Why is there no “three-legged creature”?


Joshua Case

Three-legged creatures are rarely seen in nature, except in cases where they have lost their feet in an accident or battle, or congenital malformations. Tracy Thomson, a major in Earth and Planetary Science at the University of California, Davis, discusses why there are no three-legged creatures.

Three-legged locomotion and the constraints on limb number: why tripeds don't have a leg to stand on-thomson-2019-bioessays-wiley online library

Why Not Three Legs?-Egghead

First of all, Thomson points out that 'I don't see any creatures with three legs, but there are many creatures that rest on two legs and another part (such as the tail).' Examples of this are meerkats and woodpeckers. Meerkat stands upright with two legs and tail to take a break.


Dušan Smetana

Woodpeckers are also caught on the tree using two legs and tail feathers.


adam muise

According to Mr. Thomson, most of the tree-like animals use the tail to support the body other than the limbs, and can be said to be doing three-limb exercise. Among them, parrots use a beak as the third support, and Thomson describes parrots as “almost three legs”.



The advantage of standing in three points is that it is easy to stabilize the body. To stay upright with two legs, you need big legs to balance and leg strength to stabilize your body.

On the other hand, there is a demerit that you cannot walk on three legs. Kangaroos are creatures with a huge tail, but they cannot walk because of their size. Kangaroos jump and move using their tails.

By picturepartners

Some animals use their tails and beaks to exercise their three limbs, but there are still few three-legged creatures in nature. For that reason, Thomson said, “It is due to heredity” and “almost all animals are symmetrical. Life has become“ symmetrical ”from the stage before it has legs and fins due to evolution. 'I think there was almost no change once the symmetry feature was established once,' he said.

Mr. Thomson said, “In order to understand evolution as a process, it is first necessary to understand“ what can happen by evolution ”and“ what cannot happen by evolution. ” , Which helps us to deepen insights about what could never happen. '

in Creature, Posted by darkhorse_log