There is a better idea. no need for impossible group migrations and exclusion of groups. this never happened. afterr the flood its impossible, in a limited timeframe to fill the earth as god commanded, for marsupials to hold hands and head to s america/australia and not placentals. IMPOSSIBLE.
therefore investigation will show all creatures migrated together with no discrimination.
the answer is that marsupials are placentals with pouches. Thats why they are the great case study of what is called convergent evolution. thats why there are marsupial wolves, lions, mice, moles etc etc living or extinct.
Yet in fact there was no convergent evolution but only a adaptation in minor details of the creatures to change reproductive modes.
On the youtube/google there are moving/still pictures of the last marsupial wolf. Watch and see if you are open to the idea its just another dog with a pouch(for the girls).!
Then the equation of post flood marsupial migration is explained.