New Zealand's First Land Mammal Discovered

Bob Beale writes to clue us to big news from New Zealand. The country has long been thought to have been devoid of land mammals until recent times. No mammal fossils had ever been found there; but now one has. From the article: "Small but remarkable fossils found in New Zealand will prompt a major rewrite of prehistory textbooks, showing for the first time that the so-called 'land of birds' was once home to mammals as well. The tiny fossilized bones — part of a jaw and hip — belonged to a unique, mouse-sized land animal unlike any other mammal known... The fact that even one land mammal had lived there, at least 16 million years ago, has put paid to the theory that New Zealand's rich bird fauna had evolved there because they had no competition from land mammals."

Comments

well

[jrwr00]

I think maybe that fossil was carried over when the birds where hunting off the island

I disagree

[joe 155]

"has put paid to the theory that New Zealand's rich bird fauna had evolved there because they had no competition from land mammals"

I don't really see how... one small mouse, even if there was 1 million of them, wouldn't really have made much difference to birds; it'd only be preditors that made a big difference

Rich bird fauna

[Anonymous Coward]

The fact that even one land mammal had lived there, at least 16 million years ago, has put paid to the theory that New Zealand's rich bird fauna had evolved there because they had no competition from land mammals.

Why? Seems easy to conclude that birds flourished and ate the rat things to extinction.

Well, It Certainly Impacts the Theory

[eldavojohn]

I don't really see how... one small mouse, even if there was 1 million of them, wouldn't really have made much difference to birds; it'd only be preditors that made a big difference

Well, I think the overall logic is that this ancient mouse and its affiliates would most likely have prospered in New Zealand and eventually evolved into something that fed on birds. In a lot of places, mammals have been more successful than birds. Now, there are a few like places Antarctica where birds are probably more successful than mammals but New Zealand and its surrounding islands (like the Dodo on Mauritius) were pretty special in this respect. So special, that (as I learned in Jared Diamond's "Guns, Germs & Steel") when humans arrived, many of the bird species had no fear of humans--only curiosity. They didn't have the thousands of years of living side by side with humans like elephants & zebras did in Africa to slowly train them to stay away at all costs. So its evident they never lived with predators but why were mice fossils found and not other mammals?

So now we need to explain that the mouse and other mammals were either restricted by food sources or eliminated. It also has to explain why there aren't more mammals. What is it about New Zealand? Did a volcano periodically remove all life from the island so that only birds could repopulate it at some point? Perhaps the only mammals that survived a food shortage were mice which were subsequently overhunted by the birds? These are the new questions that now must be answered.

So we're still left with this question of why these 1 million mice didn't evolve or why their bird eating relatives didn't thrive on the island. I heavily endorse and suggest Guns, Germs & Steel if you haven't had the time to read it. It asks questions about subjects like these that for a long time people just used the creation theories to explain. Now we're finally starting to look for answers as to why the way things are the way they are and why some populations of humans are better off or have more 'cargo' than others.

Re:Well, It Certainly Impacts the Theory

[jd]

The birds in New Zealand are curious creatures. From the extinct Moa and Haast Eagle (both absolute giants) to the Kea, Kakapo and Kiwi, the birds in New Zealand have no characteristics that indicate ground-based predators. Your car is far more likely to be ripped to shreds by a psychotic flightless parrot than it is to be damaged in an accident with another vehicle. Fear? Those creatures show no fear! (In fact, their total reckless abandon probably drove the poor mouse out of its mind - I think it went extinct from the cost of psychiatric treatment.)

Interesting. (Obligatory eyebrow raise.)

[M0b1u5]

Interesting.

The fact we have native mammals (bats) in NZ hasn't really been discussed yet. How does that fit in with the observation of a mouse-sized land mammal 16 million years ago?

I find it annoyingly hard to reconcile, as we know that "Life will find a way" - and historically, land mammals have been particularly agressive in their expansion into new habitats, even going back to the sea (Ambulocetus) and taking on the birds (Bats et al).

Someone suggested volcanic activity - but this only applies to the North Island and the top of the South Island. The Taupo "eruption" og 86AD was reported by the chinese and the romans at the time. More than 30 cubic kilometres of matter was ejected in as little as 7 minutes.

However, this is dwarfed by the explosion 20,000 years ago, where over 2,000 cubic kilometres were ejected, as the magma chamber below Lake Taupo collapsed. The ferocity of this event is simply too large to imagine, and the landscape of the North Island was almost totally covered in ignumbrite, a gassy, fast flowing lava, expanding our from the crater at close to the speed of sound, in a wall some 200-300 metres tall...

The resulting Rhyolite domes from previosu explosions were actually topped by the outflow.

However, even as close as 5 kilomtres from the vent, some plant and animal life survived, and as the trillions of litres of water held loosely by the ignumbrite ran swiftly back to the lake area, and the remains of the North Island forests burned in one of the greatest fires in pre-history, and the rock cracked and cooled under muddy rain, the animals, birds, and plants made their way back into the landscape.

So - no - Taupo couldn't wipe out the land mammals of New Zealand, and the South of the South Island is almost entirely devoid of volcanos: Dunedin and Lyttleton volcanos were small, and not very violent in terms of the entire island.

There is an alternative available. The "Pukeko" is a common bird in New Zealand, and they are very poor flyers - certainly not capable of flying from Australia, where they evolved (They are the Australian "Swamp Hen") and yet they florish in New Zealand. They have only been here for a few thousand years. The best theory is that they came across on flotsam ejected from rivers during large storm events in Australia.

If Pukeko cxan arrive that way, then small mammals might also survive to arrive in New Zealand, but the number who arrived might not have been sufficient to maintain a good breeding pool, so the species might go extinct due to the lack of genetic diversity.

This would explain the discovery, the lack of other land mammals and the lack of fossils: if there were bugger all who ever floated over, then we are spectacularly lucky to even have found these ones.

That's my story anyway.

Re:Interesting. (Obligatory eyebrow raise.)

[Anonymous Coward]

The authors don't think so though:
"It is theoretically possible that this SB mammal was natatorial and dispersed or rafted across the open ocean from Australia to NZ sometime after the Oligocene, subsequently going extinct in Australia, but three factors make this seem improbable. First, the preserved portion of the femur is rather conventionally shaped with little if anything to suggest that its owner would have been a good swimmer (and certainly nothing to suggest it was a good flyer). Second, despite discovery of many early Tertiary mammals from Murgon, southeastern Queensland (32), and highly diverse mammals from the Oligocene to Pliocene of central Australia and Riversleigh (33), nothing like the SB remains have been recovered from these richly fossiliferous Australian deposits. Third, NZ was #1,000 km distant from Australia, Antarctica, and South America by 65 Ma, further reducing the probability that a terrestrial group of mammals, otherwise unknown from any of the closest land masses, dispersed sometime in the Cenozoic to NZ."

Re: Birds hunting off-shore

[jd]

The Haast Eagle (the largest eagle that ever lived, the largest bird capable of flight and the largest an animal could physically get and still lift itself on wings) might well have had a range of 2,000 Km. If reports of giant eagles of similar size in other countries are to be believed, then it must have had the range as they certainly never evolved anywhere else.

Re:Bats

[Conanymous Award]

Bats do, of course, count as mammals, but we are speaking ground-dwelling mammals here. New Zealand supposedly never had those before the human invasion. No we know they had, once.

Still, I don't see this that hard a fact to reconcile with the traditional view of NZ as a Kingdom of Birds. The animal was still only a small critter. Sure, critters as small as rats are known to have exterminated ground-dwelling bird species from isolated island ecosystems. But NZ is much bigger than Hawaii, Mauritius, Galápagos and other famous examples of island extinction. This would mean its bird-dominated ecosystems and bird species would have been much more robust and resistant to a mammalian threat. Why, there were large, flightless predatory birds on the island continent of South Africa before the Great American Interchange. And how about the ostrich, emu & co.?

This new fossil mammal also appears to represent a very ancient lineage dating back to early Cretaceous mammals. We know for fact these critters were not necessarily some übermammal bird-pwners: after the KT extinction (the one that killed the dinosaurs, y'know), for a short while birds were among the top predators, and there were many other flightless birds, too, all over the world. This seems to indicate that early mammals were not the bird menace modern placental mammals like rats, pigs, and cats (and us) are. Nothing mysterious going on here, methinks. You simply cannot compare an advanced Neogene placental to a primitive Cretaceous type of proto-shrew in terms of predatory efficiency.

And how about this possibility: NZ only became a bird paradise after this critter and its relatives went the way of the dodo, for some reason or another?