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Quadruped
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Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet" (from the Latin quad for "four" and ped for "foot").
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Encyclopedia
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet" (from the Latin quad for "four" and ped for "foot"). The majority of walking animals are quadrupeds, including mammals such as cattle and cats, and reptiles, like lizards.
Birds, humans, insects, crustaceans, and snakes are not quadrupeds. However, there are some exceptions. For example, among the insects, the praying mantis is a quadruped. A few birds may use quadrupedal movement in some circumstances, for example the shoebill will sometimes use its wings to right itself after lunging at prey.
Quadrupeds vs. tetrapods
Not all four-limbed animals are quadrupeds. Although arms and wings are, in the evolutionary sense, modified legs, four-limbed animals are in fact classed as tetrapods, members of the taxonomic unit Tetrapoda. These include all vertebrates with quadrupedal ancestors, including mammals, reptiles, amphibians, and birds. (For further information, see Pierson v. Post, 3 Cai. R. 175, 2 Am. Dec. 264 (N.Y. 1805). Read this case for common law knowledge of quadrupeds ferae naturae.)
The distinction between quadrupeds and tetrapods is important in evolutionary biology, particularly in the context of bipeds, winged animals, and animals whose limbs have adapted to other roles (e.g. fins, in the case of cetaceans and pinnipeds). All of these animals are tetrapods, but none are quadrupeds. Even snakes, whose limbs have become entirely vestigial, are nevertheless tetrapods.
Quadrupedalism in humans
In July 2005, in rural Turkey, scientists discovered five Kurdish siblings who had learned to walk naturally on their hands and feet. Unlike chimpanzees, who ambulate on their knuckles, the Turkish siblings (ranging from 18 to 34 years old) walked on their palms, allowing them to preserve the dexterity of their fingers. Calluses found on their hands make the possibility of a hoax unlikely. Another similar case has been reported in Chile, but the case is still being investigated and reports are not released as of March 22, 2006.
The discovery of the family has provided scientists a unique view into human evolutionary history. Nicholas Humphrey and John Skoyles from the London School of Economics and Roger Keynes from Cambridge University have suggested that their gait is due to two rare phenomena coming together. First, instead of initially crawling as infants on their knees, they started off learning to move around with a “bear crawl” on their feet. Second, due to their congenital brain impairment, they found balancing on two legs difficult. Because this, their motor development was channelled into turning their bear crawl into a substitute for bipedality.
Other scientists, such as Stefan Mundlos of the Max Planck Institute, believe that the family's unusual gait may result from a genetic abnormality. Mundlos has found a region on chromosome 17 that might be responsible for human bipedalism.
Quadrupedal movement for exercise
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