Also according to creation science theories, after the Flood, kangaroos bred from the Ark passengers migrated to Australia. There is debate whether this migration happened over land[2] -- as Australia was still for a time connected to Europe by a land bridge similar to the one that connected Asia to America[3] -- or if they rafted on mats of vegetation torn up by the receding flood waters.[2]
Another theory is that God simply generated kangaroos into existence there.