OCCIPITAL FLAPS, THE MYSTERIOUS MORPHOLOGICAL STRUCTURES IN CHAMELEONS

The chameleons are the dragons of our times. They are equally bizarre and unusual with all the strange horns and scales and casques and structures on their heads and bodies…

Some species of three chameleon genera, the continental genera Chamaeleo and Trioceros and the Malagasy genus Calumma wear behind the casque a strange skin duplicature resembling elephant ears in some of their biggest expressions. These structures are called occipital flaps or occipital lobes, lat. lobus occipitalis. In some species, they are well developed in a form of semilunar flaps, some species have only small or tiny ones or even residual ones grown to the neck skin and unmovable.

What is this strange structure used for?

First, let us clearly state what it is NOT used for.

Despite of close resemblance to ears in mammals, the occipital flaps have nothing to do with hearing sense of the chameleons. They do not hear at all in strict sense; just limitedly, they can detect some selected low frequencies.

The usage of the occipital flaps by the chameleons is limited to two occasions:

I Aposematic behavior.

When facing a danger or predator, the chameleons erect the flaps transversally to the body axis or open and close them or even vibrate them (only T. melleri) and they attack the predator with the intention to bite (with open mouth) or punch with the snout (with closed or even sometimes with open mouth). The occipital flaps make the head appear much bigger from the front and can contribute to chasing the predator away. Same fits to the threatening behaviour towards a potential conspecific rival or rejected sexual partner.

II Courtship.

The occipital flaps are part of the imposing behaviour of males showing the strength and fitness. Exposing them to the female, the males enables her to identify properly the belonging to same species to allow sexual act. There is namely no overlapping of same size of occipital lobes amongst species living in any autochthonous (naturally inhabited, not introduced, feral) area in the world. The female can so unmistakably identify their mates and assess their fitness, strength and compatibility. This prevents interspecific or even intergeneric crossbreeding, which is from the evolutionary perspective unwanted and harmful. Females use within the courtship behaviour the occipital flaps merely for rejecting the male, which actually falls to the first mentioned category.

Last but not least, for the science, the occipital lobes are a very important diagnostic feature. Based on their size, scalation, form, fusion or separation, colour and other characteristics, they serve as an important feature for identification of different species and their forms.

List of genera and respective species with occipital flaps:

Calumma

amber, ambreense, boettgeri, brevicorne, capuroni, crypticum, cucullatum, glawi, hafahafa, hilleniusi, jejy, juliae, lefona, linotum, malthe, oshaughnessyi, parsonii, peltierorum, roaloko, tsaratananense, uetzi, vencesi.

Chamaeleo

calyptratus, calcarifer, chamaeleon, dilepis, gracilis, monachus, necasi, ruspolii, zeylanicus.

Trioceros

deremensis, fuelleborni, incornutus, laterispinis, melleri, montium, oweni, tempeli, werneri.