Reptiles are widely distributed in both temperate and warm regions of the world. However, they are abundantly found in the tropics. The members belonging to the class Reptilia include crocodiles, snakes, lizards, tuataras, tortoises and turtles. Reptiles can be distinguished in having a dry and scaly skin, absence of hairs, feathers, mammary glands and presence of a few or no skin glands. The jaws are set with simple teeth. They have four limbs (except snakes) that are projected to the sides. The heart is imperfectly chambered in most reptiles and the two aortic arches arise from the ventricular region of the heart. The kidneys tend to excrete insoluble uric acid so as to conserve body water. With the exception of burrowing reptiles most species have well developed eyes. Tongue can be protruded in some reptiles.
Reptiles are cold blooded (poikilotherm) animals i.e. their body temperatures fluctuate with the atmospheric temperature. In temperate regions, they hibernate during winter months. Basking is an important behavioural function of many reptiles. They may be terrestrial, aquatic or arboreal. All male reptiles except tuatara possess copulatory organs. Females are mostly oviparous. Eggs are laid in a nest or under cover shortly after fertilization. The development of embryos occurs largely after the laying of eggs. Some species of reptiles, however, are viviparous. The number of eggs laid by reptiles varies from one to two hundred depending on the species. Many reptiles are long-lived animals.
Exploitation of reptilian resources in many parts of the globe has caused a great concern towards the conservation of reptile population. They are hunted for flesh and eggs as food; hide, skin and shell for fancy leather articles and handicrafts (e.g. belts, gloves, luggage, handbags etc.); teeth and bones as charms; fats for medicinal properties; and venom for preparation of medicinal products. As a consequence, many species of reptiles have become extinct or are on the verge of extinction.