Lizard Features

PHYSICAL FEATURES
Lizards range in size from 30 mm to over 3 m, but most are closer to 400 mm in length.  Limbs are generally well developed, and some species can stand up and run on their hind legs. Burrowing forms often have degenerate limbs, and legless lizards move in the same manner as snakes.  In some species in the genus, the tail is vertically flattened, from side to side, an adaptation to swimming. The lizard's skin is dry and scaly and shed periodically, but unlike that of most snakes, it is shed in patches. Many species can darken or lighten their skin color in response to light, temperature, or emotional state.

DEFENSE
Many lizards are cryptically colored and thereby avoid detection. When disturbed, however, lizards have a variety of defensive actions that include threatening with an open mouth, hissing, inflating the body, positioning the body in such a fashion as to appear as large as possible, biting and scratching, and lashing with the tail. With very few exceptions, only the geckos have a voice and can produce threatening calls. Many species are equipped with spine-like scales that make it difficult for a predator to swallow them. Some forms expose brightly colored surfaces in an attempt to frighten enemies.

TAILS
Many lizards break their tails when they are confronted by an enemy or roughly handled. Predators are often attracted to the thrashing, dismembered tail, which allows the lizard to escape. Specialized vertebrae in the tail can be voluntarily split by muscular contraction and sphincter muscles in the tail stump close off the caudal artery to prevent excessive bleeding. A new tail, although not identical to the original, is soon regenerated.

TEMPERATURE REGULATION
Lizards are cold-blooded and thus depend primarily on an external heat source to regulate their body temperature.  Lizards can however vary their temperature by basking directly in the sun, by positioning themselves in such a way as to gain heat through conduction, or by seeking shade. Most lizards exhibit marked seasonal changes in activity. In order to avoid harsh weather conditions, lizards hibernate in temperate regions during the winter, generally seeking refuge beneath the frost line. During hot, dry climatic conditions lizards crawl into deep crevices or fissures in the ground, where they can best retain body moisture.

THE HEART
Lizards depend almost entirely on paired lungs to aerate the blood. The heart has only three chambers. The right atrium, which receives deoxygenated blood from the body, is separate from the left atrium, which receives oxygenated blood from the lungs, but the ventricle, which pumps blood to both the body and the lungs, is single.

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