The Yudum were first discovered by ancient travelers when Australia was being founded. The discovered the Yudum to be hostile, so the killed them, and regarded them as an enemy. We know this because of cave drawings made by these ancient people. They were commonly hunted by the people of Australia. This continued until the Mushroom Kingdom forced a few hundred toads to go out and explore this unknown area. It turns out, the Yudums and toads started breeding, and the Pac-People were their children.