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Velociraptor - Wiki
Subject: Velociraptor - Wiki
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Velociraptor - Wiki


Velociraptor
From Wikipedia, the free encyclopedia

[Photo] Graphite drawing of Velociraptor sp. From http://en.wikipedia.org/wiki/Image:Velociraptor_dinoguy2.jpg Date 2006-08-04. Author Matt Martyniuk

Velociraptor (IPA: RP /v????l??si????æpt??/, GA /v????l??s??????æpt????/; meaning 'swift thief') is a genus of dromaeosaurid theropod dinosaur that existed approximately 83 to 70 Ma (million years ago) during the later part of the Cretaceous Period. The type species, V. mongoliensis, is the only species recognized today, although others have been assigned in the past. Fossils of this species have been discovered in both Inner and Outer Mongolia in central Asia.

Smaller than other dromaeosaurids like Deinonychus and Achillobator, the turkey-sized Velociraptor nevertheless shared many of the same anatomical features. It was a bipedal carnivore with a long, stiffened tail and had 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.

Due in large part to its prominent role in Michael Crichton's novel Jurassic Park and the subsequent motion picture series, Velociraptor (commonly shortened to 'raptor') is one of the dinosaur genera most familiar to the general public. Velociraptor was portrayed as an incredibly intelligent dinosaur close to humans in size; however, the size, intelligence, and abilities of this animal were embellished. 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.

Description
Velociraptor was small for a dromaeosaurid, with adults measuring up to 2.07 meters (6.7 ft) long, 0.5 meters (1.6 ft) high at the hip, and weighing 15 kilograms (33 lb). The skull, which grew up to 250 millimeters (10 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.

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. 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 65 millimeters (2.5 in) long around its outer edge, was most likely a predatory device used to tear into prey, possibly delivering a fatal blow.

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.

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. 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). 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. 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.

Between 1988 and 1990, a joint Chinese-Canadian team discovered Velociraptor remains in northern China. 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.

Provenance
All known specimens of Velociraptor mongoliensis were discovered in the Djadochta Formation, in both the Mongolian province of ??mn??govi and Chinese Inner Mongolia. A species of Velociraptor, possibly V. mongoliensis, is also preserved in the slightly younger Barun Goyot Formation of Mongolia. These geologic formations are estimated to date back to the Campanian stage (about 83 to 70 million years ago) of the Late Cretaceous Epoch.

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), while the "Fighting Dinosaurs" were found at the Tugrig locality (also known as Tugrugeen Shireh). More recently, fossils of V. mongoliensis were recovered from Bayan Mandahu, a prolific site from the Djadochta of Inner Mongolia in China. The well-known Barun Goyot localities of Khulsan and Khermeen Tsav have also produced remains which may belong to the genus Velociraptor.

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. 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, and alvarezsaurid theropods.

Taxonomy
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. Other analyses have included other genera, usually Deinonychus and Saurornitholestes. A recent cladistic analysis indicated a monophyletic Velociraptorinae containing Velociraptor, Deinonychus, Tsaagan, and a closely related (but uncertainly positioned) Saurornitholestes.

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. However, the only currently recognized species of Velociraptor is V. mongoliensis.

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).[2] 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).[4]


[edit] Paleobiology

[edit] Predatory behavior
The "Fighting Dinosaurs" specimen, found in 1971, preserves a Velociraptor and Protoceratops in combat and provides direct evidence of predatory behavior. When originally reported, it was hypothesized that the two animals drowned.[9] 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.[20]

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.[21] 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 at all sharp, which may have precluded any sort of cutting or slashing action, although only the bony core of the claw is known. A living Velociraptor would have had a keratin sheath around its claws, which may have had a sharper edge. However, it is unlikely that any sharp edge could be maintained, as the claw was not retractable for its protection, nor could it easily be sharpened by scraping against other objects, as seen in cats. The thick abdominal wall of skin and muscle would have been difficult to slash with such a dull cutting surface.[20] 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. The sickle claw did not fully penetrate the abdominal wall, 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 is also occasionally found in association with a larger herbivore, Tenontosaurus, which has been seen as evidence of cooperative hunting.[22][23] Although many isolated fossils of Velociraptor and other dromaeosaurids have been found in Mongolia, none were closely associated with any other individuals.[19] Therefore, while Velociraptor is commonly depicted as a pack hunter, as in Jurassic Park, no fossil evidence currently supports this theory.


[edit] 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 probably 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.[4]


[edit] Feathers
Fossils of dromaeosaurids more primitive than Velociraptor are known to have had feathers covering their bodies, and fully-developed, feathered wings.[24] In light of the fact that the ancestors of Velociraptor were feathered and possibly capable of flight, it is most likely that Velociraptor bore feathers too, since even flightless birds today retain most of their feathers. While there is as yet no direct fossil evidence to confirm that Velociraptor had feathers, there is no reason to suspect it of being an exception.[4]


[edit] In popular culture
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.[1] 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.[25]

Director Steven Spielberg may also have increased the size of the film's Velociraptor for dramatic reasons.[26] 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 other maniraptoran theropods, was likely covered in feathers, although no direct fossil evidence of integument of any kind exists for Velociraptor itself. 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. 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, and it is more probable that, while intelligent by dinosaur standards, they were less intelligent than modern big cats.[27]

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 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.

http://en.wikipedia.org/wiki/Velociraptor
Fossil range: Late Cretaceous
The text in this page is based on the copyrighted Wikipedia article shown in above URL. It is used under the GNU Free Documentation License. You may redistribute it, verbatim or modified, providing that you comply with the terms of the GFDL.

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