Fourtoed

Fourtoed is a descriptive term used in biology to denote that an animal or other vertebrate has four toes on one or more of its limbs. It is commonly found in field guides and common names, but it is not a formal taxonomic category. The term can apply to forelimbs or hindlimbs and is used across various groups, including birds, reptiles, amphibians, and mammals.

In birds, feet typically consist of four digits, three pointing forward and one backward; this arrangement is frequently described as four-toed. Among mammals, most species are pentadactyl (five toes), but four-toed configurations occur in some lineages due to evolutionary reduction or retention of a four-toed pattern. In fossil remains, toe counts are used to infer relationships and locomotor adaptations, with some extinct taxa described as four-toed.

Toe number is determined during embryonic development by genetic and developmental pathways that regulate digit formation. Variation arises through evolutionary modification, functional specialization, or developmental constraints. The four-toed trait can be a defining feature in a local population or a widely used descriptor in a species’ common name.

Fourtoed may also appear in zoological names and popular references to indicate the presence of four toes. In taxonomy and anatomy, the term is primarily descriptive and helps distinguish limb morphology from related forms with different digit counts, such as three-toed or five-toed forms. See also: digit, tetrapod, pentadactyl, limb development.