Placental mammals are a group of animals that give birth to live young, which develop inside the mother's womb. They are characterized by having a specialized organ called the placenta, which provides nutrients and oxygen to the developing fetus while removing waste products. This allows the young to grow more fully before birth compared to other mammals. Examples of placental mammals include humans, dogs, whales, and elephants. They are distinct from other types of mammals, such as marsupials, which give birth to underdeveloped young that continue to grow in a pouch. Placental mammals are found in diverse habitats around the world.