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Informal group of reptiles

Lizard is the common name used for all squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The grouping is paraphyletic as some lizards are more closely related to snakes than they are to other lizards. Lizards range in size from chameleons and geckos a few centimeters long to the 3 meter long Komodo dragon. Most lizards are quadrupedal, running with a strong side to side motion. Some lineages (known as "legless lizards") have secondarily lost their legs, and have long snake like bodies. Some lizards, such as the forest dwelling Draco, are able to glide. They are often territorial, the males fighting off other males and signalling, often with bright colours, to attract mates and to intimidate rivals. Lizards are mainly carnivorous, often being sit and wait predators; many smaller species eat insects, while the Komodo eats mammals as big as water buffalo. Lizards make use of a variety of antipredator adaptations, including venom, camouflage, reflex bleeding, and the ability to sacrifice and regrow their tails.

The adult length of species within the suborder ranges from a few centimeters for chameleons such as Brookesia micra and geckos such as Sphaerodactylus ariasae to nearly in the case of the largest living varanid lizard, the Komodo dragon. Most lizards are fairly small animals.

Lizards typically have rounded torsos, elevated heads on short necks, four limbs and long tails, although some are legless. Lizards and snakes share a movable quadrate bone, distinguishing them from the rhynchocephalians, which have more rigid diapsid skulls. Some lizards such as chameleons have prehensile tails, assisting them in climbing among vegetation. The dentitions of lizards reflect their wide range of diets, including carnivorous, insectivorous, omnivorous, herbivorous, nectivorous, and molluscivorous. Species typically have uniform teeth suited to their diet, but several species have variable teeth, such as cutting teeth in the front of the jaws and crushing teeth in the rear. Most species are pleurodont, though agamids and chameleons are acrodont. In addition, the toes of chameleons are divided into two opposed groups on each foot (zygodactyly), enabling them to perch on branches as birds do. efn|Chameleon forefeet have groups composed of 3 inner and 2 outer digits; the hindfeet have groups of 2 inner and 3 outer digits. and a few can prop themselves up on their hindlimbs and tail while stationary. Several small species such as those in the genus Draco can glide: some can attain a distance of , losing in height. Some species, like geckos and chameleons, adhere to vertical surfaces including glass and ceilings.

Lizards make use of their senses of sight, touch, olfaction and hearing like other vertebrates. The balance of these varies with the habitat of different species; for instance, skinks that live largely covered by loose soil rely heavily on olfaction and touch, while geckos depend largely on acute vision for their ability to hunt and to evaluate the distance to their prey before striking. Monitor lizards have acute vision, hearing, and olfactory senses. Some lizards make unusual use of their sense organs: chameleons can steer their eyes in different directions, sometimes providing non overlapping fields of view, such as forwards and backwards at once. Lizards lack external ears, having instead a circular opening in which the tympanic membrane (eardrum) can be seen. Many species rely on hearing for early warning of predators, and flee at the slightest sound. As in snakes and many mammals, all lizards have a specialised olfactory system, the vomeronasal organ, used to detect pheromones. Monitor lizards transfer scent from the tip of their tongue to the organ; the tongue is used only for this information gathering purpose, and is not involved in manipulating food.

Until 2006 it was thought that the Gila monster and the Mexican beaded lizard were the only venomous lizards. However, several species of monitor lizards, including the Komodo dragon, produce powerful venom in their oral glands. Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its pharmacological effects, both lowering blood pressure and preventing blood clotting. Nine classes of toxin known from snakes are produced by lizards. The range of actions provides the potential for new medicinal drugs based on lizard venom proteins. Genes associated with venom toxins have been found in the salivary glands of a wide range of lizards, including species traditionally thought of as non venomous, such as iguanas and bearded dragons. This suggests that these genes evolved in the common ancestor of lizards and snakes, some 200 million years ago (forming a single clade, the Toxicofera).

Recent studies (2013 and 2014) on the lung anatomy of the savannah monitor and green iguana found them to have a unidirectional airflow system, which involves the air moving in a loop through the lungs when breathing. This was previously thought to only exist in the archosaurs (crocodilians and birds). This may be evidence that unidirectional airflow is an ancestral trait in diapsids.

Most social interactions among lizards are between breeding individuals. Territoriality is common and is correlated with species that use sit and wait hunting strategies. Males establish and maintain territories that contain resources that attract females and which they defend from other males. Important resources include basking, feeding, and nesting sites as well as refuges from predators. The habitat of a species affects the structure of territories, for example, rock lizards have territories atop rocky outcrops. Some species may aggregate in groups, enhancing vigilance and lessening the risk of predation for individuals, particularly for juveniles. Agonistic behaviour typically occurs between sexually mature males over territory or mates and may involve displays, posturing, chasing, grappling and biting. and darker colours when they submit or "give up". Several gecko species are brightly coloured; some species tilt their bodies to display their coloration. In certain species, brightly coloured males turn dull when not in the presence of rivals or females. While it is usually males that display, in some species females also use such communication. In the bronze anole, head bobs are a common form of communication among females, the speed and frequency varying with age and territorial status. Chemical cues or pheromones are also important in communication. Males typically direct signals at rivals, while females direct them at potential mates. Lizards may be able to recognise individuals of the same species by their scent. Acoustic communication is less common in lizards. Hissing, a typical reptilian sound, is mostly produced by larger species as part of a threat display, accompanying gaping jaws. Some groups, particularly geckos, snake lizards, and some iguanids, can produce more complex sounds and vocal apparatuses have independently evolved in different groups. These sounds are used for courtship, territorial defense and in distress, and include clicks, squeaks, barks and growls. The mating call of the male tokay gecko is heard as "tokay tokay!". Tactile communication involves individuals rubbing against each other, either in courtship or in aggression.

Lizards are found worldwide, excluding the far north and Antarctica, and some islands. They can be found in elevations from sea level to They prefer warmer, tropical climates but are adaptable and can live in all but the most extreme environments. Lizards also exploit a number of habitats; most primarily live on the ground, but others may live in rocks, on trees, underground and even in water. The marine iguana is adapted for life in the sea. Chameleons prey on numerous insect species, such as beetles, grasshoppers and winged termites as well as spiders. They rely on persistence and ambush to capture these prey. An individual perches on a branch and stays perfectly still, with only its eyes moving. When an insect lands, the chameleon focuses its eyes on the target and slowly moves toward it before projecting its long sticky tongue which, when hauled back, brings the attached prey with it. Geckos feed on crickets, beetles, termites and moths. Species of skink and alligator lizards eat snails and their power jaws and molar like teeth are adapted for breaking the shells. Around 2 percent of lizard species, including many iguanids, are herbivores. Adults of these species eat plant parts like flowers, leaves, stems and fruit, while juveniles eat more insects. Plant parts can be hard to digest, and, as they get closer to adulthood, juvenile iguanas eat faeces from adults to acquire the microflora necessary for their transition to a plant based diet. Perhaps the most herbivorous species is the marine iguana which dives to forage for algae, kelp and other marine plants. Some non herbivorous species supplement their insect diet with fruit, which is easily digested. The Moorish gecko is able to change colour for camouflage: when a light coloured gecko is placed on a dark surface, it darkens within an hour to match the environment. The chameleons in general use their ability to change their coloration for signalling rather than camouflage, but some species such as Smith's dwarf chameleon do use active colour change for camouflage purposes. The flat tail horned lizard's body is coloured like its desert background, and is flattened and fringed with white scales to minimise its shadow.

Many lizards, including geckos and skinks, are capable of shedding their tails (autotomy). The detached tail, sometimes brilliantly coloured, continues to writhe after detaching, distracting the predator's attention from the fleeing prey. Lizards partially regenerate their tails over a period of weeks. Some 326 genes are involved in regenerating lizard tails. The fish scale gecko Geckolepis megalepis sheds patches of skin and scales if grabbed.

Many lizards attempt to escape from danger by running to a place of safety; for example, wall lizards can run up walls and hide in holes or cracks.

The closest living relatives of lizards are rhynchocephalians, a once diverse order of reptiles, of which is there is now only one living species, the tuatara of New Zealand. Some reptiles from the Early and Middle Triassic, like Sophineta and Megachirella, are suggested to be stem group squamates, more closely related to modern lizards than rhynchocephalians, however, their position is disputed, with some studies recovering them as less closely related to squamates than rhynchocephalians are. The oldest undisputed lizards date to the Middle Jurassic, from remains found In Europe, Asia and North Africa. Lizard morphological and ecological diversity substantially increased over the course of the Cretaceous. Mosasaurs likely evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. Dolichosauridae is a family of Late Cretaceous aquatic varanoid lizards closely related to the mosasaurs.

The position of the lizards and other Squamata among the reptiles was studied using fossil evidence by Rainer Schoch and Hans Dieter Sues in 2015. Lizards form about 60% of the extant non avian reptiles.

Both the snakes and the Amphisbaenia (worm lizards) are clades deep within the Squamata (the smallest clade that contains all the lizards), so "lizard" is paraphyletic. The cladogram is based on genomic analysis by Wiens and colleagues in 2012 and 2016. Excluded taxa are shown in upper case on the cladogram.

Most lizard species are harmless to humans. Only the largest lizard species, the Komodo dragon, which reaches in length and weighs up to , has been known to stalk, attack, and, on occasion, kill humans. An eight year old Indonesian boy died from blood loss after an attack in 2007.

thumb|left|Green iguanas (Iguana iguana), are popular pets. Numerous species of lizard are kept as pets, including bearded dragons, and geckos (such as the popular leopard gecko). Monitor lizards such as the savannah monitor and tegus such as the Argentine tegu and red tegu are also kept. Green iguanas are eaten in Central America, where they are sometimes referred to as "chicken of the tree" after their habit of resting in trees and their supposedly chicken like taste, while spiny tailed lizards are eaten in Africa. In North Africa, Uromastyx species are considered dhaab or 'fish of the desert' and eaten by nomadic tribes. thumb|Red tegu drinking water out of a dispenser. Lizards such as the Gila monster produce toxins with medical applications. Gila toxin reduces plasma glucose; the substance is now synthesized for use in the anti diabetes drug exenatide (Byetta).

Lizards appear in myths and folktales around the world. In Australian Aboriginal mythology, Tarrotarro, the lizard god, split the human race into male and female, and gave people the ability to express themselves in art. A lizard king named Mo'o features in Hawaii and other cultures in Polynesia. In the Amazon, the lizard is the king of beasts, while among the Bantu of Africa, the god UNkulunkulu sent a chameleon to tell humans they would live forever, but the chameleon was held up, and another lizard brought a different message, that the time of humanity was limited. A popular legend in Maharashtra tells the tale of how a common Indian monitor, with ropes attached, was used to scale the walls of the fort in the Battle of Sinhagad. In the Bhojpuri speaking region of India and Nepal, there is a belief among children that, on touching skink's tail three (or five) time with the shortest finger gives money. Lizards in many cultures share the symbolism of snakes, especially as an emblem of resurrection. This may have derived from their regular molting. The motif of lizards on Christian candle holders probably alludes to the same symbolism. According to Jack Tresidder, in Egypt and the Classical world, they were beneficial emblems, linked with wisdom. In African, Aboriginal and Melanesian folklore they are linked to cultural heroes or ancestral figures.