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For other uses, see Lizard (disambiguation).

Lizards
Temporal range: Late Triassic - Recent, 220–0 Ma
Central bearded dragon, Pogona vitticeps
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Superclass:
Tetrapoda
Class:
Reptilia
Subclass:
Diapsida
Order:
Squamata
Suborder:
Lacertilia*

Günther, 1867
Families

Many, see text.

Lizards are a widespread group of squamate reptiles, with nearly 3800 species,[1] 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.[2] 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. While lizards are commonly associated with prehistoric reptiles such as dinosaurs, scientists are still unsure as to whether or not contemporary lizards and dinosaurs are of same evolutionary chain. The prevailing notion among lizard experts is that, while remarkably similar to prehistoric reptilian creatures, modern lizards are an evolutionary off shoot of mammals. They have, however, adapted and learned to survive by the same means as many dinosaurs.


Physiology

Feral Jackson's Chameleon from a population introduced to Hawaii in the 1970s

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

Fossil mosasaur Prognathodon, a varanoid

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 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.[3] 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.[4] Because snakes have a faster molecular clock than other squamates,[4] and there are few early snake and snake ancestor fossils,[5] it is difficult to resolve the relationship between snakes and other squamate groups.

Lizard diversification

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.[6]

Iguania

Anoles mating, Gainesville, FL

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:

Gekkota

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:

Relationship with humans

Komodo dragons on Rinca
Green iguanas (Iguana iguana), are popular exotic pets

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.[7] 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 worshipped animals and often depicted lizards in their art.[8] 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.[9]

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.[10]

Classification

Gekko gecko in Thailand
Close-up of the head of the legless fossorial amphisbaenid Rhineura
Underside of a Thorny devil, an agamid, Western Australia
The Eastern blue-tongued lizard, a scincomorph

Suborder Lacertilia (Sauria) - (Lizards)

References

Picture of a lizard clinging to an Enterolobium Cyclocarpum seedling / sapling
The venomous Gila monster, Heloderma s. suspectum
Burton's legless lizard, a pygopodid lizard found in Australia and New Guinea
  1. ^ Lizards at eduscape.com
  2. ^ Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama: University of Alabama Press. p. 164. ISBN 978-0817301354.
  3. ^ Datta, P.M. and Ray, S. (2006). "Earliest lizard from the Late Triassic (Carnian) of India." Journal of Vertebrate Paleontology, 26(4): 795-800.
  4. ^ a b Kumazawa, Yoshinori (2007). "Mitochondrial genomes from major lizard families suggest their phylogenetic relationships and ancient radiations". Gene. 388 (1–2): 19–26. doi:10.1016/j.gene.2006.09.026. PMID 17118581.
  5. ^ "Lizards & Snakes Alive!". American Museum of Natural History. Retrieved 2007-12-25.
  6. ^ ITIS http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=173861
  7. ^ http://www.msnbc.msn.com/id/19026658/
  8. ^ Berrin, Katherine & Larco Museum. The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames and Hudson, 1997.
  9. ^ Auffenberg, Walter (1994). The Bengal Monitor. University Press of Florida. p. 494. ISBN 0813012953.
  10. ^ pg 48, Grzimek, Bernhard. Grzimek’s Animal Life Encyclopedia (Second Edition) Vol 7 - Reptiles. (2003) Thomson - Gale. Farmington Hills, Minnesota. Vol Editor - Neil Schlager. ISBN 0-7876-5783-2 (for vol.7)
General references
Wikimedia Commons has media related to Sauria.

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