* Marsupial mammals: This group of mammals gives birth to live young that are born in a very underdeveloped state and continue to develop while attached to the mother's nipple. Marsupial mammals include kangaroos, koalas, wombats, and opossums.
What are two types of mammals?
* Placental mammals: This group of mammals gives birth to live young that have developed inside the mother's uterus. Placental mammals include humans, dogs, cats, whales, and dolphins.