Do all mammals give birth to live young?
No. Most mammals give birth to live young, but monotremes, the platypus and four species of echidna, lay eggs. After hatching, the young still drink their mother's milk.
Monotremes live only in Australia and New Guinea. The platypus lays one to three small, leathery eggs in a burrow and curls around them to keep them warm for about ten days. Echidnas lay a single egg directly into a temporary pouch on their belly, where it hatches.
Monotremes are still mammals because they have hair and produce milk to feed their young. However, they have no nipples. Milk seeps from patches of skin, and the babies lap it up. Scientists think monotremes split from other mammals about 180 million years ago, keeping the ancient trait of egg laying.
Two kinds of live birth
Among mammals that give live birth, placental mammals, like humans, dogs and whales, nourish their young inside the womb through a placenta until they are well developed. Marsupials, like kangaroos and koalas, give birth to tiny, undeveloped young that continue growing in a pouch.
Did You Know?
A baby echidna is called a puggle. It stays in its mother's pouch until its spines start to grow.