THE MAMMALS

 Mammals are one class of animal. 

Mammals are vertebrate

But what  makes an animal a mammal are more things:

First, they must have glands that give milk. This is to feed their babies. 

Second, they are warm-blooded. 

Third, all mammals have fur or hair. Humans are mammals and also they are dogs, whales, lions, monkeys, zebras and many more. 

Most mammals have teeth with the exception of the ant eater which doesn't have any teeth. 

Mammals have unique brains and are often very intelligent. Humans are the most intelligent. Other intelligent mammals include the dolphin, the elephant, the chimpanzee for example

Mammals that eat meat are called carnivores. Carnivores include lions, tigers, wolves, seals, and the biggest carnivore which is the polar bear. Mammals that eat only plants are called herbivores. Some herbivores are hippos, elephants, and kangarroos.

Scientists have classified about 5,000 species as mammals. 

A good place to know which animals are mammals is in this link