Chameleons are Very Special Lizards
Chameleons belong to a very specialized family of lizards. Approximately 160 species have been described so far, more than half of them are endemic to Madagascar, raising the possibility that they originated on the Island.
Although the most widely known chameleon fact is that they can change their colours they have many more remarkable adaptations to their life in the forests of Madagscar, Africa, Yemen, India and Southern Europe.
Their eyes, tongues and limbs are all unusual and specially adapted to their unique niche. Although different species share the same characteristics, there is a lot of variation between the different species. They can range in size from the largest, Parson's chameleon, Calumma parsoni, which reaches up to 68 cm (27 in) in length to the tiny pygmy chameleons, the smallest of which is thought to be Brookesia micro where a female reaches up to 29 millimetres (1.1 in) long.
Although most chameleons are arboreal, i.e. live in treas, Brookesia live on the ground, where they hid amongst leaf litter
The Largest Chameleon
Fact 1: the Weird Tongue
Chameleons move very slowly and with great deliberation. To allow them to catch their prey they have evolved a very special tongue, which is extremely long, often it is longer than the body. The tongue can shoot out of the mouth and catch its prey with extraordinary speed, approximately 30 milliseconds (30 thousandths of a second). At the tip of the tongue there is a suction cup like structure, covered in mucus. When a chameleon sees an insect, it is very still, and captures the prey with its tongue, before the insect realizes that it is about to become dinner.
Fact 2, its Eyes Can Move Independently
Chameleon eyes are also unusual. The upper and lower eyelids are fused, covering most of the eye except for the pupil. The eyes are very mobile, and can swivel independently of each other. Thus giving them almost 360o degree vision and allowing to focus on 2 objects at once. This allows the chameleon to search for food in its vicinity very effectively. When an insect is spotted, it can focus on it with both eyes, so it can judge distance and extend its tongue out with great accuracy.
Pincer like feet
Chameleon foot anatomy is also unlike that of other lizards, and is perfectly adapted to grasping branches and twigs. The toes on each foot are partially fused into two groups, one consisting of 2 toes while the other has 3. This makes chameleons didactyl and gives their feet a pincer-like appearance, allowing them to grasp objects. On the front feet the 2 toed group is on the outside, while the 3 toed group is on the inside, and on the back feet this order is reversed. Each toe ends in a sharp claw which allows helps with climbing tree bark.
Changing Colour for Social Interactions
Many lizards can change colour to a certain extent, but chameleons can do this to a remarkable degree. Although this aides camouflage, the main purpose is communication with other lizards, either warning off rivals, or attracting females.
Chameleons are solitary and very territorial animals, males do not tolerate other males in their territory, and will colour up to warn them off. They generally turn dark when they are angry. Changing colour also helps them thermoregulate, they become darker when cold, to absorb more sunshine, and paler when they are too hot.
Chameleons can alter their colour rapidly because their skins contain three types of pigment cells arranged in three layers. The top layer consists of xanthophores, and erythrophores, which contain yellow pigment. The layer below that consists of cells called iridophores which appear white or blue. Below that are the melanophores, containing melanin which is black. The distribution of the pigment granules in the cytoplasm of each type of cell is controlled by the nervous system and controls the appearance of the skin, when the pigment granules are distributed evenly thoughout the cell, it appears intensely coloured, whereas when the pigment is concentrated in a tight spot in the centre, the cell becomes almost transparent. Hence the chameleon can have different patterns, which can rapidly change depending on its mood.
David Attenborough on the panther chameleon
5. Some chameleon species are livebearers
Many species lay eggs, usually in a hole dug by the female in the ground. Small species usually deposit 2-4 eggs while larger chameleons can lay as many as 100 eggs. Eggs take a long time to hatch, 4-12 months. Parson’s Chameleon’s eggs can take up to 24 months to hatch.
However, in some species, such as Jackson’s chameleon (Trioceros jacksonii ) the eggs are retained within the female’s body until they hatch, and she gives birth to fully formed baby lizards. This is different from gestation in mammals, since there is no placenta and the young are entirely reliant on the yolk sac in the egg for nutrition, they do not share their mother’s circulation.
This method of reproduction obviously has the advantage that the eggs are not exposed to adverse weather conditions, or the danger of being eaten by other animals. The young are born inside a sticky membrane, which attaches to tree branches, as the female drops the young, which immediately struggle out of their membrane and grasp twigs.