"Krypton"
Green Iguana
"Krypton"
Green Iguana
Large-bodied, with robust limbs and tails, most species of iguanas live in the New World (American) tropics. They occur from Mexico to Southern Brazil, Paraquay and in the Lesser Antilles. Although basically a New World family of some 700 species, iguanids are also found on Madagascar and Fiji. Green Iguanas have also been introduced in several areas oncluding Hawaii and South Florida.
The common iguana, Iguana iguana, is widely used as food throughout its range and is an arboreal tropical forest animal, attaining more than 1.5 m (5 ft) in total length, often found in the vicinity of rivers and streams. Young iguanas have been popular as pets because of their bright green skin color, which dulls with age. Large ground iguanas, Cyclura, inhabit islands of the Caribbean and attain total lengths of up to 1.2 m (4 ft). Large iguanas are also found on the Galapagos Islands. The land iguanas, Conolophus, feed on terrestrial plants, including cactus, whereas the marine iguanas, Amblyrhynchus cristatus, feed on marine algae. These marine iguanas, up to 1.5 m (5 ft) in length, are the only lizards that regularly make use of the nearby marine environment--they usually swim close to shore and can dive to depths more than 35 feet to eat plants, particularly seaweed growing on the bottom. They can remain submerged for up to 30 minutes.
An iguana's skin is shed periodically, but, unlike that of most snakes, it is shed in patches. Metachrosis, or the ability to change color under the influence of external stimuli, is a common characteristic of iguanas and all lizards. Iguanas can darken or lighten their color in response to light, temperature, or emotional state, but unlike true chameleons, have not developed the ability to completely alter their color.
In addition to the pair of eyes possessed by most vertebrates, many lizards have a third, or parietal, eye located on the upper rear surface of the head. In some North American species in the family Iguanidae the parietal eye is well developed, having a cornea, a lens, and a retina with sensory elements. The parietal eye has been shown to act as a sort of light meter that helps to regulate the amount of time a lizard exposes itself to the sun. The majority of lizards have eardrums (tympanic membranes), usually located nearly flush with the surface of the skin or just below it. Behind the eardrum is the middle ear cavity, which leads to the middle ear. The ear provides a sense of balance as well as hearing. Some species, such as Holbrookia, appear to lack ears because the ear opening is covered by scaly skin. In burrowing species the external ear opening is small or absent and the middle ear degenerated. The Jacobson's organs are important to the lizard's sense of smell. These organs are paired chambers in the front area of the roof of the mouth that have a connection to the olfactory (scent) lobes of the brain. These chambers detect not only particles present in the mouth cavity but also particles brought to them by the lizard's tongue. By protruding its tongue, a lizard is able to pick up airborne particles, which dissolve in the fluid on the tongue; these particles are then transferred by the tongue to the Jacobson's organs. This process is most efficient in lizards with deeply forked tongues, the tips of which are placed against or thrust into the chambers. In such lizards the sense of smell is relatively keen. The lizard's tongue is not ordinarily used directly in feeding, as an amphibian's is; in chameleons, however, the tongue is long and unforked (and the Jacobson's organs are rudimentary) and is used to catch prey.
Temperature is one of the most important environmental factors influencing lizard behavior; it directly determines a lizard's metabolic rate. Lizards are ectothermic and thus depend primarily on an external heat source to regulate their body temperature. This does not mean, however, that a lizard's body temperature will be the same as that of its immediate environment. Lizards can control their temperature by various behaviors, such as by basking directly in the sun (heliothermy), by positioning themselves (such as under a sunlit rock) in such a way as to gain heat through conduction (thigmothermy), or by seeking shade. As a result, iguanas prefer trees near the edges of the forest, where they can make maximum use of the sunlight. A lizard's temperature may be 20 to 30 C degrees (35 to 55 F degrees) higher than the ambient (surrounding) temperature. Most lizards exhibit marked seasonal changes in activity. In order to avoid harsh weather conditions, lizards hibernate in temperate regions during the winter, generally seeking refuge beneath the frost line, or they may estivate during hot, dry climatic conditions, often in deep crevices or fissures in the ground, where they can best retain body moisture.
Many lizards are cryptically colored and thereby avoid detection. When disturbed, however, lizards have a variety of defensive actions that include threatening with an open mouth, hissing, inflating the body, positioning the body in such a fashion as to appear as large as possible, biting and scratching, and lashing with the tail. With very few exceptions, only the geckos have a voice and can produce threat calls. Many species are equipped with spinelike scales that make it difficult for a predator to swallow them. Some forms expose brightly colored surfaces in an attempt to frighten enemies. Horned lizards, Phrynosoma, may eject blood from their eyes. Many lizards break their tails (autotomy) when they are confronted by an enemy or roughly handled. This break does not occur between the vertebrae (tail bones) but rather in a zone of weakness in a vertebra itself. These specialized vertebrae can be voluntarily split by muscular contraction; sphincter muscles in the tail stump close off the caudal artery to prevent excessive bleeding. Predators are often attracted to the thrashing, dismembered tail, which allows the lizard to escape. Although tail autotomy may seem like a drastic measure, in actuality it does the lizard little harmand in the case of most lizards--excluding iguanas--a new tail is soon regenerated.
The common iguana of Central and South America grows seven feet (two meters) long and may weigh up to 30 pounds (13 kilograms). It lives in trees, where it sprawls out on a branch with its legs dangling. The green iguana can eat both plants and animals, however it is primarily an herbivore (although it shows a fondness for insects in its juvenille stages). Ground iguanas are predators of birds and small mammals but eat vegetation as well.
Lizards' teeth are not set in separate sockets but are fused either to the upper surface of the jaws (acrodont) or to the inside edges (pleurodont). The teeth are generally sharp and conical but may be extremely elongated in some predatory species or serrated or blunt in the larger herbivorous forms or among species with certain feeding specializations. In general, there is little chewing of food among lizards. Many lizards simply seize their prey, bite it and move it about the mouth, and then swallow it.
Skin glands are not numerous in lizards. Most lizards have scent glands at the base of the tail, and males often have glands in front of the anus (preanal) or on the thigh (femoral) that become filled with a hard, waxy, yellow substance. This material may extend from the glands in hairlike columns that rub off on rocks and other surfaces. The significance of these glands is not precisely known, but because they are larger in males, whereas some females lack them completely, and are active during the breeding season, they appear to play a role in courtship. Iguanas show some sexual dimorphism, especially in older mature specimens. Male iguanas develop larger nuchal and dorsal crests than females, males have alrger sclaes beneath the tympanum than females and develop large broad jowls compared to females. Femoral pores are also much more pronounced on male iguanas.
Female lizards, like other reptiles but in contrast to mammals, have saclike (saccular) ovaries rather than solid ones, and their eggs are polylecithal (large-yolked). Males have two copulatory organs called hemipenes, one on each side of the base of the tail. These are generally short and broad, with pleats or folds, but may also be forked. Either one of the two hemipenes may be used in mating. The majority of lizards lay eggs, but at least half of the lizard families have species that bear live young, with varying degrees of placental formation (mother-embryo connection).
Iguanas lay their eggs in burrows that they excavate themselves. Females lay approximately 30 eggs per clutch which hatch after about 2 months. Most nest individually, but marine iguanas nest communally, several females laying eggs in a single burrow. Iguana hatchlings tend to congregate after emergence from their eggs, and have a total body length (body + tail) from 7 to 10 inches.
With proper care, captive iguanas tend to live 10-15 years.
Green iguanas are also called the "chickens of the trees". Twenty years ago they were so plentiful that they were taken to market by truckload, as they were used as a food protein source in Central and South America. Today the green iguana is no longer common with drastically decreased popualtions in the wild.
Today the green iguana faces extinction in many parts of Central America, this is primarily due to the destruction of habitat. However, many countries are presently breeding iguanas on iguana farms to be released into the pet trade so perhaps the green iguana will be with us a little while longer.
Burghardt, G.M., ed., Iguanas of the World (1983);
Frost, D.R., and Etheridge, R., A Phylogenetic Analysis and Taxonomy of
Iguanian Lizards (1989);
Halliday, Tim and Adler, Kraig, eds., The Encyclopedia of Reptiles and
Amphibians (1986);
Mattison, C., Lizards of the World (1989);
Roberts, Mervin and Martha, All About Iguanas (1976).
Vosjoli, Philippe de. The Green Iguana Manual (1992)