Ectrodactyly

In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of an animal. It comes from the Greek word δακτυλος, meaning "finger". more...

Sometimes the ending "-dactylia" is used. The adjectival forms end with "-dactyl" or "-dactylous".

By number

Pentadactyly is the condition of having five digits on each limb. All land vertebrates are descended from an ancestor with a pentadactyl limb, although many groups of species have lost or transformed some or all of their digits.

Tetradactyly is the condition of having four digits on a limb, as in amphibians and many birds

Tridactyly is the condition of having three digits on a limb, as in some birds and ancestors of the horse such as Protohippus and Hipparion.

Bidactyly or didactyly is the condition of having two digits on each limb, as in the Two-toed Sloth, Choloepus didactylus. In humans this name is used for an abnormality in which the middle digits are missing, leaving only the thumb and fifth finger.

Monodactyly is the condition of having a single digit on a limb, as in modern horses.

Syndactyly is a condition where two or more digits are fused together. It occurs normally in some mammals, such as the siamang. It occurs as a rare abnormality in humans.

In birds

Anisodactyly is the most common arrangement of digits in birds, with three toes forward and one back. This is common in songbirds and other perching birds, as well as hunting birds like eagles, hawks, and falcons.

Syndactyly in birds is like anisodactyly, except that the third and fourth toes (the outer and middle forward-pointing toes) are fused together, as in the Belted Kingfisher, Ceryle alcyon.

Zygodactyly (from Greek ζυγον, a yoke) is an arrangement of digits in birds, with two toes facing forward (digits 2 and 3) and two back (digits 1 and 4). This arrangement is most common in arboreal species, particularly those that climb tree trunks or clamber through foliage. Zygodactyly occurs in the woodpeckers and flickers, nuthatches, and parrots.

Heterodactyly is like zygodactyly, except that it is digits 3 and 4 that point forward and digits 1 and 2 that point back. This is only found in trogons.

Other terms

An excess of digits is called hyperdactyly or polydactyly, such as in the extremely rare case that a person has six fingers or toes on a single hand or foot.

A lack of digits not caused by an amputation is called hypodactyly.

Ectrodactyly is the congenital absence of all or part of one or more fingers or toes. This term is used for a range of conditions from aphalangia (in which the some of the phalanges or finger bones are missing), to adactyly (the absence of a digit).

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