Quadrupedalism is a form of locomotion where animals have four legs are used to bear weight and move around. An animalormachine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (from Latinquattuor for "four", and pes, pedis for "foot"). Quadruped animals are found among both vertebrates and invertebrates.
Although the words ‘quadruped’ and ‘tetrapod’ are both derived from terms meaning ‘four-footed’, they have distinct meanings. A tetrapod is any member of the taxonomic unit Tetrapoda (which is defined by descent from a specific four-limbed ancestor), whereas a quadruped actually uses four limbs for locomotion. Not all tetrapods are quadrupeds and not all entities that could be described as ‘quadrupedal’ are tetrapods. This last meaning includes certain artificial objects; almost all quadruped organisms are tetrapods (one exception is some raptorialarthropods adapted for four-footed locomotion, such as the Mantodea. Another example is brush-footed butterflies (Nymphalidae), the largest butterfly family with ~6000 species, including the well-known Monarch (shown in photo).
The distinction between quadrupeds and tetrapods is important in evolutionary biology, particularly in the context of tetrapods whose limbs have adapted to other roles (e.g., hands in the case of humans, wings in the case of birds and bats, and fins in the case of whales). All of these animals are tetrapods, but none are a quadrupeds. Even snakes, whose limbs have become vestigial or lost entirely, are, nevertheless, tetrapods.
Quadrupedalism is sometimes referred to as being "on all fours", and is observed in crawling, especially by infants.[1]
In the 20th century quadrupedal movement was popularized as a form of physical exercise by Georges Hebert.[2]Kenichi Ito is a Japanese man famous for speed running on four limbs in competitions.[3]
In July 2005, in rural Turkey, scientists discovered five Turkish siblings who had learned to walk naturally on their hands and feet. Unlike chimpanzees, which ambulate on their knuckles, the Ulas family walked on their palms, allowing them to preserve the dexterity of their fingers.[4][5][6]
A related concept to quadrupedalism is pronogrady, or having a horizontal posture of the trunk. Although nearly all quadrupedal animals are pronograde, bipedal animals also have that posture, including many living birds and extinct dinosaurs.[9]
^Mondschein, Emily R., Karen E. Adolph, and Catherine S. Tamis-LeMonda. "Gender bias in mothers' expectations about infant crawling." Journal of experimental child psychology 77.4 (2000): 304–316.
