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The Living Edens Madagascar-A World Apart Creature Features




A Truly Bizarre Lizard

Almost half of the world’s chameleon species live on the island of Madagascar. This chameleon community is not only the world’s largest, it is also the world’s most unique; with Chameleon on tree branch59 different species existing nowhere outside of Madagascar.

Beyond their uniqueness to the island, chameleons are unique creatures in their own right. Known for their ability to change color, they can be seen wearing a variety of colors, including brown, green, blue, yellow, red, black or white. Communication is an important reason behind these color changes. With color, chameleons can communicate with others, expressing attitudes such as their willingness to mate. Contrary to popular belief, chameleons cannot display limitless colors and do not change Three different chameleonscolors in a camouflage response to their surroundings. Instead, their skin changes in response to temperature, light, and mood.

A chameleon’s colorful beauty is truly skin deep. Under the transparent outer skin are two cell layers that contain red and yellow pigments, or chromatophores. Below the chromatophores are cell layers that reflect blue and white light. Even deeper down is a layer of brown melanin (which gives human skin its various shades). Levels of external light and heat, and internal chemical reactions cause these cells to expand or contract. A calm chameleon, for example, may exhibit green, because the somewhat contracted yellow cells allow blue-reflected light to pass through. An angry chameleon may exhibit yellow, because the yellow cells have fully expanded, thus blocking off all blue-reflected light from below.

Other lizards, like the green anole, can also change color. But this green-to-brown color change is much less dramatic than the vivid, distinct color and pattern changes of chameleons.

Chameleons have many other features that distinguish them from their lizard cousins. They are the only lizards with zygodactyle feet, or pincers. These grasping feet are ideal for tree climbing. Chameleons also have an extremely extensile tongue. The tongue is used to snap up insects and out-of-reach food, and can be up to twice the length of a chameleon’s body. Also distinctive are the independently moveable eyes, whichChameleon eye and tail allow chameleons the ability to survey the world with nearly 360-degree vision.

Chameleons belong to their own subfamily, Chamaeleoninae, which is divided into two tribes: Brookesiini (dwarf chameleons) and Chamaeleonini (typical chameleons). Currently it is believed that 134 chameleon species exist, 33 Brookesiini species and 100 Chamaeleonini species. Eight new species of dwarf chameleons have been recently discovered since 1990.

The fossil record provides very little evidence to date the evolution of chameleons, although they are likely to be an ancient group. Fossils have only been found in Africa and Europe. The biogeographic history of the group is unclear. The modern restricted distribution of the group in Africa, Southern Europe (southern Spain and Crete), Madagascar, Seychelles, Comoros, and Asia (India, Sri Lanka, Pakistan) suggests that the evolutionary radiation of chameleons may have been associated with the final breakup of Gondwana (an ancient continent once located in the southern hemisphere), during the separation of Africa, Madagascar, and Greater India, during the late Jurassic and Cretaceous period.

Some of chameleons in Madagascar are very rare and poorly known, such as Chamaeleo belalandaensis, found in the southwest. This chameleon’s natural habitat is degraded gallery forest, which has now been almost completely cleared. The Chamaeleo belalandaensis is an example of a species for which studies are urgently needed, so that conservation efforts can be improved. The species has already been collected for the pet trade, and the impact on the population is not known. Very localized distribution combined with apparently tiny surviving populations suggest that this species is vulnerable to extinction.

Contributing author:
Christopher J. Raxworthy is a curator of Herpetology at the Kansas University Museum of Natural History, and has worked in Madagascar since 1985. His research has involved the exploration of some of the most remote regions of the island, and the discovery of many new species, including chameleons.

 



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