I saw a video (I couldn't get the URL) where an atheist challenged the veracity of the account of Noah's flood in Genesis. He reasoned that it couldn't have been true because of the existence of animal species endemic to Australia. I don't doubt the Biblical account, and I came up with an explanation that I think might be consistent with the evidence. I figured that Noah's flood might have only been local, but big enough to destroy all human life apart from Noah's family. Since the dispersal and migration of people with similar languages happened after the flood when human population has sufficiently recovered (Genesis 11), then it's possible that the flood didn't need to be universal. It simply needed to be big enough to destroy the existing human population at the time, which I assume would've been relatively small and concentrated in a certain locality. Assuming this is how it happened, then the flood wouldn't have needed to be universal. This would've allowed for animal species endemic to Australia to not need to be in the arc. I figured this is as good an explanation as any, but I'll be the first to admit that this is highly speculative. Please let me know your thoughts. Thanks.
I agree that your explanation of the flood is a reasonable one which agrees with most or all of the evidence we have. The only thing I would add is that, given that there are flood "myths" in nearly every ancient culture, it seems to me that this flood was more universal that you propose, but perhaps it was not so complete in its destruction as to destroy all life, including kangaroos in Australia and llamas in South America. I agree with your explanation as a likely one.