Reptiles

Reptiles Class Reptilia are cold-blooded vertebrates that diverged from ancestral amphibians about million years ago. There are two characteristics that distinguished early reptiles from amphibians and enabled them to colonize terrestrial habitats more extensively than their ancestors, scales and the ability to lay hard shelled amniotic eggs. Scales protect reptiles from abrasion and loss of body moisture. Hard shelled eggs provide a protective environment in which the embryo can develop.
Reptiles includes snakes, amphisbaenians, lizards, alligators, caimans, crocodiles, tortoises, turtles, and tuataras. There are over species of reptiles. Since reptiles do not produce their own body heat they are cold-blooded, also known as ectothermic, they modify their activity and behavior to best adapt to changing environmental temperatures.
When air temperatures are low night, early morning, evening a reptile, for example a lizard, often seeks shelter. As the temperature increases in the morning, the lizard might bask in the sunlight to increase its body temperature. It may then be active for several hours, seeking shelter if afternoon heat is too extreme.

One major characteristic of reptiles is the presence of scales composed of a protein called keratin. These scales form a waterproof barrier of skin, which allows reptiles to exist away from water without the threat of dehydration. Another characteristic is the regulation of internal body temperature by the external absorption of heat. Thus, reptiles are ectothermic. Unlike endothermic creatures, which must use calories from food to regulate body temperature, reptiles don't require much food to maintain body temperature and survive.