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Dactyly



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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 = "finger".

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

Pentadactyly

Pentadactyly (from Greek pente-="five" plus δακτυλος = "finger") is the condition of having five digits on each limb. It appears that all land vertebrates 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. Despite the individual variations listed below, the relationship to the original five-digit 'model' can be traced. This phenomenon featured in the work of Charles Darwin who noteably said; "What could be more curious than that the hand of man formed for grasping, that of a mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should all be constructed on the same pattern and should include similar bones and in the same relative positions?" Darwin was suggesting that the pentadactyl limb represents some of the strongest evidence for the theory of evolution as it indicates a common ancestry for all land vertebrates.

Tetradactyly

Tetradactyly (from Greek tetra-="four" plus δακτυλος = "finger") is the condition of having four digits on a limb, as in many amphibians and birds. Some mammals also exhibit tetradactyly (for example the hind limbs of dogs and cats).

Tridactyly

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 belong to the Perissodactyla. Some birds also have three toes.

Didactyly

Didactyly (from Greek di-="two" plus δακτυλος = "finger") or bidactyly 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. Cloven-hoofed mammals (such as deer, sheep and cattle - 'Artiodactyla') walk on two digits.

Monodactyly

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.

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. It occurs as an unusual condition in humans.

Polydactyly

Polydactyly (from Greek πολυ- = "many" plus δακτυλος = "finger") (or hyperdactyly, from Greek hyper- = "too many" plus δακτυλος = "finger") is when a limb has more than five digits. This can be:-

  • As a result of congenital abnormality in a normally pentadactyl animal. Polydactyly is very common among domestic cats.
  • Normality in some early tetrapod aquatic animals, such as Acanthostega gunnari (Jarvik 1952), which is one of an increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing insights into the appearance of tetrapods and the origin of limbs with digits. For more information, see polydactyly.

Hypodactyly

Hypodactyly (from Greek hypo- = "too few" plus δακτυλος = "finger") is having too few digits when not caused by an amputation.

Ectrodactyly

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 some of the phalanges or finger bones are missing), to adactyly (the absence of a digit).

A fusing of almost all digits on all of the hands and feet is ectrodactyly. 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

 

Anisodactyly

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

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 Ceryle alcyon. This is characteristic of Coraciiformes (Kingfishers, Bee-eaters, Rollers, and relatives).

Zygodactyly

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 (including flickers), in cuckoos, and in parrots.

Heterodactyly

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

Pamprodactyly

Pamprodactyly is an arrangement in which all four toes point forward. It is a characteristic of swifts (Apodidae).

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dactyly". A list of authors is available in Wikipedia.
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