E MICHAEL WITE RESPONDS:
PANGEA
Some scientists have suggested that there once was a super continent called Pangea.
And that eventually the continents broke away to where there are now.
And the marsupials and others were the first to reach Australia before it split away.
And the marsupial that didn't make it there were killed off by fiercer predators on the other continents.
But those predators could not make it to Australia after the split due to it's remote location.
It was a question of good timing for the marsupials in Australia and other species in Madagascar.