Spinosaurus
From Wikipedia, the free encyclopedia
Jump to: navigation, search
SpinosaurusFossil range: Early-Late Cretaceous
Spinosaurus aegyptiacus
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Superorder:
Dinosauria
Order:
Saurischia
Suborder:
Theropoda
Family:
Spinosauridae
Subfamily:
Spinosaurinae
Genus:
SpinosaurusStromer, 1915
Species
S. aegyptiacus Stromer, 1915 (type)
?S. marocannus Russell, 1996
Spinosaurus (meaning "spine lizard") is a genus of theropod dinosaur which lived in what is now North Africa, from the Albian to early Cenomanian stages of the Cretaceous Period, about 100 to 93 million years ago. This genus was first known from Egyptian remains discovered in the 1910s and described by German paleontologist Ernst Stromer. These original remains were destroyed in World War II, but additional skull material has come to light in recent years. It is unclear whether one or two species are represented in the described fossils. The best known species is S. aegyptiacus from Egypt, although a potential second species, S. marocannus, has been recovered from Morocco.
The distinctive spines of Spinosaurus, which were long extensions of the vertebrae, grew up to 2 meters (6.6 ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that they were covered in muscle and formed a hump or ridge. Multiple functions have been put forward for this structure, including thermoregulation and display. According to recent estimates, Spinosaurus is the largest of all known carnivorous dinosaurs, even larger than Tyrannosaurus rex and Giganotosaurus. These estimates suggest that it was around 16 to 18 meters in length (52.5 to 59.1 ft) and 7 to 9 tonnes (7.7 to 9.9 tons) in weight.[1]
Contents
1 Description
2 Classification
3 Discovery and species
3.1 Specimens
4 Paleoecology
4.1 Feeding ecology
5 Paleobiology
5.1 Size
5.2 Sail
5.3 Posture
6 In popular culture
7 References
8 External links
Description
Spinosaurus based on the 2005 dal Sasso reconstruction
Although Spinosaurus is well-known to dinosaur enthusiasts due to its size, sail, and elongated skull, it is mostly known from remains that have been destroyed, aside from a few more recently discovered teeth and skull elements. Additionally, so far only the skull and backbone have been described in detail, and limb bones have not been found. Jaw and skull material published in 2005 show that it had one of the longest skulls of any carnivorous dinosaur, estimated at about 1.75 meters long (5.75 ft). The skull had a narrow snout filled with straight conical teeth that lacked serrations. There were six or seven teeth on each side of the very front of the upper jaw, in the premaxilla bones, and another twelve in both maxillae behind them. The second and third teeth on each side were noticeably larger than the rest of the teeth in the premaxilla, creating a space between them and the large teeth in the anterior maxilla; large teeth in the lower jaw faced this space. The very tip of the snout holding those few large anterior teeth was expanded, and a small crest was present in front of the eyes.[1]
The sail of Spinosaurus was formed of very tall neural spines growing on the back vertebrae. These spines were seven to eleven times the height of the vertebrae from which they grew.[2] The spines were slightly longer front to back at the base than higher up, and were unlike the thin rods seen in the pelycosaur finbacks Edaphosaurus and Dimetrodon.
Classification
A cladogram of the Spinosauridae showing the position of Spinosaurus
Spinosauridae
?Chilantaisaurus
?Suchosaurus
Baryonychinae
Baryonyx
Cristatusaurus
Suchomimus
Spinosaurinae
Irritator
Angaturama
?Siamosaurus
Spinosaurus
Spinosaurus gives its name to a family of dinosaurs, the Spinosauridae, of which other members include Baryonyx from southern England, Irritator and Angaturama (which is probably synonymous with Irritator) from Brazil, Suchomimus from Niger in central Africa, and possibly Siamosaurus, which is known from fragmentary remains in Thailand. Spinosaurus is closest to Irritator, which shares its unserrated straight teeth, and the two are included in the subfamily Spinosaurinae.[3] In 2003, Oliver Rauhut suggested that Stromer's Spinosaurus holotype was a chimera, composed of back vertebrae from a carcharodontosaurid similar to Acrocanthosaurus and a dentary from a large theropod similar to Baryonyx.[4] This analysis, however, has been rejected in recent papers.[3][1]
Discovery and species
Life restoration of Spinosaurus
The first described remains of Spinosaurus were found in the Bahariya Valley of Egypt in 1912, and were named by German paleontologist Ernst Stromer in 1915.[5] Fragmentary additional remains from Bahariya, including vertebrae and hindlimb bones, were designated by Stromer as "Spinosaurus B" in 1934.[6] Stromer considered them different enough to belong to another species, and this has been borne out; with the advantage of more expeditions and material, it appears that they either pertain to Carcharodontosaurus[7] or to Sigilmassasaurus.[8] Some of the Spinosaurus fossils were damaged during transport back to the Deutsches Museum, in Munich, Germany, and the remaining bones were completely lost due to Allied bombing in 1944.[1]
Two species of Spinosaurus have been named: Spinosaurus aegyptiacus (meaning "Egyptian spine lizard") and Spinosaurus marocannus (meaning "Moroccan spine lizard"). S. marocannus was originally described by Dale Russell as a new species based on the length of its neck vertebrae.[8] Later authors have been split on this topic, some considering the length of the vertebrae to be variable from individual to individual and therefore regarding S. marocannus as invalid or a synonym of S. aegyptiacus,[7][9][1] and others retaining it as valid.[3]
Specimens
Stromer's original reconstruction of S. aegyptiacus, 1915
Six partial specimens of Spinosaurus have been described. The probable size of these individual spinosaurs can be estimated using comparison to known material from other spinosaurid dinosaurs. The estimates below are based on the Theropod Database[9] and Dal Sasso et al, 2005.[1]
IPHG 1912 VIII 19, described by Stromer in 1915, was the holotype.[5] This specimen, from a subadult individual, was destroyed in World War II. However, detailed drawings and descriptions of the specimen remain. The individual is estimated to have been around 14 meters (46 ft) long and to have weighed about 6.7 tonnes (7.4 tons). The material consisted of a maxilla (upper jaw) fragment, an incomplete dentary (lower jaw) measuring 750 millimeters (29.5 in) long, (the skull is estimated to have been 1.45 meters (4.76 ft) long with a mandible approximately 1.34 meters (4.40 ft) long), nineteen teeth, two incomplete cervical vertebrae, seven back vertebrae, dorsal ribs, gastralia, and eight caudal centra. This was the specimen that Rauhut thought was chimeric.
S. marocannus jaw fossil, Muséum national d'Histoire naturelle, Paris
CMN 50791, described by Russell in 1996, is the holotype of Spinosaurus marocannus. The material it is based on includes a mid-cervical vertebra which is 195 millimeters (7.68 in) long, an anterior dorsal neural arch, an anterior dentary, and a mid-dentary. MNHN SAM 124, described by Taquet and Russell in 1998, consists of partial premaxillae, partial maxillae, vomers, and a dentary fragment. They came from an individual estimated to have been about 14 meters (46 ft) long and to have weighed about 6.7 tonnes (7.38 tons). The skull is estimated at approximately 1.42 meters (4.66 ft) long. Office National des Mines nBM231, described by Buffetaut and Ouaja in 2002, consists of an anterior dentary from Tunisia which is very similar to existing material of S. aegyptiacus.[10]
Photograph of the Dal Sasso specimen of S. aegyptiacus, 2008
MSNM V4047, described by Cristiano Dal Sasso of the Civic Natural History Museum in Milan and his colleagues in 2005, consists of premaxillae, partial maxillae, and partial nasals, which together measure 988 millimeters (3.24 ft) long. The massive skull is estimated at 1.75 meters (5.74 ft) long, and the entire animal is estimated to have been around 16 to 18 meters (52 to 59 ft) in length and weighed around 7 to 9 tonnes (7.7 to 9.9 tons). UCPC-2, also described by Dal Sasso et al. in 2005, consists of a 'fluted crest' from the region in front of the eyes.[1]
Paleoecology
The environment inhabited by Spinosaurus is only partially understood, and covers a great deal of what is now northern Africa. Those Spinosaurus that lived in what is now Egypt, for example, may have contended with shoreline conditions on tidal flats and channels, living in mangrove forests alongside similarly large dinosaurian predators Bahariasaurus and Carcharodontosaurus, giant titanosaur sauropod Paralititan, smaller titanosaur Aegyptosaurus, 10 meter (33 ft) long crocodilian Stomatosuchus, and the coelacanth Mawsonia.[11]
Feeding ecology
It is unclear whether Spinosaurus was primarily a terrestrial predator or a fisher, as indicated by its elongated jaws, conical teeth and raised nostrils. The complete lack of serrated teeth in Spinosaurus as well as relatively weak jaws, do to their long slender shape would have made for a very ineffective predatory bite, where as the shape and design of the teeth are ideal for skewering small to medium sized prey. This fact has lead to a strong support to the fisher theory. The only direct evidence for spinosaur diet comes from related Europe and an South American taxa. Baryonyx was found with both fish scales and bones from juvenile Iguanodon in its stomach, while a tooth embedded in a South American pterosaur bone suggests that spinosaurs occasionally preyed on these flying archosaurs.[12] Spinosaurus was likely to have been a generalized and opportunistic predator, possibly a Cretaceous equivalent of large grizzly bears, being biased toward fishing, though it undoubtedly scavenged and took many kinds of small or medium-sized prey.[13] Anything Spinosaurus could fit in its mouth would have been fair game.
Paleobiology
Size
Size comparison of selected giant theropod dinosaurs, Spinosaurus in red.
Since its discovery, Spinosaurus has been a top contender for longest and largest theropod dinosaur, though this fact did not reach the public consciousness until its depiction in the film Jurassic Park III and the description of a new specimen in 2005. Both Friedrich von Huene[14] and Donald F. Glut,[15] decades apart, listed it as among the most massive theropods or the most massive in their surveys, at upwards of 6 tons in weight and 15 meters (50 feet) in length. In 1988, Gregory S. Paul also listed it as the longest theropod at 15 meters (50 feet), but gave a lower mass estimate.[16] More recent estimates, based on new specimens, list Spinosaurus at 16 to 18 metres (53.3 to 60 feet) long and 7 to 9 tonnes in weight (7.7 to 9.9 tons).[1]
François Therrien and Donald Henderson, in a 2007 paper using scaling based on skull length, challenged previous estimates, finding the length too great and the weight too small. Their estimates include a length of 12.6 to 14.3 meters (41.3 to 47.0 ft) and a mass of 12.0 to 20.9 tonnes (13.2 to 23.0 tons).[17] Their study has been criticized for the choice of large theropods used for comparison (most of the skeletons of large theropods used to set the initial equations are of tyrannosaurids and carnosaurs, which have a different build than spinosaurids) and for issues relating to their spinosaurid skull reconstructions.[18] Resolution awaits more complete remains.
Sail
Illustration of Spinosaurus dorsal vertebrae by Ernst Stromer.
Spinosaurus sails were unusual, although other dinosaurs of the same time and area, namely the ornithopod Ouranosaurus and the sauropod Rebbachisaurus, might have developed a similar structural adaptation of their dorsal vertebrae (however, this is not uncontroversial; see the articles about these animals for more information). The sail is possibly analogous (not homologous) to that of the Permian mammal-like reptile, Dimetrodon, which lived before the dinosaurs even appeared; these similarities are due to parallel evolution. The sail may also have been more hump-like than sail-like; as noted by Jack Bowman Bailey most recently, spinosaur spines are not thin rods but broad front to back, rather like those of some types of buffalo, and so may have supported a thicker, fatty structure as opposed to a skin sail.[19]
The function of these sails is uncertain; scientists have proposed several hypotheses including heat regulation and display. In addition, such a prominent feature on its back could also make it appear even larger than it was, intimidating other animals.
If the sail contained abundant blood vessels, the animal could have used the sail's large surface area to absorb heat. This would imply that the animal was only partly warm-blooded at best and lived in climates where nighttime temperatures were cool or low and the sky usually not cloudy. It is thought that Spinosaurus and Ouranosaurus both lived in or at the margins of an earlier version of the Sahara Desert, which could explain this. It is also possible that the sail was used to radiate excess heat from the body, rather than to collect it. Large animals, due to the relatively small ratio of surface area of their body compared to the overall volume (Haldane's principle), face far greater problems of dissipating excess heat at higher temperatures than gaining it at lower. Sails of these dinosaurs added considerably to the skin area of the body, with minimum increase of volume. Furthermore, if the sail was turned away from the sun, or positioned at a 90 degree angle towards a cooling wind, the animal would quite effectively cool itself in the warm climate of Cretaceous Africa.[20]
Elaborate body structures of many modern-day animals usually serve to attract members of the opposite sex during mating. It is quite possible that the sails of these dinosaurs were used for courtship, in a way similar to a peacock's tail. Stromer speculated that males and females may have differed in the size of the neural spine.[5] If this was the case, the sails may have been brightly colored, but this is purely speculative.
Finally, it is quite possible that the sail combined these functions, acting normally as a heat regulator, becoming a courting aid during the mating season, being used to cool itself and, on occasions, turning into an intimidating device when an animal was feeling threatened.
Posture
Although traditionally depicted as a biped, it has been suggested since the early 1980s that Spinosaurus was at least an occasional quadruped.[15] This has been bolstered by the discovery of Baryonyx, a relative with robust arms.[21] Bailey (1997) was sympathetic to a possible quadrupedal posture,[19] leading to new restorations of it as such.[21] This hypothesis has fallen out of favor, at least as a typical gait, though spinosaurids may have crouched in a quadrupedal posture.[22]
[edit] In popular culture
Spinosaurus has long been depicted in popular books about dinosaurs, although only recently has there been enough information about spinosaurids for an accurate depiction. After an influential 1955 skeletal reconstruction by Lapparent and Lavocat, it has been treated as a generalized upright theropod, with a skull similar to that of other large theropods and a sail on its back.[21]
Spinosaurus was the main antagonist in the 2001 film Jurassic Park III. It was portrayed as larger and more powerful than Tyrannosaurus: in a scene depicting a battle between the two resurrected predators, Spinosaurus emerges victorious by snapping the tyrannosaur's neck. In reality, such a battle could never have taken place while the species were extant, since Spinosaurus and Tyrannosaurus lived thousands of kilometres and millions of years apart. After appearing in Jurassic Park III, Spinosaurus was featured in a wide variety of merchandise related to the Jurassic Park films, including a number of video games such as Jurassic Park: Operation Genesis from Vivendi Universal. Before Jurassic Park III Spinosaurus was an unlockable character in Warpath: Jurassic Park, but was much shorter than the film version and had a shorter mouth. It should be noted that a Suchomimus is playable at the start of the game and looks very similar to the Spinosaurus in the film
Friday, September 12, 2008
velociraptor
Velociraptor (IPA: /vɨˈlɒsɨræptɚ/; meaning 'swift thief', 'swift plunderer' or 'swift bird of prey'[1]) is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 Ma (million years ago) during the later part of the Cretaceous Period.[2] Only two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils of this species have been discovered in both Inner and Outer Mongolia in central Asia. A second species, V. osmolskae, was named in 2008 for skull material from Inner Mongolia.
Smaller than other dromaeosaurids like Deinonychus and Achillobator, the turkey-sized Velociraptor nevertheless shared many of the same anatomical features. It was a bipedal, feathered carnivore with a long, stiffened tail and an enlarged sickle-shaped claw on each hindfoot, which is thought to have been used to kill its prey. Velociraptor can be distinguished from other dromaeosaurids by its long and low skull, with an upturned snout.
Velociraptor (commonly shortened to 'raptor') is one of the dinosaur genera most familiar to the general public due to its prominent role in the Jurassic Park motion picture series, although in the films it was shown much larger than it was in reality and without feathers as well as having other anatomical inaccuracies. It is also well-known to paleontologists, with over a dozen recovered fossil skeletons — the most of any dromaeosaurid. One particularly famous specimen preserves a Velociraptor locked in combat with a Protoceratops.
Contents
1 Description
2 History
3 Provenance
4 Taxonomy
5 Paleobiology
5.1 Predatory behavior
5.2 Metabolism
5.3 Feathers
6 In popular culture
7 References
Description
Velociraptor compared in size to a human.
Velociraptor was a mid-sized dromaeosaurid, with adults measuring up to 2.07 m (6.8 ft) long, 0.5 m (1.6 ft) high at the hip, and weighing up to 15 kg (33 lb).[3] The skull, which grew up to 25 cm (9.8 in) long, was uniquely up-curved, concave on the upper surface and convex on the lower. The jaws were lined with 26–28 widely-spaced teeth on each side, each more strongly serrated on the back edge than the front — possibly an adaptation that improved its ability to catch and hold fast-moving prey.[4][5]
Velociraptor mongoliensis.
Velociraptor, like other dromaeosaurids, had a large manus ('hand') with three strongly-curved claws, which were similar in construction and flexibility to the wing bones of modern birds. The second digit was the longest of the three digits present, while the first was shortest. The structure of the carpal (wrist) bones prevented pronation of the wrist and forced the 'hands' to be held with the palmar surface facing inwards (medially), not downwards.[6] The first digit of the foot, as in other theropods, was a small dewclaw. However, whereas most theropods had feet with three digits contacting the ground, dromaeosaurids like Velociraptor walked on only their third and fourth digits. The second digit, for which Velociraptor is most famous, was highly modified and held retracted off of the ground. It bore a relatively large, sickle-shaped claw, typical of dromaeosaurid and troodontid dinosaurs. This enlarged claw, which could be over 6.5 cm (2.6 in) long around its outer edge, was most likely a predatory device used to tear into prey, possibly delivering a fatal blow.[7][8]
Long bony projections (prezygapophyses) on the upper surfaces of the vertebrae, as well as ossified tendons underneath, stiffened the tail of Velociraptor. The prezygapophyses began on the tenth tail (caudal) vertebra and extended forward to brace four to ten additional vertebrae, depending on position in the tail. The stiffening forced the entire tail to act as a single rod-like unit, preventing vertical motion between vertebrae. However, at least one specimen preserves a series of intact tail vertebrae curved sideways into an S-shape, suggesting that there was considerably more horizontal flexibility. These adaptations of the tail probably provided balance and stability while turning, especially at high speeds.[7][8]
In 2007, paleontologists Alan Turner, Peter Makovicky, Mark Norell and colleagues reported the discovery of quill knobs on a well-preserved Velociraptor mongoliensis forearm from Mongolia, confirming the presence of feathers in this species.[9]
History
Henry Fairfield Osborn's drawing of the type skull of Velociraptor mongoliensis from 1924
The type skull of Velociraptor mongoliensis on display at the American Museum of Natural History
An American Museum of Natural History expedition to the Outer Mongolian Gobi Desert in 1922 recovered the first Velociraptor fossil known to science: a crushed but complete skull, associated with one of the raptorial second toe claws (AMNH 6515). In 1924, museum president Henry Fairfield Osborn designated the skull and claw (which he assumed to come from the hand) as the type specimen of his new genus, Velociraptor. This name is derived from the Latin words velox ('swift') and raptor ('robber' or 'plunderer') and refers to the animal's cursorial nature and carnivorous diet. Osborn named the type species V. mongoliensis after its country of origin.[4] Earlier that year, Osborn had mentioned the animal in a popular press article, under the name "Ovoraptor djadochtari" (not to be confused with the similarly named Oviraptor).[10] However, because the name "Ovoraptor" was not published in a scientific journal or accompanied by a formal description, it is considered a nomen nudum ('naked name'), and the name Velociraptor retains priority.
While North American teams were shut out of communist Mongolia during the Cold War, expeditions by Soviet and Polish scientists, in collaboration with Mongolian colleagues, recovered several more specimens of Velociraptor. The most famous is part of the legendary "Fighting Dinosaurs" specimen (GIN 100/25), discovered by a Polish-Mongolian team in 1971. This fossil preserves a single Velociraptor in the midst of battle against a lone Protoceratops.[7][11][12] This specimen is considered a national treasure of Mongolia, although in 2000 it was loaned to the American Museum of Natural History in New York City for a temporary exhibition.[13]
Between 1988 and 1990, a joint Chinese-Canadian team discovered Velociraptor remains in northern China.[14] American scientists returned to Mongolia in 1990, and a joint Mongolian-American expedition to the Gobi, led by the American Museum of Natural History and the Mongolian Academy of Sciences, turned up several well-preserved skeletons.[8][15] One such specimen, IGM 100/980, was nicknamed "Ichabodcraniosaurus" by Norell's team because the fairly complete specimen was found without its skull (an allusion to the Washington Irving character Ichabod Crane).[16] This specimen may belong to Velociraptor mongoliensis, but Norell and Makovicky concluded that it was not complete enough to say for sure, and it awaits a formal description.[8]
Maxillae and a lacrimal (the main tooth-bearing bones of the upper jaw, and the bone that forms the anterior margin of the eye socket, respectively) recovered in 1999 by the Sino-Belgian Dinosaur Expeditions were found to pertain to Velociraptor, but not to the type species V. mongoliensis. Pascal Godefroit and colleagues named these bones V. osmolskae (for Polish paleontologist Halszka Osmólska) in 2008.[2]
Provenance
Mounted skeleton of Velociraptor mongoliensis, Museum voor Natuurwetenschappen, Brussels.
All known specimens of Velociraptor mongoliensis were discovered in the Djadochta Formation (also spelled Djadokhta), in both the Mongolian province of Ömnögovi and Chinese Inner Mongolia. A species of Velociraptor, possibly V. mongoliensis, is also preserved in the slightly younger Barun Goyot Formation of Mongolia.[17] These geologic formations are estimated to date back to the Campanian stage (about 83 to 70 million years ago[18]) of the Late Cretaceous Epoch.[19]
V. mongoliensis has been found at many of the most famous and prolific Djadochta localities. The type specimen was discovered at the Flaming Cliffs site (also known as Bayn Dzak and Shabarakh Usu),[4] while the "Fighting Dinosaurs" were found at the Tugrig locality (also known as Tugrugeen Shireh).[12] More recently, fossils of V. mongoliensis were recovered from Bayan Mandahu, a prolific site from the Djadochta of Inner Mongolia in China.[14] The well-known Barun Goyot localities of Khulsan and Khermeen Tsav have also produced remains which may belong to the genus Velociraptor.[20]
All of these sites preserve an arid environment with fields of sand dunes and only intermittent streams, although the younger Barun Goyot environment seems to have been slightly wetter than the older Djadochta.[19] Aside from Protoceratops, upon which it preyed, Velociraptor shared its environment with other basal ceratopsians like Udanoceratops and ankylosaurids like Pinacosaurus, along with several species of oviraptorid, troodontid, other dromaeosaurids (such as Adasaurus), and alvarezsaurid theropods.[17]
V. osmolskae was found in the Bayan Mandahu Formation, contemporaneous with the Djadochta Formation. As in the Djadochta, Pinacosaurus, Protoceratops, oviraptorid, and troodontid theropods were present.[2]
Taxonomy
Illustration of Velociraptor mongoliensis.
Velociraptor is a member of the subfamily Velociraptorinae, a derived sub-group of the larger family Dromaeosauridae. In phylogenetic taxonomy, Velociraptorinae is usually defined as "all dromaeosaurs more closely related to Velociraptor than to Dromaeosaurus." Dromaeosaurid classification is highly variable. Originally, the subfamily Velociraptorinae was erected solely to contain Velociraptor.[7] Other analyses have included other genera, usually Deinonychus and Saurornitholestes.[21] A recent cladistic analysis indicated a monophyletic Velociraptorinae containing Velociraptor, Deinonychus, Tsaagan, and a closely related (but uncertainly positioned) Saurornitholestes.[22]
In the past, other dromaeosaurid species, including Deinonychus antirrhopus and Saurornitholestes langstoni, have sometimes been classified in the genus Velociraptor. Since Velociraptor was the first to be named, these species were renamed Velociraptor antirrhopus and V. langstoni.[3] However, the only currently recognized species of Velociraptor are V. mongoliensis[5][6][23] and V. osmolskae.[2]
When first described in 1924, Velociraptor was placed in the family Megalosauridae, as was the case with most carnivorous dinosaurs at the time (Megalosauridae, like Megalosaurus, functioned as a sort of 'wastebin' taxon, where many unrelated species were grouped together).[4] As dinosaur discoveries multiplied, Velociraptor was later recognized as a dromaeosaurid. All dromaeosaurids have also been referred to the family Archaeopterygidae by at least one author (which would, in effect, make Velociraptor a flightless bird).[6]
Paleobiology
Predatory behavior
Velociraptor and Protoceratops in combat
The "Fighting Dinosaurs" specimen, found in 1971, preserves a Velociraptor mongoliensis and Protoceratops andrewsi in combat and provides direct evidence of predatory behavior. When originally reported, it was hypothesized that the two animals drowned.[12] However, as the animals were preserved in ancient sand dune deposits, it is now thought that the animals were buried in sand, either from a collapsing dune or in a sandstorm. Burial must have been extremely fast, judging from the lifelike poses in which the animals were preserved. Both forelimbs and one hindlimb of the Protoceratops are missing, which has been seen as evidence of scavenging by other animals.[24]
Close-up of a replica of the "Fighting Dinosaurs".
The distinctive claw, on the second digit of dromaeosaurids, has traditionally been depicted as a slashing weapon; its assumed use being to cut and disembowel prey.[25] In the "Fighting Dinosaurs" specimen, the Velociraptor lies underneath, with one of its sickle claws apparently embedded in the throat of its prey, while the beak of Protoceratops is clamped down upon the right forelimb of its attacker. This suggests Velociraptor may have used its sickle claw to pierce vital organs of the throat, such as the jugular vein, carotid artery, or trachea (windpipe), rather than slashing the abdomen. The inside edge of the claw was rounded and not unusually sharp, which may have precluded any sort of cutting or slashing action, although only the bony core of the claw is known. The thick abdominal wall of skin and muscle of large prey species would have been difficult to slash without a specialized cutting surface.[24] The slashing hypothesis was tested during a 2005 BBC documentary, The Truth About Killer Dinosaurs. The producers of the program created an artificial Velociraptor leg with a sickle claw and used a pork belly to simulate the dinosaur's prey. Though the sickle claw did penetrate the abdominal wall, it was unable to tear it open, indicating that the claw was not used to disembowel prey. However, this experiment has not been published or repeated by other scientists, so its results cannot be confirmed.
Remains of Deinonychus, a closely related dromaeosaurid, have commonly been found in aggregations of several individuals. Deinonychus has also been found in association with a large herbivore, Tenontosaurus, which has been seen as evidence of cooperative hunting.[26][27] The only solid evidence for social behavior among dromaeosaurids comes from a Chinese trackway of fossil footprints, which shows six individuals of a large species moving as a group, though no evidence of cooperative hunting was found.[28] Although many isolated fossils of Velociraptor have been found in Mongolia, none were closely associated with any other individuals.[23] Therefore, while Velociraptor is commonly depicted as a pack hunter, as in Jurassic Park, there is only limited fossil evidence to support this theory for dromaeosaurids in general, and none specific to Velociraptor itself.
Metabolism
Velociraptor was probably warm-blooded to some degree, as it required a significant amount of energy to hunt. Modern animals that possess feathery or furry coats, like Velociraptor did, tend to be warm-blooded, since these coverings function as insulation. However, bone growth rates in dromaeosaurids and some early birds suggest a more moderate metabolism, compared with most modern warm-blooded mammals and birds. The kiwi is similar to dromaeosaurids in anatomy, feather type, bone structure and even the narrow anatomy of the nasal passages (usually a key indicator of metabolism). The kiwi is a highly active, if specialized, flightless bird, with a stable body temperature and a fairly low resting metabolic rate, making it a good model for the metabolism of primitive birds and dromaeosaurids.[6]
[edit] Feathers
Velociraptor mongoliensis.
Fossils of dromaeosaurids more primitive than Velociraptor are known to have had feathers covering their bodies, and fully-developed, feathered wings.[29] The fact that the ancestors of Velociraptor were feathered and possibly capable of flight long suggested to paleontologists that Velociraptor bore feathers as well, since even flightless birds today retain most of their feathers.
In September 2007, researchers found quill knobs on the forearm of a Velociraptor found in Mongolia.[9] These bumps on bird wing bones show where feathers anchor, and their presence on Velociraptor indicate it too had feathers. According to paleontologist Alan Turner,
A lack of quill knobs does not necessarily mean that a dinosaur did not have feathers. Finding quill knobs on Velociraptor, though, means that it definitely had feathers. This is something we'd long suspected, but no one had been able to prove.[30]
Co-author Mark Norell, Curator-in-Charge of fossil reptiles, amphibians and birds at the American Museum of Natural History, also weighed in on the discovery, saying:
The more that we learn about these animals the more we find that there is basically no difference between birds and their closely related dinosaur ancestors like velociraptor. Both have wishbones, brooded their nests, possess hollow bones, and were covered in feathers. If animals like velociraptor were alive today our first impression would be that they were just very unusual looking birds.[30]
According to Turner and co-authors Norell and Peter Makovicky, quill knobs are not found in all prehistoric birds, and their absence does not mean that an animal was not feathered – flamingos for example have no quill knobs. However, their presence confirms that Velociraptor bore modern-style wing feathers, with a rachis and vane formed by barbs. The forearm specimen on which the quill knobs were found (specimen number IGM 100/981) represents an animal 1.5 meters in length (5 ft) and 15 kilograms (33 lbs) in weight. Based on the spacing of the six preserved knobs in this specimen, the authors suggested that Velociraptor bore 14 secondaries (wing feathers stemming from the forearm), compared with 12 or more in Archaeopteryx, 18 in Microraptor, and 10 in Rahonavis. This type of variation in the number of wing feathers between closely related species, the authors asserted, is to be expected, given similar variation among modern birds.
Turner and colleagues interpreted the presence of feathers on Velociraptor as evidence against the idea that the larger, flightless maniraptorans lost their feathers secondarily due to larger body size. Furthermore, they noted that quill knobs are almost never found in flightless bird species today, and that their presence in Velociraptor (presumed to have been flightless due to its relatively large size and short forelimbs) is evidence that the ancestors of dromaeosaurids could fly, making Velociraptor and other large members of this family secondarily flightless, though it is possible the large wing feathers inferred in the ancestors of Velociraptor had a purpose other than flight. The feathers of the flightless Velociraptor may have been used for display, for covering their nests while brooding, or for added speed and thrust when running up inclined slopes.[9]
[edit] In popular culture
See also: Biological issues in Jurassic Park#Velociraptor
Velociraptor is well-known from its role as a vicious and cunning killer in the 1990 novel Jurassic Park by Michael Crichton and its 1993 film adaptation, directed by Steven Spielberg. The "raptors" portrayed in Jurassic Park were modeled after a larger relative, Deinonychus, which Gregory Paul at the time called Velociraptor antirrhopus.[3] The paleontologists in the film and the novel excavate a so-called Velociraptor skeleton in Montana, far from the central Asian range of Velociraptor but well within the range of Deinonychus. A character in Crichton's novel also states that "…Deinonychus is now considered one of the velociraptors", indicating that Crichton used Paul's taxonomy, though the "raptors" in the novel are referred to as V. mongoliensis.[31]
Steven Spielberg may also have increased the size of the film's Velociraptor for dramatic reasons.[32] Additionally, the forelimbs of the film animals differed in structure and posture from those of real dromaeosaurids and their tails were too short and flexible, anatomical errors which directly contradict fossil evidence. The film version of Velociraptor was also covered in scales. In life, Velociraptor, like many other maniraptoran theropods, was covered in feathers. In Jurassic Park III, the Velociraptor are depicted with quill-like structures along the back of the head and neck, although these do not resemble the down-like feathers known from real-life dromaeosaurids, and the quill knobs on some Velociraptor specimens show that they had fully-developed feathers akin to those of modern birds.[9] Also in Jurassic Park III, Dr. Alan Grant, played by Sam Neill, states that Velociraptor were smarter than dolphins, whales and some primates. Based on fossil evidence, this is highly unlikely. It is more probable that, while intelligent by dinosaur standards, they were less intelligent than modern big cats.[33]
Due to the success of most Jurassic Park-related products, Velociraptor has become a ubiquitous representation of dinosaurs in popular culture. It has been featured in numerous toy lines, animated films, video games and television series for children, along with several recent television documentaries. In 1995, the city of Toronto was awarded a National Basketball Association expansion team, which was named the Toronto Raptors.
Smaller than other dromaeosaurids like Deinonychus and Achillobator, the turkey-sized Velociraptor nevertheless shared many of the same anatomical features. It was a bipedal, feathered carnivore with a long, stiffened tail and an enlarged sickle-shaped claw on each hindfoot, which is thought to have been used to kill its prey. Velociraptor can be distinguished from other dromaeosaurids by its long and low skull, with an upturned snout.
Velociraptor (commonly shortened to 'raptor') is one of the dinosaur genera most familiar to the general public due to its prominent role in the Jurassic Park motion picture series, although in the films it was shown much larger than it was in reality and without feathers as well as having other anatomical inaccuracies. It is also well-known to paleontologists, with over a dozen recovered fossil skeletons — the most of any dromaeosaurid. One particularly famous specimen preserves a Velociraptor locked in combat with a Protoceratops.
Contents
1 Description
2 History
3 Provenance
4 Taxonomy
5 Paleobiology
5.1 Predatory behavior
5.2 Metabolism
5.3 Feathers
6 In popular culture
7 References
Description
Velociraptor compared in size to a human.
Velociraptor was a mid-sized dromaeosaurid, with adults measuring up to 2.07 m (6.8 ft) long, 0.5 m (1.6 ft) high at the hip, and weighing up to 15 kg (33 lb).[3] The skull, which grew up to 25 cm (9.8 in) long, was uniquely up-curved, concave on the upper surface and convex on the lower. The jaws were lined with 26–28 widely-spaced teeth on each side, each more strongly serrated on the back edge than the front — possibly an adaptation that improved its ability to catch and hold fast-moving prey.[4][5]
Velociraptor mongoliensis.
Velociraptor, like other dromaeosaurids, had a large manus ('hand') with three strongly-curved claws, which were similar in construction and flexibility to the wing bones of modern birds. The second digit was the longest of the three digits present, while the first was shortest. The structure of the carpal (wrist) bones prevented pronation of the wrist and forced the 'hands' to be held with the palmar surface facing inwards (medially), not downwards.[6] The first digit of the foot, as in other theropods, was a small dewclaw. However, whereas most theropods had feet with three digits contacting the ground, dromaeosaurids like Velociraptor walked on only their third and fourth digits. The second digit, for which Velociraptor is most famous, was highly modified and held retracted off of the ground. It bore a relatively large, sickle-shaped claw, typical of dromaeosaurid and troodontid dinosaurs. This enlarged claw, which could be over 6.5 cm (2.6 in) long around its outer edge, was most likely a predatory device used to tear into prey, possibly delivering a fatal blow.[7][8]
Long bony projections (prezygapophyses) on the upper surfaces of the vertebrae, as well as ossified tendons underneath, stiffened the tail of Velociraptor. The prezygapophyses began on the tenth tail (caudal) vertebra and extended forward to brace four to ten additional vertebrae, depending on position in the tail. The stiffening forced the entire tail to act as a single rod-like unit, preventing vertical motion between vertebrae. However, at least one specimen preserves a series of intact tail vertebrae curved sideways into an S-shape, suggesting that there was considerably more horizontal flexibility. These adaptations of the tail probably provided balance and stability while turning, especially at high speeds.[7][8]
In 2007, paleontologists Alan Turner, Peter Makovicky, Mark Norell and colleagues reported the discovery of quill knobs on a well-preserved Velociraptor mongoliensis forearm from Mongolia, confirming the presence of feathers in this species.[9]
History
Henry Fairfield Osborn's drawing of the type skull of Velociraptor mongoliensis from 1924
The type skull of Velociraptor mongoliensis on display at the American Museum of Natural History
An American Museum of Natural History expedition to the Outer Mongolian Gobi Desert in 1922 recovered the first Velociraptor fossil known to science: a crushed but complete skull, associated with one of the raptorial second toe claws (AMNH 6515). In 1924, museum president Henry Fairfield Osborn designated the skull and claw (which he assumed to come from the hand) as the type specimen of his new genus, Velociraptor. This name is derived from the Latin words velox ('swift') and raptor ('robber' or 'plunderer') and refers to the animal's cursorial nature and carnivorous diet. Osborn named the type species V. mongoliensis after its country of origin.[4] Earlier that year, Osborn had mentioned the animal in a popular press article, under the name "Ovoraptor djadochtari" (not to be confused with the similarly named Oviraptor).[10] However, because the name "Ovoraptor" was not published in a scientific journal or accompanied by a formal description, it is considered a nomen nudum ('naked name'), and the name Velociraptor retains priority.
While North American teams were shut out of communist Mongolia during the Cold War, expeditions by Soviet and Polish scientists, in collaboration with Mongolian colleagues, recovered several more specimens of Velociraptor. The most famous is part of the legendary "Fighting Dinosaurs" specimen (GIN 100/25), discovered by a Polish-Mongolian team in 1971. This fossil preserves a single Velociraptor in the midst of battle against a lone Protoceratops.[7][11][12] This specimen is considered a national treasure of Mongolia, although in 2000 it was loaned to the American Museum of Natural History in New York City for a temporary exhibition.[13]
Between 1988 and 1990, a joint Chinese-Canadian team discovered Velociraptor remains in northern China.[14] American scientists returned to Mongolia in 1990, and a joint Mongolian-American expedition to the Gobi, led by the American Museum of Natural History and the Mongolian Academy of Sciences, turned up several well-preserved skeletons.[8][15] One such specimen, IGM 100/980, was nicknamed "Ichabodcraniosaurus" by Norell's team because the fairly complete specimen was found without its skull (an allusion to the Washington Irving character Ichabod Crane).[16] This specimen may belong to Velociraptor mongoliensis, but Norell and Makovicky concluded that it was not complete enough to say for sure, and it awaits a formal description.[8]
Maxillae and a lacrimal (the main tooth-bearing bones of the upper jaw, and the bone that forms the anterior margin of the eye socket, respectively) recovered in 1999 by the Sino-Belgian Dinosaur Expeditions were found to pertain to Velociraptor, but not to the type species V. mongoliensis. Pascal Godefroit and colleagues named these bones V. osmolskae (for Polish paleontologist Halszka Osmólska) in 2008.[2]
Provenance
Mounted skeleton of Velociraptor mongoliensis, Museum voor Natuurwetenschappen, Brussels.
All known specimens of Velociraptor mongoliensis were discovered in the Djadochta Formation (also spelled Djadokhta), in both the Mongolian province of Ömnögovi and Chinese Inner Mongolia. A species of Velociraptor, possibly V. mongoliensis, is also preserved in the slightly younger Barun Goyot Formation of Mongolia.[17] These geologic formations are estimated to date back to the Campanian stage (about 83 to 70 million years ago[18]) of the Late Cretaceous Epoch.[19]
V. mongoliensis has been found at many of the most famous and prolific Djadochta localities. The type specimen was discovered at the Flaming Cliffs site (also known as Bayn Dzak and Shabarakh Usu),[4] while the "Fighting Dinosaurs" were found at the Tugrig locality (also known as Tugrugeen Shireh).[12] More recently, fossils of V. mongoliensis were recovered from Bayan Mandahu, a prolific site from the Djadochta of Inner Mongolia in China.[14] The well-known Barun Goyot localities of Khulsan and Khermeen Tsav have also produced remains which may belong to the genus Velociraptor.[20]
All of these sites preserve an arid environment with fields of sand dunes and only intermittent streams, although the younger Barun Goyot environment seems to have been slightly wetter than the older Djadochta.[19] Aside from Protoceratops, upon which it preyed, Velociraptor shared its environment with other basal ceratopsians like Udanoceratops and ankylosaurids like Pinacosaurus, along with several species of oviraptorid, troodontid, other dromaeosaurids (such as Adasaurus), and alvarezsaurid theropods.[17]
V. osmolskae was found in the Bayan Mandahu Formation, contemporaneous with the Djadochta Formation. As in the Djadochta, Pinacosaurus, Protoceratops, oviraptorid, and troodontid theropods were present.[2]
Taxonomy
Illustration of Velociraptor mongoliensis.
Velociraptor is a member of the subfamily Velociraptorinae, a derived sub-group of the larger family Dromaeosauridae. In phylogenetic taxonomy, Velociraptorinae is usually defined as "all dromaeosaurs more closely related to Velociraptor than to Dromaeosaurus." Dromaeosaurid classification is highly variable. Originally, the subfamily Velociraptorinae was erected solely to contain Velociraptor.[7] Other analyses have included other genera, usually Deinonychus and Saurornitholestes.[21] A recent cladistic analysis indicated a monophyletic Velociraptorinae containing Velociraptor, Deinonychus, Tsaagan, and a closely related (but uncertainly positioned) Saurornitholestes.[22]
In the past, other dromaeosaurid species, including Deinonychus antirrhopus and Saurornitholestes langstoni, have sometimes been classified in the genus Velociraptor. Since Velociraptor was the first to be named, these species were renamed Velociraptor antirrhopus and V. langstoni.[3] However, the only currently recognized species of Velociraptor are V. mongoliensis[5][6][23] and V. osmolskae.[2]
When first described in 1924, Velociraptor was placed in the family Megalosauridae, as was the case with most carnivorous dinosaurs at the time (Megalosauridae, like Megalosaurus, functioned as a sort of 'wastebin' taxon, where many unrelated species were grouped together).[4] As dinosaur discoveries multiplied, Velociraptor was later recognized as a dromaeosaurid. All dromaeosaurids have also been referred to the family Archaeopterygidae by at least one author (which would, in effect, make Velociraptor a flightless bird).[6]
Paleobiology
Predatory behavior
Velociraptor and Protoceratops in combat
The "Fighting Dinosaurs" specimen, found in 1971, preserves a Velociraptor mongoliensis and Protoceratops andrewsi in combat and provides direct evidence of predatory behavior. When originally reported, it was hypothesized that the two animals drowned.[12] However, as the animals were preserved in ancient sand dune deposits, it is now thought that the animals were buried in sand, either from a collapsing dune or in a sandstorm. Burial must have been extremely fast, judging from the lifelike poses in which the animals were preserved. Both forelimbs and one hindlimb of the Protoceratops are missing, which has been seen as evidence of scavenging by other animals.[24]
Close-up of a replica of the "Fighting Dinosaurs".
The distinctive claw, on the second digit of dromaeosaurids, has traditionally been depicted as a slashing weapon; its assumed use being to cut and disembowel prey.[25] In the "Fighting Dinosaurs" specimen, the Velociraptor lies underneath, with one of its sickle claws apparently embedded in the throat of its prey, while the beak of Protoceratops is clamped down upon the right forelimb of its attacker. This suggests Velociraptor may have used its sickle claw to pierce vital organs of the throat, such as the jugular vein, carotid artery, or trachea (windpipe), rather than slashing the abdomen. The inside edge of the claw was rounded and not unusually sharp, which may have precluded any sort of cutting or slashing action, although only the bony core of the claw is known. The thick abdominal wall of skin and muscle of large prey species would have been difficult to slash without a specialized cutting surface.[24] The slashing hypothesis was tested during a 2005 BBC documentary, The Truth About Killer Dinosaurs. The producers of the program created an artificial Velociraptor leg with a sickle claw and used a pork belly to simulate the dinosaur's prey. Though the sickle claw did penetrate the abdominal wall, it was unable to tear it open, indicating that the claw was not used to disembowel prey. However, this experiment has not been published or repeated by other scientists, so its results cannot be confirmed.
Remains of Deinonychus, a closely related dromaeosaurid, have commonly been found in aggregations of several individuals. Deinonychus has also been found in association with a large herbivore, Tenontosaurus, which has been seen as evidence of cooperative hunting.[26][27] The only solid evidence for social behavior among dromaeosaurids comes from a Chinese trackway of fossil footprints, which shows six individuals of a large species moving as a group, though no evidence of cooperative hunting was found.[28] Although many isolated fossils of Velociraptor have been found in Mongolia, none were closely associated with any other individuals.[23] Therefore, while Velociraptor is commonly depicted as a pack hunter, as in Jurassic Park, there is only limited fossil evidence to support this theory for dromaeosaurids in general, and none specific to Velociraptor itself.
Metabolism
Velociraptor was probably warm-blooded to some degree, as it required a significant amount of energy to hunt. Modern animals that possess feathery or furry coats, like Velociraptor did, tend to be warm-blooded, since these coverings function as insulation. However, bone growth rates in dromaeosaurids and some early birds suggest a more moderate metabolism, compared with most modern warm-blooded mammals and birds. The kiwi is similar to dromaeosaurids in anatomy, feather type, bone structure and even the narrow anatomy of the nasal passages (usually a key indicator of metabolism). The kiwi is a highly active, if specialized, flightless bird, with a stable body temperature and a fairly low resting metabolic rate, making it a good model for the metabolism of primitive birds and dromaeosaurids.[6]
[edit] Feathers
Velociraptor mongoliensis.
Fossils of dromaeosaurids more primitive than Velociraptor are known to have had feathers covering their bodies, and fully-developed, feathered wings.[29] The fact that the ancestors of Velociraptor were feathered and possibly capable of flight long suggested to paleontologists that Velociraptor bore feathers as well, since even flightless birds today retain most of their feathers.
In September 2007, researchers found quill knobs on the forearm of a Velociraptor found in Mongolia.[9] These bumps on bird wing bones show where feathers anchor, and their presence on Velociraptor indicate it too had feathers. According to paleontologist Alan Turner,
A lack of quill knobs does not necessarily mean that a dinosaur did not have feathers. Finding quill knobs on Velociraptor, though, means that it definitely had feathers. This is something we'd long suspected, but no one had been able to prove.[30]
Co-author Mark Norell, Curator-in-Charge of fossil reptiles, amphibians and birds at the American Museum of Natural History, also weighed in on the discovery, saying:
The more that we learn about these animals the more we find that there is basically no difference between birds and their closely related dinosaur ancestors like velociraptor. Both have wishbones, brooded their nests, possess hollow bones, and were covered in feathers. If animals like velociraptor were alive today our first impression would be that they were just very unusual looking birds.[30]
According to Turner and co-authors Norell and Peter Makovicky, quill knobs are not found in all prehistoric birds, and their absence does not mean that an animal was not feathered – flamingos for example have no quill knobs. However, their presence confirms that Velociraptor bore modern-style wing feathers, with a rachis and vane formed by barbs. The forearm specimen on which the quill knobs were found (specimen number IGM 100/981) represents an animal 1.5 meters in length (5 ft) and 15 kilograms (33 lbs) in weight. Based on the spacing of the six preserved knobs in this specimen, the authors suggested that Velociraptor bore 14 secondaries (wing feathers stemming from the forearm), compared with 12 or more in Archaeopteryx, 18 in Microraptor, and 10 in Rahonavis. This type of variation in the number of wing feathers between closely related species, the authors asserted, is to be expected, given similar variation among modern birds.
Turner and colleagues interpreted the presence of feathers on Velociraptor as evidence against the idea that the larger, flightless maniraptorans lost their feathers secondarily due to larger body size. Furthermore, they noted that quill knobs are almost never found in flightless bird species today, and that their presence in Velociraptor (presumed to have been flightless due to its relatively large size and short forelimbs) is evidence that the ancestors of dromaeosaurids could fly, making Velociraptor and other large members of this family secondarily flightless, though it is possible the large wing feathers inferred in the ancestors of Velociraptor had a purpose other than flight. The feathers of the flightless Velociraptor may have been used for display, for covering their nests while brooding, or for added speed and thrust when running up inclined slopes.[9]
[edit] In popular culture
See also: Biological issues in Jurassic Park#Velociraptor
Velociraptor is well-known from its role as a vicious and cunning killer in the 1990 novel Jurassic Park by Michael Crichton and its 1993 film adaptation, directed by Steven Spielberg. The "raptors" portrayed in Jurassic Park were modeled after a larger relative, Deinonychus, which Gregory Paul at the time called Velociraptor antirrhopus.[3] The paleontologists in the film and the novel excavate a so-called Velociraptor skeleton in Montana, far from the central Asian range of Velociraptor but well within the range of Deinonychus. A character in Crichton's novel also states that "…Deinonychus is now considered one of the velociraptors", indicating that Crichton used Paul's taxonomy, though the "raptors" in the novel are referred to as V. mongoliensis.[31]
Steven Spielberg may also have increased the size of the film's Velociraptor for dramatic reasons.[32] Additionally, the forelimbs of the film animals differed in structure and posture from those of real dromaeosaurids and their tails were too short and flexible, anatomical errors which directly contradict fossil evidence. The film version of Velociraptor was also covered in scales. In life, Velociraptor, like many other maniraptoran theropods, was covered in feathers. In Jurassic Park III, the Velociraptor are depicted with quill-like structures along the back of the head and neck, although these do not resemble the down-like feathers known from real-life dromaeosaurids, and the quill knobs on some Velociraptor specimens show that they had fully-developed feathers akin to those of modern birds.[9] Also in Jurassic Park III, Dr. Alan Grant, played by Sam Neill, states that Velociraptor were smarter than dolphins, whales and some primates. Based on fossil evidence, this is highly unlikely. It is more probable that, while intelligent by dinosaur standards, they were less intelligent than modern big cats.[33]
Due to the success of most Jurassic Park-related products, Velociraptor has become a ubiquitous representation of dinosaurs in popular culture. It has been featured in numerous toy lines, animated films, video games and television series for children, along with several recent television documentaries. In 1995, the city of Toronto was awarded a National Basketball Association expansion team, which was named the Toronto Raptors.
Sunday, September 7, 2008
Tyrannosaurus Rex
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. It 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 meters (43 ft) in length,[1] up to 4 meters (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, 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.
Contents[hide]
1 Description
2 Classification
2.1 Manospondylus
3 Paleobiology
3.1 Life history
3.2 Sexual dimorphism
3.3 Posture
3.4 Arms
3.5 Soft tissue
3.6 Skin and feathers
3.7 Thermoregulation
3.8 Footprints
3.9 Locomotion
3.10 Feeding strategies
4 History
4.1 Earliest finds
4.2 Notable specimens
5 Appearances in popular culture
6 References
7 See also
8 External links
//
[edit] Description
Various specimens of Tyrannosaurus rex with a human for scale.
Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 meters (42 feet) long, and was 4.0 meters (13 ft) tall at the hips.[2] Mass estimates have varied widely over the years, from more than 7.2 metric tons (8 short tons),[4] to less than 4.5 metric tons (5 tons),[5][6] with most modern estimates ranging between 5.4 and 6.8 metric tons (between 6 and 7.5 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]
Size comparison of selected giant theropod dinosaurs, Tyrannosaurus in purple.
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]
The largest known T. rex skulls measure up to 1.5 meters (5 ft) in length. 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.[13] 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.[14][15][16] 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.[17][18]
Life restoration of a Tyrannosaurus rex.
The teeth of T. rex displayed marked heterodonty (differences in shape).[19][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.[20] 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 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur.[21]
[edit] Classification
T. rex head reconstruction at the Oxford University Museum of Natural History.
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,[22][23] both of which have occasionally been synonymized with Tyrannosaurus.[18] 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.[17]
Profile view of a Tyrannosaurus skull (AMNH 5027).
In 1955, Soviet paleontologist Evgeny Maleev named a new species, Tyrannosaurus bataar, from Mongolia.[24] By 1965, this species had been renamed Tarbosaurus bataar.[25] Despite the renaming, many phylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex,[23] and it has often been considered an Asian species of Tyrannosaurus.[17][26][27] 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.[28] 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.[22]
Other tyrannosaurid fossils found in the same formations as T. rex were originally classified as separate taxa, including Aublysodon and Albertosaurus megagracilis,[18] the latter being named Dinotyrannus megagracilis in 1995.[29] However, these fossils are now universally considered to belong to juvenile T. rex.[30] A small but nearly complete skull from Montana, 60 cm (2 ft) long, may be an exception. This skull was originally classified as a species of Gorgosaurus (G. lancensis) by Charles W. Gilmore in 1946,[31] but was later referred to a new genus, Nanotyrannus.[32] Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile T. rex.[33] 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.[23][34]
[edit] Manospondylus
Skull of T. rex, type specimen at the Carnegie Museum of Natural History. This was heavily and inaccurately restored with plaster using Allosaurus as a model, and has since been disassembled.
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 T. rex as early as 1917 but, due to the fragmentary nature of the Manospondylus vertebrae, he could not synonymize them conclusively.[35]
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 T. rex. According to the rules of the International Code of Zoological Nomenclature (ICZN), the system that governs the scientific naming of animals, Manospondylus gigas should therefore have priority over Tyrannosaurus rex, because it was named first.[36] However, the Fourth Edition of the ICZN, which took effect on January 1, 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 easily qualifies 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 gigas would then be deemed a nomen oblitum ("forgotten name").[38]
[edit] Paleobiology
[edit] Life history
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.[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 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.[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 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.[42]
[edit] Sexual dimorphism
Tyrannosaurus skeleton casts mounted in a mating position, Jurassic Museum of Asturies.
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 of eggs.[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 T. 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 T. rex specimens have been found from Saskatchewan 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 T. 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
Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose.
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.[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 T. 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] Despite its inaccuracies, the 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) 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.[18]
[edit] Arms
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.[50] For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of Allosaurus.[35] However, a year earlier, Lawrence Lambe described the short, two-fingered forelimbs of the closely-related Gorgosaurus.[51] 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").[52] The remains of "Sue" also include complete forelimbs.[1] T. rex arms are very small relative to overall body size, measuring only one meter (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.[53] 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. 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 kg (438 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.[54]
[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.[55] 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.[56] 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.[57] 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 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."[59]
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."[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
Main article: Feathered dinosaurs
Tyrannosaurus baby covered with downy 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.[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 like Tyrannosaurus, especially in warm Cretaceous climates.[64]
[edit] Thermoregulation
Main article: Physiology of dinosaurs
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.[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 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.[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 T. 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
The probable Tyrannosaurus rex footprint from New Mexico.
Two isolated fossilized footprints have been tentatively assigned to Tyrannosaurus rex. The first was discovered in Philmont, 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 in ornithopod 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 centimeters (33 in) long by 71 cm (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 cm (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
A sequence of sauropod footprints. No such sequence has yet been reported for tyrannosaurs, making gait and speed estimates difficult.
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 an ice skater pulls his or her arms closer in order to spin faster).[76]
Scientists have produced a wide range of maximum speed estimates, mostly around 11 meters/second (25 mph), but a few as low as 5-11 meters/second (12-25 mph), and a few as high as 20 meters/second (45 mph). Researchers have to rely on various estimating techniques because, while there are many tracks 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 km/h or 25–45 mph).[78]
Skeletal anatomy of a T. rex right leg.
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.[52] 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 interlocked metatarsus 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]
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 meters/second (about 24 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 6-8 ton Tyrannosaurus 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][81] However, giraffes have been known to gallop at 50 km/h (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.[82][83] Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks.[84][85]
Foot of a Tyrannosaurus rex.
Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 km/h (11 mph) to 40 km/h (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[86]) to gauge the leg muscle mass needed for fast running (over 40 km/h [25 mph]). They found that proposed top speeds in excess of 40 km/h (25 mph) were unfeasible, because they would require very large leg muscles (more than approximately 40–86% of total body mass.) Even moderately fast speeds would have required large leg muscles. 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 km/h (~11 mph) walking/jogging might have been possible.[87][78]
A study in 2007 used computer models to estimate running speeds, based on data taken directly from fossils, and claimed that T. rex had a top running speed of 8 meters per second (18 mph). An average professional football (soccer) player would be slightly slower, while a human sprinter can reach 12 m/s (27 mph). Note that these computer models predict a top speed of 17.8 m/second (about 45 mph) for a 3 kilogram (7 lb) Compsognathus[88][89] (probably a juvenile individual).[90]
Those who argue that Tyrannosaurus was incapable of running estimate the top speed of Tyrannosaurus at about 17 km/h (11 mph). This is still faster than its most likely prey species, hadrosaurids and ceratopsians.[87] In addition, some advocates of the idea that Tyrannosaurus was a predator (see below) claim that tyrannosaur running speed is not important, since it may have been slow but still faster than its probable prey.[91] 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.[92] 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 that Tyrannosaurus did not have to be fast to catch its prey. Alternatively, perhaps Tyrannosaurus used ambush tactics to attack faster prey animals.[78] The debate about Tyrannosaurus’ speed seems far from finished.
[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.[93] 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.[94][95]
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.[96][52] Horner has presented several arguments to support the pure scavenger hypothesis:
Cast of a Tyrannosaurus rex braincase at the Australian Museum, Sydney.
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 modern vultures do. 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.[96][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.[87][91] It may also have used ambush tactics to attack faster prey animals.[78]
The eye-sockets of T. rex faced mainly forwards, giving it good binocular vision.
Other evidence suggests hunting behavior in Tyrannosaurus. Stevens (2006) found that 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 that stereoscopic vision provides.[13] In modern animals, binocular vision is found mainly in predators (the principal exceptions are primates, which need it for leaping from branch to branch).
At the site where the very large tyrannosaur named Sue was found, a skeleton of the hadrosaurid Edmontosaurus annectens was also found, 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][102] A Triceratops was found in Mexico found with bite marks on its ilium. These were also inflicted by a tyrannosaur and they too appear healed, indicating active predation by the tyrannosaur.[103] This is consistent with the results of a study in 2003 which found that Tyrannosaurus’ estimated bite force of 183,000 newtons (180 LT/202 ST) to 235,000 newtons (231 LT/259 ST) made a single T. rex very capable of killing a Triceratops horridus.[16]. 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, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would be competition for food and mates or active cannibalism is unclear.[104] 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.[105]
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.
[edit] History
Skeletal restoration by William D. Matthew from 1905, which was the first reconstruction of Tyrannosaurus rex ever published[106]
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.[50]
[edit] Earliest finds
Scale model of the never-completed Tyrannosaurus rex exhibit planned for the American Museum of Natural History by H.F. Osborn.
Teeth from what is now documented as a T. 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 considered T. rex. Vertebral fragments found by E. D. Cope in western South Dakota in 1892 and named as Manospondylus gigas have also been reclassified as T. rex.[107]
Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of T. rex in eastern Wyoming in 1900. H. F. Osborn originally named this skeleton Dynamosaurus 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.[108] 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.[109]
In total, Brown found five Tyrannosaurus partial skeletons. In 1941, Brown's 1902 find 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.[52]
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.[110]
[edit] Notable specimens
Main article: Specimens of Tyrannosaurus
"Sue" the Tyrannosaurus, Field Museum of Natural History, Chicago, showing the forelimbs. The 'wishbone' is between the forelimbs.
Sue Hendrickson, amateur paleontologist, discovered the most complete (more than 90%) and, until 2001 the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation near Faith, South Dakota, on August 12, 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, and the fossil collection was sold at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. It has now been reassembled and is currently exhibited 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.[111] The "Sue" specimen apparently died from a massive bite to the head, which could only have been inflicted by another tyrannosaur.[112] Researchers reported that a subadult and a juvenile skeleton were found in the same quarry as the "Sue" specimen, which has been used to support the hypothesis that tyrannosaurs may have lived in social groups of some kind.[113]
Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota, in the spring of 1987. After 30,000 hours of digging and preparing, a 65% complete skeleton emerged. Stan is currently on display in the Black Hills Museum of Natural History Exhibit in Hill City, South Dakota, after an extensive world tour. This tyrannosaur, too, was found to have many bone pathologies, including broken and healed ribs, a broken (and healed) neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth. Both Stan and Sue were examined by Peter Larson.
"Jane" at the Burpee Museum in Rockford, Illinois
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 tyrannosaurid Nanotyrannus but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus.[114] 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.[115][116]
Also in 2001, Dr. Jack Horner discovered a specimen of T. rex around 10% larger than "Sue". Dubbed C. rex (or "Celeste" after Jack's wife), this specimen is currently under study.
In a press release on April 7, 2006, Montana State University revealed that it possessed the largest Tyrannosaurus 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%.[117][118]
[edit] Appearances in popular culture
Main article: Cultural depictions of Tyrannosaurus
Since it was first described in 1905, Tyrannosaurus rex has become the most widely-recognized dinosaur in popular culture. It is the only dinosaur which is routinely referred to by its full scientific name (Tyrannosaurus rex) among the general public, and the scientific abbreviation T. rex has also come into wide usage (commonly misspelled "T-Rex").[1] Robert T. Bakker notes this in The Dinosaur Heresies and explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."[6]
Museum exhibits featuring T. rex are very popular; an estimated 10,000 visitors flocked to Chicago's Field Museum on the opening day of its "Sue" exhibit in 2003.[119] T. rex has appeared numerous times on television and in films, notably (in chronological order) The Lost World, King Kong, The Land Before Time, the Jurassic Park films, Barney and Friends, Toy Story, Toy Story 2, Walking with Dinosaurs, and Night at the Museum, among many others. A number of books and comic strips, including Calvin and Hobbes and Dinosaur Comics, have also featured Tyrannosaurus, which is typically portrayed as the biggest and most terrifying carnivore of all. At least one musical group, the band T.Rex, is named after the species. Tyrannosaurus-related toys, including numerous video games and other merchandise, remain popular. Various businesses have capitalized on the popularity of Tyrannosaurus rex by using it in advertisements.
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 meters (43 ft) in length,[1] up to 4 meters (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, 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.
Contents[hide]
1 Description
2 Classification
2.1 Manospondylus
3 Paleobiology
3.1 Life history
3.2 Sexual dimorphism
3.3 Posture
3.4 Arms
3.5 Soft tissue
3.6 Skin and feathers
3.7 Thermoregulation
3.8 Footprints
3.9 Locomotion
3.10 Feeding strategies
4 History
4.1 Earliest finds
4.2 Notable specimens
5 Appearances in popular culture
6 References
7 See also
8 External links
//
[edit] Description
Various specimens of Tyrannosaurus rex with a human for scale.
Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 meters (42 feet) long, and was 4.0 meters (13 ft) tall at the hips.[2] Mass estimates have varied widely over the years, from more than 7.2 metric tons (8 short tons),[4] to less than 4.5 metric tons (5 tons),[5][6] with most modern estimates ranging between 5.4 and 6.8 metric tons (between 6 and 7.5 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]
Size comparison of selected giant theropod dinosaurs, Tyrannosaurus in purple.
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]
The largest known T. rex skulls measure up to 1.5 meters (5 ft) in length. 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.[13] 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.[14][15][16] 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.[17][18]
Life restoration of a Tyrannosaurus rex.
The teeth of T. rex displayed marked heterodonty (differences in shape).[19][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.[20] 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 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur.[21]
[edit] Classification
T. rex head reconstruction at the Oxford University Museum of Natural History.
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,[22][23] both of which have occasionally been synonymized with Tyrannosaurus.[18] 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.[17]
Profile view of a Tyrannosaurus skull (AMNH 5027).
In 1955, Soviet paleontologist Evgeny Maleev named a new species, Tyrannosaurus bataar, from Mongolia.[24] By 1965, this species had been renamed Tarbosaurus bataar.[25] Despite the renaming, many phylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex,[23] and it has often been considered an Asian species of Tyrannosaurus.[17][26][27] 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.[28] 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.[22]
Other tyrannosaurid fossils found in the same formations as T. rex were originally classified as separate taxa, including Aublysodon and Albertosaurus megagracilis,[18] the latter being named Dinotyrannus megagracilis in 1995.[29] However, these fossils are now universally considered to belong to juvenile T. rex.[30] A small but nearly complete skull from Montana, 60 cm (2 ft) long, may be an exception. This skull was originally classified as a species of Gorgosaurus (G. lancensis) by Charles W. Gilmore in 1946,[31] but was later referred to a new genus, Nanotyrannus.[32] Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile T. rex.[33] 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.[23][34]
[edit] Manospondylus
Skull of T. rex, type specimen at the Carnegie Museum of Natural History. This was heavily and inaccurately restored with plaster using Allosaurus as a model, and has since been disassembled.
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 T. rex as early as 1917 but, due to the fragmentary nature of the Manospondylus vertebrae, he could not synonymize them conclusively.[35]
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 T. rex. According to the rules of the International Code of Zoological Nomenclature (ICZN), the system that governs the scientific naming of animals, Manospondylus gigas should therefore have priority over Tyrannosaurus rex, because it was named first.[36] However, the Fourth Edition of the ICZN, which took effect on January 1, 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 easily qualifies 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 gigas would then be deemed a nomen oblitum ("forgotten name").[38]
[edit] Paleobiology
[edit] Life history
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.[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 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.[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 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.[42]
[edit] Sexual dimorphism
Tyrannosaurus skeleton casts mounted in a mating position, Jurassic Museum of Asturies.
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 of eggs.[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 T. 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 T. rex specimens have been found from Saskatchewan 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 T. 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
Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose.
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.[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 T. 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] Despite its inaccuracies, the 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) 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.[18]
[edit] Arms
.jpg){kind=link}
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.[50] For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of Allosaurus.[35] However, a year earlier, Lawrence Lambe described the short, two-fingered forelimbs of the closely-related Gorgosaurus.[51] 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").[52] The remains of "Sue" also include complete forelimbs.[1] T. rex arms are very small relative to overall body size, measuring only one meter (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.[53] 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. 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 kg (438 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.[54]
[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.[55] 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.[56] 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.[57] 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 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."[59]
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."[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
Main article: Feathered dinosaurs
Tyrannosaurus baby covered with downy 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.[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 like Tyrannosaurus, especially in warm Cretaceous climates.[64]
[edit] Thermoregulation
Main article: Physiology of dinosaurs
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.[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 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.[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 T. 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
The probable Tyrannosaurus rex footprint from New Mexico.
Two isolated fossilized footprints have been tentatively assigned to Tyrannosaurus rex. The first was discovered in Philmont, 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 in ornithopod 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 centimeters (33 in) long by 71 cm (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 cm (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
A sequence of sauropod footprints. No such sequence has yet been reported for tyrannosaurs, making gait and speed estimates difficult.
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 an ice skater pulls his or her arms closer in order to spin faster).[76]
Scientists have produced a wide range of maximum speed estimates, mostly around 11 meters/second (25 mph), but a few as low as 5-11 meters/second (12-25 mph), and a few as high as 20 meters/second (45 mph). Researchers have to rely on various estimating techniques because, while there are many tracks 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 km/h or 25–45 mph).[78]
Skeletal anatomy of a T. rex right leg.
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.[52] 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 interlocked metatarsus 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]
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 meters/second (about 24 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 6-8 ton Tyrannosaurus 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][81] However, giraffes have been known to gallop at 50 km/h (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.[82][83] Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks.[84][85]
.JPG){kind=link}
Foot of a Tyrannosaurus rex.
Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 km/h (11 mph) to 40 km/h (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[86]) to gauge the leg muscle mass needed for fast running (over 40 km/h [25 mph]). They found that proposed top speeds in excess of 40 km/h (25 mph) were unfeasible, because they would require very large leg muscles (more than approximately 40–86% of total body mass.) Even moderately fast speeds would have required large leg muscles. 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 km/h (~11 mph) walking/jogging might have been possible.[87][78]
A study in 2007 used computer models to estimate running speeds, based on data taken directly from fossils, and claimed that T. rex had a top running speed of 8 meters per second (18 mph). An average professional football (soccer) player would be slightly slower, while a human sprinter can reach 12 m/s (27 mph). Note that these computer models predict a top speed of 17.8 m/second (about 45 mph) for a 3 kilogram (7 lb) Compsognathus[88][89] (probably a juvenile individual).[90]
Those who argue that Tyrannosaurus was incapable of running estimate the top speed of Tyrannosaurus at about 17 km/h (11 mph). This is still faster than its most likely prey species, hadrosaurids and ceratopsians.[87] In addition, some advocates of the idea that Tyrannosaurus was a predator (see below) claim that tyrannosaur running speed is not important, since it may have been slow but still faster than its probable prey.[91] 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.[92] 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 that Tyrannosaurus did not have to be fast to catch its prey. Alternatively, perhaps Tyrannosaurus used ambush tactics to attack faster prey animals.[78] The debate about Tyrannosaurus’ speed seems far from finished.
[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.[93] 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.[94][95]
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.[96][52] Horner has presented several arguments to support the pure scavenger hypothesis:
Cast of a Tyrannosaurus rex braincase at the Australian Museum, Sydney.
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 modern vultures do. 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.[96][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.[87][91] It may also have used ambush tactics to attack faster prey animals.[78]
The eye-sockets of T. rex faced mainly forwards, giving it good binocular vision.
Other evidence suggests hunting behavior in Tyrannosaurus. Stevens (2006) found that 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 that stereoscopic vision provides.[13] In modern animals, binocular vision is found mainly in predators (the principal exceptions are primates, which need it for leaping from branch to branch).
At the site where the very large tyrannosaur named Sue was found, a skeleton of the hadrosaurid Edmontosaurus annectens was also found, 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][102] A Triceratops was found in Mexico found with bite marks on its ilium. These were also inflicted by a tyrannosaur and they too appear healed, indicating active predation by the tyrannosaur.[103] This is consistent with the results of a study in 2003 which found that Tyrannosaurus’ estimated bite force of 183,000 newtons (180 LT/202 ST) to 235,000 newtons (231 LT/259 ST) made a single T. rex very capable of killing a Triceratops horridus.[16]. 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, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would be competition for food and mates or active cannibalism is unclear.[104] 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.[105]
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.
[edit] History
Skeletal restoration by William D. Matthew from 1905, which was the first reconstruction of Tyrannosaurus rex ever published[106]
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.[50]
[edit] Earliest finds
Scale model of the never-completed Tyrannosaurus rex exhibit planned for the American Museum of Natural History by H.F. Osborn.
Teeth from what is now documented as a T. 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 considered T. rex. Vertebral fragments found by E. D. Cope in western South Dakota in 1892 and named as Manospondylus gigas have also been reclassified as T. rex.[107]
Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of T. rex in eastern Wyoming in 1900. H. F. Osborn originally named this skeleton Dynamosaurus 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.[108] 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.[109]
In total, Brown found five Tyrannosaurus partial skeletons. In 1941, Brown's 1902 find 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.[52]
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.[110]
[edit] Notable specimens
Main article: Specimens of Tyrannosaurus
"Sue" the Tyrannosaurus, Field Museum of Natural History, Chicago, showing the forelimbs. The 'wishbone' is between the forelimbs.
Sue Hendrickson, amateur paleontologist, discovered the most complete (more than 90%) and, until 2001 the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation near Faith, South Dakota, on August 12, 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, and the fossil collection was sold at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. It has now been reassembled and is currently exhibited 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.[111] The "Sue" specimen apparently died from a massive bite to the head, which could only have been inflicted by another tyrannosaur.[112] Researchers reported that a subadult and a juvenile skeleton were found in the same quarry as the "Sue" specimen, which has been used to support the hypothesis that tyrannosaurs may have lived in social groups of some kind.[113]
Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota, in the spring of 1987. After 30,000 hours of digging and preparing, a 65% complete skeleton emerged. Stan is currently on display in the Black Hills Museum of Natural History Exhibit in Hill City, South Dakota, after an extensive world tour. This tyrannosaur, too, was found to have many bone pathologies, including broken and healed ribs, a broken (and healed) neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth. Both Stan and Sue were examined by Peter Larson.
"Jane" at the Burpee Museum in Rockford, Illinois
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 tyrannosaurid Nanotyrannus but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus.[114] 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.[115][116]
Also in 2001, Dr. Jack Horner discovered a specimen of T. rex around 10% larger than "Sue". Dubbed C. rex (or "Celeste" after Jack's wife), this specimen is currently under study.
In a press release on April 7, 2006, Montana State University revealed that it possessed the largest Tyrannosaurus 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%.[117][118]
[edit] Appearances in popular culture
Main article: Cultural depictions of Tyrannosaurus
Since it was first described in 1905, Tyrannosaurus rex has become the most widely-recognized dinosaur in popular culture. It is the only dinosaur which is routinely referred to by its full scientific name (Tyrannosaurus rex) among the general public, and the scientific abbreviation T. rex has also come into wide usage (commonly misspelled "T-Rex").[1] Robert T. Bakker notes this in The Dinosaur Heresies and explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."[6]
Museum exhibits featuring T. rex are very popular; an estimated 10,000 visitors flocked to Chicago's Field Museum on the opening day of its "Sue" exhibit in 2003.[119] T. rex has appeared numerous times on television and in films, notably (in chronological order) The Lost World, King Kong, The Land Before Time, the Jurassic Park films, Barney and Friends, Toy Story, Toy Story 2, Walking with Dinosaurs, and Night at the Museum, among many others. A number of books and comic strips, including Calvin and Hobbes and Dinosaur Comics, have also featured Tyrannosaurus, which is typically portrayed as the biggest and most terrifying carnivore of all. At least one musical group, the band T.Rex, is named after the species. Tyrannosaurus-related toys, including numerous video games and other merchandise, remain popular. Various businesses have capitalized on the popularity of Tyrannosaurus rex by using it in advertisements.
Subscribe to:
Posts (Atom)