Answer:
Platypuses are mammals, but not marsupials (pouched mammals). They are monotremes, that is, egg-laying mammals.
After a short gestation period, the mother lays an egg containing the baby. About ten days later, the egg hatches, and the baby emerges. Marsupials also have short gestation periods, but after it is done, there is live birth. Baby marsupials crawl from the birth canal to the mother's nipple, to which they attach themselves for several weeks.