Reptiles are lung-breathing, scale-covered animals that are ectothermic, or “cold-blooded“. Being “cold-blooded” means that reptiles cannot regulate their own body heat so their warmth has to come from the environment around them. All reptiles are vertebrates, which means they have a backbone. Some reptiles lays eggs and some give birth to live young like mammals do. There are over 9,300 species of reptiles.
Birds are members of the class Aves, which boasts over 10,000 species. Most birds are able to fly, but some, like ostriches, kiwis, penguins, and emus, have wings but cannot fly, and other birds are far better at swimming than they are at flying.
There are over 5,500 different species of mammals. Mammals live on land, underground, in the air, or in fresh or salt water, but despite their diverse habitats, there are several things that mammals have in common: All mammals are vertebrates, meaning they have a backbone, they all make their own body heat, they all produce milk for their young, and they all have some type of hair or fur.