Hobbies And Interests
Dry, Scaly Body
While fish and their relatives also sport scales and some mammals and birds have scale-like structures, reptiles are the only type of animals with completely dry, scaly bodies. Their scales are made from keratin, the same material that forms hair in mammals, feathers in birds, and nails or claws. Since these scales aren't flexible, reptiles shed them as they grow, sloughing off the old skin to reveal a new one underneath. Most reptiles shed their skins more often when young, since growth is fastest in this stage.
Three-Chambered Heart
Reptiles have three-chambered hearts, composed of two atria, or auricles, and one ventricle. The atria are the chambers where the blood enters the heart. The ventricle is the chamber that pushes the blood back out of the organ and into the rest of the circulatory system. This heart structure is more complex than that of fish, which have a two-chambered heart, but less complex than that of mammals, which have four chambers.
Leathery Eggs
All reptiles produce eggs, though not all of them actually lay these eggs. Reptiles reproduce by means of internal fertilization, unlike many fish and amphibians, which simply release eggs and sperm into the water. The majority of reptiles lay leathery eggs in moist soil or sand. Unlike most birds' eggs, reptile eggs do not have shells with a high calcium content. A few species, such as the vipers, are ovoviviparous. They produce eggs, but the female carries the fertilized eggs inside her body until the young hatch. This looks much like mammalian live birth, but does not involve a placenta.
Ectothermy
While reptiles are often referred to as "cold-blooded," this term is inaccurate and somewhat outdated. Reptiles can be either warm or cold-blooded, depending on the ambient temperature of their environment. These creatures obtain their body heat from their surroundings, becoming more active in warm weather and less active in cold weather. Many reptiles shut down or slow their body functions in cold weather in a behavior called brumation or hibernation. They become active again when the weather warms.