbosaurus bataar
T. efremovi (Maleev, 1955) (originally Tarbosaurus) genus misassigned, now Tarbosaurus bataar
T. torosus (D. A. Russell, 1970) (originally Daspletosaurus) genus misassigned, now Daspletosaurus torosus
T. novojilovi (Maleev, 1955) (originally Gorgosaurus) = Tarbosaurus bataar
T. turpanensis Zhai, Zheng & Tong, 1978 species misassigned, now Tarbosaurus bataar
T. luanchuanensis Dong, 1979 nomen dubium genus misassigned, now Tarbosaurus luanchuanensis
T. lancinator (Maleev, 1955) (originally Gorgosaurus) species misassigned, now Tarbosaurus bataar
T. lanpingensis Yeh, 1975 nomen dubium genus misassigned, now Tarbosaurus lanpingensis

Refer to Tyrannosauridae for a complete list of advanced tyrannosaurs, like Gorgosaurus, Albertosaurus and Alectrosaurus. Refer to Tyrannosauroidea for a discussion of primitive tyrannosaurs, such as Dilong, Guanlong and Eotyrannus.

Other giant theropods

A number of other giant carnivorous dinosaurs have been discovered, including Carcharodontosaurus, Giganotosaurus, Tyrannotitan, Mapusaurus, Torvosaurus, Acrocanthosaurus and a giant species of Allosaurus. Giganotosaurus appears to have been larger than Tyrannosaurus - longer, although possibly not as heavy. In the film Jurassic Park 3, Spinosaurus is depicted as being larger than Tyrannosaurus and fossils described in 2006 support this, showing that Spinosaurus was about 4 meters longer and 4 tons heavier than Tyrannosaurus (a size comparison of the largest theropods can be found in the article Dinosaur size). There is still no clear scientific explanation for exactly why these animals grew so much larger than the predators that came before and after them.

Appearances in popular culture

Tyrannosaurus is by far the most widely-recognised dinosaur in popular culture. It has appeared in a number of films and books and is typically portrayed as the biggest and most terrifying dinosaur of all. There are also numerous Tyrannosaurus toys and other merchandise.

At Sue's debut, on 17 May 2000, more than 10,000 visitors went to see her, at the Chicago Field Museum of Natural History. A new piece of music, performed by the Chicago Chamber Musicians and written especially for the opening, made its own debut. It is called Tyrannosaurus Sue: A Cretaceous Concerto.

Footnotes

References

External links

Cretaceous dinosaurs | North American dinosaurs | Tyrannosaurs | Jurassic Park species

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