Marsupials are from Mars, according to Ruthie in One Big Happy:
Faced with marsupial, which looks like it has Mars as its first element (and sounds pretty close to that), Ruthie chops out the Mars and comes up with a second element upial. So she’s treating the whole word as a N + N compound, which means that upial is the head N, and if the compound is as simple as possible, it’s subsective: a marsupial is then a kind of upial — a variety from Mars.
Ruthie has then given marsupial the demi-eggcorn treatment, analyzing Mars in it and flying with the possibility that upial is an English noun (with a meaning she doesn’t happen to know).
