Marsupials are another one of those strange types of mammals. They actually birth underdeveloped offspring that have to remain in a pouch, which contains the mammary gland nipple. So basically, these offspring come out and they are not fully developed like the live birth offspring of most mammals that you're used to. They look almost like they are still partly like a fetus in many ways, and that's why they have to remain in that protective pouch. You can see this little baby kangaroo poking its head out of the pouch there; well, that is a much more developed kangaroo than what it looks like when they first come out. And just to give you some examples of marsupials, we have a koala bear here, a kangaroo here, and an opossum here. Now, most marsupials are only found in Australia, like the koala bear and the kangaroo. Opossums, on the other hand, made it to the Americas.
So moving on, finally, we get to placental mammals. These are mammals like you are probably most used to. These mammals give birth to live developed offspring after a long gestation period, what we normally call pregnancy. And the defining feature of these organisms is the placenta, this organ pictured here, that connects the developing fetus to the uterus wall and allows the fetus to get nutrients from the mother to do gas exchange, as in breathe. This is how the fetus breathes, essentially. And, it also allows for waste disposal from the fetus. So here we have an example of a developing fetus in the uterus with placenta pictured. And here is an example of a placental mammal, a three-toed sloth. By far the most regal, if not also one of the nicest placental mammals out there. That's all I have for this video. I'll see you guys next time.