Tyrannosaurus

? Tyrannosaurus rex Conservation status: Fossil
Fossil skeleton at National Museum of Natural History, Washington, DC
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Superorder: Dinosauria Order: Theropoda Family: Tyrannosauridae Genus: Tyrannosaurus Species: T. rex
Binomial name
Tyrannosaurus rex Osborn, 1905

Tyrannosaurus rex (ty-RAN-o-sawr-us) meaning "king tyrant lizard" because of its size and large teeth and claws ( Greek tyrannos = "tyrant" + sauros = "lizard"; Latin rex = "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, 68–65 million years ago. As of 2005 30 specimens had been found, including three complete skulls. The first specimens found played an important role in the Bone Wars. T. rex is the best known predatory dinosaur, particularly because for a long time it was regarded as the largest to have ever existed. While there have been published reports of larger predatory dinosaurs (such as Giganotosaurus and Spinosaurus), T. rex will very likely remain a prime 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 fossil 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. 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 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. Therefore, regardless of the result of the discovery, the "Tyrannosaurus rex" name is still used by biologists today .

Characteristics

About 12-13 m (39-43 ft) in length, 5 m (16 ft) tall and estimated to be from 4 tonnes to 8 tonnes in weight, T. rex was one of the largest land 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.

The neck was short and muscular, 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 mating 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, remain unknown. A site in Alberta has at least nine individuals of Albertosaurus sarcophagus (a closely related animal) of different ages preserved together, but whether these animals lived together or simply died together is unclear.

Feathers

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 tyrannosauroid 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.

Evidence for scavenging

Most debate about T. rex centers on its feeding patterns and locomotion. One paleontologist, noted hadrosaur expert Jack Horner, claims that T. rex was exclusively a scavenger, and did not engage in active hunting at all . Horner has only presented this in an official scientific context once, mainly discussing it in his books and in the media. His hypothesis is based on the following: 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. T. rex teeth could crush bone; a skill perhaps needed most when last to a kill and in need of extracting as much food ( bone 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 (see more on this below) .

All scientists who have published on the subject since insist that T. rex was both a predator and a scavenger, taking whatever meat it could get depending on the opportunity it was presented with . Modern carnivores are seldom strict predators or scavengers. Lions, for example, sometimes scavenge prey that hyenas have killed (and vice versa). Scavenging behaviour depends on prey availability, among other factors.

Evidence for hunting

Some evidence exists that suggests hunting behaviour in T. rex. 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 which have binocular vision yet are mostly scavangers). Bite marks in other animals and even other T. rex suggest predatory behaviour.

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. If correct, it might be strong evidence for aggressive behaviour between tyrannosaurs, but whether it would be competition for food/mates or active hunting ( 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. The fact that the scars seem healed suggests active predation instead of scavenging a previous kill.

The rarity of surviving tyrannosaur fossils itself suggests that T. rex was a predator, due to the ratio of predators to prey in most ecosystems.

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 T. rex could run, and exactly how fast it might have been; speculation has been up to 70 km/h (45 mph) or even more.

Evidence for fast running T. rex

Scientists who think that T. rex was able to run quickly point out that hollow T. rex bones and other features that would have lightened its body may have kept adult weight to a mere 5 tonnes 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 T. rex had relatively larger leg muscles than any animal alive today, which could have enabled fast running (40-70 km/h or 25-45 mph).

Evidence for walking T. rex

Some old studies of leg anatomy and living animals suggested that T. rex 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 T. rex was a specialized walker, like modern elephants. 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 tonnes would produce a lethal impact force if the dinosaur fell. It should be noted, however, that giraffes have been known to gallop at 50 km/h (31 mph) [10]; at those speeds, the animal risks breaking a leg or worse, which can be fatal even when the accident occurs in "safe" environments such as zoos [11]. If it could run, T. rex may have been a risk-taker in much the same way as animals alive today are. Yet estimates of leg bone strength in T. rex 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.

Walking proponents estimate the top speed of T. rex at about 17 km/h (11 mph). This is still faster than the most likely prey species that co-existed with tyrannosaurs: hadrosaurs and ceratopsians . 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 , or it may have used ambush tactics to attack faster prey animals.

A moderate case for a reasonably athletic T. rex

The most recent research on T. rex locomotion does not specify how fast T. rex may have run, but admits that we have 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 Nature (Hutchinson & Garcia 2002) 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 -- the problem is, it is unknown how large the leg muscles were. If they were smaller, only ~11 mph walking/jogging might have been possible.

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.

The world of Tyrannosaurus rex

North America in the times of Tyrannosaurus 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, 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 around, including waterfowl. Other inhabitants of the landscape are more unfamiliar. There were birds with teeth, and some of the giant pterosaurs still thrived, such as Quetzalcoatlus, which had an estimated wingspan of 12 m. Herds of Triceratops and duck-billed dinosaurs (hadrosaurs) such as Edmontosaurus and Maiasaura roamed the land. 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.

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 USD 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 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 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 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 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. [18]

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	12 m	4.2 m	5 tonnes	China, Mongolia	Lower Maastrichtian
T. rex (Osborn, 1905)	1.75 m	13.8 m	5 m	5.5 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 .

Other giant theropods

A number of other giant carnivorous dinosaurs have been discovered, including Carcharodontosaurus, Giganotosaurus, Torvosaurus, 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, and fossils described in 2006 support this, showing that Spinosaurus was about 4 meters longer and 4 tons heavier than 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.