Either that, or a new category of animals will be created for it: like "montreme" or "cryptid."
Only on paper.
Australia and NZ are interesting. Their wildlife supports the theory of evolution, and is a puzzle if you think god created creatures fully formed.
NZ broke away from the mainland (Gondwana) first (or perhaps was never part of it), before mammals existed. Not that long ago, before humans landed on NZ, the only mammal we had was a bat, it managed to get to NZ because it could fly. We had no rats, mice, stouts, ferrets, weazles, foxes, cats, dogs, no mammals other than the bat. Many of our birds lost the power of flight (because they had no predators and no need to fly). We had Moa (now extinct), kiwi, kakapo, takahe, penguin, weka, three flightless wrens and two adzebills.
Australia broke away from the mainland a bit after that, it had some mammals, especially marsupials and monotremes, but lacked many of the placental mammals such as rats, mice, cats, dogs etc. Many of their marsupials and monotremes managed to survive without these predatorial placental mammals.
Now since the placental mammals evolved afterwards, they were able to run rampant on much of the world, but not on NZ and Australia because there was a great body of water between these island countries and the rest of the world. It wasn't until humans created boats and traveled the oceans, bringing with them these creatures that these environments were then plagued with these predators.
However, if evolution is false and if god creation is true, then isolated islands wouldn't have been a problem. The god could have created these predators on these isolated islands, no problem. Question: When the god created animals (fully formed) did the god just provide two of each (one male, one female) in the entire world, just to get the ball rolling, or did the god create several of them, spread over the world?
When the flood came, how did Noah gather these creatures up, and how did they then make it back to their homelands after the flood?