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Tyrannosaurus

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Manetho
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« Reply #15 on: July 23, 2007, 01:39:53 pm »



A computer-generated T. rex roars as a banner reading "When Dinosaurs Ruled the Earth" glides down, asserting its dominance as king of the dinosaurs. Shot taken from the 1993 Steven Spielberg film Jurassic Park.
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« Reply #16 on: July 23, 2007, 01:40:48 pm »

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. 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.[43] 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.[44] Research on some of the tissues involved have suggested that birds are closer relatives to tyrannosaurs than other modern animals.[45]

In subsequent studies reported in the journal Science in April 2007, Asara and colleagues concluded that seven traces of 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."
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Manetho
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« Reply #17 on: July 23, 2007, 01:42:25 pm »



A baby T. Rex, covered with down.
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« Reply #18 on: July 23, 2007, 01:43:58 pm »

Skin

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. 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.
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« Reply #19 on: July 23, 2007, 01:44:53 pm »

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 Bakker and John Ostrom in the early years of the "Dinosaur Renaissance", beginning in the late 1960s.[48][49] Tyrannosaurus rex itself was claimed to have been endothermic ("warm-blooded"), implying a very active lifestyle.[4] 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.[28]

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.[50] 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).[51] 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).[52] Ornithischian dinosaurs also showed evidence of homeothermy, while varanid lizards from the same formation did not.[53] Even if Tyrannosaurus rex does exhibit evidence of homothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy, as in some living sea turtles.
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« Reply #20 on: July 23, 2007, 01:46:19 pm »



Tyrannosaurus rex skull and upper vertebral column, Palais de la Découverte, Paris.
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« Reply #21 on: July 23, 2007, 01:47:03 pm »

Feeding strategies

Most debate about Tyrannosaurus centers on its feeding patterns and locomotion. One paleontologist, noted hadrosaur expert Jack Horner, claims that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all.[40] Horner has only presented this in an official scientific context once, while mainly discussing it in his books and in the media. His hypothesis is based on the following: Tyrannosaurs have large olfactory bulbs and olfactory nerves (relative to their brain size). These suggest a highly developed sense of smell, allegedly used to sniff out carcasses over great distances. Tyrannosaur teeth could crush bone, a skill perhaps used to extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Since at least some of Tyrannosaurus's prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.[56][57]

Most scientists who have published on the subject since insist that Tyrannosaurus was both a predator and a scavenger, taking whatever meat it could acquire depending on the opportunity that was presented.[58] Modern carnivores such as lions and hyenas will often scavenge what other predators have killed, suggesting that tyrannosaurs may also have done so.[59]

Some other evidence exists that suggests hunting behavior in Tyrannosaurus. The ocular cavities of tyrannosaurs are positioned so that the eyes would point forward, giving the dinosaur binocular vision.[60] A scavenger might not need the advanced depth perception that stereoscopic vision affords; in modern animals, binocular vision is found primarily in predators.

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« Reply #22 on: July 23, 2007, 01:48:03 pm »



T. rex right hind foot (medial view) Oxford University Museum of Natural History.
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« Reply #23 on: July 23, 2007, 01:48:34 pm »

When examining Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurus embedded in a neck vertebra. If correct, it might be strong evidence for aggressive behavior between tyrannosaurs but whether it would be competition for food and mates or active cannibalism is unclear.[61] However, further 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.[62] In the Sue excavation site, an Edmontosaurus annectens skeleton was also found with healed tyrannosaur-inflicted scars on its tail. The fact that the scars seem to have healed suggests active predation instead of scavenging a previous kill.[63][64] Another piece of evidence is a Triceratops found with bite marks on its ilium. Again, these were inflicted by a tyrannosaur and they too appear healed.[65]

There have been conflicting studies regarding the extent to which Tyrannosaurus could run and exactly how fast it might have been; speculation has suggested speeds up to 70 km/h (45 mph) or even more. However, according to James Farlow, a palaeontologist at Indiana-Purdue University in Fort Wayne, Indiana, "If T. rex had been moving fast and tripped, it would have died."[66] If it tripped and fell while running, a tumbling tyrannosaur's torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 m/s²).[5] (See also Locomotion, below.)

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 as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills from smaller predators.
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« Reply #24 on: July 23, 2007, 01:50:08 pm »



T. rex right hind foot (lateral) Oxford University Museum of Natural History.
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« Reply #25 on: July 23, 2007, 01:51:00 pm »

Locomotion

Scientists who think that Tyrannosaurus was able to run slowly point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere 5 tons or so, or that other animals like ostriches and horses with long, flexible legs are able to achieve high speeds through slower but longer strides. Additionally, some have argued that Tyrannosaurus had relatively larger leg muscles than any animal alive today, which could have enabled fast running (40–70 km/h or 25–45 mph).[67]

Some old studies of leg anatomy and living animals suggested that Tyrannosaurus could not run at all and merely walked. The ratio of femur (thigh bone) to tibia (shank bone) length (greater than 1, as in most large theropods) could indicate that Tyrannosaurus was a specialized walker, like a modern elephant. In addition, it had tiny 'arms' that could not have stopped the dinosaur's fall, had it stumbled while running; standard estimates of Tyrannosaurus weight at 6 to 8 tons would produce a lethal impact force, should it have fallen.[68] It should be noted, however, that giraffes have been known to gallop at 50 km/h (31 mph).[69] At those speeds, the animal risks breaking a leg or worse, which can be fatal even when the accident occurs in a 'safe' environment, such as a zoo.[70] If it could run, Tyrannosaurus may have been a risk-taker, in much the same way as animals alive today are. Yet estimates of leg bone strength in Tyrannosaurus show that its legs were little stronger, if at all, than those of elephants, which are relatively limited in their top speed and do not ever become 'airborne', as would happen in running.

Walking proponents estimate the top speed of Tyrannosaurus at about 17 km/h (11 mph). This is still faster than the most likely prey species that co-existed with tyrannosaurs; the hadrosaurs and ceratopsians.[71] In addition, some predation advocates claim that tyrannosaur running speed is not important, since it may have been slow but better designed for speed than its probable prey[72] or it may have used ambush tactics to attack faster prey animals.
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« Reply #26 on: July 23, 2007, 01:51:44 pm »

The most recent research on Tyrannosaurus locomotion does not specify how fast Tyrannosaurus may have run, but admits that there is little capacity to narrow down speeds further than a range from 17 km/h (11 mph), which would be only walking or slow running, to 40 km/h (25 mph), which would be moderate-speed running. For example, a paper in Nature[71] used a mathematical model (validated by applying it to two living animals, alligators and chickens) to gauge the leg muscle mass needed for fast running (over 25 mph / 40 km/h). 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.)[73] Even moderately fast speeds would have required large leg muscles. This discussion is difficult to resolve, as it is unknown how large the leg muscles were. If they were smaller, only ~11 mph (18 km/h) walking/jogging might have been possible.[67]

According to Thomas R. Holtz Jr however, it is notable that in terms of any animal as massive as it was (5-7 tons), the tibia/femur and metatarsus/femur ratio of tyrannosaurs are the most gracile known of any animal in the Mesozoic or Cenozoic fossil record.

At the typical size of an adult Tyrannosaurus, gracile limb proportions appear bulky. However, when compared to the hindlimbs of other similarly sized animals, like an elephant (as a modern example), a Triceratops, or Edmontosaurus, the legs of Tyrannosaurus rex are more slender and have relatively longer tibiae and metatarsi.

In relation to other large theropod families, tyrannosaurids had limb proportions that are more gracile. The smaller tyrannosaurids were even more gracile, and the smallest had the same limb proportions to the largest ornithomimids: in terms of measurement, the legs of Alectrosaurus and Gallimimus are identical (Holtz).

Additionally, tyrannosaurids had ornithomimid-like feet, which were smaller and more slender than that of other large theropod families, which would equate to more efficient locomotion as the leg was articulated while the animal was moving.

According to Holtz, with functional morphology as a guide, tyrannosaurids would be better adapted for speed than any other family of large theropod, including allosauroids, megalosauroids and neoceratosaurs. This may not mean that T. rex was capable of the more fantastic speed figures estimated for it, but that it was, for an animal for its size, optimised for speed, and in relevance to the predator/scavenger debate, faster than its prey.[74]

New evidence based on biomechanic computer models suggests Tyrannosaurus had a poor turning circle. According to John Hutchinson, expert on biomechanics at the University of London's Royal Veterinary College in England, Tyrannosaurus would probably have taken one to two seconds to turn only 45° – an amount that humans, being vertically oriented and tail-less, can spin in just a fraction of a second.
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« Reply #27 on: July 23, 2007, 01:52:38 pm »



T. rex mounted skeleton
(Oxford University Museum of Natural History).
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« Reply #28 on: July 23, 2007, 01:54:31 pm »

History

Henry Fairfield Osborn, president of the American Museum of Natural History, named Tyrannosaurus rex in 1905. The generic name is derived from the Greek words τυραννος (tyrannos, meaning "tyrant") and σαυρος (sauros, meaning "lizard"). Osborn used the Latin word rex, meaning "king", for the specific name. The full binomial therefore translates to "tyrant lizard king," emphasizing the animal's size and perceived dominance over other species of the time.

Earliest finds

The vertebrae named Manospondylus by Cope in 1892 can be considered the first known specimen of Tyrannosaurus rex. Barnum Brown, assistant curator of the American Museum of Natural History, found the second Tyrannosaurus skeleton in Wyoming in 1900. This specimen was originally named Dynamosaurus imperiosus in the same paper in which Tyrannosaurus rex was described.[76] Had it not been for page order, Dynamosaurus would have become the official name. The original "Dynamosaurus" material resides in the collections of the Natural History Museum, London.

In total, Barnum Brown found five Tyrannosaurus partial skeletons. Brown collected his second Tyrannosaurus in 1902 and 1905 in Hell Creek, Montana. This is the holotype used to describe Tyrannosaurus rex Osborn, 1905. In 1941 it was sold to the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. Brown's fourth and largest find, also from Hell Creek, is on display in the American Museum of Natural History in New York.[40]

Although there are numerous skeletons in the world, only one track has been documented -- at Philmont Scout Ranch in northeast New Mexico. It was discovered in 1983 and identified and documented in 1994.


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« Reply #29 on: July 23, 2007, 01:55:49 pm »



Scale model of the never-completed Tyrannosaurus rex exhibit planned for the American Museum of Natural History by H.F. Osborn.
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