Anolis carolinensis

Anolis carolinensis or green anole (US: /əˈnoʊ.li/ ^ⓘ) (among other names below) is a tree-dwelling species of anole lizard native to the southeastern United States and introduced to islands in the Pacific and Caribbean. A small to medium-sized lizard, the green anole is a trunk-crown ecomorph and can change its color to several shades from brown to green.

Other names include the Carolina anole, Carolina green anole, American anole, American green anole, North American green anole and red-throated anole. It is commonly called chameleon in the southeastern United States and sometimes referred to as the American chameleon (typically in the pet trade) due to its color-changing ability; however, it is not a true chameleon.

Anolis carolinensis is a species of the large lizard genus Anolis within the family Dactyloidae (anole lizards). This species was named by Friedrich Siegmund Voigt (1781-1850) in 1832.

Phylogenetic evidence indicates that the Carolina anole belongs to the Anolis carolinensis anole series, a wider clade of Caribbean Anolis which are all also known as "green anoles". This group is composed of mid-sized trunk-crown anoles with large, conspicuously elongated heads and extreme levels of sexual dimorphism. Other members of this thirteen-species clade include A. brunneus & A. smaragdinus from the Bahamas, A. longiceps from Navassa Island, A. maynardii from the Cayman Islands, and A. allisoni & A. porcatus from Cuba; A. carolinensis is the only member of this clade native to the American mainland. Genetic analysis indicates that A. carolinensis originates from an oceanic dispersal event of an ancestral green anole from Cuba to the southern United States during the late Miocene or Pliocene. This is a rare example of an insular species successfully colonizing the mainland of a continent rather than the more common vice versa, although several other Caribbean animal and plant groups have similarly successfully colonized mainland North America via Florida. The present diversity of Central and South American anoles is also thought to originate from a colonization of the American mainland by an insular Caribbean anole taxon.

The anole is a small to medium-sized lizard, with a slender body. Males of this species are slightly larger than females. The head is long and pointed with ridges between the eyes and nostrils, and smaller ones on the top of the head. The toes have adhesive pads to facilitate climbing. Green anoles use jumping for their primary means of locomotion. They exhibit sexual dimorphism, the males being fifteen percent larger. Adult males within a population can be classified within a heavyweight and a lightweight morph. The male dewlap (throat fan) is three times the size of the female's and bright orange to red, whereas that of the female is lighter in color. The dewlap is usually pink for Anolis carolinensis (more orange-red in A. sagrei) and is very rarely present in females. The color of the dewlap is variable and different from the lizard eye to the human eye. Green anoles are thought to be capable of seeing a larger range of the UV spectrum, and that the dewlap reflects ultraviolet light to attract mates. Female anoles do, however, often have a dorsal line down their back. Extension of the dewlap from the throat is used for communication. Males can form a pronounced dorsal ridge behind the head when displaying or when under stress. Females and juveniles have a prominent white stripe running along their spine, a feature most males lack.

Adult males are usually 12.5–20.3 cm (4.9–8.0 in) long, with about 60-70% of which is made up of its tail. They have a body length, also known as a snout to vent length (SVL), up to 7.5 cm (3.0 in) and can weigh from 3–7 g (0.11–0.25 oz).

Colour varies from brown to green and can be changed like many other kinds of lizards, but anoles are closely related to iguanas and are not true chameleons. Although A. carolinensis is sometimes called an 'American chameleon', true chameleons do not naturally occur in the Americas, and A. carolinensis is not the only lizard currently in its area of distribution capable of changing colour. In contrast, many species of true chameleons display a greater range of color adaptation, though some can hardly change color at all.

Typical coloration for a green anole ranges from bright green to dark brown, with little variation in between. The color spectrum is a result of three layers of pigment cells or chromatophores: the xanthophores, responsible for the yellow pigmentation; cyanophores, responsible for the blue pigmentation, and melanophores, responsible for the brown and black pigmentation. The anole changes its color depending on mood, level of stress, activity level and as a social signal (for example, displaying dominance). Anolis carolinensis takes darker coloration as its base color at the beginning of the breeding season when it is generally cooler, and the adult males change their body coloration to more greenish when they need to advertise their territorial possession. Although often claimed, evidence does not support that they do it in response to the color of the background (camouflage). Whether they do it in response to temperature (thermoregulation) is less clear, with studies both supporting it and contradicting it. Changing color while under a sharply contrasting shadow can cause a "stencil effect", where the outline of the shadow is temporarily imprinted in the animal's coloration (see image in gallery, below). When stressed—while fighting, for example—the skin just behind the lizard's eyes may turn black independently from the rest of the animal's coloration, forming "postocular spots".