Tripedalism (from the Latin tri = three + ped = foot) is locomotion by the use of three legs. There are no known naturally occurring three-legged animals, although the movement of some macropods such as kangaroos, which can alternate between resting their weight on their muscular tails and their two hind legs, may be an example of tripedal locomotion in animals. There are also the tripod fish. This fish rests on the ocean bottom on two rays from its two pelvic fins and one ray from its caudal fin ().
Quadrupedal amputees and mutations
There are however some three-legged creatures in the world today, namely four-legged animals (such as pet dogs and cats) who have had one limb amputated. With proper medical treatment most of these injured animals can go on to live fairly normal lives, despite being artificially tripedal. There are also cases of mutations or birth abnormalities in animals (including humans) which have resulted in three legs.
Use of tripedalism in science fiction and fantasy
Tripedalism is more at home within a science fiction or fantasy theme, such as where mysterious alien life forms walk upon three legs and on other worldly planets where all the Earthly conventions of two or four legged animals are vastly different.
- In H. G. Wells' 1898 novel The War of the Worlds a tripedal theme is ever present. Although it is not used in the biological sense (excluding the 2005 cinematic version, which did include three-legged aliens), the Martians use tripedal-themed machines known as Tripods.
- John Wyndham's novel "The Day of the Triffids" (1951) had tripedal plants called triffids which walked around.
- Pierson's Puppeteers are a tripedal alien race in the Known Space universe by author Larry Niven — they have two forelegs and a single hind leg ending in hooved feet and two snake-like heads instead of a humanoid upper body.
- In the Rama series of novels by Arthur C. Clarke, humans come into contact with a number of extraterrestrial space habitats populated by many forms of life based on a tripedal theme.
- In Wayne Barlowe's science fiction book Expedition (and the TV adaptation Alien Planet) some of the creatures on the fictional planet Darwin IV walk on three legs. Barlowe calls them "tripedaliens".
- The Tripods, a trilogy of novels written by John Christopher, is a post-apocalyptic story set one hundred years after the invasion of Earth by tripedal aliens. The first two novels became the basis of a science fiction TV-series of the same name, produced in the United Kingdom in the mid-1980s.
- In Iain M. Banks' 1987 novel Consider Phlebas, several of the major alien species are tripedal, the Idirans and the Homomdans, amongst others.
- The 1997 Science fiction TV show Star Trek: Voyager presented Species 8472, an advanced and aggressive tripedal race (they have three, five-jointed legs), who, when encountered are at war with the Borg, they were one of the more unusual alien creatures to be shown in Star Trek.
- In the computer game Half-Life (and its sequel Half-Life 2) there are numerous tripedal, alien animals seen throughout the series, including Houndeyes, as well as synthetic creatures created by the Combine called Striders and Hunters. Also, it is interesting to note there are a lot of bipedal, sentient, alien species in the game who have three arms, which may have evolved from a tripedal three legs.
- In the Star Wars prequels, a battle droid is introduced called a destroyer (also known as a "droideka"), which has tripedal as well as rolling locomotion.
- Lieutenant Arex, a character in Star Trek: The Animated Series.
- In the Pocoyo cartoon, tripedals are again the aliens (in this case, friendly).
- In a 2005 presentation of the PC Game Spore, Will Wright made a tripedal race of aliens, now known to fans as the Willosaur.
- In the 2012 video game Borderlands 2 there is a tripedal animal called Crystalisk.
- Extraterrestrial life
- List of extraterrestrials in fiction
- Terrestrial locomotion
Illustrated research essay Three-Legged Animals in Mythology and Folklore.