Why are marsupials common in PNG and Australia and not Asia?

Marsupials are considered as less"evolved" and a bit living fossil-ish. It is likely marsupials were outcompeted by mammals in other areas and that Australia and Papua New Guinea, being more isolated become a safe haven for marsupials as there were no bears, foxes, big cats, rabbits competing with them. read more

Yes, it’s like there’s a line drawn where there’s ‘normal’ mammals on one side (southeast Asia) and marsupial mammals on the other (Australia and Oceania). * And we call that the Wallace line [1]. read more

It is likely marsupials were outcompeted by mammals in other areas and that Australia and Papua New Guinea, being more isolated become a safe haven for marsupials as there were no bears, foxes, big cats, rabbits competing with them. Take for example the echidna, one of the few mammals that still lay eggs. read more

I am intrigued as to why Australia ( along with Tasmania, Papua new Guinea) is home to various marsupial mammals and also monotremes like the duck-billed platypus, but these are not found in any other continent. I recently read a book which said that fossils of marsupials have been found in South america. read more