If you’re a New Zealander you will “know” that prior to the arrival of humans there were no mammals in New Zealand apart from bats. “Knowing” this is part of the DNA of being a New Zealander, like knowing that kiwi don’t fly and the All Blacks play rugby. However, if you had no connection with New Zealand whatsoever, and just so happened to have read Parts 1 and 2 of this series of articles on mammals, you wouldn’t be expecting that answer at all. You would be expecting me to say there are, or at least, were mammals in New Zealand (apart from bats) prior to the arrival of humans. And you would be perfectly right—and most New Zealanders perfectly wrong. New Zealand did indeed have mammals (other than bats) prior to the arrival of humans.

You don’t believe me? Not even if I say it with a smile? Let me try and convince you in other ways then…

Let’s summarise where we got to in the previous articles. Once upon a time New Zealand was joined to Australia and Antarctica. New Zealand began to separate from Australia/Antarctica about 105 MYA (million years ago) and continued to do so until sea completely separated them about 80 MYA, with the gap increasing substantially over the next 20+ million years. Globally, mammals evolved about 205 to 210 MYA. Mammals have been in Australia right from beginning of mammal-dom (1), starting with monotremes (i.e. mammals like the platypus and echidna), followed by some long since extinct lineages that I’ve informally called Allotheria (and whānau). Marsupials and placentals (the predominant mammalian lineages today, especially the latter) didn’t arrive in Australia until much later, almost certainly well after New Zealand separated from Australia. Monotremes and Allotheria (and whānau), on the other hand, were definitely in Australia when New Zealand and Australia were still joined. There is every reason to believe that New Zealand took some of these sorts of mammals with it when it broke away. Indeed, it would be very odd if it didn’t.

This is precisely why I have written parts 1 and 2 of this series. I could have easily written this present article without the others (now he tells me!). But if what’s being said here is going to bust a myth, then I’ve got some explaining to do about why busting the myth makes sense. I need to explain why it shouldn’t be a surprise that the myth is indeed a myth, i.e. it isn’t true.

I repeat. New Zealand did indeed have mammals (other than bats) prior to the arrival of humans. The evidence for this is actually quite simple and concrete (rock, to be precise). It is some mammalian fossil bones from about 16 to 19 MYA that were reported in a scientific paper in 2006 (2) This isn’t some obscure paper by some second-rate amateurs, but a mainstream article by Trevor Worthy (and team), one of the most respected professional palaeontologists working in the New Zealand field today. It is a bonafide and convincing result. Mammalian fossils dating from about 16 to 19 MYA have been found in New Zealand.

So what was this mammal like? For a start, it was very small. It was only about mouse-size. However that’s where the comparison with mice ends. Mice are placentals. This “not-a-mouse” (3) probably belonged somewhere in the now extinct group of lineages I have called Allotheria (and whānau) (4). Where in that group, though, is anybody’s guess. “Not-a-mouse” appears to be from a unique mammalian lineage that nobody knew about before. Not only that, as far as is currently known, all Allotheria (and whānau) lineages elsewhere in the world died out millions of years before “not-a-mouse” was alive. In other words, this New Zealand mammal was probably an ancient relict—a mammal of a type that had long since become extinct elsewhere. That New Zealand had such an ancient relict shouldn’t be a surprise. After all, this is precisely what the tuatara is in the reptile world.

It should also not be a surprise that “not-a-mouse” was a member of Allotheria (and whānau), rather than a marsupial or placental. According to Trevor Worthy and team, the most likely explanation for the existence of “not-a-mouse” is that it belonged to a population of mammals that had been in New Zealand continuously since it separated from Australia. Marsupials and placentals wouldn’t have been in this population because they weren’t in Australia at the time of separation.

So what happened to the mammals that were in New Zealand after it separated from Australia up until the time of “not-a-mouse”? Well, clearly they became extinct. (5) The next question is why? Why did they become extinct? One common explanation for pre-human extinctions in New Zealand is loss of habitat. New Zealand sank after it broke away from Australia and a lot of land disappeared into the sea. However the low point of this sinking was about 22 to 25 MYA. (6) “Not-a-mouse” comes from 16 to 19 MYA, so mammals clearly survived past this low point. Instead, the extinction of mammals in New Zealand was probably caused by global climate change. This isn’t the recent extremely rapid human-made global climate change, but a very much slower and more extensive change that occurred after 16 MYA (cooling in this case). (7)

Next question. Why has it taken so long for (non-bat) mammal fossils to appear in New Zealand? There is a fairly simple answer for this. New Zealand is very frustrating when it comes to fossils. While there are tons of very recent fossils (or pre-fossilised remains because they’re so recent) and tons of fossils of sea creatures, there are almost no older fossils of land animals at all. It is only relatively recently that a small patch with a decent selection of such fossils has been found, and then even more recently excavated and studied (with work still very much in progress—watch this space!). This patch is near St Bathans in Otago. “Not-a-mouse” was found here.

In summary then, New Zealand almost certainly had mammals when it broke away from Australia. In fact New Zealand has almost certainly had non-bat mammals for most of the time since then. The sole non-bat mammal that has been discovered so far was small and probably belonged to a lineage totally distinct from the modern successful mammalian lineages that rule the world today. Not only that, it survived in New Zealand long after any remotely similar mammals remained elsewhere in the world (like the tuatara in the reptile world). It became extinct sometime after about 16 MYA, probably because of global cooling. Mammalian fossils have only just been found because New Zealand has an extremely poor fossil record of land animals, apart from the very recent past. While these conclusions may well bust a New Zealand myth, there is nothing unexpected about the results from a rational point of view. They are completely in keeping with, and to be expected from wider global stories of geology and evolution.

One final musing before I let you go. If, as seems likely, “not-a-mouse” was descended from mammals that were in New Zealand when it broke away from Australia, then many of our New Zealand birds will have evolved in the presence of mammals e.g. moa, kiwi, New Zealand wrens (e.g. rifleman) and the New Zealand wattle birds (e.g. kōkako). (8) How does this fit into the argument—and indeed much practical observation—that New Zealand birds don’t cope well with mammals? In the first place, the ancient New Zealand birds would have initially evolved alongside the New Zealand mammals. They had plenty of time to get used to each other, unlike contemporary New Zealand birds and recent placental arrivals. In the second place, if global cooling is the culprit in causing the extinction of New Zealand’s non-bat mammals, then it’s most likely they became extinct several million years ago, rather than comparatively recently. This will have given New Zealand birds plenty of time to forget about mammals altogether. Thirdly, the sort of mammals that New Zealand birds don’t cope at all well with are killing machines like rats, stoats and cats, and to a lesser extent mammals like deer, possums and rabbits. These are all placentals. “Not-a-mouse” was totally different. It was survivor from the days when mammals were small and largely kept in check by pesky dinosaurs. Perhaps, like the tuatara, New Zealand mammals retained their ancient features and were never much of a threat to birds in the first place?

I started this series of articles on mammals with a statement that many of us guides say to our visitors when they arrive on Tiritiri Matangi in order to explain the unique flora and fauna they’re about to see: “New Zealand broke away from the rest of the world about 60 MYA before mammals evolved.” Having completely demolished that statement on three accounts, what should we say instead? How about, “New Zealand broke away from the rest of the world about 80 MYA before modern mammals like rats and stoats evolved with their ruthless efficiency at killing”? What do you think we should say? Suggestions on the back of a postcard please!

P.S. A video

If you want to see the fossils of “not-a-mouse”, the paper by Trevor Worthy and team has photos (which can’t be reproduced here for copyright reasons). Alternatively, check out this video from Te Papa (Museum of New Zealand): https://collections.tepapa.govt.nz/topic/2918. (Caution: you may be disappointed when you see the fossils—you have been warned!)

P.P.S. A word on bats

Bats, like birds, have wings, and so a watery ditch isn’t going to be as big an obstacle to cross as it is for other land mammals. So it’s not surprising New Zealand had bats prior to human arrival when it didn’t have any other placentals. New Zealand has two types of bats, long-tailed and short-tailed, represented by just two living species today. (9) The long-tailed bat is nothing special from an evolutionary point of view. It arrived in New Zealand about 2 MYA and has close relatives in Australia and surrounding islands (e.g. New Guinea and New Caledonia). The short-tailed bats are much more unique. In Part 2 of this series on mammals I mentioned an Australian bat fossil from about 26 MYA. Lo and behold this bat was a relative of New Zealand’s short-tailed bats, so it seems likely that the New Zealand short-tailed bats came from Australia at some point. Any Australian relatives, though, are long since extinct. The closest living relative of New Zealand’s short-tailed bats today are in South America, but it’s a very distant connection indeed. This would make sense, given that the Australian bats are thought to have originated in South America.