Mammals (formally Mammalia) are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.

Birds (class Aves) are winged, bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates.

Reptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded"amniotes whose skin is usually covered in scales or scutes. They are tetrapods and lay amniotic eggs, in which the embryo is surrounded by a membrane called the amnion. Modern reptiles inhabit every continent with the exception of Antarctica, and four living orders are currently recognized:

Amphibians (class Amphibia), such as frogs, toads and salamanders.Unlike other land vertebrates, amphibians lay eggs in water.