The Role of Humans in Late Pleistocene Megafaunal Extinction, with Particular Reference to Northern Eurasia and North America
A.J. Stuart, Norfolk Museum Services/Castle Museum
As we've been hearing, you've got a major extinction of large mammals -- that's
megafauna, according to your definition of greater than 40 kilograms,
or taking strictly megafauna in the sense of over a metric ton.
You've got major extinction in North America, South America.
Quite minor extinction in Africa and southern Asia, not shown
here -- where, of course, the largest megaherbivores of the Pleistocene
still survive. And then in northern Eurasia, which is something
I'm going to concentrate on, where you still lose a lot of these
large mammals. And I didn't mention, Australia, of course, where
you also have major loss of large mammals.
Now, as we keep hearing, of course, the two contending hypotheses
for causes of extinction -- firstly, there's overkill, human predation,
shown by yet another dramatic reconstruction here. And, of course,
Paul Martin is the great advocate of this view, and pointing out
that (or interpreting the record as that) extinctions follow
the spread of humans around the world. The problem with the overkill
idea in itself is that it doesn't explain the extinction in northern
Eurasia very well, which is something I'm going to consider in
detail in a minute.
Now, if we turn to the climate environmental change hypothesis, extinction
by environmental change can only be a viable hypothesis if you
can show that the Holocene was unique in the Pleistocene. Or,
more particularly, that the transition between the last cold stage
of the Pleistocene and the Holocene was unlike any of the previous
cold/warm transitions in the Pleistocene. Because you do not
-- as the last speaker was showing -- you do not get major extinctions
coinciding with any of these earlier phases.
Now, if we look at the deep ocean and oxygen isotope proxy record
here (here's the present-day) and the warm -- or high sea levels,
or low global ice -- coincide with these peaks. You can see that
there are number of sharp rises in the well temperatures at these
points. This is the Last Interglacial stage 5e, with a steep
rise here, and looking very much like that at the beginning of
the Holocene. I'll show you some more examples of this. Sorry,
this isn't a very good slide. This shows a deep pollen core from a lake deposit -- in this case in Greece. And what this shows,
if you could see it properly, is that well back into the Pleistocene -- back to 400,000 years or so up to the
present -- at this site you have alternations of forest and open
conditions, forest, open conditions recurring right through this
time, of which the Holocene forested phase is simply the last
If you can compare pollen diagrams from Europe -- this is from the
Last Interglacial site, showing the succession of tree species through
the Last Interglacial stage 5e, around 120,000 years ago
-- you get this succession of vegetational change. You see this
in a whole number of previous interglacials, as well. And then,
when you go on to the Holocene, you get fundamentally the same
pattern -- except, of course, that the Holocene is, as it were,
an unfinished interglacial stage. So the various interglacials certainly
differ in detail, but fundamentally, a number of these
stages were of the same nature.
And in detail -- this is a detailed comparison of some of the
deep-sea cores, oxygen isotope, and carbon changes here.
If you compare this one, which is for the Holocene -- that's
present-day there -- here's the transition from the last cold
stage, a steep rise. This diagram is actually showing a comparison
of a cooling event here, which we're not so interested in. If
you compare that with this curve, which is for the Last Interglacial,
you see there's a similar, very similar, pattern in time and in
amplitude of the changes that are going on here. So this is a
transition from the penultimate cold stage to the Last Interglacial,
from the last cold stage, into the Holocene. And very much the
same thing that you're seeing.
This is a reconstruction by Tzedakis and Van Andel for the Last
Interglacial in Europe, and, again, it shows the same things and illustrates
the point I'm making, perhaps at some length here, that you've
got interglacials that are essentially similar to the Holocene.
Not exactly. The Last Interglacial was actually warmer, the
sea levels were higher -- so Scandinavia is actually cut off here.
Britain was an island then, which it wasn't through most of the
Pleistocene, but is, of course, in the Holocene. You've got temperate
forests through much of Europe; Mediterranean vegetation in the
south, much as today -- boreal forest and tundra in the north.
Now, it's time we saw some animals. If we go on, this is a reconstruction
for the Last Interglacial. This is from a book by Tony
Sutcliffe of the Natural History Museum, and it shows the kind
of animals that were around in western Europe. This is Britain.
And here you've got -- this is Last Interglacial, about 120,000
years ago, and some of the spectacular animals that were running
around. We have the straight-tusked elephant, hippopotamus.
There's an interglacial rhino here. There are actually two species
in Europe; only one made it to Britain, because Britain was
cut off as an island. You've got spotted hyenas, lions, and things
like red deer, and lots of the smaller fauna
which, as usual, aren't well-illustrated.
Oh, I should have said that these interglacial faunas
are, essentially, like the vegetation, similar to one another as you go through time. There are changes,
there's evolution, there's some immigration. There's a small
degree of extinction which comes in. But, essentially, each
interglacial fauna is similar to the one before. However, when
you come onto the Holocene -- this is a reconstruction of the
Holocene fauna -- you've still got quite rich fauna around. But,
strikingly, there are no elephants anymore, there are no rhinos,
there are no giant deer, there are no hyenas, and so on. And
so there's been a dramatic change. But, otherwise, other than
stripping away the megafauna, you've still got much the same sorts
of animals around.
So what I want to do is to focus on northern Eurasia, which I
am taking as Europe, plus Siberia, essentially. I'm mainly, in
fact, concerned with Europe, where we've got the best data. This
gives an idea of the range of animals, since it's mostly animals
that became extinct in Europe during the Late Pleistocene. And
I want to make the point, first of all, that the extinction of
large mammals in Europe -- that's large megafauna in the sense
of over 40 kilograms or over 1,000 kilograms, however you want
to take it -- was really significant. It was a real phenomenon.
There is rather a tendency in some quarters to kind of dismiss
Europe, as if extinction didn't really quite happen in Europe
-- but it did. And what's really striking -- if you
look at the megafauna in the sense of over 1,000 kilos -- then all
six species, all six species of over 1,000 kilos, over one metric
ton, became extinct. This is a very significant change. If you
look at the fauna, megafauna, in the wider sense, over 40 kilos,
then you've lost about 30% of the species over 40 kilos in Europe.
I was hoping, for this presentation, to do a detailed
comparison of faunal change through the Pleistocene with that
of the end-Pleistocene, to see any changes in rate there may have
been. We haven't quite got to the point where the stratigraphy,
which is in a state of flux at the moment, has been worked out
in fine enough detail, I think, to convincingly do this. But
taking it crudely, if you eliminate species that are evolving
one into another, and only consider extinctions that occur without
replacement by producing another species, then if you take the
Middle and Upper Pleistocene, from approximately 780,000 years ago,
up to the Late Pleistocene -- so let's say it's 700,000 years
-- only around five species of megafauna that are over 40 kilos
become extinct in that time. And that's probably rather a
generous estimate. If you take the next 40,000 years of the Late
Pleistocene, we actually lose eight in that 40,000 years. So
there's an enormous change, even in that crude comparison,
in the rate of extinction. So it's a very real effect that we're
looking at here.
And this is perhaps stating the obvious, but if you go around
Europe as you would in North America or many other parts of the
world, finds of large mammals are relatively common. I mean,
you look back in the past -- these are not strange prehistoric
monsters that don't really belong to our world at all. These
animals roamed around. They really were -- they really existed
in the relatively recent past. And the fauna of Europe today,
as, indeed, in most parts of the world, is zoologically impoverished.
It is peculiar. Changes have occurred, profound changes have
occurred to the fauna. And then, of course, the knock-on effects
onto the vegetation, and in turn, the smaller members of the
fauna following from this. So this is a really profound change
that's taken place. . . .
I want to go on to talk about cold-stage faunas
in Europe. You can distinguish quite clearly a cold stage in
interglacial groups. The cold-stage faunas -- as you might expect,
the climate is changing in very complex ways, as shown from the
deep-ocean sequences from the Greenland ice cores, from pollen
records, and so on. So I'm just making a fairly crude generalization
here. But you're looking -- here, this is, again, a reconstruction
from Britain of the last cold-stage fauna -- and this is a non-analogue
fauna in that you have mixtures of animals which do not live
together today. Here -- I'll just point out some of the animals
here. There's the extinct things like woolly rhinoceros; woolly
mammoth; there's spotted hyenas, which, again, are quite happy
in interglacial and cold-stage conditions; lions here, likewise;
there are reindeer; red deer; horses; bison could have been shown
-- and all sorts of the smaller creatures, as well.
Now, there's a reasonable body of data about the extinction of the latest survivals of some
of these animals into the Late Pleistocene. There's a fair amount
of radiocarbon information. There's a great deal more stratigraphic
information, where faunas are associated with the archeological
record -- say, for example, from France, where there's a very
good archeological control, which is, in turn, dated. There's
lots of stratigraphic information -- pollen, and so on -- which
all backs up the radiocarbon data. So we're not just relying
on radiocarbon data for this information.
Having said that, the best radiocarbon dates are really for the
giant deer -- the strange animal often called the Irish elk, most
incorrectly; giant deer is the better name, Megaloceros -- and
for woolly mammoth, that we'll look at in a minute. Now, the
giant deer -- this was a compilation of dates that I did a little
while ago. There are one or two to add to this now, but they
don't affect the general picture. And you can see here that,
like the North American mammals, the giant deer goes way up into
the -- these are noncalibrated dates; this is radiocarbon years
ago, so I'll put the boundary there at 10,000 years ago. And
the last giant deer go to about 10.5 thousand years ago.
Now, the woolly mammoth has rather more dates. Again, there's
not been much data accumulated since I did this for Europe. And
here, for western Europe, the radiocarbon dates and the stratigraphic
information agree very much -- the mammoth in Europe becomes
extinct by 12,000 radiocarbon years ago. So it doesn't go up
into the last part of the last cold stage, like the giant deer
does. And faunas from this period contain things -- say, from
Britain -- contain lemmings, arctic fox, reindeer, and so on.
So there's still a good cold fauna here, but the mammoth is gone.
A series of detailed vegetational reconstructions for the end
of the last cold stage, from about -- well, in fact, they go into
the Holocene, but I haven't shown them all here -- from about
13,000 radiocarbon years ago. This was work done by Huntley and
Birks a few years ago, and here I've just colored it in to show
the dark green here is forest, mainly conifer forest, boreal
forest. This is 13,000 years ago, and there were large areas
here, shown in yellow, which are steppe tundra vegetation, prairie-type
vegetation -- open, largely treeless. These are the ice sheets
shown here. Thirteen thousand years ago, large areas here --
but there's this great wedge of forest in the east. As you go
through time, the forest moves in and eventually more or less
-- in fact, by 9,000 years ago has eliminated all of the steppe
tundra vegetation. Mammoths are becoming extinct 12,000 years ago, but
there are still extensive areas of open vegetation here. . . . In Siberia -- this is an old diagram
-- we've now got dates going -- or the Russians, rather -- have
got dates going up to 10,000 years ago -- and, of course, the
Wrangel Island data to later than 4,000 years ago. . . .
This is the crucial diagram.
If we take the -- this is the summary pattern. This
is much the same as Paul Martin showed in the first talk. This
is the boundary between the Holocene last cold stage, there's
the Last Interglacial. And in Europe you get two groups of fauna.
You get the interglacial faunas, which retreat into the south
of Europe with the onset of the cold stage, and then become extinct
-- but they become extinct rather raggedly.
The second group, these cold-adapted animals, go through into
the last part of the cold stage, and then become extinct up here.
So you've actually got two phases of extinction. Now, neither
of these coincide -- these are Neanderthals here being replaced
by modern humans. There's no obvious coincidence between the
arrival of humans or climatic change alone and these extinctions.
You have to get the two in combination. Here, these interglacial
animals that retreated into the south of Europe -- they should
have expanded their ranges again into the Holocene, but become
extinct. Humans arrive. There's a climatic change here, so there's
a double effect here. Again, as you come through to the last
part of the cold stage, here there's a fundamental change in the
climate, reorganization of vegetation, and the combination, in
my mind, of the climatic change and the presence of humans --
of advanced Paleolithic humans -- causes this wave of extinction.
profound difference between the North American data and that of
Europe, which summarize, you can say, that the extinctions in
northern Eurasia, in Europe, are moderate and staggered, and in
North America severe and sudden. And I think these things relate
to the differences in the timing of human arrival. So what I'm
saying is, the extinctions follow from human predation, but only
at times of fundamental changes in the environment.