Tripedal

Tripedal (from the Latin tri = three + ped = foot) is the term used for (or would be used for) any animal that stands on three legs. The terms Bipedal and Quadrupedal are used more commonly when referring to animals that either walk on two legs (i.e. humans who walk upright) or animals such as dogs and cats who walk on four legs.

The terms triped, tripedal and tripedalism are rarely, if ever, used in a real scientific context, as there are no known naturally occurring three-legged animals on Earth. 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.

Quadrapedal amputees
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.

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 the H. G. Wells novel The War of the Worlds (and the 2005 movie remake) the tripedal theme is ever present. Again following the science fiction themes of strange and odd alien creatures the alien invaders from the movie walk upon three legs in much the same way their Tripods roam the Earth in their missions of destruction.

In 1997 the 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 a 2005 presentation of the PC Game Spore, Will Wright made a tripedal race of aliens, now known to fans as the Willosaur.

There are also Tripeds known as Muddlets in the Deltora series.

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.