Hexadactyly in Chameleons

Chameleons have a highly specialized arrangement of their fingers and toes, uniquely adapted for gripping branches with precision. This configuration, known as chamaeleodactylia, is distinctive among reptiles and plays a crucial role in their arboreal lifestyle.

Chamaeleodactyly: A Unique Grip

Instead of individually moving digits, chameleons possess %n fingers fused in groups of two and three that function as a pincer-like grasp:

• Front feet (forelimbs): Two groups: inner one with three fused fingers and the outer one with two fused fingers.

• Hind feet (hindlimbs): Reversed configuration: inner group has two fused fingers, and the outer one has three fused fingers.

This chamaeleodactylous structure enables chameleons to firmly grasp branches, improving their stability and climbing efficiency. The split between digit groups provides maximum surface contact enhanced with special filamentous microstructures similar to setae in geckos, ensuring secure, effortless movement through trees.

Polydactyly: A Rare Developmental Anomaly

Occasionally, chameleons exhibit polydactylia, where extra fingers form due to developmental irregularities during embryogenesis. Though rare, such cases usually result from genetic mutations or errors in limb formation.

Asymmetric Anterior Bilateral Hexadactyly in male Furcifer pardalis, Ambilobe:

A Concrete Case of Six Digit Anomaly

On the photos, a case of a captive bred male Furcifer pardalis, Ambilobe, chameleons exhibit polydactylia, where on each of the front feet one extra fingers developed on the external part of the fused finger groups, which normally consist of two fingers. The extra finger is situated medially and is not developed fully symmetrically, on one side it is bigger than the other. The specimen was growing slower than its siblings and dies short after reaching sexual maturity.

Etymology

The term Hexadactyly (latin Hexadactylia, latinized from Greek)  originates from Greek roots, combining:

• ἕξ (héx) – meaning six

• δάκτυλος (dáktylos) – meaning finger

Thus, hexadactyly (hexadactylia) directly translates to "having six fingers" based on these Greek components. This condition falls under the broader category of polydactyly, which refers to having extra digits.