Chameleons (family Chamaeleonidae) are a distinctive and highly specialized clade of lizards. They are distinguished by their zygodactylous feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a prehensile tail, crests or horns on their distinctively shaped heads, and the ability of some to change color. Colors include pink, blue, red, orange, turquoise, yellow, and green. Uniquely adapted for climbing and visual hunting, the approximately 160 species of chameleon range from Africa, Madagascar, Spain and Portugal, across south Asia, to Sri Lanka, have been introduced to Hawaii, California and Florida, and are found in warm habitats that vary from rain forest to desert conditions. Chameleons are often kept as household pets.

Etymology

The English word chameleon (also chamaeleon) derives from Latin chamaeleō, a borrowing of the Ancient Greek χαμαιλέων (khamailéōn), a compound of χαμαί (khamaí) "on the ground" and λέων (léōn) "lion". The Greek word is a calque translating the Akkadian nēš qaqqari, "ground lion".^[1]

Evolution

The oldest known chameleon is Anqingosaurus brevicephalus from the Middle Paleocene (about 58.7-61.7 mya) of China.^[2]

Other chameleon fossils include Chamaeleo caroliquarti from the Lower Miocene (about 13-23 mya) of the Czech Republic and Germany, and Chamaeleo intermedius from the Upper Miocene (about 5-13 mya) of Kenya.^[2]

The chameleons are probably far older than that, perhaps sharing a common ancestor with iguanids and agamids more than 100 mya (agamids being more closely related). Since fossils have been found in Africa, Europe and Asia, chameleons were certainly once more widespread than they are today. Although nearly half of all chameleon species today are found in Madagascar, this offers no basis for speculation that chameleons might originate from there.^[3] Monophyly of the family is supported by several studies.^{[citation needed]}

Description

Oustalet's Chameleon, Ambalavao, Madagascar

Bradypodion pumilum, the "Cape dwarf chameleon" in the act of defecation. The typical action by which it avoids fouling its own branch incidentally displays the difference between the arrangement of its fore and hind toes.

Chameleons vary greatly in size and body structure, with maximum total length varying from 15 millimetres (0.6 in) in male Brookesia micra (one of the world's smallest reptiles) to 68.5 centimetres (30 in) in the male Furcifer oustaleti.^[4][5] Many have head or facial ornamentation, such as nasal protrusions, or horn-like projections in the case of Trioceros jacksonii, or large crests on top of their head, like Chamaeleo calyptratus. Many species are sexually dimorphic, and males are typically much more ornamented than the female chameleons.

Typical sizes of species of chameleon commonly kept as pets are:

The feet of chameleons are highly adapted to arboreal locomotion, though species such as Chamaeleo namaquensis, that have secondarily adopted a terrestrial habit, have retained the same foot morphology with little modification. On each foot there are five clearly distinguished toes that are grouped into two fascicles. The toes in each fascicle are bound into a flattened group of either two three, giving each foot a tongs-like appearance. On the front feet the outer, lateral, group contains two toes, whereas the inner, medial, group contains three. On the rear feet this arrangement is reversed, the medial group containing two toes, and the lateral group three. These specialized feet allow chameleons to grip tightly onto narrow or rough branches. Furthermore, each toe is equipped with a sharp claw to afford a grip on surfaces such as bark when climbing. It is common to refer to the feet of chameleons as didactyl or zygodactyl, though neither term is fully satisfactory, both being used in describing totally different feet, such as the zygodactyl feet of parrots or didactyl feet of sloths or ostriches, none of which are significantly like chameleon feet. Although "zygodactyl" is reasonably descriptive of chameleon foot anatomy, their foot structure does not resemble that of parrots, to which the term was first applied. As for didactyly, chameleons visibly have five toes on each foot, not two.

Some chameleons have a crest of small spikes extending along the spine from the proximal part of the tail to the neck; both the extent and size of the spikes varies between species and individual. No generally convincing functional explanation for this feature has been proposed.

Senses

Chameleons have the most distinctive eyes of any reptile. The upper and lower eyelids are joined, with only a pinhole large enough for the pupil to see through. They can rotate and focus separately to observe two different objects simultaneously, this lets their eyes move independently from each other. This gives them a full 360-degree arc of vision around their body. When prey is located, both eyes can be focused in the same direction, giving sharp stereoscopic vision and depth perception. Chameleons have very good eyesight for reptiles, letting them see small insects from a long (5–10 m) distance.^{[citation needed]}

Like snakes, chameleons do not have an outer or a middle ear, so there is neither an ear opening nor an eardrum.^[6]:31 However, chameleons are not deaf: they can detect sound frequencies in the range 200–600 Hz.^[6]:31

Tongue structure

Chameleons have very long tongues (sometimes longer than their own body length) which they are capable of rapidly extending out of the mouth. The tongue extends out faster than human eyes can follow, at around 26 body lengths per second. The tongue hits the prey in about 30 thousandths of a second.^[7] The tongue of the chameleon is a complex arrangement of bone, muscle and sinew. At the base of the tongue there is a bone and this is shot forward giving the tongue the initial momentum it needs to reach the prey quickly. At the tip of the elastic tongue there is a muscular, club-like structure covered in thick mucus that forms a suction cup.^[8] Once the tip sticks to a prey item, it is drawn quickly back into the mouth.

Chameleons can see in both visible and Ultraviolet light.^[9] Chameleons exposed to ultraviolet light show increased social behavior and activity levels, are more inclined to bask and feed and are also more likely to reproduce as it has a positive effect on the pineal gland.

Distribution and habitat

The tiny, usually brown-colored Brookesia which include 33 different species of chameleons are mainly terrestrial

Chameleons are primarily found in the mainland of sub-Saharan Africa and on the island of Madagascar, although a few species are also found in northern Africa, southern Europe, the Middle East, southern India, Sri Lanka and several smaller islands in the western Indian Ocean. There are introduced, feral populations of veiled and Jackson's chameleons in Hawaii and isolated pockets of feral Jackson's chameleons have been reported in California and Florida.

Chameleons inhabit all kinds of tropical and mountain rain forests, savannas and sometimes deserts and steppes. The typical chameleons from the subfamily Chamaeleoninae are arboreal and usually found in trees or bushes, although a few (notably the Namaqua Chameleon) are partially or largely terrestrial. Most species from the subfamily Brookesiinae, which includes the genera Brookesia, Rieppeleon and Rhampholeon, live low in vegetation or on the ground among leaf litter. Many species of chameleon are threatened by extinction. Declining chameleon numbers are due to pollution and deforestation.^{[citation needed]}

Reproduction

West Usambara Two-Horned Chameleon (Kinyongia multituberculata) in the Usambara mountains, Tanzania.

Chameleons are mostly oviparous, some being ovoviviparous.

The oviparous species lay eggs 3–6 weeks after copulation. The female will climb down to the ground and begin digging a hole, anywhere from 10–30 cm (4–12 in.) deep depending on the species. The female turns herself around at the bottom of the hole and deposits her eggs. Clutch sizes vary greatly with species. Small Brookesia species may only lay 2–4 eggs, while large Veiled Chameleons (Chamaeleo calyptratus) have been known to lay clutches of 80–100 eggs. Clutch sizes can also vary greatly among the same species. Eggs generally hatch after 4–12 months, again depending on species. The eggs of Parson's Chameleon (Calumma parsonii), a species which is rare in captivity, are believed to take upwards of 24 months to hatch.^{[citation needed]}

The ovoviviparous species, such as the Jackson's Chameleon (Trioceros jacksonii) have a 5–7 month gestation period. Each young chameleon is born within the sticky transparent membrane of its yolk sac. The mother presses each egg onto a branch, where it sticks. The membrane bursts and the newly born chameleon frees itself and climbs away to hunt for itself and hide from predators. The female can have up to 30 live young from one gestation.^[10]

Diet

Chameleons generally eat insects, but larger species such as the Common Chameleon may also take other lizards and young birds.^[11]:5 The range of diets can be seen from the following examples:

• The Veiled Chameleon, Chamaeleo calyptratus from Arabia, is insectivorous, but eats leaves when other sources of water are not available. It can be maintained on a diet of Crickets. ^[12] They can eat as many as 15-20 large crickets a day.

• Jackson's Chameleon (Trioceros jacksonii) from Kenya and northern Tanzania eats a wide variety of small animals including ants, butterflies, caterpillars, snails, worms, lizards, geckos, amphibians and other chameleons, as well as plant material such as leaves, tender shoots, and berries. It can be maintained on a mixed diet including kale, dandelion leaves, lettuce, bananas, tomatoes, apples, crickets and waxworms.^[10]

• The Common Chameleon of Europe, North Africa, and the Near East, Chamaeleo chamaeleon, mainly eats wasps and mantises; such arthropods form over three quarters of its diet.^[11]:5 Some experts advise that the Common Chameleon should not be fed exclusively on Crickets: these should make up no more than half the diet, with the rest a mixture of waxworms, earthworms, grasshoppers, flies and plant materials such as green leaves, oats and fruit.^[11]:5-6

• Temperature influence the amount of food eaten.

Change of color

Camouflage of a Common Chameleon in its natural environment (vicinity of Oueslatia, Tunisia)

This Common Chameleon (Chamaeleo chamaeleon) turned black

Some chameleon species are able to change their skin colors. Different chameleon species are able to change different colors which can include pink, blue, red, orange, green, black, brown, light blue, yellow, turquoise and purple.^[13]

The primary purpose of color change in chameleons is social signaling, with camouflage secondary. Color change signals a chameleon's physiological condition and intentions to other chameleons.^[14][15] Chameleons tend to show darker colors when angered, or attempting to scare or intimidate others, while males show lighter, multi-colored patterns when courting females.^{[citation needed]}

Some species, such as Smith's dwarf chameleon, adjust their colors for camouflage in accordance with the vision of the specific predator species (bird or snake) that they are being threatened by.^[16]

The desert dwelling Namaqua Chameleon also uses color change as an aid to thermoregulation, becoming black in the cooler morning to absorb heat more efficiently, then a lighter grey color to reflect light during the heat of the day. It may show both colors at the same time, neatly separated left from right by the spine.^{[citation needed]}

Mechanism of color change

Chameleons have specialized cells, chromatophores, which contain pigments in their cytoplasm, in three layers below their transparent outer skin:

1. The cells in the upper layer, called xanthophores and erythrophores, contain yellow and red pigments respectively.
2. Below these is a second layer of cells called iridophores or guanophores; these contain guanine, appearing blue or white.
3. The deepest layer of cells, melanophores, contain the dark pigment melanin, controlling how much light is reflected.

Dispersion of the pigment granules in the chromatophores sets the intensity of each color. When the pigment is equally distributed in a chromatophore, the whole cell is intensively colored. When the pigment is located only in the centre of the cell, the cell appears mainly transparent. Chromatophores can rapidly relocate their particles of pigment, thereby influencing the animal's color. Chromatophores change because the cells get a message from the brain.^[17]

Video

Classification

Family Chamaeleonidae

• Subfamily Brookesiinae
• the Subfamily Chamaeleoninae

Parasites

Chameleons are parasitised by nematode worms including threadworms (Filaria) and roundworms. Threadworms can be transmitted by biting insects such as ticks and mosquitoes. Roundworms are transmitted through food contaminated with roundworm eggs; the larvae burrow through the wall of the intestine into the bloodstream.^[18]

Chameleons are subject to several protozoan parasites such as Plasmodium which causes malaria, Trypanosoma which causes sleeping sickness, and Leishmania which causes leishmaniasis.^[19]

Chameleons are subject to parasitism by coccidia,^[19] including species of the genera Choleoeimeria, Eimeria and Isospora.^[20]

Bibliography

Popular books

• François Le Berre and Richard D. Bartlett. The Chameleon Handbook. Barron's Educational Series. 3rd Edition, 2009.
• Linda J. Davison. Chameleons: Their Care and Breeding. Hancock House Publishers, 1997.
• Philippe de Vosjoli. Essential Care of Chameleons. Advanced Vivarium Systems, 2004.

References