Animals that have dry scaly skin and are ectothermic (cold-blooded) vertebrates are called reptiles. The major way reptiles differ from mammals and birds is that they are ectothermic (cold-blooded). This does not mean that they necessarily have cold blood but rather that they cannot regulate their own body temperature through any means other than modifying their behavior. To heat up they use an external heat source within their environment such as basking in the sun or sitting on a hot rock (most mammals would shiver). To cool down they choose a cooler area to rest (most mammals would sweat). Due to this they are generally found through out the warmer regions of the world although a few have adapted to quite cold areas (even where it snows)! Most reptiles though are found in the tropics. The majority of reptile groups also live on land, although there are a few that have specialized to live in water. Reptiles can only breathe air and do not possess gills. They have thick waterproof skins to retain their body moisture.
Most reptiles lay eggs (oviparous), however there are a few species that incubate and hatch their eggs internally (ovoviviparous). Reptile eggs contain a large quantity of yolk to nourish the embryo, and they have a porous shell. Most reptiles are carnivorous.
Our Amazing Reptiles
Reptile Fact - Crocodilians
Crocodiles have salt glands, whereas alligators don't.