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 Tyrannosauridae

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PostSubject: Tyrannosauridae   Wed Oct 19, 2016 5:52 pm

Tyrannosaurus (/tᵻˌrænəˈsɔːrəs/ or /taɪˌrænəˈsɔːrəs/, meaning "tyrant lizard", from the Ancient Greek tyrannos (τύραννος), "tyrant", and sauros (σαῦρος), "lizard"[1]) is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex (rex meaning "king" in Latin), is one of the most well-represented of the large theropods. Tyrannosaurus lived throughout what is now western North America, on what was then an island continent known as Laramidia. Tyrannosaurus had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper Cretaceous Period, 68 to 66 million years ago.[2] It was the last known member of the tyrannosaurids,[3] and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, Tyrannosaurus fore limbs were short but unusually powerful for their size and had two clawed digits. The most complete specimen measures up to 12.3 m (40 ft) in length,[4] up to 3.66 meters (12 ft) tall at the hips,[5] and up to 10.2 metric tons (11.2 short tons) in weight.[6] Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it is still among the largest known land predators and is estimated to have exerted the largest bite force among all terrestrial animals.[7][8] By far the largest carnivore in its environment, Tyrannosaurus rex was most likely an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods.[9] Some experts, however, have suggested the dinosaur was primarily a scavenger. The question of whether Tyrannosaurus was an apex predator or a pure scavenger was among the longest ongoing debates in paleontology.[10] It is accepted now that Tyrannosaurus rex acted as a predator, and scavenged as modern mammalian and avian predators do.

More than 50 specimens of Tyrannosaurus 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 its life history and biomechanics. The feeding habits, physiology and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second Tyrannosaurus species while others maintain Tarbosaurus is a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.


Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, located at the Field Museum of Natural History under the name FMNH PR2081 and nicknamed Sue, measured 12.3 meters (40 ft) long,[4] and was 3.66 meters (12 ft) tall at the hips.[5] Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons),[11] to less than 4.5 metric tons (5.0 short tons),[12][13][page needed] with most modern estimates ranging between 5.4 metric tons (6.0 short tons) and 6.7 metric tons (7.4 short tons).[14][15][16][17] One study in 2011 found that the maximum weight of Sue, the largest Tyrannosaurus, was between 9.5 and 18.5 metric tons (9.3–18.2 long tons; 10.5–20.4 short tons), though the authors stated that their upper and lower estimates were based on models with wide error bars and that they "consider [them] to be too skinny, too fat, or too disproportionate".[4] Packard et al. (2009) tested dinosaur mass estimation procedures on elephants and concluded that those of dinosaurs are flawed and produce over-estimations; thus, the weight of Tyrannosaurus could have been much less than previously thought.[18] Other estimations have concluded that the largest known Tyrannosaurus specimens had masses approaching[19] or exceeding 9 tonnes.

The neck of Tyrannosaurus rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs had only two clawed fingers,[20] along with an additional small metacarpal representing the remnant of a third digit.[21] 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.[20]

The largest known Tyrannosaurus rex skulls measure up to 1.45 meters (4.8 ft) in length.[22] Large fenestrae (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects Tyrannosaurus's 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.[23][24] 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.[7][8][25] 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.[26][27]

The teeth of Tyrannosaurus rex displayed marked heterodonty (differences in shape).[20][28] 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.[29] 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 30.5 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.[30]

While there is no direct evidence for Tyrannosaurus rex having had feathers, many scientists now consider it likely that T. rex had feathers on at least parts of its body,[31] due to their presence in related species. Mark Norell of the American Museum of Natural History summarized the balance of evidence by stating that: "we have as much evidence that T. rex was feathered, at least during some stage of its life, as we do that australopithecines like Lucy had hair."[32]

The first evidence for feathers in tyrannosauroids came from the small species Dilong paradoxus, found in the Yixian Formation of China, and reported in 2004. 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.[33] Because all known skin impressions from larger tyrannosauroids known at the time showed evidence of scales, the researchers who studied Dilong speculated that feathers may correlate negatively with body size—that juveniles may have been feathered, then shed the feathers and expressed only scales as the animal became larger and no longer needed insulation to stay warm.[33] However, subsequent discoveries showed that even some large tyrannosauroids had feathers covering much of their bodies, casting doubt on the hypothesis that they were a size-related feature.[34]

While skin impressions from a Tyrannosaurus rex specimen nicknamed "Wyrex" (BHI 6230) discovered in Montana in 2002,[35] as well as some other giant tyrannosauroid specimens, show at least small patches of mosaic scales,[36] others, such as Yutyrannus huali (which was up to 9 meters (30 ft) long and weighed about 1,400 kilograms (3,100 lb)), preserve feathers on various sections of the body, strongly suggesting that its whole body was covered in feathers.[34] It is possible that the extent and nature of feather covering in tyrannosauroids may have changed over time in response to body size, a warmer climate, or other factors.[34]

Research has suggested that large theropods like Tyrannosaurus had teeth covered in lips like modern day lizards, rather than having bare teeth like crocodiles. This is based on the presence of enamel, which needs to remain hydrated, an issue not faced by aquatic species like crocodilians or toothless species like birds, which have lipless and toothless beaks. In modern terrestrial animals with bare teeth, the teeth typically lack some or all of the standard amount of tooth enamel. Because Tyrannosaurus and other toothed theropods had enamel-covered teeth, they would have required some sort of lip-like covering to seal the mouth when closed.[37]

Tyrannosaurus is the type genus of the superfamily Tyrannosauroidea, the family Tyrannosauridae, and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American Daspletosaurus and the Asian Tarbosaurus,[38][39] both of which have occasionally been synonymized with Tyrannosaurus.[27][page needed] Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as megalosaurs and carnosaurs, although more recently they were reclassified with the generally smaller coelurosaurs.[26]


Diagram showing the differences between a generalized Tarbosaurus (A) and Tyrannosaurus (B) skull
In 1955, Soviet paleontologist Evgeny Maleev named a new species, Tyrannosaurus bataar, from Mongolia.[40] By 1965, this species had been renamed Tarbosaurus bataar.[41] Despite the renaming, many phylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex,[39] and it has often been considered an Asian species of Tyrannosaurus.[26][42][43] A recent redescription of the skull of Tarbosaurus bataar has shown that it was much narrower than that of Tyrannosaurus rex and that during a bite, the distribution of stress in the skull would have been very different, closer to that of Alioramus, another Asian tyrannosaur.[44] A related cladistic analysis found that Alioramus, not Tyrannosaurus, was the sister taxon of Tarbosaurus, which, if true, would suggest that Tarbosaurus and Tyrannosaurus should remain separate.[38] The discovery and description of Qianzhousaurus would later disprove this and revealed that Alioramus belonged to the clade Alioramini.[45][46] The discovery of the tyrannosaurid Lythronax further indicates that Tarbosaurus and Tyrannosaurus are closely related, forming a clade with fellow Asian tyrannosaurid Zhuchengtyrannus, with Lythronax being their sister taxon.[47][48] A further study from 2016 by Steve Brusatte, Thomas Carr et al., also indicates Tyrannosaurus may have been an immigrant from Asia, as well as a possible descendent of Tarbosaurus. The study further indicates the possibility that Tyrannosaurus may have driven other tyrannosaurids that were native to North America extinct through competition.[49]

Other tyrannosaurid fossils found in the same formations as Tyrannosaurus rex were originally classified as separate taxa, including Aublysodon and Albertosaurus megagracilis,[27] the latter being named Dinotyrannus megagracilis in 1995.[50] However, these fossils are now universally considered to belong to juvenile Tyrannosaurus rex.[51] A small but nearly complete skull from Montana, 60 centimeters (2.0 ft) long, may be an exception. This skull was originally classified as a species of Gorgosaurus (G. lancensis) by Charles W. Gilmore in 1946,[52] but was later referred to a new genus, Nanotyrannus.[53] Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile Tyrannosaurus rex.[54] There are minor differences between the two species, including the higher number of teeth in N. lancensis, which lead some scientists to recommend keeping the two genera separate until further research or discoveries clarify the situation.[39][55]
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PostSubject: Re: Tyrannosauridae   Wed Oct 19, 2016 6:29 pm

T-Rex is one of my favourite dinosaurs!
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PostSubject: Re: Tyrannosauridae   Wed Oct 19, 2016 10:02 pm

I think it is better to discuss all the Tyrannosauridae in this topic, so I changed the name of the thread for Tyrannosauridae.

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