MAMMALS

Mammals are the vertebrates within the class Mammalia, an animal family separated from reptiles.

Females of all mammal species nurse their young with milk, secreted from the glands.

This is by the possession of hair, three middle ear bones, and glands. 

AMPHIBIANS

They inhabit a wide variety of habitats, with most species living within terrestrial, arboreal or freshwater aquatic ecosystems.

Amphibians are vertebrates of the class Amphibia. Modern amphibians are all Lissamphibia.

The Lissamphibia are a group of tetrapods that includes all modern amphibians. 

Alligator

Crocodile

REPTILES

Reptiles are tetrapods animals in the class Reptilia.

The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology.

They include today's turtles, crocodiles, snakes, lizards, tuatara, and their extinct relatives.