The kangaroo is a marsupial. A distinctive characteristic common to marsupials is that, with most, the young are carried around in a pouch. They are mainly found in the Americas and Australia, the kangaroo being from the latter.
Australia has some of the driest environments on the planet so the kangaroo has evolved some brilliant baby making machinery to cope. Baby kangaroos, called joeys, when born (after only a maximum of 38 days inside the womb), are indeed about the size of a paperclip. They may weigh as little as 0.3 g (0.01 oz).
Not only do they come into this world like a tiny piece of office stationery, but like most new born marsupials they are also hairless and blind. It also barely has any hind legs, as these form later on. And as if that wasn’t enough of a challenge, once born, they have to climb up the outside of the pouch quickly enough so as not to be killed from exposure, get over the edge of it before climbing down inside to find their mummy’s teat.
It can take 10 months or more for the joey to emerge from the pouch. The first time it leaves is usually by accident. It will then stay outside for longer and longer, staying near their mummy until they are about 18 months old. If it’s a boy it will reach sexual maturity after 2 or 3 years, if it’s a girl it will be several years more.
Once sexual maturity is reached, they can hop off into the sunset to make lots of little paperclips of their own.