Definitions

lizard

lizard

[liz-erd]
lizard, a reptile of the order Squamata, which also includes the snake. Lizards form the suborder Sauria, and there are over 3,000 lizard species distributed throughout the world (except for the polar regions), with the greatest number found in warm climates. They range in size from species under 21/2 in. (6.4 cm) long to the 10-ft (3-m) Komodo dragon (see monitor) of SE Asia.

Lizards typically have four legs with five toes on each foot, although a few, such as the worm lizard and the so-called glass snake, are limbless, retaining only internal vestiges of legs. Lizards are also distinguished from snakes by having ear openings, movable eyelids, and less flexible jaws. As in snakes, there is a chemosensory organ opening in the roof of the mouth. The tongue, which may be short and wide, slender and forked, or highly extendible, conveys particles from the environment to this organ. The skin of the lizard is scaly and in most species is molted in irregular patches. Members of several lizard families, notably the chameleons, undergo color changes under the influence of environmental and emotional stimuli.

Many lizards are arboreal, and many terrestrial species are well adapted for climbing. They are often fast runners, some achieving speeds of over 15 mi (24 km) per hr. Some are adapted for burrowing. Most can swim and a few lead a semiaquatic existence, among them the single marine species, an iguana of the Galapagos Islands. Gliding forms, the flying dragons, are found in the forests of SE Asia. The gila monster and the related beaded lizard of the North American deserts are the only known poisonous lizards; some other lizards, such as the lace monitor of Australia, produce a nonfatal venom. Despite folklore, the bite of the gecko is not poisonous. Members of most species are carnivorous, feeding especially on insects, but some are herbivorous or omnivorous.

Fertilization is internal in lizards; males have paired copulatory organs, characteristic of the order. In most species females lay eggs, which they bury in the ground, but in some the eggs are incubated in the oviducts and hatched as they are laid. In both types the young have a special temporary tooth for rupturing the shell. In a few species there is true viviparity, or live birth, with the young nourished by a simple placenta.

The greatest number of species in the United States is found in the South and West. The majority are members of the iguana family, including the collared lizards, swifts, utas, horned lizards (popularly known as horned toads), and the so-called American chameleon, or anole. These are day-active lizards commonly seen basking on rocks. Most are valuable destroyers of insects.

Lizards are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, suborder Sauria.

See W. M. Milstead, ed., Lizard Ecology (1967); H. S. Fitch, Reproductive Cycles of Lizards and Snakes (1970); B. R. Headstrom, Lizards as Pets (1971).

Lizard, The, peninsula, Cornwall, SW England. Its southern extremity (the southernmost point of Great Britain) is called Lizard Point or Lizard Head. The coast has colored serpentine rocks, small coves and bays, wave-hollowed caves, islets (e.g., Asparagus Island), and dangerous reefs. Two lighthouses and a satellite earth station are on the peninsula.

Any of about 4,450 species of reptiles constituting the suborder Sauria. They are most diverse and abundant in the tropics but are found from the Arctic Circle (one species) to southern Africa, South America, and Australia. Like snakes, lizards have scales, paired male copulatory organs, and a flexible skull. Typical lizards have a moderately cylindrical body, four well-developed legs (although some lizards are legless), a tail slightly longer than the head and body combined, and movable lower eyelids. They range in size from 1-in. (3-cm) geckos to the 10-ft (3-m) Komodo dragon, but most are about 12 in. (30 cm) long. Ornamentation includes crests on the head, back, or tail; spines; brightly coloured throat fans; and throat frills. Most species feed on insects and rodents, but some, such as the iguana, eat plants. Seealso Gila monster; horned toad.

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or horned lizard

Any of about 14 species of lizards of the genus Phrynosoma, family Iguanidae. They usually have daggerlike head spines (horns) and a flattened oval body with pointed fringe scales along the sides. Species range from about 3 to 5 in. (8 to 13 cm) long. They are found from British Columbia, Can., south to Guatemala and from the U.S. states of Arkansas and Kansas westward, usually in desert or semidesert sandy country. They eat mainly ants. They hide by changing their colour pattern and wriggling sideways into the sand until all but the head is covered. They may defend themselves by inflating the body quickly and (rarely) spurting blood from the eyes.

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Lizards are a large and widespread group of reptiles of the order Squamata, with nearly 5,000 species and ranging across all continents except Antarctica. Most lizards have four limbs, external ears, and a tail. Many lizards can shed their tails in order to escape from predators, although this trait is not universal. Vision, including color vision, is particularly well developed in lizards, and most communicate with body language or bright colors on their bodies as well as via pheromones. The adult length of species within the order range from a few centimeters for some Caribbean geckos to nearly three meters in Komodo Dragons.

Description

Any generic description of lizards is often complicated by the fact that many typical lizard traits are either retentions from their evolutionary ancestors (such as the basic, 4-limbed, tetrapod body form) or are either lost or changed in some species (loss of limbs, loss of external ears, loss of the tail, etc.)

Lizards are reptiles, and universally possess scaly skin and a skull with many fused or reduced bones. Most lizards retain the typical tetrapod body plan of a short neck, four limbs of roughly equal size ending in five toes each, a moderately long body, and a long tail. Most lizards possess external ears and have movable eyelids. Encompassing forty families, there is tremendous variety in colour, appearance and size. Most lizards are oviparous, though a few species are viviparous. Many are also capable of regeneration of lost limbs or tails. Almost all lizards are carnivorous, though most are so small that insects are their primary prey. About 120 species (3%) are known to be herbivorous. A few species are omnivorous, and others have reached sizes where they can prey on other vertebrates. Many lizards are good climbers or fast sprinters. Some can run bipedally, such as the collared lizard, and some can even run across the surface of water to escape, namely the basilisk. Many lizards can change colour in response to their environments or in times of stress. The most familiar example is the chameleon, but more subtle colour changes occur in other lizard species as well, such as the anole, also known as the "American chameleon," "house chameleon" or "chamele".

Some lizard species, including the glass lizard and flap-footed lizards, have lost their legs or reduced them to the point they are non-functional. However, some vestigial structures remain. Snakes, which evolved from the ancestors of monitor lizards, are characterized by lack of eyelids, lack of an external ear, a forked tongue, and having a highly elongate body (as opposed to a normal body but extremely long tail). While any given legless lizard species (of which there are many) may match on one or two of these characteristics, they invariably differ from snakes in others. For example, flap-footed lizards lack eyelids as do true snakes, but can be distinguished by their external ears.

Lizards are part of the reptile family, meaning that they have no inner means of achieving homeostatis. As a result, they must keep careful watch of their body temperature. This need requires lizards to live in areas with consistently high temperatures. Lizards are rarely seen in the upper half of the United States and most European countries.

Senses and communication

Lizards employ many diverse methods of communication. Like many other animals, they have an acute sense of smell, detecting scents of their prey or pheromones from other lizards. The primary organ of scent in lizards is a vomeronasal organ in the roof of the mouth, and lizards gather scents by flicking out their tongues, then retracting them and delivering the captured odor molecules to this organ. Some large carnivorous lizards, such as tegus and monitor lizards, have forked tongues like snakes, to take advantage of this organ better. As a result, many male lizards possess enlarged pores on the underside of their thighs, which they rub against objects to mark their territory.

While most lizards can hear well, few are capable of vocalizations or otherwise making noise. The exception to this rule is the geckos, which communicate through a wide variety of barks, chirps and whistles, with each species having specific patterns and sounds.

Sight is quite important for most lizards, both for locating prey and for communication, and as such, many lizards have highly acute color vision. Most lizards rely heavily on body language, using specific postures, gestures and movements to define territory, resolve disputes, and entice mates. Some species of lizard also utilize bright colors, such as the iridescent patches on the belly of Sceloporus. These colors would be highly visible to predators, so are often hidden on the underside or between scales and only revealed when necessary.

A particular innovation in this respect is the dewlap, a brightly colored patch of skin on the throat, usually hidden between scales. When a display is needed, the lizards erect the hyoid bone of their throat, resulting in a large vertical flap of brightly colored skin beneath the head which can be then used for communication. Anoles are particularly famous for this display, with each species having specific colors, including patterns only visible under ultraviolet light, as lizards can often see UV.

Evolution and relationships

The retention of the basic tetrapod body form by lizards makes it tempting to assume any similar animal, alive or extinct, is also a lizard. However, this is not the case, and lizards are part of a well-defined group.

The first reptile was superficially lizard-like, but had a solid, box-like skull, with openings only for eyes, nostrils, etc (termed Anapsid). These organisms later gave rise to two new groups with additional holes in the skull to make room for and anchor larger jaw muscles. Those with a single hole, the Synapsids, became modern mammals. The Diapsids, possessing two holes, continued to diversify. The Archosaurs retained the basic Diapsid skull, and gave rise to a bewildering array of animals, most famous being the dinosaurs and their descendants, birds. The Lepidosaurs began to reduce the skull bones, making the skull lighter and more flexible. Modern tuataras retain the basic Lepidosaur skull, distinguishing them from true lizards in spite of superficial similarities. Squamates, including snakes and all true lizards, further lightened the skull by eliminating the lower margin of the lower skull opening.

Relationship to humans

Most lizard species are harmless to humans. Only the very largest lizard species pose threat of death; the Komodo dragon, for example, has been known to stalk, attack, and kill humans. The venom of the Gila monster and beaded lizard is not usually deadly but they can inflict extremely painful bites due to powerful jaws. The chief impact of lizards on humans is positive as they are significant predators of pest species; numerous species are prominent in the pet trade; some are eaten as food (for example, Green Iguanas in Central America); and lizard symbolism plays important, though rarely predominant roles in some cultures (e.g. Tarrotarro in Australian mythology). The Moche people of ancient Peru worshiped animals and often depicted lizards in their art. According to a popular legend in Maharashtra, a Common Indian Monitor, with ropes attached, was used to scale the walls of the Sinhagad fort in the Battle of Sinhagad.

Classification

'''Suborder Lacertilia (Sauria) - (Lizards)

References

General references

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