The origin of reptiles on this planet has been traced back to 200 million years. Lizards belong to this category of vertebrates and are known to be the largest group amongst reptiles encompassing approximately 5,000 species. These reptiles can be found in almost all realms of the world except in the extreme cold of Antarctica.
Lizards can vary in size from two inches to ten feet in length. There is a variation amongst lizards with respect to the number of limbs present as well. While some of the species possess four limbs, there are others with only two. In fact, there are some varieties that have no limbs at all.
The characteristic features of lizards include scaly skin, presence of lungs for respiration and cold blooded metabolism. Being cold blooded aids these reptiles to survive in desert conditions where there is dearth of food. The body temperature changes with respect to the surroundings, therefore the reptile does not require surplus food as a source of body heat as in the case of mammals.
Although most lizards are harmless, the gila monster and the Mexican beaded lizard are said to be poisonous in nature. There are certain species such as the collared lizard that are hostile in nature and are capable of attacking and consuming other lizards. Lizards are endowed with the unique feature of changing their body color compatible with its surroundings. This adaptation is used as a weapon by the reptile to protect itself from predators. The chameleon is well known in this respect. Common iguanas are good swimmers, an attribute utilized for self defense. The marine iguanas can even dive to a depth of 50 meters in water. Nature has blessed these reptiles with special features to protect them from being preyed upon. While Basilisks use their tremendous running potential, the flying dragon Lizard glides away from its predator with the help of its wing like flaps of skin.
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