Defining Characteristics:
* Hair or fur: Though some mammals have very little fur, all mammals have hair at some point in their lives.
* Mammary glands: Mammals produce milk to nourish their young.
* Warm-blooded: Mammals maintain a constant body temperature, regardless of the environment.
* Live birth: Most mammals give birth to live young, with the exception of the monotremes (platypus and echidnas).
* Three middle ear bones: Mammals have a unique bone structure in their middle ear that allows for hearing.
* Four-chambered heart: Mammals have a highly efficient circulatory system with a four-chambered heart.
Examples of Mammals:
Mammals can be divided into several groups:
* Monotremes: lay eggs (e.g., platypus, echidnas)
* Marsupials: give birth to underdeveloped young that complete their development in a pouch (e.g., kangaroos, koalas, opossums)
* Placental mammals: give birth to fully developed young after a period of gestation in the womb (e.g., humans, dogs, cats, whales, elephants)
Here are some examples of mammals:
* Humans
* Dogs
* Cats
* Whales
* Elephants
* Monkeys
* Bats
* Bears
* Lions
* Tigers
* Giraffes
* Kangaroos
* Koalas
* Opossums
* Platypus
* Echidnas
This list is not exhaustive, as there are thousands of different species of mammals around the world.