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Why do marsupial young continue developing after birth?

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Red kangaroos on the move — kangaroo A group of red kangaroos (*Macropus rufus*) using their powerful hind legs and feet to hop.

Marsupials give birth to their young while they are still in a very vulnerable, embryonic state. Because the female's uterine wall is not specialized for long-term embryo implantation—unlike that of placental mammals—the period of intrauterine development is quite short, ranging from about 8 to 40 days.123

Consequently, the newborn must complete the remainder of its development outside the womb. Immediately after birth, the young crawl to the mother's belly, where they attach themselves to the teats. The teats then swell, firmly fastening the young to the mother to provide the necessary nourishment, warmth, and shelter for them to continue growing. This process allows the young to develop over several weeks or months until they are mature enough to be weaned and survive independently.142