1911 Encyclopædia Britannica/Iguana

IGUANA, systematically Iguanidae (Spanish quivalent of Carib iwana), a family of pleurodont lizards, comprising about 50 genera and 300 species. With three exceptions, all the genera of this extensive family belong to the New World, being specially characteristic of the Neotropical region, where they occur as far south as Patagonia, while extending northward into the warmer parts of the Nearctic regions as far as California and British Columbia. The exceptional genera are Brachylophus in the Fiji Islands, Hoplurus and Chalarodon in Madagascar. The iguanas are characterized by the peculiar form of their teeth, these being round at the root and blade-like, with serrated edges towards the tip, resembling in this respect the gigantic extinct reptile Iguanodon. The typical forms belonging to this family are distinguished by the large dewlap or pouch situated beneath the head and neck, and by the crest, composed of slender elongated scales, which extends in gradually diminishing height from the nape of the neck to the extremity of the tail. The latter organ is very long, slender and compressed. The tongue is generally short and not deeply divided at its extremity, nor is its base retracted into a sheath; it is always moist and covered with a glutinous secretion. The prevailing colour of the iguanas is green; and, as the majority of them are arboreal in their habits, such colouring is generally regarded as protective. Those on the other hand which reside on the ground have much duller, although as a rule equally protective hues. Some iguanas, however (e.g. Anolis carolinensis), possess, to an extent only exceeded by the chameleon, the power of changing their colours, their brilliant green becoming transformed under the influence of fear or irritation, into more sombre hues and even into black. They differ greatly in size, from a few inches to several feet in length.

Fig. 1.—Iguana.

One of the largest and most widely distributed is the common iguana (Iguana tuberculata), which occurs in the tropical parts of Central and South America and the West Indies, with the closely allied I. rhinolophus. It attains a length of 6 ft., weighing then perhaps 30 ℔, and is of a greenish colour, occasionally mixed with brown, while the tail is surrounded with alternate rings of those colours. Its food consists of vegetable substances, mostly leaves, which it obtains from the forest trees among whose branches it lives and in the hollows of which it deposits its eggs. These are of an oblong shape about 11/2 in. in length, and are said by travellers to be very pleasant eating, especially when taken raw, and mixed with farina. They are timid, defenceless animals, depending for safety on the comparative inaccessibility of their arboreal haunts, and their protective colouring, which is rendered even more effective by their remaining still on the approach of danger. But the favourite resorts of the iguana are trees which overhang the water, into which they let themselves fall with a splash, whatever the height of the tree, and then swim away, or hide at the bottom for many minutes. Otherwise they exhibit few signs of animal intelligence. “The iguana,” says H. W. Bates (The Naturalist on the Amazons), “is one of the stupidest animals I ever met. The one I caught dropped helplessly from a tree just ahead of me; it turned round for a moment to have an idiotic stare at the intruder and then set off running along the path. I ran after it and it then stopped as a timid dog would do, crouching down and permitting me to seize it by the neck and carry it off.” Along with several other species, notably Ctenosura acanthinura, which is omnivorous, likewise called iguana, the common iguana, is much sought after in tropical America; the natives esteem its flesh a delicacy, and capture it by slipping a noose round its neck as it sits in fancied security on the branch of a tree.

Fig. 2.—Head of Iguana rhinolophus.

Although chiefly arboreal, many of the iguanas take readily to the water; and there is at least one species, Amblyrhynchus cristatus, which leads for the most part an aquatic life. These marine lizards occur only in the Galapagos Islands, where they are never seen more than 20 yds. inland, while they may often be observed in companies several hundreds of yards from the shore, swimming with great facility by means of their flattened tails. Their feet are all more or less webbed, but in swimming they are said to keep these organs motionless by their sides. Their food consists of marine vegetation, to obtain which they dive beneath the water, where they are able to remain, without coming to the surface to breathe, for a very considerable time. Though they are thus the most aquatic of lizards, Darwin, who studied their habits during his visit to those islands, states that when frightened they will not enter the water. Driven along a narrow ledge of rock to the edge of the sea, they preferred capture to escape by swimming, while if thrown into the water they immediately returned to the point from which they started. A land species belonging to the allied genus Conolophus also occurs in the Galapagos, which differs from most of its kind in forming burrows in the ground.