Reptiles are a cold-blooded vertebrate animal class that regularly sheds their outer layer of skin, yet are also very similar to birds (in fact, the crocodile is more closely related to a bird than to a lizard). Reptiles are not as old as fish, with the earliest reptile on record emerging 315 million years ago, but they were the dominant class during the Mesozoic age until the extinction of the dinosaurs. Like birds, reptiles are an air-breathing class with many of its species laying eggs instead of giving birth to live young. In fact, out of all the reptiles, the only species to give birth to live young are boas and pythons. Being cold-blooded without the ability to regulate their internal temperature, Reptiles become inactive during the cooler times of the year.
Reptiles are typically carnivores and feed on eating other animals like insects, mollusks, birds, frogs, mammals, fishes, or sometimes other reptiles. Some reptile species like land tortoises are vegetarians and eat leaves, grass, or cactus while the marine iguana dives into the sea to obtain seaweed for consumption.
Reptiles shed their skin so that they can continue to grow. When they shed, reptiles grow a new layer of skin underneath their old skin and then shed their old one. When they shed their skin reptiles also get rid of any parasites during the process. The process of shedding is referred to as sloughing.
Reptiles first appeared 315 million years ago during the time period known as the Late Carboniferous Period. This time period is also referred to as the Pennsylvanian and the Coal Age. The first reptile is considered to be the Hylonomus lyelli and is also the first animal known to have fully adapted to life on land.