Kangaroo Island, Australia
Where the Wild Things Are
Think about the tremendous diversity of mammals in the world: giraffes gamboling across the African savanna, wide-eyed lemurs climbing trees in Madagascar, narwhals poking their unicorn horns through the Arctic ice. They may seem to have little in common, but evolutionarily speaking, their differences are trivial.
There are really only three ways to be a mammal, an animal characterized by hair, milk, a fused lower jaw and three bones in the middle ear. What distinguishes one mammal from another is how it bears its young. Giraffes, lemurs, narwhals and humans are all placental mammals, gestating fetuses internally. Marsupials, such as kangaroos, give birth to underdeveloped offspring that in many species climb into a pouch to suckle. And monotremes, the oldest, weirdest and rarest of the mammal lineages, which includes the duck-billed platypus, lay eggs.
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