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For the rock group Tyrannosaurus Rex, see T. Rex (band).

Template:Taxobox begin
Template:StatusFossil Template:Taxobox image Template:Taxobox begin placement Template:Taxobox regnum entry Template:Taxobox phylum entry Template:Taxobox classis entry Template:Taxobox superordo entry Template:Taxobox ordo entry Template:Taxobox familia entry Template:Taxobox genus entry Template:Taxobox species entry Template:Taxobox end placement Template:Taxobox section binomial Template:Taxobox end Tyrannosaurus rex ("tyrant lizard king"), also known colloquially as The King of the Dinosaurs, was a giant carnivorous theropod dinosaur from the Upper Maastrichtian, the last stage of the Cretaceous period, 65–66 million years ago. Its fossil remains are rare; as of 2005 only 30 specimens had been foundTemplate:Fn, including three complete skulls. The first specimens found played an important role in the Bone Wars. T. rex is the best known carnivorous dinosaur, particularly because it was regarded as the largest to have ever existed for a long time. While there have been sensationalistic claims of new, larger theropods "dethroning" T. rex as the King of the Dinosaurs, evidence remains scant and open to debate. Although evidence shows that Giganotosaurus was larger, T. rex will very likely remain a subject of ongoing scientific research and popular culture.

Discoveries

The locations of all of the discoveries are restricted to North America. The first specimen (a partial vertebra) was found by Edward Cope in 1892 and was described as Manospondylus gigas. It was assigned to Tyrannosaurus rex in 1912 by Henry Osborn. Barnum Brown, assistant curator of the American Museum of Natural History, found the second T. rex skeleton in Wyoming in 1900. This specimen was originally named Dynamosaurus imperiosus in the same paper in which Tyrannosaurus rex was described. Were it not 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 2000, there was a controversy regarding its name because the dinosaur bones unearthed in South Dakota in June may have been part of a fossil known as Manospondylus gigas. According to the rules of International Commission on Zoological Nomenclature, the system that gives animals their Latin designation, Cope's name—Manospondylus gigas—should have priority because his discovery came first. However, in the ICZN 4th edition, which took effect on 1 January 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. Therefore, regardless of the result of the discovery, the "Tyrannosaurus rex" name is still used by biologists today.

Characteristics

Up to 13 meters (43 feet) in length and 4–7 tons in weight, T. rex was one of the largest carnivorous dinosaurs of all time. Compared to other carnivorous dinosaurs, the skull of Tyrannosaurus is heavily modified. 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 wear and the bite marks found on bones of other dinosaurs indicate that these teeth could bite into solid bone. The teeth are often worn or broken at the tips from heavy use but, unlike mammals, were continually grown and shed throughout the life of the animal. Compared to other giant carnivorous dinosaurs such as Allosaurus, Tyrannosaurus appears to have had a sizeable brain, but was probably not particularly intelligent by mammalian standards.

The neck was short and contained a large number of muscles. The arms of T. rex were small, perhaps to make up for the weight of its enormous head, but were very sturdy. Paleontologists continue to argue about what purpose, if any, they served. They may have been used by males to grab the female during sex, and certainly helped the animal to stand upright, temporarily supporting the front body. The legs were relatively long and slender for an animal of its size. Recent research suggests that an adult Tyrannosaurus could not run much, but juveniles might have been easily as fast as a modern lion. Most scientists and paleontologists believe adults were not fast runners. The formation of its hip bone relative to the legs and spine suggests a muscle tissue development and posture that would have enabled the animal to run close to 30 mph (50 km/h) in adulthood. Evidence of its prey in fossils and migrating patterns suggests this animal would probably have needed to sustain a speed adequate enough to hunt its prey. To compensate for its immense bulk, the interior of many bones were hollow. This considerably reduced the weight of the skeleton while maintaining much of the strength of the bones.

Biology

As with all dinosaurs, much of Tyrannosaurus' biology—its lifespan, breeding strategy, coloration, ecology and physiology—remains unknown. A site in Alberta has at least nine Albertosaurus sarcophagus individuals of different ages preserved together, but whether these animals lived together or simply died together is unclear.

Blood

It is debated whether T. rex was warm- or cold-blooded, and no definitive evidence exists to disprove either argument. Opinion may favor the dinosaur being homeothermic (warm-blooded), although probably not as warm-blooded as modern mammals. There is some speculation that the creature's homeothermic strategy might have changed at times in its life cycle.

Feathers

From the mid-1990s on, feathered tyrannosaurs were a controversial subject. But at least some tyrannosaurids appear to have been feathered. Small coelurosaurs 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 as well. In 2004, the primitive tyrannosaurid Dilong paradoxus was discovered from the same formation with preserved long tail plumes. However, (adult) tyrannosaurs in Alberta and Mongolia have skin impressions which appear to show the pebbly scales typical of other dinosaurs. It is possible that tyrannosaurs lost their feathers as they grew, similar to the hair density of an elephant as it grows, or were only feathered on parts of their bodies. In general, small animals need insulation more than large ones because of their proportionately larger surface areas.

Feeding patterns

The discussion about the feeding patterns of T. rex and other large carnivorous dinosaurs remains active. Most paleontologists have portrayed them as highly active predators, while others see them as obligate scavengers (Lambe 1917; Colinvaux 1978; Halstead and Halsted 1981; Barsbold 1983; Horner and Lessem 1993; Horner 1994; Horner and Dobb 1997). The scavenger hypothesis has been re-proposed by Jack Horner in the 1990s and appeared in Horner's 1993 book "The Complete T. rex".

Clues proposed by Horner speaking in favor of the scavenger hypothesis are their large (relative to their brain size) olfactory bulbs and olfactory nerves, as wide as the spinal cord. These suggest a highly developed sense of smell, allegedly used to sniff out carcasses over great distances, like modern vultures. Their teeth could crack bone; a skill perhaps needed most when last to a kill and in need of extracting as much food (marrow) as possible from a carcass's least nutritious parts. Horner also pointed out that modern hunters use their forelimbs to capture prey, while T. rex could hardly manipulate carcasses with its short and useless forelimbs. With new evidence that T. rex might have had feathers, the possibility of long bristle feathers on its forelimbs changes the certainty of this argument. Bristle feathers are stiff, tapering feathers with a large rachis but few barbs.

T. rex had incredibly powerful jaws with serrated teeth; one bite could break most anything in half. But why be so well armed if T. rex were a scavenger? The scavenger role of T. rex does not implicitly fit very well. Tyrannosaurus was very well equipped to drive other predators from their kills. The incredibly powerful neck muscles and huge cervical vertebrae projections, far bigger than on other theropods of similar size, even those of the larger Gigantosaurus from another era, and binocular vision, prove that Tyrannosaurus was adapted to move its head and bite very fast indeed—and usually outfight anything but perhaps its own species. Tyrannosaurus also had far stronger jaws than other kinds of carnosaur, even those like Gigantosaurus that were bigger in size. A coprolite of Tyrannosaurus has been found filled with fossilized bone fragments that demonstrate the power of this animal's jaws. When Tyrannosaurus fought any opponent, the first solid bite-hold would win the fight. It probably bit off chunks of meat and bone from prey and then backed up to tear it off, as Tyrannosaurus could on solid ground have about the same traction as an elephant. The swallowing of bone also allowed the animal to absorb calcium and other minerals for replacement teeth.

The ocular cavities of Tyrannosaurus are positioned so that the eyes would point forward, like a lion or a human. A scavenger rex would not need the advanced depth perception that stereoscopic vision affords. If Tyrannosaurus fed only from carrion, then a panoramic vision system would help to fine-tune location of a kill in any direction, after sense of smell would point the way. Stereoscopic vision is essential for predatory animals which catch other animals (owls, for example), but has secondary importance for animals which are chased (such as rabbits or deer).

Adaptations for running

Many scientists currently believe the "T. rex" was a predator and able to run. However, this is debated by many other scientists, including Horner. Horner's main argument is that T. rex adults were walkers and not runners. Therefore, Horner said, it is more likely to be a scavenger. However, predators do not have to be swift. A walking Tyrannosaurus could still cover many miles of territory with little fatigue. It may have hunted as primitive humans often do, simply dogging prey until the prey was exhausted or trapped by some geographic obstacle such as a cliff, river or steep slope.

Speed can be measured in some ways, using an analogy with living animals and sports (the femur/tibia ratio), using biomechanics, or using footprints (trace fossils). For instance, bicyclists with longer thighs are said to have better endurance.

Horner claims that the femur (thigh bone) to tibia (shin bone) ratio (>1, as in almost all large theropods) suggests a specialized walker rather than a runner—hence a slow scavenger rather than a fast-running predator. However, T. rex's legs were better designed for speed than its probable prey .

Another argument from Jack Horner regarding T. rex's slow speed is its useless forelimbs mentioned above. It could not catch itself should it fall over in a high-speed hunt (and perhaps sustain severe injuries because of its heavy skull size) and would therefore have to play it safe by walking rather than running. This claim has been substantiated by Farlow et al. (1995): they used a mathematical model using impact forces and decelerations for an animal weighing 6000 kg to gauge that a fall at very high speed (20 m/s or 72 km/h, the top speed used in most models) would kill it. They speculate a top speed of adult individuals of about 10 m/s (36 km/h).

The claim that T. rex's legs were not suitably adapted for high speed is an important point independent of the predator/scavenger debate. A paper in Nature (Hutchinson and Garcia 2002) states that Tyrannosaurus was not a fast runner. It used a mathematical model (based on chickens and alligators) to gauge the leg-muscle mass needed for some top speeds. They found that some proposed top speeds (40 km/h or 25 mph, or even 72 km/h or 45 mph) are quite unfeasible, because they require very large leg muscles (needing ~86% of total body mass as leg muscles). They specify a very rough upper estimate of 18 km/h or 11 mph.

However, those figures depend on the popular assumption that T. rex weighed around 6–8 tons. Some have suggested that T. rex may have weighed a mere four tons , since its bones were rather hollow and its breathing style would have required less mass. This would probably result in a much higher top speed. Even if T. rex or other large theropods were rather slow (as argued by Farlow et al. 1995; Hutchinson and Garcia 2002), it does not necessarily mean they were incapable of hunting prey. The dinosaurs they probably hunted were likely even slower, and ambush tactics were very likely. Also, younger examples of Tyrannosaurus were of course smaller, and young members of the species could probably run very fast, in contrast with large, older specimens. Most modern-day carnivores are not exclusively scavengers or active predators, and this was probably true of T. rex as well.

However, the fact that T. rex had longer femurs and legs than other theropods points to the fact that T. rex could indeed reach higher speeds than implicated. Secretary birds have long femurs and legs to improve the distance covered by each step, so even when taking a "slow pace" T. rex would still be moving 12 to 15 mph (the speed of a sprinting human). (Hutchinson and Garcia 2002) The mathematical model of chickens and alligators was not an accurate parallel of T. rex in most respects. For one thing, T. rex was a bipedal carnivore (unlike alligators), and the skeletal structure was more streamlined to decrease wind resistance (unlike chickens). Since it is almost impossible to definitively say what kind of muscle structure T. Rex had, no one can be certain as to what its true speed was.

Horner's claims

Powerful forelimbs are not necessary for all living predators, crocodiles and birds of prey like the Secretary Bird being prime examples. Obviously, these animals use their heads or hind legs as a main weapon, and T. rex's powerful jaws were its main weapon.

The available evidence of bite marks in other animals and even other T. rex, combined with the enormous serrated teeth and large jaw, seems to speak in favor of a role as predator. 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 T. rex embedded in a neck vertebra. This is strong evidence for aggressive behavior between tyrannosaurs, but whether it is competition for food/mates or active hunting (cannibalism) is unclear. In the Sue excavation site, an Edmontosaurus annectens skeleton was also found with healed scars. The fact that the scars seem healed suggests active predation instead of scavenging a previous kill.

Although not much is known about the vision of T. rex, the skulls clearly show that the eye sockets are positioned in such a way that they had binocular vision. Binocular (or stereoscopic) vision is typically seen in active predators such as hawks, owls, cats, and humans. But these animals have the benefit of being fast and relatively small, so they can sneak up on their prey first. An animal the size of T. rex could unlikely hunt in this manner, although T. rex is sometimes depicted as a "forest stalker". The option of being an active predator still remains open, however, because prey animals like Triceratops and duck-billed dinosaurs were possibly also comparably slow. Additionally, most predators prefer weakened opponents. Sharks and Komodo dragons all hunt the weaker members of the prey species. They rely on one surprise bite followed by a steady pursuit, watching the injured, fear-stricken prey until they can attack again. Tyrannosaurus may have used a similar strategy.

Being a scavenger has important ecological implications. 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 T. rex bully size and power allowed them to steal kills from smaller predators. While this is certainly a possibility, because (obviously) few animals will pass up a chance for a free meal, so T. rex probably did scavenge and hunt as well. Many carnivorous land animals have had such a lifestyle, such as the later mammalian predators Andrewsarchus, the modern Lion, the giant, piglike Entelodonts, and even the extinct Great Plains race of grizzly bear. All of these needed a well-tuned ecosystem producing reliable supplies of large animals, whether dead or alive, for food.

A consideration that should be made is that living carnivores are seldom strict predators or scavengers. Lions, for example, sometimes scavenge prey that hyenas have killed (and vice versa). Scavenging behavior depends on prey availability, among other causes.

The World of Tyrannosaurus rex

North America in the times of T. rex had both familiar and strange elements. The soft-shelled turtles, crocodiles, pike (Esocidae), and gar (Lepisosteidae) alive at the time are quite similar to those living today. Frogs and monitor lizards were other familiar animals. Ferns, palms, and shrubs were some of the dominant plants, but grasses had not yet evolved. Conifers such as sequoias were common. 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 around, including waterfowl. Other inhabitants of the landscape are more unfamiliar. There were birds with teeth, and birds had by then replaced most of the pterosaurs. Some giant pterosaurs still thrived, like Pteranodon and Quetzalcoatlus, which had a wingspan up to 35 feet. Herds of Triceratops and duck-billed dinosaurs (hadrosaurs) roamed the land. Mammals (predominantly multituberculates and marsupials) were mostly small, shrew- to rat-sized nocturnal animals. There were some mammals up to the size of a medium modern dog, as shown by recent fossils in China. Such mammals presumably lived in swamps or very heavy vegetation for cover as they could not run fast. Primitive primates may have been around (this issue is open to debate). Snakes had evolved by this time, very similar to some snakes today.

Individual specimens

In total Barnum Brown found five T. rex partial skeletons. Brown collected his second T. rex 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 T. rex fossil skeleton currently known, in the Hell Creek Formation near Faith, South Dakota, on August 12, 1990 . The T. rex, 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 $7.6 million. It has now been reassembled and is currently exhibited at the Field Museum of Natural History. Based on Sue's fossilized bones, she died at age 28 years, having reached her full size at age 19 yearsTemplate:Fn. Researchers report that a subadult and a juvenile skeleton were found in the same quarry as Sue; this lends evidence to the possibility that T. rex ran in packs or other groups.

Another T. rex, 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 currently is 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 T. rex tooth. Both Stan and Sue were examined by Peter Larson.

In 2001, a 50% complete skeleton of a juvenile Tyrannosaurus was discovered by a crew from the Burpee Museum 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.

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 T. Rex. 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, and simply not looking; since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.

Other tyrannosaurids

Tyrannosaurus rex was not the only member of the Tyrannosauridae. The following species have been identified:

(measurements given are based on found fossils and estimates)

The classification of these varies a little. For instance, T. bataar is mostly placed in the genus Tarbosaurus, and T. torosus is nearly always classified as a distinct genus Daspletosaurus. Nonetheless, Daspletosaurus, Tarbosaurus and Tyrannosaurus are very closely related, and belong to the tribe Tyrannosaurini.

Other tyrannosauroid and tyrannosaurid species include Dilong paradoxus, Eotyrannus lengi, Gorgosaurus libratus, Albertosaurus sarcophagus, and Alectrosaurus olseni.

Synonymies

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

They are believed to have required extensive geographic feeding ranges—nearly as large as a U.S. state. Theropods the size of T. rex 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 Template:Fn.

Other giant theropods

A number of other giant carnivorous dinosaurs have been discovered, including Carcharodontosaurus, Giganotosaurus, Acrocanthosaurus, and a giant species of Allosaurus. Giganotosaurus appears to have been larger than Tyrannosaurus. In the film Jurassic Park 3, Spinosaurus is depicted as being larger than Tyrannosaurus, but there is insufficient actual fossil material to accurately estimate the size of that animal. 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.

Notes

• Template:Fnb In the Field, January-February 2005 issue, Field Museum of Natural History.
• Template:Fnb Scientific American, 290, no. 2, February 2004 pp. 23-24.

References

• Farlow, J. O., Smith, M. B., Robinson, J. M. (1995). Body mass, bone "strength indication," and cursorial potential of Tyrannosaurus rex. Journal of Vertebrate Paleontology, 15: 713-725.
• Holtz, T. R. (1994). The phylogenetic position of the Tyrannosauridae: implications for theropod systematics. Journal of Paleontology 68(5): 1100-1117.
• Horner, John R. and Lessem, Don. The Complete T. Rex. How Stunning New Discoveries Are Changing Our Understanding of the World's Most Famous Dinosaur. Simon and Schuster, 1993. ISBN 0-671-74185-3
• Hutchinson, J. R., Garcia, M. (2002). Tyrannosaurus was not a fast runner. Nature 415:1018-1021.
• Osborn, H. F. (1905). Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the American Museum of Natural History 35:733-771.
• Osborn, H. F. (1917). Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus. Bulletin of the American Museum of Natural History 35: 733-71.
• Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R., Toporski, J. K. (2005). Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. Science 5717: 1952-1955.

External links

• The secret of T. rex's colossal size: a teenage growth spurt (The Guardian August 12, 2004)
• Sue's homepage
• Stan's homepage
• Pictures of a replica of Sue the T. rex
• History of the first T. rex finds
• Article on T. rex' life
• Tree of Life discussing Tyrannosauridae
• Unearthing Tyrannosaurus rex
• T.rex juvenile Jane

• Dinosaurs
• Theropods
• Jurassic Park species