- Most mammals give birth to live young. The developing embryo/fetus receives nourishment and oxygen from the mother via a placenta that forms in the uterus.
- When fully developed, the fetus is expelled through the birth canal during the birthing process. Examples of viviparous mammals include humans, cats, dogs, cows, and whales.
2. Laying of eggs (Oviparity):
- A small group of mammals known as monotremes, which include the platypus and echidna, lay eggs.
- After mating, the female monotreme lays one or two leathery-shelled eggs, similar to reptile eggs. These eggs are incubated in a burrow or nest until they hatch, and the young are nourished by egg yolk.
3. Marsupial birth and pouch (Marsupiality):
- Marsupials, such as kangaroos, koalas, and opossums, have a unique reproductive strategy. After a relatively short gestation period, marsupials give birth to underdeveloped young called joeys.
- Joeys are born in a very immature state and crawl into the mother's pouch, where they attach to a nipple and continue their development while receiving milk and protection.