ok dmcg I shall keep my word, when you have given the evolutionary explanation. it had better be convincing because I still fail to see why it cant be , because that's where they ended up. of course as you said yourself MOST MARSUPIALS ARE CONCENTRATED in one large area, thus allowing some in other areas, and maybe those areas had more in the past, but selection pressure had thinned them out.
I look forward to your explanation, so I at least know what the argument is.
btw, and you have the advantage here as the scientist,...are there nostril breathing animals that compare to your beetle challenge?