lizards, (suborder Sauria), any of the more than 5,500 species of reptiles in the order Squamata (also including snakes, suborder Serpentes). Lizards are scaly reptiles, often distinguished from snakes by their legs, movable eyelids, and external ears. However, some traditional lizards (that is, non-snakes) lack one or more of these characteristics. For example, degeneration and loss of limbs have occurred in glass lizards (Ophisaurus) and other groups of lizards. Movable eyelids have been lost in some species of geckos, lizards, and nocturnal lizards. The outer ear has disappeared in some species of the genera Holbrookia and Cophosaurus. Most lizards live in warm regions, but some are found near the Arctic Circle in Eurasia and others in the southernmost tip of South America.
Snakes arose from lizards and are therefore considered a highly specialized group of limbless lizards. In addition to the common features they share with non-snake lizards, snakes are often separated from other lizards in the popular literature because they share a series of unique features that are relatively easy to observe. . For a complete description of snakes, see snakes.
General Features
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Lizards are by far the most diverse group of modern reptiles in terms of body shape and size. They range in size from 2 cm (0.8 inches) snout to vent in geckos (family Gekkonidae) to a total length of 3 meters (10 feet) in monitor lizards (family iguanas). The weight of adult lizards ranges from less than 0.5 grams (0.02 ounces) to more than 150 kilograms (330 pounds). The popular notion of a lizard as a fast-running reptile measuring about 30 centimeters (12 inches) in total length with a tapered tail can be accurately applied to only a handful of species. Representatives of some families are limbless and snake-like, while others have long hind legs that allow bipedal movement. Male lizards can be equipped with a variety of decorations — such as fans and frills on the expandable throat, throat spikes, horns or crests on the head, and the crest of the tail.
Lizards occupy diverse habitats, from underground burrows and burrows to surface and elevated vegetation. Some move slowly and rely on mysterious colors for protection, while others can run fast across the desert sands. Lizards of the family Mosasauridae, an extinct group, lived entirely in the sea. Some spear dragons were giants and were up to 10 meters (33 feet) in length. A species of living lizard, the marine iguana (Amblyrhynchus cristatus) of the Galapagos Islands, which feeds on algae in the sea. However, it spends most of its time basking in the lava rocks on the islands. No other extant species of lizard live in the sea, but some are partially aquatic and feed on freshwater organisms.
Little is known about the role of lizards in the human ecosystem. Some lizards are food and clothing sources or pest control agents, while others are pests. Some of the larger lizards (such as the iguanas [Iguana and Ctenosaura] of Mexico, Central America, and South America) are carnivorous and an important food source. Others are used for leather goods. Iguanas and tegus (family Teiidae) are harvested for their hides, and these pelts have a great influence on the local economy of rural areas in Third World countries. Although lizards are often depicted as eating insects, many species also eat small vertebrates and at least some plant material; Strict herbivores have evolved independently in several groups of lizards. However, lizards eat a large number of insects and other invertebrates, especially in the tropics and deserts. These pest control services affect people in many subtle ways; However, such effects have not been well studied. Large predatory lizards (such as screen and tegus) can be pests—often preying on farm animals or stealing eggs—affecting the livelihoods of ranchers and farmers.
Some relatively small lizards, such as geckos, not only colonized many islands by rafting with humans in boats, but also invaded cities and towns around the world. For example, throughout Brazil, one of the most famous lizards, the Mediterranean gecko (Hemidactylus mabouia), is so common in homes and buildings that most Brazilians know a lot about it, based on it. their own observations, than they knew about any of them. endemic species. As is the case with many introduced lizards, Mediterranean geckos seem to do well with people in disturbed areas but do not appear to colonize undisturbed habitats.
For the most part, lizards are not vectors of disease and pose little danger to humans, who take proper precautions when handling them. Lizards are often infected with a variety of parasites, including one malaria, but these parasites tend to be species-specific. Salmonella bacteria can be passed from lizards to humans, especially if the lizard is introduced into a person’s mouth. Tuberculosis (Mycobacterium tuberculosis) and some viral and fungal infections can also be transmitted from lizards to humans. People handling lizards should practice good personal hygiene.
Only two species, the Gila monster (Helodermanghium) of the southwestern United States and northwestern Mexico and the Mexican beaded lizard (H. horridum) of western Mexico, are venomous. Both species only bite humans when provoked and are very rarely fatal. Among the most harmless lizards is the gecko, which is considered highly venomous by many indigenous cultures around the world. The reason for this suspicion is not clear; However, the geckos’ nocturnal activity, elliptical pupils, and ability to walk on smooth vertical surfaces may make them seem supernatural to some cultures.
Lizards are also considered biological objects of study. Their diverse modes of reproduction and their ability to regulate body temperature are two of the many areas studied by comparative physiologists (see thermoregulation). The abundance and observability of many species make them ideal subjects for ecologists and ethologists. The ability of some species to regenerate broken tails has led to them being used by behavioral ecologists and developmental biologists as subjects of study. Because they are relatively clean and easy to keep, lizards are also quite popular as house pets.
Natural history
Life cycle
Most lizards reproduce by laying eggs. In some small species, the number of eggs is quite uniform in each lay or litter. For example, all geckos (Anolis) lay only one egg at a time, many geckos lay one or two eggs (depending on the species), and some geckos have two eggs. A more general rule of thumb is that clutch size varies with the size, age, and condition of the mother. A litter of 4 to 8 eggs might be considered typical, but large lizards like iguanas can lay 50 or more eggs at a time. Lizard eggs often have rough and spongy shells; they can expand by absorbing moisture as the embryo develops. An exception occurs in most egg-laying geckos, whose eggs harden as soon as they are settled and then show no further change in size or shape.
Embryonic development and sex determination
Viviparity, or the birth of live young, occurs in some species of lizards. For skinks, this is true for about a third of species, many of which live in tropical climates. In most other families with live representatives, species that are frequently exposed to cold conditions—at high altitudes or at extreme latitudes—tend to become live carriers. For example, all New Zealand geckos give birth, while all other geckos lay eggs. There are many diverse mechanisms that lead to the production of live offspring. In some lizards, the only difference between ovipositor (egg-laying) and oviparous (egg-laying) is that the shell never forms around the “egg”. The female keeps them inside the fallopian tube until development is complete and each egg already contains all the energy needed for development in its large yolk. In these cases, no additional nutrients are passed from mother to child.
In other lizards, the egg released from the ovary contains most, but not all, of the energy needed for the development of the yolk. Several types of placenta can develop, depending on the species of lizard. As a result, some nutrients pass from mother to child during development. Only in some species, such as Mabuya heathi, are small eggs with almost no yolk released from the ovaries and deposited in the fallopian tubes. An advanced and complex placenta develops, and more than 99% of the nutrients needed for embryonic development are passed from mother to child. In these species the gestation period is usually very long (8–12 months).
Sex in most lizards is rigidly and genetically determined; A young usually has a male or female reproductive structure. In representatives of most iguanian lizard families (Iguania) and in some lizards, tegus, geckos, and lizards, males have dissimilar sex chromosomes, comparable to an infection system. sex chromosomes of most mammals. Some female geckos, wall lizards, and all monitor lizards have sex chromosome differences similar to those found in snakes. In some lizards (some iguanas, geckos, and wall lizards), no sex chromosomes exist. They rely on temperature-dependent sex determination (TSD)—that is, the temperature present in the nest during egg development controls the sex of the offspring.
unisexual reproduction
Most lizard populations are divided equally between females and males. Deviations from this pattern are found in unisexual species, in which young are born from unfertilized eggs. Reproduction in lizards was first detected in all-female Lacerta strains of the Caucasus, but it is now known to occur in all-female whiptail lizards (Aspidoscelis) of the southwestern United States. and parts of Mexico, several other Teiidae and Gymnophthalmidae species. (glass lizards or microteiids) of South America and a few Gekkonidae. Parthenogenetic lizards seem to live in areas that are ecologically marginal to representatives of their genus. In Aspidoscelis and some other dioecious species, there is compelling evidence that the forms of parthenogenesis arise through the crossing of two hermaphrodites. The number of chromosomes in such species is usually twice that of sexually reproducing species, but in some cases the number of chromosomes is tripled. This is the result of mating of a sexually reproducing species with a heterosexual species. These offspring are called allotriploids because they represent a reverse crossover that produces three sets of chromosomes.
Parental care
Parental care for lizards tends to diminish after spawning, but there are notable exceptions. Many species dig holes to lay their eggs, while others bury them under fallen leaves or deposit them in hollows or caves. In contrast, the females of some species, notably the American five-striped skink (Eumeces fasciatus) and many of their relatives, stay with their eggs for the duration of the incubation period (about six weeks); they don’t often leave the clutch to eat. These mollusks turn their eggs regularly, and if the eggs are spread in a test way, they will return them to the nest cavity. As soon as the young people dispersed, family ties were severed. The glass lizard (Ophisaurus, family Anguidae) seems to do the same thing. In addition, some viviparous lizards remove and eat placental membranes from their young when they are born.
In Australia, juvenile sleepy lizards (Tiliqua rugosa) remain within their mother’s home range for a long time, and this behavior suggests that they gain a survival advantage in doing so. The sleepy female and the Baudin Island spinyel lizard (Egernia stokesii aethiops) recognize their offspring on the basis of chemical signals. As a result, parental care for lizards may be more common than previously thought. However, because recognition systems are so sophisticated, they are difficult to study.
Some lizards, especially some species of the family Gekkonidae, are known to have common egg layers, with multiple females laying eggs at the same site. Also, it seems that the same female may return to a specific location during her lifetime to lay eggs. In Tropidurus semitaeniatus and T. hispidus, two South American land lizards, the females nest together under rocks atop large rocks. In this specialized habitat, there are only a few suitable nesting sites and therefore they are a limited resource. Males seem to take advantage of this situation, especially if the nesting sites are in their territory. It is likely that if a male guards a good nesting site, he will have access to more females than males who govern areas without a high-quality nesting site.
