Dactyly

In biology, dactyly is the arrangement of (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".

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". 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.

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