Marsupials have a different take on how to give birth. What happens is the fetal young or joey is born in a very undeveloped state compared to other animals. They can do this because in the marsupial system the mother has a special pouch where the joey can continue to develop in safety. Most animals have a placenta to nourish and develop the unborn young in the uterus. Marsupials and placental animals diverged in their evolution over 100 million years ago.
More than seventy percent of marsupials live in Australia and the surrounding islands, but there are a good number in the Americas as well, about 100 species out of 334 in total.