However, the fact that it DID happen that they are so similar to a counterpart is still very strange to me.
I don't know just how odd it should seem, but consider that marsupials and placentals all descended from an ancestor that was already in possession of four legs, fur, a particular style of jaw, a three-bone middle ear, live births and milk glands.....quite a lot in common. And consider the wolf and the thylacine: both make/made their living mostly by hunting smallish critters, and relied on being able to gover lots of ground in a day. Both need to be able to snap up a rat-sized meal. How many different ways are there to make a living like that, given the constraints their common ancestry puts on them?
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