From Wikipedia, the free encyclopedia
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains. The group, traditionally recognized as the suborder Lacertilia, is defined as all extant members of the Lepidosauria (reptiles with overlapping scales), which are neither sphenodonts (i.e., tuatara) nor snakes – they form an evolutionary grade. While the snakes are recognized as falling phylogenetically within the anguimorph lizards from which they evolved, the Sphenodonts are the sister group to the Squamates, the larger monophyletic group, which includes both the lizards and the snakes.
Lizards typically have limbs and external ears, while snakes lack both these characteristics. However, because they are defined negatively as excluding snakes, lizards have no unique distinguishing characteristic as a group. Lizards and snakes share a movable quadrate bone, distinguishing them from the sphenodonts, which have a more primitive and solid diapsid skull. Many lizards can detach their tails to escape from predators, an act called autotomy, but this ability is not shared by all lizards. Vision, including color vision, is particularly well developed in most lizards, and most communicate with body language or bright colors on their bodies as well as with pheromones.
The adult length of species within the suborder ranges from a few cm for some chameleons and geckos to nearly three metres (9 feet, 6 inches) in the case of the largest living varanid lizard, the Komodo Dragon. Some extinct varanids reached great size. The extinct aquatic mosasaurs reached 17 metres, and the giant monitor Megalania prisca is estimated to have reached perhaps seven metres.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Bartagame_fcm.jpg
Sight is very 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.
The 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 (UV) light, as lizards can often see UV (Which is required for their survival, otherwise they develop metabolic bone disease).
Evolution and relationships
The retention of the basic 'reptilian' amniote 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 as squamates are part of a well-defined group.
The earliest amniotes were superficially lizard-like, but had solid, box-like skulls, with openings only for eyes, nostrils, termed the anapsid condition. Turtles retain this skull form. Early anapsids later gave rise to two new groups with additional holes in the skull to make room for and anchor larger jaw muscles. The Synapsids, with a single fenestra, gave rise to the superficially lizard-like Pelycosaurs, which include Dimetrodon and the Therapsids, including the Cynodonts, from which the modern mammals would evolve.
The Diapsids, possessing one temporal fenestra in front of the eye and one behind it, continued to diversify. One branch, the Archosaurs, retained the basic Diapsid skull, and gave rise to a bewildering array of animals, most famous being the crocodilians, the pterosaurs, the dinosaurs and their descendants, birds. The Ichthyosaurs and Plesiosaurs radiated from the same basal Diapsid group.
The smaller Lepidosaur branch, which would give rise to the lizards, began to reduce the skull bones, making the skull lighter and more flexible. The modern Tuatara retains the basic Lepidosaur skull, distinguishing it 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.
The earliest known fossil remains of a lizard belong to the iguanian species Tikiguania estesi from the Tiki Formation of India, which dates to the Carnian stage of the Triassic period, about 220 million years ago. However, mitochondrial phylogenetics suggests that the first lizards evolved in the late Permian. Most evolutionary relationships within the squamates are not yet completely worked out, with the relationship of snakes to other groups being most problematic. From morphological data, Iguanid lizards have been thought to have diverged from other squamates very early, but recent molecular phylogenies, both from mitochondrial and nuclear DNA, do not support this early divergence. Because snakes have a faster molecular clock than other squamates, and there are few early snake and snake ancestor fossils, it is difficult to resolve the relationship between snakes and other squamate groups.
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Prognathodon3.jpg
Within the Lacertilia are found four generally recognized suborders, Iguania, Gekkota, Amphisbaenia and Autarchoglossa, with the "blind skinks" in the family Dibamidae having an uncertain position. While traditionally excluded from the lizards, the snakes are usually classified as a clade with a similar subordinal rank.
The suborder Iguania, found in Africa, south Asia, Australia, the New World, and with iguanas colonizing the islands of the west Pacific, form the sister group to the remainder of the squamata. They are largely arboreal, and have primitively fleshy, non-prehensile tongues, some even have scales, but this condition is obviously highly modified in the chameleons. This clade includes the following families:
Family Agamidae – Agamid Lizards, Old World Arboreal Lizards
Family Chamaeleonidae – Chameleons
Family Corytophanidae – Helmet Lizards
Family Crotaphytidae – Collared Lizards, Leopard Lizards
Family Hoplocercidae – Dwarf and Spiny Tail Iguanas
Family Iguanidae – American Arboreal Lizards, Chuckwallas, Iguanas, Iguanids
Family Opluridae – Malagasy Iguanas
Family Phrynosomatidae – North American Spiny Lizards
Family Polychrotidae – Anoles and kin
Family Tropiduridae – Tropidurid Lizards
Active hunters, the Gekkota includes three families comprising the distinctive cosmopolitan geckos and the legless flap-footed lizards of Australia and New Zealand. Like snakes, the flap-footed lizards and most geckos lack eyelids. Unlike snakes, they use their tongues to clean their often highly developed eyes. While gecko feet have unique surfaces that allow them to cling to glass and run on ceilings, the flapfoot has lost its limbs. The three families of this suborder are:
Family Eublepharidae – 'Eyelid' Geckos
Family Gekkonidae – Geckos
Family Pygopodidae – Flap-footed Lizards
Relationship with humans
Most lizard species are harmless to humans. Only the largest lizard species, the Komodo dragon, which reaches 3.3 metres (11 feet) in length and weighs up to 166 kg (365 pounds), 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. The venom of the Gila monster and beaded lizard is not usually deadly but they can inflict extremely painful bites due to powerful jaws.
Numerous species of lizard are kept as pets.
Lizard symbolism plays important though rarely predominant roles in some cultures (e.g., Tarrotarro in Australian Aboriginal 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.
Green Iguanas are eaten in Central America and Uromastyx in Africa. In North Africa, Uromastyx are considered dhaab or 'fish of the desert' and eaten by nomadic tribes.
Suborder Lacertilia (Sauria) - (Lizards)
Family Corytophanidae (casquehead lizards)
Family Iguanidae (iguanas and spinytail iguanas)
Family Phrynosomatidae (earless, spiny, tree, side-blotched and horned lizards)
Family Polychrotidae (anoles)
Family Leiosauridae (see Polychrotinae)
Family Tropiduridae (neotropical ground lizards)
Family Liolaemidae (see Tropidurinae)
Family Leiocephalidae (see Tropidurinae)
Family Crotaphytidae (collared and leopard lizards)
Family Opluridae (Madagascar iguanids)
Family Hoplocercidae (wood lizards, clubtails)
Family Agamidae (agamas)
Family Chamaeleonidae (chameleons)
Family Gekkonidae (geckos)
Family Pygopodidae (legless lizards)
Family Dibamidae (blind lizards)
Family Scincidae (skinks)
Family Cordylidae (spinytail lizards)
Family Gerrhosauridae (plated lizards)
Family Xantusiidae (night lizards)
Family Lacertidae (wall lizards or true lizards)
Family Teiidae (tegus and whiptails)
Family Gymnophthalmidae (spectacled lizards)
Family Anguidae (glass lizards)
Family Anniellidae (American legless lizards)
Family Xenosauridae (knob-scaled lizards)
Infraorder Platynota (Varanoidea)
Family Varanidae (monitor lizards)
Family Lanthanotidae (earless monitor lizards)
Family Helodermatidae (gila monsters & beaded lizards)
Family †Mosasauridae (marine lizards)FONTE:
From Wikipedia, the free encyclopedia
Geckos are lizards belonging to the family Gekkonidae, found in warm climates throughout the world. They range from 1.6 cm to 60 cm.
Geckos are unique among lizards in their vocalizations, making chirping sounds in social interactions with other geckos. Gekkonidae is the largest family of lizards, with over 2000 different species worldwide and many others likely yet to be discovered. The name stems from the Indonesian-Javanese word Tokek, inspired by the sound these animals make.
All geckos, excluding the Eublepharinae subfamily, have no eyelids and instead have a transparent membrane which they lick to clean. Many species will, in defense, expel a foul-smelling material and feces onto their aggressors. There are also many species that will drop their tails in defense, a process called autotomy. Many species are well known for their specialized toe pads that enable them to climb smooth and vertical surfaces, and even cross indoor ceilings with ease (one hypothesis explains the ability in terms of the van der Waals force). These antics are well-known to people who live in warm regions of the world, where several species of geckos make their home inside human habitations. These species (for example the House Gecko) become part of the indoor menagerie and are often welcome guests, as they feed on insects, including mosquitoes.
The largest species, the Kawekaweau, is only known from a single, stuffed specimen found in the basement of a museum in Marseille, France, and one documented sighting in the wild in 1870. This gecko was 60 cm (24 in) long and it was endemic to New Zealand, where it lived in native forests. It was probably wiped out along with much of the native fauna of these islands in the late 19th century, when new invasive species such as rats and stoats were introduced to the country during European colonization. The smallest gecko, the Jaragua Sphaero, is a mere 1.6 cm long and was discovered in 2001 on a small island off the coast of the Dominican Republic.
Geckos come in various patterns and colors such as purple, pink, blue, and black, and are among the most colorful lizards in the world.
Some are subtly patterned and somewhat rubbery looking, while others are brightly colored. Some species can change color to blend in with their environment or with particular temperatures. Some species are parthenogenic, which means the female is capable of reproducing without copulating with a male. This improves the gecko's ability to spread to new islands. However, in a situation where a single female gecko populates an entire island, the island will suffer from a lack of genetic variation within the geckos that inhabit it. The gecko's mating call sounds like a shortened bird chirping which attracts males, when they are around. This allows a female to reproduce with more genetic variation, by using sexual reproduction instead of asexual.
The toes of the gecko have a special adaptation that allows them to adhere to most surfaces without the use of liquids or surface tension. The spatula tipped setae on gecko footpads allow attractive forces called van der Waals interactions to arise between the adhesive setae and the surface. One study suggested that capillary adhesion might play a role, but that hypothesis has been rejected by more recent studies  .
These van der Waals interactions involve no fluids; in theory, a boot made of synthetic setae would adhere as easily to the surface of the International Space Station as it would to a living room wall, although adhesion varies with humidity . The setae on the feet of geckos are also self cleaning and will usually remove any clogging dirt within a few steps. Teflon, which has very low van der Waals forces, is more difficult for geckos to adhere to than many other surfaces.
Geckos' toes seem to be "double jointed", but this is a misnomer. Their toes actually bend in the opposite direction from our fingers and toes. This allows them to overcome the van der Waals force by peeling their toes off surfaces from the tips inward. In essence, this peeling action alters the angle of incidence between millions of individual setae and the surface, reducing the Van der Waals force. Geckos' toes operate well below their full attractive capabilities for most of the time. This is because there is a great margin for error depending upon the roughness of the surface, and therefore the number of setae in contact with that surface.
Use of small van der Waals attraction force requires very large surface areas: every square millimeter of a gecko's footpad contains about 14,000 hair-like setae. Each seta has a diameter of 5 micrometers. Human hair varies from 18 to 180 micrometers, so a human hair could hold between 3 and 36 setae. Each seta is in turn tipped with between 100 and 1,000 spatulae. Each spatula is 0.2 micrometer long (one five-millionth of a meter), or just below the wavelength of visible light.
If a typical mature 70 g (2.5 oz) gecko had every one of its setae in contact with a surface, it would be capable of holding aloft a weight of 133 kg (290 lb): each spatula can exert an adhesive force of 10 nanonewtons (0.0010 mgf). Each seta can resist 10 milligrams-force (100 µN), which is equivalent to 10 atmospheres of pull. This means a gecko can support about eight times its weight hanging from just one toe on smooth glass.
Common species of geckos
Pachydactylus, genus of geckos of which there are many species.
Bibron's gecko, Pachydactylus bibroni — Native to Southern Africa, this hardy arboreal gecko is considered a household pest.
Crocodile gecko or Moorish gecko, Tarentola mauritanica — very strong and heavily built for their size usually growing up to 15 cm (6 in). They are commonly found in the Mediterranean region from the Iberian Peninsula and southern France to Greece and northern Africa. Their most distinguishing characteristic is their pointed head and spiked skin with their tail resembling that of a crocodile's.
Cyrtopodion, genus of geckos of which there are many species.
Cyrtopodion brachykolon; commonly known as "bent-toed gecko", found in north-western Pakistan.
Rhacodactylus, genus of Geckos of which there are a few species.
Suras Gecko belonging to the genus Rhacodactylus.
Crested gecko, Rhacodactylus ciliatus — Believed extinct until rediscovered in 1994. Gaining in popularity as a pet.
Gargoyle gecko, Rhacodactylus auriculatus — commonly known as the New Caledonian bumpy gecko or gargoyle gecko.
Gold dust day gecko (Phelsuma laticauda laticauda (Boettger, 1880) (syn. Pachydactylus laticauda Boettger, 1880)) is a diurnal subspecies of geckos. It lives in northern Madagascar and on the Comoros. It is also an introduced species in Hawaii.
Golden Gecko, Gekko ulikovskii — native to the warm rainforests of Vietnam.
Hemidactylus, genus of geckos of which many varieties belong.
Common House Gecko, Hemidactylus frenatus — A species that thrives around man and human habitation structures in the tropics and subtropics world wide.
Indo-Pacific Gecko, Hemidactylus garnotii — Also known as a fox gecko because of its long, narrow snout. This species is found in houses throughout the tropics. This gecko may eat leafcutter ants.
New Caledonian giant gecko, Rhacodactylus leachianus — first described by Cuvier in 1829, is the largest of the Rhacodactylus geckos.
Leopard gecko, Eublepharis macularius — The most common gecko kept as a pet is the leopard gecko, which does not have toe pads with setae, but rather claws. These enable it to more easily climb on rough surfaces like tree bark. This gecko cannot climb the glass of a terrarium. The leopard gecko tends to be docile and calm. This gecko can eat butterworms, cockroaches, crickets, mealworms, waxworms, superworms, and pink mice.
Mediterranean gecko, Hemidactylus turcicus — residential and wild, introduced species (USA).
Mourning gecko, originally an East Asian and Pacific species, Lepidodactylus lugubris is equally at home in the wild as in residential neighborhoods. Found in Hawaii, it may have been an early Polynesian introduction. A parthenogenic species. There is a report from Hawaii of someone having seen a larger gecko of this type eating a smaller one (or rather, running away from view with a smaller gecko halfway out of its mouth) on three or more occasions.
Ptychozoon, — a genus of arboreal gecko from Southeast Asia, known as Flying Geckos or Parachute Geckos, has wing-like flaps from the neck to the upper leg, to help it conceal itself on trees and provide lift while jumping.
Stump-toed gecko, Gehyra mutilata (Peropus mutilatus) — This gecko, commonly referred to as a gheckl, can vary its color from very light to very dark to blend into a background. At home in the wild as well as in residential neighborhoods.
Tree gecko, Hemiphyllodactylus typus — Tree geckos are forest dwellers.
Tokay gecko, Gekko gecko — a large, common, Southeast Asian gecko known for its aggressive temperament, loud mating calls, and bright markings.
Western banded gecko, Coleonyx variegatus — Native to southwestern United States and northwest Mexico.
Dwarf gecko, Sphaerodactylus ariasae — native to the Caribbean islands, and the world's smallest lizard
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Gekkoninae_Rhacodactylus_ciliatus_orange.png
FONTE IMMAGINE: http://en.wikipedia.org/wiki/File:Hemidactylus_frenatus.jpg