If the Story of Noah is true?

If the story of Noah is true then why are there some animals that are only found on certain continents? It says that after the flood subsided Noah’s boat came to rest on the Mountains of Ararat (which is throught to be Mount Ararat in Turkey). Hence, all of the animals were let off here. But, if this is true then why are some animals only found on certain continents. You could say they migrated throughout Europe and Asian then into Africa. Then crossed the land bridge into North America and then into South America. But,what about the animals such as the Kangaroos and Koala that are only found in Australia. There is no way they could have gotten from Eurasia to Australia. And there is no possible way that Eurasia and Australia were connected in the time frame of 5000 years or so then drifted apart. So how do you account for this if you believe in the story of Noah?