The Strange Occipital Flaps: What Is Their Structure and Function?

Amongst chameleons, some species of the genera Calumma, Chamaeleo and Trioceros possess a strange structure on the back of their heads: the occipital flaps.

STRUCTURE

The occipital flap (lobus occipitalis) is a skin duplicature of a semilunar shape, attached to the head at the back of the skull, along the causal margin of it, freely hanging over the neck and partly covering it. In some species, they are smallish, with the largest width much les than the orbit diameter (e.g. C. nasutum or Ch. gracilis) butnin some species, it grows to a big-sized elephant-ear-like formation reaching the flanks (e.g. C. cuccullatum; Ch. monachus; T. melleri).It is covered by scales of standard size, always in the case of the hidden aide attached to neck and in the case of small occipital flaps in some species outside, while in the case if large flaps, the scales on the outer side, can be remarkably enlarged.The occipital flaps are in many species movable and can be everted to right-angle position to the body axis, in some species (e.g. T. melleri) they can be even shaken and vibrated.

FUNCTION

Based on decades of research and observations, there is a passive and active way how the occipital lobes work in fact. 

Active function 

Pics:1. Antipredatory display in female T. werneri

2. same in Ch. dilepis

3. Imposing male of Ch. monachus