This is apparently unique to the animal kingdom, but it must be also noted that the whole family of marsupials represent an unusual classd onto themselves that challenge our thinking in regard to the evolutionary pathway that we try to impose.
It is a little like a lab running wild. Yet the marsupial is a branch and not a part of the pathway that produced the modern mammal. It is simply different and generally as successful as well. Also recall that bipedalism such as this dominated during the Age of Dinosaurs. It is not hard to imagine a Dinosaur adopting this gait and not too hard to see such a dinosaur evolving into this.
I also note that the only place that a part of the Age of Dinosaurs could have survived is the Sahul until the end of the Ice Age flooded them out. This is the shelf between Northern Australia and New Guinea. Remnants have been encountered even into modern times.