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===Skin and feathers===
 
===Skin and feathers===
 
In 2004, the scientific journal ''[[wikipedia:Nature (journal)|Nature]]'' published a report describing an early tyrannosauroid, ''[[wikipedia:Dilong paradoxus|Dilong paradoxus]]'', from the famous [[wikipedia:Yixian Formation|Yixian Formation]] of China. As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feathers. It has also been proposed that ''Tyrannosaurus'' and other closely related tyrannosaurids had such protofeathers. However, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs.<ref>[http://www.dinosauria.com/jdp/trex/skin.htm Tyrannosaur Skin Impression Found In Alberta.] (1996-03-25). D. Tanke.</ref> While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of [[wikipedia:thermal insulation|insulatory]] body covering is consistent with modern multi-ton mammals such as elephants, hippopotamus, and most species of rhinoceros. As an object increases in size, its ability to retain heat increases due to its decreasing surface area-to-volume ratio. Therefore, as large animals evolve in or [[wikipedia:Biological dispersal#Dispersal in animals|disperse]] into warm climates, a coat of fur or feathers loses its [[wikipedia:natural selection|selective]] advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids like ''Tyrannosaurus'', especially in warm Cretaceous climates.<ref name="xuetal2004">Xing Xu, Mark A. Norell, Xuewen Kuang, Xiaolin Wang, Qi Zhao and Chengkai Jia. ''Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids'', from the Journal of Nature, vol. 431, issue 7009, pp. 680–684 (2004-10-07).</ref>
 
In 2004, the scientific journal ''[[wikipedia:Nature (journal)|Nature]]'' published a report describing an early tyrannosauroid, ''[[wikipedia:Dilong paradoxus|Dilong paradoxus]]'', from the famous [[wikipedia:Yixian Formation|Yixian Formation]] of China. As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feathers. It has also been proposed that ''Tyrannosaurus'' and other closely related tyrannosaurids had such protofeathers. However, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs.<ref>[http://www.dinosauria.com/jdp/trex/skin.htm Tyrannosaur Skin Impression Found In Alberta.] (1996-03-25). D. Tanke.</ref> While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of [[wikipedia:thermal insulation|insulatory]] body covering is consistent with modern multi-ton mammals such as elephants, hippopotamus, and most species of rhinoceros. As an object increases in size, its ability to retain heat increases due to its decreasing surface area-to-volume ratio. Therefore, as large animals evolve in or [[wikipedia:Biological dispersal#Dispersal in animals|disperse]] into warm climates, a coat of fur or feathers loses its [[wikipedia:natural selection|selective]] advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids like ''Tyrannosaurus'', especially in warm Cretaceous climates.<ref name="xuetal2004">Xing Xu, Mark A. Norell, Xuewen Kuang, Xiaolin Wang, Qi Zhao and Chengkai Jia. ''Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids'', from the Journal of Nature, vol. 431, issue 7009, pp. 680–684 (2004-10-07).</ref>
  +
  +
===Thermoregulation===
  +
''Tyrannosaurus'', like most dinosaurs, was long thought to have an ectothermic ("cold-blooded") reptilian metabolism. The idea of dinosaur ectothermy was challenged by scientists like [[wikipedia:Robert T. Bakker|Robert T. Bakker]] and [[wikipedia:John Ostrom|John Ostrom]] in the early years of the "[[wikipedia:Dinosaur Renaissance|Dinosaur Renaissance]]", beginning in the late 1960s.<ref name="bakker1968">Bakker, Robert T. 1968, ''The superiority of dinosaurs'', from the Journal of ''Discovery'', vol. 3, issue 2, pp. 11–12 [http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/Bakker%201968%20-%20Superiority%20of%20DInos.pdf]</ref><ref name="bakker1972">Robert T. Bakker, 1972. ''Anatomical and ecological evidence of endothermy in dinosaurs'', from the Journal of Nature, vol. 238, pp. 81–85. [http://bio.fsu.edu/~amarquez/Evolutionary%20Morphology%20fall%202004/Bakker/14-%20Bakker%201972%20-%20dino%20endothermy.pdf].</ref> ''Tyrannosaurus rex'' itself was claimed to have been endothermic ("warm-blooded"), implying a very active lifestyle.<ref name="bakker1986"/> Since then, several paleontologists have sought to determine the ability of ''Tyrannosaurus'' to [[wikipedia:thermoregulation|regulate]] its body temperature. Histological evidence of high growth rates in young ''T. rex'', comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, ''T. rex'' growth was limited mostly to immature animals, rather than the [[wikipedia:Indeterminate growth|indeterminate growth]] seen in most other vertebrates.<ref name="hornerpadian2004"/>
  +
  +
Oxygen isotope ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than 4 to 5°C (7 to 9°F) between the vertebrae of the torso and the tibia of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and [[wikipedia:geochemistry|geochemist]] William Showers to indicate that ''T. rex'' maintained a constant internal body temperature ([[wikipedia:Homeotherm|homeothermy]]) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals.<ref name="barrettshowers1994">Reese E. Barrick & William J. Showers. ''Thermophysiology of Tyrannosaurus rex: Evidence from Oxygen Isotopes'', from the Journal of Science, in New York City, vol. 265, issue 5169, pp. 222–224. 1994, July. [http://www.sciencemag.org/cgi/content/abstract/265/5169/222].</ref> Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization (diagenesis).<ref name="truemanetal2003">Clive Trueman, Carolyn Chenery, David A. Eberth and Baruch Spiro, 2003. ''Diagenetic effects on the oxygen isotope composition of bones of dinosaurs and other vertebrates recovered from terrestrial and marine sediments'', from the Journal of the Geological Society, vol. 160, issue 6, page 895.</ref> Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (''[[Giganotosaurus]]'').<ref name="barrickshowers1999">Barrick, Reese E. & William J. Showers, October 1999. "Thermophysiology and biology of ''Giganotosaurus'': comparison with ''Tyrannosaurus''", from the Journal of ''Palaeontologia Electronica'', vol. 2, issue 2, [http://palaeo-electronica.org/1999_2/gigan/issue2_99.htm].</ref> [[wikipedia:Ornithischia|Ornithischian]] dinosaurs also showed evidence of homeothermy, while [[wikipedia:varanidae|varanid]] lizards from the same formation did not.<ref name="barrickstevens1997">James O. Farlow and M. K. Brett-Surman, ''The Complete Dinosaur'', published by the Indiana University Press in Bloomington, 1999. pp. 474–490. ISBN 0-253-21313-4 Chapter: Oxygen isotopes in dinosaur bones. By Reese E. Barrick, Michael K. Stoskopf, and William J. Showers.</ref> Even if ''Tyrannosaurus rex'' does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by [[wikipedia:Gigantothermy|gigantothermy]], as in some living sea turtles.<ref name="paladinoetal1997">James O. Farlow and M. K. Brett-Surman, ''The Complete Dinosaur'', published by Indiana University Press in Bloomington, 1999. pp. 491–504. ISBN 0-253-21313-4 Chapter: A blueprint for giants: modeling the physiology of large dinosaurs, by Frank V. Paladino, James R. Spotila and Peter Dodson.</ref><ref name="chinsamyhillenius2004">David B. Weishampel, Peter Dodson and Halszka Osmólska ''The dinosauria'' University of California Press, in Berkeley, 2004. pp. 643–659. ISBN 0-520-24209-2 Chapter: Physiology of nonavian dinosaurs, by Anusuya Chinsamy, and Willem J. Hillenius.</ref>
 
[[Category:Dinosaurs]]
 
[[Category:Dinosaurs]]
 
[[Category:Carnivores]]
 
[[Category:Carnivores]]

Revision as of 20:16, 6 April 2017

Tyrannosaurus Rex
JW T-Rex
'Tyrannosaurus as it appeared in Jurassic World'

Suborder:

Therapoda

Name Translation:

Tyrant Lizard King

Period:

Late Cretaceous (68-65 mya)

Length:

42-49 feet long(12.8-14.9 meters)

Height:

15-21 feet tall (4.5-6.4 meters)

Weight:

6.6-9 tonnes

Tyrannosaurus (pronounced /tɨˌrænəˈsɔːrəs/ or /taɪˌrænoʊˈsɔːrəs/, meaning 'tyrant lizard') is a genus of theropod dinosaur. The famous species Tyrannosaurus rex ('rex' meaning 'king' in Latin), commonly abbreviated to T. rex, is a fixture in popular culture around the world, and is extensively used in scientific television and movies, such as documentaries and Jurassic Park, and in children's series such as The Land Before Time. Tyrannosaurus lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils of T. rex are found in a variety of rock formations dating to the last three million years of the Cretaceous Period, approximately 68 to 65 million years ago; it was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two primary digits, along with a possible third vestigial digit. Although other theropods rivaled or exceeded T. rex in size, it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 13 metres (43 ft.) in length,[1] up to 4 metres (13 ft.) tall at the hips,[2] and up to 6.8 metric tonnes (7.5 short tons) in weight.[3] By far the largest carnivore in its environment, T. rex may have been an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger.

More than 30 specimens of T. rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including life history and biomechanics. The feeding habits, physiology and potential speed of T. rex are a few subjects of debate. Its taxonomy is also controversial, with some scientists considering Tarbosaurus bataar from Asia to represent a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.


Description

Tyrannosaurusscale

Various specimens of Tyrannosaurus rex with a human for scale.

Theropodscalewithhuman

Size comparison of selected giant theropod dinosaurs, with Tyrannosaurus in purple.

Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 metres (42 ft) long, and was 4.0 metres (13 ft) tall at the hips.[2] Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons),[4] to less than 4.5 metric tons (5.0 short tons),[5][6] with most modern estimates ranging between 5.4 and 6.8 metric tons (6.0 and 7.5 short tons).[7][8][9][3] Although Tyrannosaurus rex was larger than the well known Jurassic theropod Allosaurus, it was slightly smaller than Cretaceous carnivores Spinosaurus and Giganotosaurus.[10][11]

The neck of T. rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs were long thought to bear only two digits, but there is an unpublished report of a third, vestigial digit in one specimen.[12] In contrast the hind limbs were among the longest in proportion to body size of any theropod. The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow, reducing its weight without significant loss of strength.[1]

Tyrannosaurus

The largest known T. rex skulls measure up to 5 feet (1.5 m) in length.[13] Large fenestrae (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects Tyrannosaurus’ skull was significantly different from those of large non-tyrannosauroid theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good binocular vision.[14][15] The skull bones were massive and the nasals and some other bones were fused, preventing movement between them; but many were pneumatized (contained a "honeycomb" of tiny air spaces) which may have made the bones more flexible as well as lighter. These and other skull-strengthening features are part of the tyrannosaurid trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids.[16][17][18] The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth.[19][20]

File:T.rex restoration.jpg

Life restoration of a Tyrannosaurus rex.

The teeth of T. rex displayed marked heterodonty (differences in shape).[21][1] The premaxillary teeth at the front of the upper jaw were closely packed, D-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards. The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers; more widely spaced and also had reinforcing ridges.[22] Those in the upper jaw were larger than those in all but the rear of the lower jaw. The largest found so far is estimated to have been 30 centimetres (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur.[2]

Paleobiology

Life history

T-rex graph

A graph showing the hypothesized growth curves (body mass versus age) of four tyrannosaurids. Tyrannosaurus rex is drawn in black. Based on Erickson et al. 2004.

The identification of several specimens as juvenile Tyrannosaurus rex has allowed scientists to document ontogenetic changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM 28471, the "Jordan theropod") is estimated to have weighed only 29.9 kg (66 lb), while the largest, such as FMNH PR2081 ("Sue") most likely weighed over 5400 kg (6 short tons). Histologic analysis of T. rex bones showed LACM 28471 had aged only 2 years when it died, while "Sue" was 28 years old, an age which may have been close to the maximum for the species.[3]

Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A T. rex growth curve is S-shaped, with juveniles remaining under 1800 kg (2 short tons) until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young T. rex would gain an average of 600 kg (1,300 lb) a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only 600 kg (1,300 lb) separated the 28-year-old "Sue" from a 22-year-old Canadian specimen (RTMP 81.12.1).[3] Another recent histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age.[23] This sudden change in growth rate may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur of a 16 to 20-year-old T. rex from Montana (MOR 1125, also known as "B-rex"). Medullary tissue is found only in female birds during ovulation, indicating that "B-rex" was of reproductive age.[24] Further study indicates an age of 18 for this specimen.[25] Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.[26]

Over half of the known T. rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile T. rex fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and so were not often fossilized. However, this rarity may also be due to the incompleteness of the fossil record or to the bias of fossil collectors towards larger, more spectacular specimens.[26]

Posture

Outdated Trex Posture

Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose.

Updated Trex posture

Replica at Senckenberg Museum, showing modern view of posture.

Like many bipedal dinosaurs, Tyrannosaurus rex was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a kangaroo. This concept dates from Joseph Leidy's 1865 reconstruction of Hadrosaurus, the first to depict a dinosaur in a bipedal posture.[27] Henry Fairfield Osborn, former president of the American Museum of Natural History (AMNH) in New York City, who believed the creature stood upright, further reinforced the notion after unveiling the first complete T. rex skeleton in 1915. It stood in this upright pose for nearly a century, until it was dismantled in 1992.[28] By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the dislocation or weakening of several joints, including the hips and the articulation between the head and the spinal column.[29] The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as Rudolph Zallinger's famous mural The Age Of Reptiles in Yale University's Peabody Museum of Natural History)[30] until the 1990s, when films such as Jurassic Park introduced a more accurate posture to the general public. Modern representations in museums, art, and film show T. rex with its body approximately parallel to the ground and tail extended behind the body to balance the head.[20]

Arms

File:T.rex arm.jpg

Closeup of forelimb; specimen at National Museum of Natural History, Washington, DC.

When Tyrannosaurus rex was first discovered, the humerus was the only element of the forelimb known.[31] For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of Allosaurus.[32] However, a year earlier, Lawrence Lambe described the short, two-fingered forelimbs of the closely related Gorgosaurus.[33] This strongly suggested that T. rex had similar forelimbs, but this hypothesis was not confirmed until the first complete T. rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex").[34] The remains of "Sue" also include complete forelimbs.[1] T. rex arms are very small relative to overall body size, measuring only 1 metre (3.3 ft) long. However, they are not vestigial but instead show large areas for muscle attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during copulation.[35] It has also been suggested that the forelimbs were used to assist the animal in rising from a prone position.[29] Another possibility is that the forelimbs held struggling prey while it was dispatched by the tyrannosaur's enormous jaws. This hypothesis may be supported by biomechanical analysis. T. rex forelimb bones exhibit extremely thick cortical bone, indicating that they were developed to withstand heavy loads. The biceps brachii muscle of a full-grown Tyrannosaurus rex was capable of lifting 199 kilograms (439 lb) by itself; this number would only increase with other muscles (like the brachialis) acting in concert with the biceps. A T. rex forearm also had a reduced range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in Deinonychus allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, extreme strength of the muscles, and limited range of motion may indicate a system designed to hold fast despite the stresses of a struggling prey animal.[36]

Soft tissue

In the March 2005 issue of Science, 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.[37] 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. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation.[38] If it is found 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.[37] Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.[39]

In studies reported in the journal Science in April 2007, Asara and colleagues concluded that seven traces of collagen proteins detected in purified T. rex bone most closely match those reported in chickens, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world."[40]

Subsequent studies in April 2008 confirmed the close connection of T. rex to modern birds. Postdoctoral biology researcher Chris Organ at Harvard University announced, "With more data, they would probably be able to place T. rex on the evolutionary tree between alligators and chickens and ostriches." Co-author John M. Asara added, "We also show that it groups better with birds than modern reptiles, such as alligators and green anole lizards."[41]

The presumed soft tissue was called into question by Thomas Kaye of the University of Washington and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy biofilm created by bacteria that coated the voids once occupied by blood vessels and cells.[42] The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually framboids; microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an ammonite. In the ammonite they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood.[43]

Skin and feathers

In 2004, the scientific journal Nature published a report describing an early tyrannosauroid, Dilong paradoxus, from the famous Yixian Formation of China. As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feathers. It has also been proposed that Tyrannosaurus and other closely related tyrannosaurids had such protofeathers. However, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs.[44] While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of insulatory body covering is consistent with modern multi-ton mammals such as elephants, hippopotamus, and most species of rhinoceros. As an object increases in size, its ability to retain heat increases due to its decreasing surface area-to-volume ratio. Therefore, as large animals evolve in or disperse into warm climates, a coat of fur or feathers loses its selective advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids like Tyrannosaurus, especially in warm Cretaceous climates.[45]

Thermoregulation

Tyrannosaurus, like most dinosaurs, was long thought to have an ectothermic ("cold-blooded") reptilian metabolism. The idea of dinosaur ectothermy was challenged by scientists like Robert T. Bakker and John Ostrom in the early years of the "Dinosaur Renaissance", beginning in the late 1960s.[46][47] Tyrannosaurus rex itself was claimed to have been endothermic ("warm-blooded"), implying a very active lifestyle.[6] Since then, several paleontologists have sought to determine the ability of Tyrannosaurus to regulate its body temperature. Histological evidence of high growth rates in young T. rex, comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, T. rex growth was limited mostly to immature animals, rather than the indeterminate growth seen in most other vertebrates.[23]

Oxygen isotope ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than 4 to 5°C (7 to 9°F) between the vertebrae of the torso and the tibia of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and geochemist William Showers to indicate that T. rex maintained a constant internal body temperature (homeothermy) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals.[48] Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization (diagenesis).[49] Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (Giganotosaurus).[50] Ornithischian dinosaurs also showed evidence of homeothermy, while varanid lizards from the same formation did not.[51] Even if Tyrannosaurus rex does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy, as in some living sea turtles.[52][53]

  1. 1.0 1.1 1.2 1.3 Brochu, Christopher A. and Richard A. Ketcham Osteology of Tyrannosaurus Rex: Insights from a Nearly Complete Skeleton and High-resolution Computed Tomographic Analysis of the Skull. 2003, Society of Vertebrate Paleontology, in Northbrook, Illinois. Cite error: Invalid <ref> tag; name "brochu2003" defined multiple times with different content
  2. 2.0 2.1 2.2 Sue's vital statistics Sue at the Field Museum. Field Museum of Natural History.
  3. 3.0 3.1 3.2 3.3 Erickson, Gregory M., Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; & Brochu, Christopher A., 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs, from the Journal of Nature, vol. 430, issue 7001, pp. 772–775. Cite error: Invalid <ref> tag; name "ericksonetal2004" defined multiple times with different content Cite error: Invalid <ref> tag; name "ericksonetal2004" defined multiple times with different content
  4. Henderson, DM, 1999. Estimating the masses and centers of mass of extinct animals by 3-D mathematical slicing, from the Journal of Paleobiology, vol. 25, issue 1, pp. 88–106 [1].
  5. Anderson, JF and Hall-Martin AJ, Russell, Dale A. 1985. Long bone circumference and weight in mammals, birds and dinosaurs, from the Journal of Zoology, vol. 207, issue 1, pp. 53–61.
  6. 6.0 6.1 Bakker, Robert T., 1986. The Dinosaur Heresies. New York, Kensington Publishing, ISBN 0-688-04287-2
  7. Farlow, James O., Smith MB, & Robinson, JM, 1995. Body mass, bone "strength indicator", and cursorial potential of Tyrannosaurus rex, from the Journal of Vertebrate Paleontology, vol. 15, issue 4, pp. 713–725. [2]
  8. Seebacher, Frank. 2001. A new method to calculate allometric length-mass relationships of dinosaurs, from the Journal of Vertebrate Paleontology, vol. 21, issue 1, pp. 51–60.
  9. Christiansen, Per & Fariña, Richard A., 2004. Mass prediction in theropod dinosaurs, from the Journal of Historical Biology, vol. 16, issues 2-4, pp. 85–92.
  10. dal Sasso, Cristiano and Maganuco, Simone; Buffetaut, Eric; & Mendez, Marcos A. 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities, from the Journal of Vertebrate Paleontology vol. 25, issue 4, pp. 888–896. [3]
  11. Calvo, Jorge O., and Rodolfo Coria, 1998, December. New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the as the largest theropod ever found, from the Journal of Gaia Revista de Geociências, vol. 15, pp. 117–122. [4]
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  13. Museum unveils world's largest T-rex skull (2006-04-07) Montana State University.
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