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Tyrannosaurus

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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 T-Rex and 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 relatively rare; as of 2005 only 30 specimens had been found[1], 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 evidence indicates that Giganotosaurus was probably larger, T. rex will very likely remain a subject of ongoing scientific research and popular culture.

Discovery and Classification

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 that year may have been part of a fossil known as Manospondylus gigas[2][3]. 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 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[4].

Characteristics

Closeup of jaws

Up to 13 meters (43 feet) in length and 4–7 tons in weight, T. rex was one of the largest carnivores 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.

Closeup of arm

The neck was short and musclular, to support the head. The arms of T. rex were very small, perhaps to make up for the weight of its enormous head, but were very sturdy. They may have been used for grasping during sex or as aids in standing. The legs were relatively long and slender for an animal of its size. 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 (a closely related animal) individuals of different ages preserved together, but whether these animals lived together or simply died together is unclear.

The size of Tyrannosaurus rex compared to a human

Feathers

Main article: Feathered dinosaurs

It has been proposed that T. rex 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 as well. In 2004, the primitive tyrannosaurid Dilong paradoxus was discovered from the same formation with preserved long tail plumes. However, skin impressions from adult tyrannosaurs in Alberta and Mongolia appear to show the pebbly scales typical of other dinosaurs. It is possible that tyrannosaurs lost their feathers as they grew, or were only feathered on parts of their bodies.

Scientific Debate

Most debate about T. rex centers on its feeding patterns and locomotion. Some scientists, including noted tyrannosaur expert Jack Horner, claim that T. rex was unable to run quickly and was primarily a scavenger. Others insist that T. rex was a fast runner and primarily a predator.

Evidence for Walking/Scavenging

T. rex have large (relative to their brain size) olfactory bulbs and olfactory nerves. 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. Since at least some T. rex prey animals could move quickly, evidence that T. rex walked instead of ran could indicate that it was a scavenger. The ratio of femur to tibia length (greater than 1, as in most large theropods) could indicate that T. rex was a specialized walker. In addition, T. rex had tiny arms that could not stop the dinosaur's fall if it stumbled while running: standard estimates of T. rex weight at 6 to 8 tons would produce a lethal impact force if the dinosaur fell. A paper in Nature (Hutchinson and Garcia 2002) used a mathematical model (based on chickens and alligators) to gauge the leg-muscle mass needed for some top speeds - they found that proposed top speeds in excess of 25 mph were unfeasible, because they would require very large leg muscles (more than ~86% of total body mass[5]). Walking/scavenging proponents estimate the top speed of T. rex at about 11 mph.

Evidence for Running/Hunting

The ocular cavities of T. rex 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 (though there are many notable exceptions, such as jackals and hyenas, which have binocular vision yet are mostly scavangers). Bite marks in other animals and even other T. rex seem 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. Scientists who believe T. rex was able to run quickly point out that hollow T. rex bones may have kept adult weight to a mere 4 tons[6], that chicken- and alligator-based models are inappopriate for a bipedal dinosaurian predator, or that other animals like secretary birds with long femurs are able to achieve high speeds through slower but longer strides. In addition, some predation advocates claim that T. rex running speed is not important, since it may have been slow but better designed for speed than its probable prey [7], or it may have used ambush tactics to attack faster prey animals.

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.

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 and China/Central Asia in the times of the tyrannosauids 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; grasses had evolved but were possibly not yet widespread. Conifers such as sequoias 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 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

File:TRex3a.jpg
Sue the T. rex, Field Museum, Chicago, showing the forearms. The wishbone is between the forearms

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.

File:Sue'sBrain.jpg
CT scan of Sue's brain. The olfactory bulbs are the most highly developed part. Scan taken at Boeing, Washington.

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 years[1]. 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. [8]

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. [9] The presence of medullary bones in this specimen is also of interest. [10]

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)

Species
reference 		Skull length Total length Hip height Weight Location Time
T. torosus
(Russell, 1970) 		1.1 m 9 m 2.5 m 2.3 tonnes Alberta, Montana Upper Campanian
T. bataar
(Maleev, 1955) 		1.35 m 10 m 2.9 m 5 tonnes China, Mongolia Lower Maastrichtian
T. rex
(Osborn, 1905) 		1.75 m 13.6 m 4.4 m 7 tonnes Alberta, Saskatchewan, Colorado,
Montana, New Mexico, N. Dakota,
S. Dakota, Wyoming, Texas? 		Upper Maastrichtian

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 [nomen 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. 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 [11].

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

  1. ^ In the Field, January-February 2005 issue, Field Museum of Natural History.
  2. ^ "Discovery could Endanger T.Rex Name". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  3. ^ ":: Discovery Channel CA ::". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  4. ^ "So why hasn't Tyrannosaurus been renamed Manospondylus?". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  5. ^ "http://www.priweb.org/ed/ICTHOL/ICTHOL04papers/86.htm". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help); External link in |title= (help)
  6. ^ "Unearthing T. rex : T.rex In-Depth : Traits". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  7. ^ "Unearthing T. rex : T.rex In-Depth : Traits (See above)". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  8. ^ "Jane lives!". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  9. ^ "BBC NEWS : Science/Nature : T. rex fossil has 'soft tissues'". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)
  10. ^ "http://www.washingtonpost.com/wp-dyn/content/article/2005/06/03/AR2005060300141.html". December 11. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help); External link in |title= (help)
  11. ^ Scientific American, 290, no. 2, February 2004 pp. 23-24.

References

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