Lizards are a very large and widespread group of squamate reptiles, with nearly 5,000 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, that is, reptiles with overlapping scales which are neither sphenodonts nor snakes.
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 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 in order to escape from predators, an act called autotomy, but this trait is not universal. Vision, including colour vision, is particularly well developed in most lizards, and most communicate with body language or bright colours on their bodies as well as with pheromones.
And sight is quite important for most lizards, both for locating prey and for communication, as such, many lizards have highly acute colour vision.
The adult length of species within the suborder ranges from a few centimetres for some chameleons and geckos to nearly three metres (nine feet, six inches) in the case of the largest living varanid lizard, the Komodo Dragon. Some extinct varanids have been known to grow to a great size. The extinct aquatic mosasaurs reached 17.5 metres, and the giant monitor Megalania prisca is estimated to have reached perhaps seven metres.
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 colours, such as the iridescent patches on the belly of Sceloporus. These colours 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 coloured 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 coloured skin beneath the head which can be then used for communication. Anoles are particularly famous for this display, with each species having specific colours, including patterns only visible under ultraviolet light, as lizards can often see UV rays.
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.
Most lizard species are harmless to humans. Only the very largest lizard species (Komodo dragon) pose threat of death and 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 however positive as they are significant predators of pest species; numerous species are prominent in the pet trade.
Lizard symbolism plays important, though rarely predominant roles in some cultures. For example Tarrotarro in Australian Aboriginal mythology and the Moche people of ancient Peru worshiped animals and often depicted lizards in their art.
(Source: Wikipedia – The Free Online Encyclopedia)
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