Land-vertebrate side toes

From EvoWiki

Suboptimal design > Land-vertibrate side toes

All but some of the earliest tetrapods (land vertebrates and aquatic relatives) have at most 5 digits on each limb; 5 digits is their inferred ancestral state. However, in many cases, some of these digits have become reduced or absent, with the reduced ones having no clear function. In walking limbs, these extra toes no longer reach the ground.

Horse evolution shows an excellent series of intermediates between Hyracotherium, with its four front toes and three rear toes, and Equus, with its single toe on each foot. The intermediates have the central toe enlarged and the toes on each side reduced, until present-day equines have only splints on each side. However, present-day horses are occasionally born with three toes on each foot!

Parallel to horses, most artiodactyls (even-toed ungulates) have had a similar side-toe reduction; the main toes are 3 and 4, with 2 and 5 reduced or absent. Likewise, several carnivorans, among them domestic dogs and cats, have shortened toes with claws (dewclaws).

Pandas' thumbs have become non-opposable, but they have evolved a new pseudo-thumb from the bones of the wrist.