quadruped

The Zebra is an example of a quadruped.

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.^[1]

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.

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.^[2] 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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Many people, especially practitioners of Parkour and Freerunning and Georges Hébert's Natural Method, find benefit in using quadrupedal movement in order to build full body strength. For added difficulty this can be done faster (for a co-ordination/cardio exercise) or slower (for a more intense muscle workout), or more exaggerated and to the effect of a push-up, or down stairs. Moving quadrupedally exercises the entire anterior: thighs, core, shoulders, and triceps. It has been used in several cases to cross structures such as bridges and walls, In Brisbane, Australia the Sunday S&C Parkour group has used Quadrupedal to cross the Goodwill Bridge, Story Bridge and recently the Kurilpa Bridge on 04/10/2009.

Quadrupedal can be achieved on a railing/wall also as a balancing exercise, required some arm strength and co-ordination in order to not fall off (the movement can be done forwards and backwards).

See also

• Bipedalism

References

External links

• Family may provide evolution clue - BBC News
• A website devoted to the above family that walks quadrupedally
• Basic training for quadrupedal locomotion