There are roughly 5,000 species of mammals, animals within the class Mammalia. That means all those animals have vertebrates, warm blood, hair or fur, they breathe using lungs, and they feed their young milk. Of course, those characteristics aside, the diversity amongst mammals is overwhelming! But perhaps the most interesting way that mammals differ is how they give birth. There are three ways that we categorize mammals based on the way they birth their young: placental mammals, marsupials, and monotremes. Let's break down the difference.
Examples of placental mammals include humans, dogs, cats, giraffes, and even blue whales! This category of mammals grows their offspring in the uterus of the mother, where the baby is provided with all the nutrients and oxygen it needs via the placenta. Because the baby has everything it needs to develop, these mammals often have relatively long gestation periods.
Marsupials, such as kangaroos, give birth to live young when their offspring are still very small and undeveloped. After the babies are born, they must finish out their development in the pouch of their mother, where they spend several months suckling on the milk from their mother. Quick side fact: did you know kangaroos have three vaginas and can actually put a pregnancy on hold if external conditions aren't satisfactory? Watch the video to learn more!
The third type of mammalian birth comes from monotremes - mammals that actually lay eggs, like the platypus or echidna. This type of mammal is quite rare nowadays, with only 5 species in total on the planet, even though there used to be hundreds of species! Watch the video to learn about their special way of giving birth!