Emerging Patterns in Australasian Quaternary Extinctions
Tim F. Flannery, Australian Museum
I must admit I got a bit of a surprise when I saw the preliminary
program for today's schedule. My paper was listed in a session
which was called "Catastrophes in Small Places." Well,
Australia isn't actually that small, and I decided at that moment
maybe I'd better give you people a bit of an outline of the nature
of the continent, before I launch into the megafaunal extinctions,
which have been particularly dramatic there.
Well, this is the place. This is Australia. It's not that small
-- 7.6 million square kilometers; approximately the same size
as the contiguous 48 states of the U.S.A. At times of lowered
sea level, at glacial maxima, that would have expanded to about
10 million square kilometers. And you could have walked from the
northern part of New Guinea right down to Tasmania, uninterrupted
by any saltwater. It's a very large piece of land.
It's the smallest of the continents, and probably the strangest.
It's certainly had a unique history. It's the only continent
with completely passive continental margins. There's no active
mountain-building going on anywhere around the edge of the continent,
New Guinea excepted, which is a separate island. The main mountain
range on the continent runs along the east coast, and it's a very
old range. It developed as New Zealand rifted away from Australia
-- and we're all very glad it did; but, anyway, it did. Unfortunately,
it took the volcanoes and the good soil with it, leaving us with
a very low mountain range, and a rather infertile one. It's eroded
very little throughout the Tertiary. Dating of basalts along
the range suggest that the major river systems have only cut down
a few tens of meters in many places over tens of millions of years
-- so produced very little in the way of soil.
It's also a very ancient land mass. This is a geological map
of Australia, which you don't really need to take any notice of
at all -- except that this western area here is the Archean plate.
It's pre-Cambrian or older -- very, very ancient rock -- and
basically very little-changed throughout the Cenozoic, in any
The ice age had a rather odd effect in Australia. It was very
different from North America, where the Laurentide ice sheet formed.
Our biggest glacier on mainland Australia at the height of the
glacial maximum was down here. It was about 50 square kilometers
in extent. It didn't produce any soils that anyone's using today,
anyway. Very different from 13 million square kilometers of Laurentide
ice sheet across the north of this continent.
What did happen in Australia, though, was that the center of the
continent dried out, and a huge anticyclonic system of sand dunes
became active throughout the central 40% of the continent, which
was basically a vegetationless, howling dry June field. And,
again, the New Zealanders won out, because the winds blow that
way; and whatever soil we had there, a lot of it ended up on their
glaciers, painting their glaciers red, or in the Tasman Sea.
So it wasn't a good time to be in Australia, during the last
The one area where we do have reasonable soils is a little archipelago
of volcanoes running down the east side -- very, very small in
extent, most of them. And they range in age from, I'd say, about
50 million years through to the last few tens of thousands of
years. And they have produced an island archipelago of reasonable
soils. The rest of Australian soils are very ancient and highly
structured, highly weathered. I suppose they're characterized
by having very low levels of soil nutrients, like nitrates and
phosphates -- generally about half the level, at best, of equivalent
soils overseas. And some recent studies, particularly on phosphates,
suggest that Australian soils from this area have about a tenth
the level of soil phosphates as equivalent soils in eastern South
Africa. And this had very dramatic effects in structuring Australian
ecosystems. The soils also have high surface temperature, very
poor water-retention ability. They're deficient in trace elements.
They're characteristically very thin. Basically, they're pretty
awful -- especially for a plant trying to grow in them.
This is just an example of an Australian landscape -- a pretty
typical western one. This is Mt. Narriyer, in the middle of Western
Australia. The oldest rocks on planet earth have been discovered
on this mountain -- some zircons that are 3.9 billion years old.
These are very, very ancient, unchanging landscapes. It looks
like that for about two weeks of the year -- the daisies and greenery.
The rest of the time it's just pretty bare.
Now, these particular soil conditions, which are so widespread in Australia,
have led to the development of rather odd plant communities. Australia
is really the home of scleromorphy -- these plants which are generally
pygmies. As you can see here, very small -- small, spiny leaves; small
internode distances, typically very heavily defended with tannins and
phenolics. So nothing eats them -- with the exception of members of the
pea family and a couple of others; have very decorporate communities even
of folivorous insects, much less mammals. But they're extremely diverse.
This is from the southwest of Western Australia. They have tremendous
diversity. It's high, in fact, in terms of absolute species. This is the Australian
rainforest, or the southeastern Asian rainforest, pretty much. And they're
very attractive in spring, covered in flowers -- basically, because there's
a lot of competition, I think, for pollinators.
Now, these infertile soils -- they may actually have contributed
to any coherence that's in my speech today -- because they also
grow excellent wines. And we drank several bottles of it last
night, and didn't get to bed till very late. So they have many,
many effects. Anyway. . . . Here's some more plants from what's
called "Kwongan ecosystems" in the southwest of Western
Australia. As I said, tremendous diversity and very spectacular
plants, but they just lack mammalian herbivores. Well, they're
opportunistic, coming in after fire. And here is some more marginal
Curiously enough, where there's not enough rain to sustain these quongan
faunas -- you get these ephemeral daisy fields. And these are, in fact,
even much more productive, even though they're only operating for a few
weeks of the year. These actually support kangaroos and things, whereas
the heath-plants really don't.
Layered on top of these rather peculiar soils that we have
in Australia is a very strange climatic pattern called the southern
oscillation. And you people here, you really do have genuine seasons;
and productivity here seems to me to be dictated by the seasons
pretty much. We seem to have seasons in Australia -- it gets
colder in winter and warmer in summer -- but that doesn't dictate
productivity. What dictates productivity in particularly eastern
Australia is rainfall, which is brought with the southern oscillation.
This is a basic diagram of the southern oscillation and how it
works. Every two to eight years, this cycle alters, and during
an El Niño year, we get cold water building up off the
coast of Australia, and that brings drought. And you can see
here, this brown area shows just how much of Australia was affected
in the 1982-1983 El Niño event. About two-thirds of the
continent, the eastern two-thirds, is profoundly affected by the
southern oscillation -- and if you'll look at the other continents,
you see that, on a percentage basis, there's nowhere else that's
as profoundly affected by this as Australia.
The typical patterns is that you'll have droughts, such as illustrated
here, which can be several years in duration. And then the warm
water floods back across the Pacific, flows back this way, and
you'll then have the droughts broken by very spectacular floods.
And then, if you're lucky, a year or two later, you'll get the
kind of average year -- the statistically average year -- which
is when your kind of Australian cow cropper makes a bit of money
and thinks the good times have come back. But, sooner or later
-- whether it be two years or eight years -- the cycle starts
again. So very irregular productivity -- it's not seasonal.
And, of course, that explains why our indigenous people never
had agriculture -- or, at least, did away with what agriculture
they had. There's simply no point storing food if you don't know
whether you're storing it for six months or 10 years. We don't
have any hibernating mammal for the same reason, or very, very
few. Some of our species in the east respond to food shortage,
but not really true hibernation. And there's a number of other
things which are affected by this. We have very few deciduous
plants, for example, for the same reason: Why throw away your
leaf when you don't know when you're going to want it back again?
Very strange systems.
And this is just to show you roughly the periodicity of major
rains caused by the southern oscillation. You can see here, running
from 1870 to 1970, about a century's worth of record for central
Australia. And through that time we've had four major episodes
of high rainfall -- followed by fire, followed by rabbit plagues,
and also, if we're lucky, successful recruitment into some of
the plant populations.
So that is the nature of the continent -- very, very different
from North America. It did have a megafauna, but quite a peculiar
one. At some stage in the Late Pleistocene, the exact timing
of which I'll return to later, Australia lost everything that
lived on the continent which was larger than a human; and there
was quite a large fauna on the continent prior to that. We lost
in all about 55 species. The majority of those lost were large
marsupials, but there were also some very spectacular large reptiles,
some large flightless birds, and even some smaller flightless
birds -- all lost at the same time.
Now, it really is a rather odd assemblage, and I'll just show
you some species -- or reconstructions. . . . Ah -- before I do
that -- I knew there was something else I had to do
-- talk about New Guinea, Australia's neighbor island, because
it is the mirror through which you can understand a little bit
more about Australian ecosystems.
New Guinea is a about one-ninth the size of Australia, and it has
a mammal fauna of about the same magnitude as Australia's -- about
the same number of species. But New Guinea is very different.
It's a mountainous island; it's covered in rainforest; some
areas get up to 11 meters of rain a year. It's affected by the southern
oscillation, but not really so much through rainfall as through
frosts -- recurrent frosts which occur during cloudless times
of the year -- which are tied in with the El Niño part
of the cycle.
Here's a representation of the mammal fauna -- the non-volant mammal
fauna of New Guinea. Don't worry about the shapes, particularly,
but the black blobs at the top are the things that became extinct,
the megafauna that became extinct in New Guinea. As you can see,
none of them are very big -- the biggest was probably 300 or 400
kilograms in weight. And out of a fauna of over 220 species,
New Guinea lost just six species. And we're now building up a
good fossil record for the island; and this is becoming evident,
that the megafauna just wasn't much more diverse than that. So
I'd say that once you leave Afro-Eurasia, this would have to be
the smallest level of impact of megafaunal extinction seen anywhere
on the planet.
The six species that were lost occurred in all environments in
-- well, they ranged from the alpine tundra, which surrounds the
glaciers in the highest parts of New Guinea. We've found fossils
from periglacial deposits with megafauna in them. We've found
fossils of other species in the mid-montane, and yet other species
in the lowland jungle. So here it didn't matter where you lived
in New Guinea -- what really mattered was just how big you are.
And you can see here that these things are all ordered according
to size, and there's a distinct cutoff there. Anything that weighed
more than about 10 kilograms went. If you were smaller, it didn't
matter where you lived. You survived.
And I should say that there's no conceivable kind of a climatic
event which could have altered significantly, or could have brought
drought to New Guinea as we know it. The bryophytes and everything
else have survived there; the small mammals have survived. There
are many things which are much more water-sensitive than large
mammals, so something else, I think, is going on in New Guinea.
I just wanted to show you something to convince you that marsupials
really are cute. This is one of the largest things that survived
in New Guinea. It's a tree-kangaroo, but it's a species which
has come out of the trees and now lives on the ground. It lives
above the tree line in New Guinea, in some of the very coldest
parts of the country, and it was only discovered about three years
ago. So there's still lots to be done, even as far as the modern
mammal fauna of New Guinea goes. That's the same beast. Very
cute, very tame.
Now here is the equivalent picture for the Australian megafauna.
The black dots, again, are those which went sometime in the Pleistocene.
And you can see there, there's many, many more species lost
than in New Guinea. Most of these are herbivores -- most of the
species you're looking at here. Most of them are browsers, curiously;
most of the lost species are browsers. There's very, very few
grazers, or clearly identified grazing mammals which were lost
during the Australian Pleistocene event. It's rather odd and
quite different to the other continents in that regard.
You can see the smaller species that were lost were about 10 kilograms
in weight; the largest, perhaps a couple of tons. And to understand the
Australian fauna, in general, it's good to keep in mind a thing that I
call a "third rule," and that is really that if it's an Australian
marsupial you're looking at, it's probably only going to be about a third
the body mass of its ecological vicar elsewhere. So our big marsupials
-- our elephant equivalents -- weighed one or two tons, compared with
five tons or more for elephants . . . (tape ends) . . . You see this repeatedly.
Our equivalent of hyenas, the Tasmanian devil, you could safely sit one
on top of this lectern -- as long as you weren't bitten -- whereas a hyena,
of course, is a much, much bigger animal. So that general rule seems to
apply. And, again, think this is due to low nutrient levels in Australian
ecosystems, as much as anything else.
Among the non-mammalian species lost were some large birds. This is one
of them, a bird called Genyornis -- a large herbivorous bird.
Seemed to be very widespread before its extinction. This is
Diprotodon, our largest marsupial. People, even in Australia,
don't understand marsupials very well. This model is fleeing
from a very large goanna, that I'll speak about in a second -- and
the preparators at the museum were very upset at putting this
on, because they said it looked like it was having a spontaneous
abortion from terror, from running away -- not realizing it's
a marsupial, it has a pouch, and the pouches point backwards on
these things. But, anyway . . . rather strange reactions. So these
animals are a ton or two in weight and was probably semi-arid adapted
-- it's probably living in the drier parts of the country.
A large browsing wallaby, of which there are a dozen or so species
in Australia and New Guinea -- next to a person, so you can see
the size of these things. Again, these are browsers. We actually
have stomach contents of some of these species that show very
coarse browse, preserved. This is an example here of some stomach
contents from an Early Pleistocene browser -- and you can see there's
skin impressions even preserved, and that there is some quite
nice Pleistocene fossils from Australia. But these remain unstudied,
though discovered 15 or 20 years ago; and, as yet, no one has
actually looked at those stomach contents, beyond the kind of
very coarse microscopic identification of them as browse.
Short-faced kangaroos -- at least 20 species, all browsers. A
very complex and rapid radiation of rather bizarre-looking kangaroos,
every one of which is now extinct. And onto the carnivores, which
are very peculiar in Australia. This is kind of a wombat-turned
carnivore, if you want -- a rather strange thing called the marsupial
lion. It's from herbivorous ancestry. It was our only catlike
predator in the Pleistocene. And it's rather curious that we
have one catlike predator, one doglike predator -- the Tasmanian
tiger; one scavenger, which is the Tasmanian devil -- and
one or two weasellike things. Whereas these guilds overseas,
or niches overseas, are filled by a large variety of species.
The catlike niche, for example -- you may have five, six or seven
species on a continent; the doglike niche likewise, that are divided
according to size and to habitat preferences. In Australia we
just have one kind of each. And this was the largest homeothermid carnivore ever to have existed
in Australia. It probably weighed about 40 kilograms -- so humans
are, in effect, the largest warm-blooded predator ever to have
existed in Australia ecosystems.
What we did have though, at the top of the food pyramid, was some things that look a bit like they're out of "Jurassic Park." This is a skeleton of a seven-meter-long goanna, which would have weighed several tons. So this was our top-order predator. And probably not since the days of tyrannosaurus was anything quite so horrible seen on any landscape anywhere.
But it was only one of a number of reptilian species which dominated
the large-carnivore niche. We also had terrestrial crocodiles,
which would have weighed several hundred kilograms and been three
or four meters long. We had some now-extinct freshwater crocodiles.
We had a whole subfamily of gigantic snakes, which lived at quite
high latitude -- which would have been six or seven meters long
and as thick around as me, perhaps -- very large. So the reptiles
were what were dominating the carnivore niche in Australia --
again, I think, a reflection of just low levels of nutrient availability
and therefore productivity. You're much better off being a cold-blooded
carnivore in Australia, because you can survive from one El Niño
cycle to the next, and you don't need to eat all that much, anyway.
Now, that's just to give you an idea of the size of this goanna
. . . a rather horrible creature. Okay, let me just stop
So when did all of this fauna become extinct? I guess this is
the great question. And if you'd asked me that some five years
ago, I would have said: Oh, it all survived until about 25,000
years ago. We had some sites which we, as a scientific community
in Australia, believe genuinely reflected the survival of this
megafauna to 25,000 years ago. At that same time, we had very
good evidence of people in Australia at least for 35,000 years.
It's now looking like it may be 50,000 to 60,000 years -- but then
at least 35,000 years. And in support of that we had cave deposits
from the far southwest of the continent -- from Tasmania, from
the southeast -- with tens of radiocarbon dates all stacked up
and conforming with each other, which reflected a human presence
at least that deep. We had a couple of open sites with what we
thought was megafauna at 25,000.
In the last couple of years, though, things have changed dramatically.
Those sites that we thought reflected late survival of megafauna
have all been reexamined. And we can now say that if you apply
the criteria of Meltzer and Mead, say, in terms of analyzing dates
on megafauna in Australia, we don't have a single instance of
a dated megafauna in Australia -- dated with 14C or any Late
Pleistocene dating. The guess is now that these things all became
extinct before about 40,000 years ago in Australia -- certainly
in New Guinea. We have five sites there where we have articulated
or associated megafaunal remains, all of them which are dated
-- all five are dated. They date to beyond 38,000 -- and
that date's probably just a residual radiocarbon
date. These sites may be older than that.
So what we have in Australasia, I think, is a very early invasion
by humans. Certainly it happened by 35,000 years ago -- possibly
by 60,000 -- and very early extinction of everything bigger than
a human in these Australian ecosystems. We have no evidence of
any late survivals, it seemed. Oh, the other thing I should say
is, we have no kill sites -- we have nowhere where people and
megafauna can be demonstrated to be coexisting. In fact, I mean, really, there are not -- what should I say?
There's a few potential sites where this kind of evidence may
turn up. One has been discovered recently in New South Wales,
which may have evidence of overlap between humans and megafauna
-- but the lack of this evidence actually isn't all that surprising.
Because if you consider that these extinctions happened before
the Last Glacial maximum -- and in Australia the glacial maximum
brought such dramatic reorganization of landscapes. There's a
lot of reworking; a lot of sites were simply eroded away. Just
to consider how rapidly this data can be lost, you consider the
case of New Zealand, where moa became extinct only perhaps 500 or
600 years ago. There the major moa-hunting sites, which were
found in the 1850s -- many of them have lost up to 50% of their
surface area just because they're at river mouths, and there's
a lot of reworking of sediments gone on. So you've lost half
there over a century. We're looking back at Australia perhaps
40,000 years, with a major glacial event in the middle of it.
You don't expect to find a lot of evidence under those conditions.