How did the kangaroos get their tails?

Only God knows

The Aborigines tell their own story about how the kangaroo got its tail.

In the aboriginal Dreamtime, Kangaroo and Wombat were men who once friends. One day, they fought over their catch after a hunting expedition. In rage, Wombat picked up a spear and threw it at Kangaroo, where it lodged at the base of his spine. Kangaroo, in turn, picked up a stone and threw it at Wombat, flattening his forehead. With that, Kangaroo bounded away into the bushland where he nursed his wounds. The spear became a tail and Kangaroo turned into the kangaroo. Wombat crawled away into a burrow, where he transformed into a wombat with a flattened head where the rock had struck. And that's how the kangaroo got its tail.