1. Monotremes:
- Monotremes are the most primitive group of mammals and are only found in Australia and New Guinea.
- They are unique in that they lay eggs, making them the only mammals that reproduce in this manner.
- Examples of monotremes include the platypus and echidna.
2. Marsupials:
- Marsupials are a diverse group of mammals that give birth to live young, but the young are born in an underdeveloped state and continue to develop in a pouch on the mother's body.
- Marsupials are mostly found in Australia, although a few species are found in the Americas.
- Kangaroos, koalas, and opossums are well-known examples of marsupials.
3. Placental Mammals:
- Placental mammals represent the vast majority of mammal species and are found all over the world.
- They are characterized by the development of a placenta during pregnancy, which allows for the exchange of nutrients and oxygen between the mother and the developing fetus.
- Placental mammals include humans, dogs, cats, elephants, whales, and many more.