Skink, (family Scincidae), any of about 1,275 species of lizards, mostly secretive ground dwellers or burrowers, that are represented throughout most of the world but are especially diverse in Southeast Asia and its associated islands, the deserts of Australia, and the temperate regions of North America.
The body of skinks is usually cylindrical in cross section, and most species have a conical head and a long, tapered tail. The largest species, the long-tailed lizard (Corucia zebrata), reaches a maximum length of about 76 centimeters (30 inches), but most species are less than 20 centimeters (8 inches) long. Ground-dwelling and burrowing skinks may exhibit adaptations such as a transparent “window” scale in place of a movable lower eyelid. This adaptation allows the animal to see and protects the eyes from rough particles when burrowing. Other skinks may have features such as reduced or absent limbs and sunken eardrums. Some species are arboreal (arboreal) and others are semi-aquatic. Skinks eat insects and similar small invertebrates; Large species are herbivores and consume fruits. Some species lay eggs, while others give birth to fully developed young.
Broad-headed (Plestiodon laticeps). Some of the more common genera are described below. Catfish (Tropidophorus), a semi-aquatic species, is found from Southeast Asia to northern Australia. Mabuya (Mabuya), with about 105 species, is terrestrial and has a worldwide distribution in the tropics. Catfish (Scincus), also known as sandfish, run across and “swim” through wind-blown sand with the help of the scales on their toes. Their concave lower jaw, partial ear flaps, distinctive nostrils, and upper eyelid margin allow them to move through the sand without the sand entering their body. Sand skinks are native to the deserts of North Africa and South Asia.
Slender skins (Lygosoma and many other genera), snake-eyed scabs (Ablepharus and Cryptoblepharus) and Plestiodon (formerly Eumeces) skins are also common. Slender skinks are found throughout the tropics of the Old World, with some species in the New World. They have thick tails and miniature legs, and their eyelids are often partially transparent. The snake-eyed snakes come in a wide variety of colors and are the only sheathing snake to have a fixed plate (glasses) over the eye instead of a movable eyelid. With the exception of South America, Cryptoblepharus has a near-worldwide distribution in the tropics, partly because it rafted debris to the islands or was brought to many islands by humans. Most of the approximately 41 species of the genus Plestiodon have longitudinal stripes, although some species, such as the Great Plains skink (P. obsoletus), are completely striped. In many striped molts, such as the five-striped molt (P. fasciatus) and the broad-headed molt (P. laticeps), the stripes fade after sexually mature molts. Plestiodon is the predominant skink genus in the northern temperate regions of the New World as well as Japan and surrounding areas; however, they are absent in Europe.
The broad-headed mollusk and to a lesser extent the five-row scab have become model organisms for the study of behavioral ecology. As a result, both species have contributed greatly to the understanding of how lizards function in the natural world. Skinks are part of a group of lizards that use chemical cues in social interactions and foraging for prey. Their ability to distinguish chemical signals is influenced by sex hormones, and similar hormones affect some aspects of their morphology, especially in males. During the breeding season, when levels of the male sex hormone testosterone are high, the males’ heads are red and the muscles on their heads increase slightly in size. The males become aggressive towards other males and they pursue the females to try to mate with them. Males can distinguish sex based on chemical signals they pick up on the tongue and send into a highly receptive sensory organ called Jacobson’s organ (or vomeronasal organ) located on the roof of the mouth. . This organ transmits signals to the lizard brain. Males can also distinguish between sexually receptive and non-reactive females using this system. During the non-breeding season when sex hormone levels are low, males are not aggressive towards other males and do not attempt to mate with females, and their heads are dull brown. Sex selection has favored males with these traits, leading to significant differences between the sexes (sexual dimorphism).
Five-lined skinks and slender skinks have also been used in studies of tail loss as a defense against predators. Like many other lizards, skinned lizards can voluntarily release their tails when grabbed by a predator. Skinks often move or wag their tails to direct predators away from their bodies. The tails of many species are brightly colored, increasing the distracting effect. When the predator has grasped the tail, the snake sheds the skin and contracts the tail muscle and the tail is released. The energy stored in the tail is used to power the rapid pulsating movements of the released tail, which further distracts the predator. Skink then walked away from the hunting attempt. The tail is usually regenerated to restore any other function of the tail. In some molting species, the lost tail itself is more likely to escape a predator due to its violent thrashing. Five-row antelopes and slender firs often return to this area and eat their released tails, thus regaining some of the lost energy.
Skinks have also contributed greatly to the understanding of reptile reproduction. Although most skink species deposit their eggs in their nests and then discard them, many species are reproductive (vivid). Among the pregnant species are some that have developed a complex placenta to transfer nutrients directly to the developing offspring. In the South American species of M. heathi, the placenta is as developed and complex as in mammals.
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