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

Real Audio Recording   

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 one.

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.

There's a 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.