Not to be confused with Dactyl (poetry).

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

Sometimes the ending "-dactylia" is used. The derived adjectives end with "-dactyl" or "-dactylous".

As a normal feature


Pentadactyly (from Greek πέντε (pénte) = "five" and δάκτυλος (dáktulos) = "finger") is the condition of having five digits on each limb. It is believed that all living tetrapods are descended from an ancestor with a pentadactyl limb, although many species have now lost or transformed some or all of their digits by the process of evolution. However, this viewpoint was challenged by Stephen Jay Gould in his 1991 essay "Eight (Or Fewer) Little Piggies".[1] Despite the individual variations listed below, the relationship is to the original five-digit 'model'.

In reptiles, the limbs are pentadactylous.


Tetradactyly (from Greek tetra-="four" plus δακτυλος = "finger") is the condition of having four digits on a limb, as in many amphibians, birds, and theropod dinosaurs. Some mammals also exhibit tetradactyly (for example pigs and the hind limbs of dogs and cats). Cartoon characters are commonly drawn with four digits on each hand/foot as it's clearer to see than five.


Tridactyly (from Greek tri- = "three" plus δακτυλος = "finger") is the condition of having three digits on a limb, as in the rhinoceros and ancestors of the horse such as Protohippus and Hipparion. These all belong to the Perissodactyla. Some birds also have three toes, including emus, bustards, and quail.


Didactyly (from Greek di-="two" plus δακτυλος = "finger") or bidactyly is the condition of having two digits on each limb, as in the Hypertragulidae and 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, or big and little toes. Cloven-hoofed mammals (such as deer, sheep and cattle - Artiodactyla) have only two digits, as do ostriches.


Monodactyly (from Greek monos- = "one" plus δακτυλος = "finger") is the condition of having a single digit on a limb, as in modern horses. These belong to the Perissodactyla.

As a congenital defect


Human foot with partial simple syndactyly.
Main article: Syndactyly

Syndactyly (from Greek συν- = "together" plus δακτυλος = "finger") is a condition where two or more digits are fused together. It occurs normally in some mammals, such as the siamang and most diprotodontid marsupials such as kangaroos. It occurs as an unusual condition in humans.


Main article: Polydactyly

Polydactyly (from Greek πολυ- = "many" plus δακτυλος = "finger") is when a limb has more than the usual number of digits. This can be:


Main article: Oligodactyly

Oligodactyly (from Greek ὀλιγο- = "few" plus δακτυλος = "finger") is having too few digits when not caused by an amputation. It is sometimes incorrectly called hypodactyly or confused with aphalangia, the absence of the phalanx bone on one or (commonly) more digits. When all the digits on a hand or foot are absent, it is referred to as adactyly.[2]


Main article: Ectrodactyly

Ectrodactyly, also known as split-hand malformation, is the congenital absence of one or more central digits of the hands and feet. Consequently, it is a form of oligodactyly. News anchor Bree Walker is probably the best-known person with this condition, which affects about one in 91,000 people. It is conspicuously more common in the Vadoma in Zimbabwe.

In birds

Main article: Bird anatomy
Types of bird feet


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. This occurs in Passeriformes, Columbiformes, falconiformes, accipitriformes, Galliformes and vast majorty of birds.


Syndactyly, as it occurs in birds, is like anisodactyly, except that the third and fourth toes (the outer and middle forward-pointing toes), or three toes, are fused together, as in the belted kingfisher (Megaceryle alcyon). This is characteristic of Coraciiformes (kingfishers, bee-eaters, rollers, and relatives).


A green-winged macaw has raised its right foot to its beak.

Zygodactyly (from Greek ζυγος, even) is an arrangement of digits in birds and chameleons, 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 parrots, woodpeckers (including flickers), cuckoos (including roadrunners), and some owls. Zygodactyl tracks have been found dating to 120–110 Ma (early Cretaceous), 50 million years before the first identified zygodactyl fossils. All Psittaciformes, Cuculiformes, the majority of Piciformes and the osprey are zygodactyl. [3]


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


Pamprodactyly is an arrangement in which all four toes point forward, outer toes (toe 1 and sometimes 4) often if not regularly reversible. It is a characteristic of swifts (Apodidae) and mousebirds (Coliiformes).


The feet of chameleons are organized into bundles of a group of two and a group of three digits which oppose one another to grasp branches in a pincer-like arrangement. This condition has been called zygodactyly or didactyly, however the specific arrangement in chameleons does not fit either definition. The feet of the front limbs in chameleons, for instance, are organized into a medial bundle of digits 1, 2 and 3, and a lateral bundle of digits 4 and 5, while the feet of the hind limbs are organized into a medial bundle of digits 1 and 2, and a lateral bundle of digits 3, 4 and 5.[5] Zygodactyly by definition, on the other hand, involves digits 1 and 4 opposing digits 2 and 3, while chameleons do not exhibit this arrangement in either front of hind limbs. Further, didactyly involves only two digits per limb, while chameleons have five digits, despite being bundled into two opposing bundles.


Schizodactyly is a primate term for grasping and clinging with the second and third digit, instead of the thumb and second digit.


  1. Stephen Jay Gould. "Stephen Jay Gould "Eight (or Fewer) Little Piggies" 1991". Retrieved 2015-10-02.
  2. József Zákány; Catherine Fromental-Ramain; Xavier Warot & Denis Duboule (1997). "Regulation of number and size of digits by posterior Hox genes: A dose-dependent mechanism with potential evolutionary implications". PNAS. 25 (94): 13695–13700. Bibcode:1997PNAS...9413695Z. doi:10.1073/pnas.94.25.13695. PMC 28368Freely accessible. PMID 9391088.
  3. "Earliest zygodactyl bird feet: evidence from Early Cretaceous roadrunner-like tracks". Naturwissenschaften. 2007.
  4. Botelho, João Francisco; Smith-Paredes, Daniel; Nuñez-Leon, Daniel; Soto-Acuña, Sergio; Vargas, Alexander O. (2014-08-07). "The developmental origin of zygodactyl feet and its possible loss in the evolution of Passeriformes". Proceedings of the Royal Society of London B: Biological Sciences. 281 (1788): 20140765. doi:10.1098/rspb.2014.0765. ISSN 0962-8452. PMC 4083792Freely accessible. PMID 24966313.
  5. Anderson, Christopher V. & Higham, Timothy E. (2014). "Chameleon anatomy". In Tolley, Krystal A. & Herrel, Anthony. The Biology of Chameleons. Berkeley: University of California Press. pp. 7–55. ISBN 9780520276055.

External links

This article is issued from Wikipedia - version of the 9/24/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.