The creatures in the southern hemisphere to a creationists would of survived on floating mats of vegetation: granted those that couldn't cling to these mats would of perished within the surface of the earth(fossil record of the creatures that perished within the earth).
I love these "floating mat" stories.
Genesis 7:23 And every living substance was destroyed which was upon the face of the ground, both man, and cattle, and the creeping things, and the fowl of the heaven; and they were destroyed from the earth: and Noah only remained alive, and they that were with him in the ark.
If the Biblical account is correct, no animals survived on floating mats of vegetation. By proposing that Australian animals survived on floating mats,
you are agreeing that the Biblical report of the flood is false.
If you accept that the biblical account is
false, why bother with these absurd contortions involving floating mats?