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| Sarcosuchus | Apatosaurus | Dimetrodon |
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| Tylosaurus | Tyrannosaurus rex from http://www.search4dinosaurs.com/raul_martin.html | Ichtyostega |
Showing posts with label DINOSAUR. Show all posts
Showing posts with label DINOSAUR. Show all posts
Wednesday, July 15, 2009
pictures
Tuesday, July 14, 2009
Customer Service
A man was in a long line at the grocery store, and as he got to the register he realized he had forgotten to get condoms, so he asked the checkout girl if she could have some brought up to the register.
She asked, "What size condoms?" The customer replied that he didn't know.
She asked him to drop his pants. He did, she reached over the counter, grabbed hold of him and called over the intercom, "One box of large condoms, Register 5."
The next man in line thought this was interesting, and like most of us, was up for a cheap thrill. When he got to the register, he told the checker that he too had forgotten to get condoms, and asked if she could have some brought to the register for him. She asked him what size, and he stated that he didn't know.
She asked him to drop his pants. He did, she gave him a quick feel, picked up the intercom and said, "One box of medium-sized condoms, Register 5."
A few customers back was this teenage boy. He thought what he had seen was way too cool. He had never had any type of sexual contact with a live female so he thought this was his chance. When he got to the register he told the checker he needed some condoms. She asked him what size and he said he didn't know.
She asked him to drop his pants and he did. She reached over the counter, gave him one quick squeeze, then picked up the intercom and said...
"Cleanup, Register 5!"
from http://mistupid.com/jokes/page052.htm
Dinosaur Bones
Some tourists in the Museum of Natural History are marveling at some dinosaur bones. One of them asks the guard, "Can you tell me how old the dinosaur bones are?"
The guard replies, "They are 3 million, four years, and six months old."
"That's an awfully exact number," says the tourist. "How do you know their age so precisely?"
The guard answers, "Well, the dinosaur bones were three million years old when I started working here, and that was four and a half years ago."
from http://mistupid.com/jokes/page051.htm
Monday, July 13, 2009
The 10 Smartest Dinosaurs
How could dinosaurs possibly have been smart? Pound for pound, they were some of the dumbest creatures ever to roam the planet. However, not all raptors, tyrannosaurs, stegosaurs and hadrosaurs were equally stupid; some may even (just barely) have attained a mammalian level of intelligence. Here’s a list of the 10 smartest dinosaurs, based on an analysis of their anatomy and behavioral patterns.
1. Troodon
Wikimedia Commons
This human-sized carnivore of the Cretaceous period has become the poster lizard for dinosaur intelligence. Based on its predatory arsenal--big eyes, fast speed, and stereo vision--paleontologists think Troodon must have had an especially big brain, "big" in this context meaning about the size of a modern opossum's (which, for its size, still placed it well ahead other dinosaurs). More aboutTroodon
2. Deinonychus
Wikimedia Commons
Despite what you saw in Jurassic Park, Deinonychus wasn't nearly clever enough to turn a doorknob (the "Velociraptors" in Steven Spielberg's movie were actually played by this much bigger raptor). But there's convincing evidence that Deinonychus hunted in packs, which must have entailed a certain level of strategic thinking and communication, and hence a bigger brain. More about Deinonychus
3. Compsognathus
Wikimedia Commons
When it comes to dinosaur intelligence, it's not how big your brain is compared to other reptiles, but how big your brain is compared to the rest of your body. In this respect, the tiny, chicken-sized Compsognathus appears to have been an honor student, perhaps as smart as a very dumb mouse (and yes, in the Mesozoic Era, this was enough to land you in the advanced-placement class). More about Compsognathus
4. Tyrannosaurus Rex
Wikimedia Commons
You wouldn't think T. Rex had to be particularly smart to hunt down its food--after all, this was the apex predator of its day, equipped with huge teeth, powerful legs, and a keen sense of smell. But based on an analysis of existing skulls, T. Rex appears to have had a fairly large brain by Cretaceous standards (although today it would be outwitted by a newborn kitten). More about T. Rex
5. Oviraptor
Wikimedia Commons
As a general rule, even the dumbest birds alive today are brainier than the dumbest dinosaurs. By this token, the feathered Oviraptor (which was not technically a raptor, by the way) must have been one of the most intelligent dinosaurs of the late Cretaceous period; for instance, it was one of the few creatures smart enough to sit on its own eggs until they hatched. More about Oviraptor
6. Maiasaura
Wikimedia Commons
It takes a certain amount of intelligence (combined with instinct, of course) to migrate in large herds, dig out nesting grounds, and look after your young after they've hatched. By those standards, Maiasaura must have been one of the most intelligent hadrosaurs of Cretaceous times; "Egg Mountain" in Montana is a testament to this dinosaur's level of parental care. More about Maiasaura
7. Allosaurus
Wikimedia Commons
This fierce, two-legged carnivore probably wasn't as quite as intelligent as T. Rex, which appeared on the scene tens of millions of years later (paleontologists have found numerous Allosaurus skeletons at a site in Utah; the theory is that they stopped to feast on herbivores trapped in mud and stupidly wound up getting stuck themselves). But fast, agile hunters tend to have fairly large brains, and Allosaurus was nothing if not fast and agile. More aboutAllosaurus
8. Ornithomimus
Wikimedia Commons
The "bird mimics," of which Ornithomimus was the poster genus, were large, fast, two-legged dinosaurs of the Cretaceous period that resembled (and behaved like) ostriches. In fact, based on the size of its brain cavity, scientists think that Ornithomimus may have been nearly as smart as a modern ostrich--which would have made it the Albert Einstein of the Mesozoic Era. More about Ornithomimus
9. Tarchia
Wikimedia Commons
The only ankylosaur on this list, Tarchia (Chinese for "brainy") was so named because its brain appears to have been a smidgen bigger than those of other ankylosaurs. Ankylosaurs were spectacularly dumb creatures, though, so what this means is that if Tarchia had studied really hard, it might have had a successful career as a giant paperweight. More about Tarchia
10. Barney
PBS
The only dinosaur ever to evolve the ability to sing and dance, Barney has been a fixture on public TV for over 15 years, a tribute to this unspecified species' intelligence, savvy, and management team. Based on a careful analysis of his PBS show, scientists have concluded that Barney possesses an almost human-sized brain, albeit slightly atrophied from extended exposure to adorable toddlers. More about Barney
Tuesday, June 23, 2009
Sauropods: The Biggest Dinosaurs that Ever Lived
Think of the word "dinosaur," and two images are likely to come to mind: a snarling Velociraptor hunting for grub, or a giant, gentle, long-necked Brachiosaurus lazily plucking the leaves off trees. In many ways, the sauropods (of which Brachiosaurus was a prominent example) are more fascinating than bipedal predators like T. Rex or Velociraptor. By far the largest creatures ever to roam the earth, sauropods branched into numerous genuses and species over the course of 100 million years, and their remains have been dug up on every continent, including Antarctica.
So what, exactly, is a sauropod? Some technical details aside, paleontologists use the term to describe large, four-legged, plant-eating dinosaurs with bulky bodies, long necks and tails, and tiny heads with small brains (in fact, sauropods are believed to have been the dumbest of all the dinosaurs, with the smallest "encephalization quotient"). The name "sauropod" itself is Greek for "lizard foot," which oddly enough was among these dinosaurs' least distinctive traits!
As with any broad definition, though, there are some important "buts" and "howevers." Not all sauropods had long necks (witness the oddly truncatedBrachytrachelopan), and not all were the size of houses (one recent discovery, Europasaurus, seems to have only been about the size of a large ox). On the whole, though, most classical sauropods--familiar beasts like Diplodocus and Apatosaurus (the dinosaur previously known as Brontosaurus)--follow the sauropod body plan to the letter.
Sauropod Evolution
According to current knowledge, the first true sauropods (such as Vulcanodon andBarapasaurus) arose about 200 million years ago, in the early to middle Jurassic. The exact evolutionary relationships are unclear, but it's possible that these huge herbivores were directly descended from smaller "prosauropods" like Anchisaurus and Massospondylus.
The sauropods reached the peak of their eminence toward the end of the Jurassic period, 150 million years ago. Fully grown adults had a relatively easy ride, since they were virtually immune to predation (although it's possible that packs of Allosaurus might have ganged up on an adult Diplodocus), and the steamy, vegetation-choked jungles covering most of the Jurassic continents provided a constant supply of food.
The Cretaceous period saw a slow slide in sauropods' fortunes; by the time the dinosaurs went extinct 65 million years ago, only the titanosaurs (such as Titanosaurus andRapetosaurus) were left. Frustratingly, while paleontologists have identified dozens of genuses of titanosaur, the lack of fully articulated fossils and the rarity of intact skulls means that much about these beasts is still shrouded in mystery. We do know, however, that many titanosaurs had rudimentary armor plating--clearly an evolutionary adaptation to predation by carnivores.
Sauropod Behavior and Physiology
As befitted their size, sauropods were eating machines: an adult had to scarf down hundreds of pounds of plants and leaves every day. Depending on their diets, sauropods came equipped with two basic kinds of teeth: either flat and spoon-shaped (as inCamarasaurus and Brachiosaurus), or thin and peglike (as in Diplodocus). Presumably, the spoon-toothed sauropods subsisted on tougher vegetation that required more powerful grinding and chewing.
Reasoning by analogy with modern giraffes, most paleontologists believe sauropods evolved their ultra-long necks in order to reach high leaves. However, this raises as many questions as it answers, since pumping blood to a height of 40 or 50 feet would strain even the most robust heart. One maverick has suggested that the necks of some sauropods contained strings of "auxiliary" hearts, but lacking solid fossil evidence, few experts are convinced.
This brings us to the question of whether sauropods were warm-blooded. Generally, even the most ardent advocates of warm-blooded dinosaurs back off when it comes to sauropods, since simulations show that these oversized animals would have baked themselves from the inside, like potatoes, if they generated too much metabolic energy. Today, the prevalence of opinion is that sauropods were cold-blooded homeotherms--that is, they managed to maintain a near-constant body temperature because they warmed up very slowly and cooled off equally slowly.
from
http://dinosaurs.about.com/od/typesofdinosaurs/a/sauropods.htm
Sunday, June 21, 2009
Tyrannosaurus
Tyrannosaurus (pronounced /tɨˌrænɵˈsɔːrəs/ or /taɪˌrænɵˈsɔːrəs/, meaning 'tyrant lizard') was agenus of theropod dinosaur. The species Tyrannosaurus rex ('rex' meaning 'king' in Latin), commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils 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 clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus 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 tons (7.5 short tons) in weight.[3] By far the largest carnivore in its environment, Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger. The debate over Tyrannosaurus as apex predator or scavenger is among the longest running debates in paleontology.
More than 30 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 life history and biomechanics. The feeding habits, physiologyand potential speed of Tyrannosaurus 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 withTyrannosaurus.
Description
Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNHPR2081 ("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).[3][7][8][9] Although Tyrannosaurus rex was larger than the well known Jurassictheropod Allosaurus, it was slightly smaller than Cretaceous carnivores Spinosaurus andGiganotosaurus.[10][11]
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,[1] along with an additional small metacarpal representing the remnant of a third digit.[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]
The largest known Tyrannosaurus 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 nasalsand 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 thetyrannosaurid 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]
The teeth of Tyrannosaurus rex displayed marked heterodonty (differences in shape).[1][21] The premaxillaryteeth 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 whenTyrannosaurus 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]
[edit]Classification
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,[23][24] both of which have occasionally been synonymized with Tyrannosaurus.[20] 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.[19]
In 1955, Soviet paleontologist Evgeny Maleev named a new species,Tyrannosaurus bataar, from Mongolia.[25] By 1965, this species had been renamed Tarbosaurus bataar.[26] Despite the renaming, manyphylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex,[24] and it has often been considered an Asian species of Tyrannosaurus.[19][27][28] 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.[29]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.[23]
Other tyrannosaurid fossils found in the same formations as Tyrannosaurus rex were originally classified as separate taxa, includingAublysodon and Albertosaurus megagracilis,[20] the latter being named Dinotyrannus megagracilis in 1995.[30] However, these fossils are now universally considered to belong to juvenile Tyrannosaurus rex.[31] A small but nearly complete skull from Montana, 60 centimetres (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,[32] but was later referred to a new genus, Nanotyrannus.[33] Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile Tyrannosaurus rex.[34] There are minor differences between the two species, including the higher number of teeth inN. lancensis, which lead some scientists to recommend keeping the two genera separate until further research or discoveries clarify the situation.[24][35]
[edit]Manospondylus
The first fossil specimen which can be attributed to Tyrannosaurus rex consists of two partial vertebrae (one of which has been lost) found by Edward Drinker Cope in 1892 and described as Manospondylus gigas. Osborn recognized the similarity between M. gigas and Tyrannosaurus rex as early as 1917 but, due to the fragmentary nature of the Manospondylus vertebrae, he could not synonymize them conclusively.[36]
In June 2000, the Black Hills Institute located the type locality of M. gigas in South Dakota and unearthed more tyrannosaur bones there. These were judged to represent further remains of the same individual, and to be identical to those of Tyrannosaurus rex. According to the rules of the International Code of Zoological Nomenclature (ICZN), the system that governs the scientific naming of animals, Manospondylus gigasshould therefore have priority over Tyrannosaurus rex, because it was named first. However, the Fourth Edition of the ICZN, which took effect on 1 January 2000, states that "the prevailing usage must be maintained" when "the senior synonym or homonym has not been used as a valid name after 1899" and "the junior synonym or homonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years ..."[37]Tyrannosaurus rex may qualify as the valid name under these conditions and would most likely be considered a nomen protectum ("protected name") under the ICZN if it was ever challenged, which it has not yet been. Manospondylus gigaswould then be deemed a nomen oblitum ("forgotten name").[38]
[edit]Paleobiology
[edit]Life history
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 Tyrannosaurus 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 Tyrannosaurus 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 youngTyrannosaurus 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.[39] 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 Tyrannosaurus 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.[40] Further study indicates an age of 18 for this specimen.[41] Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.[42]
Over half of the known Tyrannosaurus 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 Tyrannosaurus 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.[42]
[edit]Sexual dimorphism
As the number of specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or morphs, similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed 'gracile.' Several morphological differences associated with the two morphs were used to analyze sexual dimorphism in Tyrannosaurus rex, with the 'robust' morph usually suggested to be female. For example, the pelvis of several 'robust' specimens seemed to be wider, perhaps to allow the passage ofeggs.[43] It was also thought that the 'robust' morphology correlated with a reduced chevron on the first tail vertebra, also ostensibly to allow eggs to pass out of the reproductive tract, as had been erroneously reported for crocodiles.[44]
In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between Tyrannosaurus rex genders.[45] A full-sized chevron was discovered on the first tail vertebra of "Sue," an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As Tyrannosaurus rex specimens have been found fromSaskatchewan to New Mexico, differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.[1]
Only a single Tyrannosaurus rex specimen has been conclusively shown to belong to a specific gender. Examination of "B-rex" demonstrated the preservation of soft tissue within several bones. Some of this tissue has been identified as medullary tissue, a specialized tissue grown only in modern birds as a source of calcium for the production of eggshell during ovulation. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive hormones like estrogen. This strongly suggests that "B-rex" was female, and that she died during ovulation.[40] Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs, aside from birds. The shared presence of medullary tissue in birds and theropod dinosaurs is further evidence of the close evolutionary relationship between the two.[46]
[edit]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.[47] 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 Tyrannosaurus rex skeleton in 1915. It stood in this upright pose for nearly a century, until it was dismantled in 1992.[48] 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.[49] The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as Rudolph Zallinger's famous mural The Age Of Reptilesin Yale University's Peabody Museum of Natural History)[50] 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 Tyrannosaurus rex with its body approximately parallel to the ground and tail extended behind the body to balance the head.[20]
[edit]Arms
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When Tyrannosaurus rex was first discovered, the humerus was the only element of the forelimb known.[51] For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of Allosaurus.[36] However, a year earlier, Lawrence Lambe described the short, two-fingered forelimbs of the closely relatedGorgosaurus.[52] This strongly suggested that Tyrannosaurus rex had similar forelimbs, but this hypothesis was not confirmed until the first complete Tyrannosaurus rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex").[53] The remains of "Sue" also include complete forelimbs.[1] Tyrannosaurus 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.[54] It has also been suggested that the forelimbs were used to assist the animal in rising from a prone position.[49] 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.
Tyrannosaurus 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 Tyrannosaurus 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.[55]
[edit]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.[56] 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.[57] 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.[56] Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.[58]
In studies reported in the journal Science in April 2007, Asara and colleagues concluded that seven traces of collagen proteins detected in purified Tyrannosaurus 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."[59]
Subsequent studies in April 2008 confirmed the close connection of Tyrannosaurus 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 alligatorsand 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."[60]
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.[61] 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.[62]
[edit]Skin and feathers
In 2004, the scientific journal Nature published a report describing an early tyrannosauroid, Dilong paradoxus, from the famous Yixian Formationof 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, skin impressions from large tyrannosaurid specimens show mosaic scales.[63] 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 likeTyrannosaurus, especially in warm Cretaceous climates.[64]
[edit]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.[65][66] 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 Tyrannosaurus 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, Tyrannosaurus rex growth was limited mostly to immature animals, rather than theindeterminate growth seen in most other vertebrates.[39]
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 Tyrannosaurus rex maintained a constant internal body temperature (homeothermy) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals.[67] 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).[68] 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).[69] Ornithischian dinosaurs also showed evidence of homeothermy, while varanid lizards from the same formation did not.[70] 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.[71][72]
[edit]Footprints
Two isolated fossilized footprints have been tentatively assigned to Tyrannosaurus rex. The first was discovered at Philmont Scout Ranch, New Mexico, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a hadrosaurid, examination of the footprint revealed a large 'heel' unknown inornithopod dinosaur tracks, and traces of what may have been a hallux, the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the ichnogenus Tyrannosauripus pillmorei in 1994, by Martin Lockley and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a Tyrannosaurus rex, which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mud flat. It measures 83 centimetres (33 in) long by 71 centimetres (28 in) wide.[73]
A second footprint that may have been made by a Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 76 centimetres (30 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus and Nanotyrannus are the only large theropods known to have existed in the Hell Creek Formation. Further study of the track (a full description has not yet been published) will compare the Montana track with the one found in New Mexico.[74]
[edit]Locomotion
There are two main issues concerning the locomotory abilities of Tyrannosaurus: how well it could turn; and what its maximum straight-line speed was likely to have been. Both are relevant to the debate about whether it was a hunter or a scavenger (see below).
Tyrannosaurus may have been slow to turn, possibly taking one to two seconds to turn only 45°—an amount that humans, being vertically oriented and tail-less, can spin in a fraction of a second.[75] The cause of the difficulty is rotational inertia, since much of Tyrannosaurus’ mass was some distance from its center of gravity, like a human carrying a heavy timber—although it might have reduced the average distance by arching its back and tail and pulling its head and forelimbs close to its body, rather like the way ice skaters pull their arms closer in order to spin faster.[76]
Scientists have produced a wide range of maximum speed estimates, mostly around 11 metres per second (25 mph), but a few as low as 5–11 metres per second (11–25 mph), and a few as high as 20 metres per second (45 mph). Researchers have to rely on various estimating techniques because, while there are manytracks of very large theropods walking, so far none have been found of very large theropods running—and this absence may indicate that they did not run.[77] Scientists who think that Tyrannosaurus was able to run 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 kilometres per hour (25–43 mph).[78]
Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run (no airborne phase in mid-stride), because its ratio of femur (thigh bone) to tibia (shin bone) length was greater than 1, as in most large theropods and like a modern elephant.[53]However, Holtz (1998) noted that tyrannosaurids and some closely related groups had significantly longer distal hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods), and that tyrannosaurids and their close relatives had a tightly interlockedmetatarsus that more effectively transmitted locomotory forces from the foot to the lower leg than in earlier theropods ("metatarsus" means the foot bones, which function as part of the leg in digitigrade animals). He therefore concluded that tyrannosaurids and their close relatives were the fastest large theropods.[79]
Skeletal anatomy of a T. rex right leg
Christiansen (1998) estimated that the leg bones of Tyrannosaurus were not significantly stronger than those of elephants, which are relatively limited in their top speed and never actually run (there is no airborne phase), and hence proposed that the dinosaur's maximum speed would have been about 11 metres per second (25 mph), which is about the speed of a human sprinter. But he also noted that such estimates depend on many dubious assumptions.[80]
Farlow and colleagues (1995) have argued that a Tyrannosaurus weighing 6 short tons (5.4 t) to 8 short tons (7.3 t) would have been critically or even fatally injured if it had fallen while moving quickly, since its torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 meters/s²) and its tiny arms could not have reduced the impact.[7] However, giraffeshave been known to gallop at 50 kilometres per hour (31 mph), despite the risk that they might break a leg or worse, which can be fatal even in a "safe" environment such as a zoo.[81][82] Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks.[83][84]
Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 to 40 kilometres per hour (11 to 25 mph), i.e. from walking or slow running to moderate-speed running. For example, a 2002 paper in the journal Nature used a mathematical model (validated by applying it to three living animals, alligators, chickens, and humans; additionally later eight more species including emus and ostriches[85]) to gauge the leg muscle mass needed for fast running (over 40 kilometres per hour (25 mph)).[78] They found that proposed top speeds in excess of 40 kilometres per hour (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. This discussion is difficult to resolve, as it is unknown how large the leg muscles actually were in Tyrannosaurus. If they were smaller, only 18 kilometres per hour (11 mph) walking/jogging might have been possible.[78]
A study in 2007 used computer models to estimate running speeds, based on data taken directly from fossils, and claimed that Tyrannosaurus rex had a top running speed of 8 metres per second (18 mph). An average professional football (soccer) player would be slightly slower, while a human sprinter can reach 12 metres per second (27 mph). Note that these computer models predict a top speed of 17.8 metres per second (40 mph) for a 3 kilograms (6.6 lb) Compsognathus[86][87] (probably a juvenile individual).[88]
Those who argue that Tyrannosaurus was incapable of running estimate the top speed of Tyrannosaurus at about 17 kilometres per hour (11 mph). This is still faster than its most likely prey species, hadrosaurids and ceratopsians.[78] In addition, some advocates of the idea thatTyrannosaurus was a predator claim that tyrannosaur running speed is not important, since it may have been slow but still faster than its probable prey.[89] However, Paul and Christiansen (2000) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast as rhinos.[90] Healed Tyrannosaurus bite wounds on ceratopsian fossils are interpreted as evidence of attacks on living ceratopsians (see below). If the ceratopsians that lived alongside Tyrannosaurus were fast, that casts doubt on the argument thatTyrannosaurus did not have to be fast to catch its prey.[84]
[edit]Feeding strategies
The debate about whether Tyrannosaurus was a predator or a pure scavenger is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of Tyrannosaurus’ close relative Gorgosaurus and concluded that it and therefore also Tyrannosaurus was a pure scavenger, because the Gorgosaurus’ teeth showed hardly any wear.[91] This argument is no longer taken seriously, because theropods replaced their teeth quite rapidly. Ever since the first discovery of Tyrannosaurus most scientists have agreed that it was a predator, although like modern large predators it would have been happy to scavenge or steal another predator's kill if it had the opportunity.[92]
Noted hadrosaur expert Jack Horner is currently the major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all.[53][93][94] Horner has presented several arguments to support the pure scavenger hypothesis:
- Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.[95]
- Tyrannosaurs had large olfactory bulbs and olfactory nerves (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modernvultures do. Research on the olfactory bulbs of dinosaurs has shown that Tyrannosaurus had the most highly developed sense of smell of 21 sampled dinosaurs.[96] Opponents of the pure scavenger hypothesis have used the example of vultures in the opposite way, arguing that the scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically.[97] However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti would provide sufficient carrion for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Warm-bloodedness of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger ecological niche from gliding birds.[98]
- Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolites (fossilized dung) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like hyenas do to extract marrow.[99]
- Since at least some of Tyrannosaurus's potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.[93][100] On the other hand, recent analyses suggest that Tyrannosaurus, while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.[78][89]
Other evidence suggests hunting behavior in Tyrannosaurus. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawks. He also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is hard to see how natural selection would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception thatstereoscopic vision provides.[14][15] In modern animals, binocular vision is found mainly in predators.
A skeleton of the hadrosaurid Edmontosaurus annectens has been described from Montana with healed tyrannosaur-inflicted damage on its tail vertebrae. The fact that the damage seems to have healed suggests that the Edmontosaurus survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation.[101] There is also evidence for an aggressive interaction between a Triceratopsand a Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on a Triceratops brow horn andsquamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor.[102] When examining Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurusembedded in a neck vertebra. If correct, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would have been competition for food and mates or active cannibalism is unclear.[103] 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.[93]
Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey was 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.[100] Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger like all large carnivores.
[edit]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 fullbinomial therefore translates to "tyrant lizard king," emphasizing the animal's size and perceived dominance over other species of the time.[51]
[edit]Earliest finds
Teeth from what is now documented as a Tyrannosaurus rex were found in 1874 by A. Lakes near Golden, Colorado. In the early 1890s, J. B. Hatcher collected postcranial elements in eastern Wyoming. The fossils were believed to be from a large species of Ornithomimus (O. grandis) but are now consideredTyrannosaurus rex. Vertebral fragments found by E. D. Cope in western South Dakota in 1892 and named as Manospondylus gigas have also been reclassified as Tyrannosaurus rex.[105]
Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of Tyrannosaurus rex in eastern Wyoming in 1900. H. F. Osborn originally named this skeletonDynamosaurus imperiosus in a paper in 1905. Brown found another partial skeleton in the Hell Creek Formation in Montana in 1902. Osborn used this holotype to describe Tyrannosaurus rex in the same paper in which D. imperiosus was described.[106] 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.[107]
In total, Brown found five Tyrannosaurus partial skeletons. In 1941, Brown's 1902 find was sold to theCarnegie 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.[53]
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.[108]
[edit]Notable specimens
Sue Hendrickson, amateur paleontologist, discovered the most complete (approximately 85%) and, until 2001, the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation near Faith, South Dakota, on 12 August 1990. This Tyrannosaurus, nicknamed "Sue" in her honor, was the object of a legal battle over its ownership. In 1997 this was settled in favor of Maurice Williams, the original land owner. The fossil collection was purchased by the Field Museum of Natural History at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. From 1998 to 1999 Field Museum of Natural History preparators spent 30,000 hours taking the rock off each of the bones. The bones were then shipped off to New Jersey where the mount was made. The finished mount was then taken apart, and along with the bones, shipped back to Chicago for the final assembly. The mounted skeleton opened to the public on May 17, 2000 in the great hall (Stanley Field Hall) at the Field Museum of Natural History. A study of this specimen's fossilized bones showed that "Sue" reached full size at age 19 and died at age 28, the longest any tyrannosaur is known to have lived.[109] Early speculation that Sue may have died from a bite to the back of the head was not confirmed. Though subsequent study showed many pathologies in the skeleton, no bite marks were found. [110] Damage to the back of the skull may have been caused by post-mortem trampling.
Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation nearBuffalo, 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 Tyrannosaurus tooth. Both Stan and Sue were examined by Peter Larson.
In the summer of 2000, Jack Horner discovered five Tyrannosaurus skeletons near the Fort Peck Reservoir in Montana. One of the specimens, dubbed "C. rex," was reported to be perhaps the largest Tyrannosaurus ever found.[111]
In 2001, a 50% complete skeleton of a juvenile Tyrannosaurus was discovered in the Hell Creek Formation in Montana, by a crew from the Burpee Museum of Natural History of Rockford, Illinois. Dubbed "Jane the Rockford T-Rex," the find was initially considered the first known skeleton of the pygmy tyrannosauridNanotyrannus but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus.[112] It is the most complete and best preserved juvenile example known to date. Jane has been examined by Jack Horner, Pete Larson, Robert Bakker, Greg Erickson and several other renowned paleontologists, because of the uniqueness of her age. Jane is currently on exhibit at the Burpee Museum of Natural History in Rockford, Illinois.[113][114]
In a press release on 7 April 2006, Montana State University revealed that it possessed the largestTyrannosaurus skull yet discovered. Discovered in the 1960s and only recently reconstructed, the skull measures 59 inches (150 cm) long compared to the 55.4 inches (141 cm) of “Sue’s” skull, a difference of 6.5%.[115][116]
[edit]Appearances in popular culture
Since it was first described in 1905, Tyrannosaurus rex has become the most widely recognized dinosaur species in popular culture. It is the only dinosaur that is commonly known to the general public by its full scientific name (binomial name) (Tyrannosaurus rex), and the scientific abbreviation T. rex has also come into wide usage (commonly abbreviated "T-Rex").[1] Robert T. Bakker notes this in The Dinosaur Heresiesand explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."[6]
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