Late Pleistocene Extinctions

Greetings,

Some time ago, there was a long discussion here about the nature and reasons of the Late Ice Age extinctions of large mammals. I did not follow the whole thread, since it soon reached a dead point. But I have my own ideas about it, and I would like to share them with you. Some of you have argued that the Ice Age mammals were victims of a rapid climatic change, while others blamed it to human impact (also known as the overkill hypothesis). Personally, I would follow the second hypothesis, especially in the light of Miller's recent work in Australia:

Pleistocene Extinction of Genyornis newtoni: Human Impact on Australian Megafauna Science, January 8, 1999.

There he showed very convincingly that a continent-wide extinction occurred simultaneously with human activities (bush firing in this case), while the climatic change during this time was rather modest.

As for the American extinctions, the case is different, since human impact and climatic fluctuations happened simultaneously, making it difficult to resolve the true reasons.

But one can approach the problem from a different direction by looking at the last 2 million years of Ice Age. The Ice Age consisted of several glacial episodes (17 as far as I know), separated by brief, warm interglacials, like the one we now live in. As far as I figured out, the last glacial/interglacial transition was short and violent, in geological terms. We know that climate zones moved for hundreds of miles within a few centuries, accompanied by glacial superfloods which sometimes released more water than all the rivers on Earth combined. It is thus a reasonable assumption that many large mammals were unable to sustain their populations during such violent times.

Looking back in time we find a whole series of other glacial/interglacial trasitions since the Ice Age began, which should have been of equal dimensions, although their documentation is much poorer, of course. But obviously, the extinction rate was much lower than, if it happened at all, or either the Americas would have run out of mammals very early in the Pleistocene. So I think that the climatic argument for Megafauna extinction is seriously flawed, and it is more likely that human impact was responsible.

We could resolve the problem if we knew more about the other transitions, if they were any different or comparable to the last one.

So I leave this question open to discussion. If you consider the points above, is there still anyone favouring a climatic trigger for the megafauna extinction? And if the answer is 'yes', how do you defend it?

Best Regards Christoph Kulmann

************************* Ein Herz für Vögel http://www.terrorvogel.de *************************

[good presentation - snipped]

So I leave this question open to discussion. If you consider the points above, is there still anyone favouring a climatic trigger for the megafauna extinction? And if the answer is 'yes', how do you defend it?

I'd think climate could have been a factor at least, but as you say it wasn't necessarily a unique occurance (but data on previous interglacials could be better). My guess would be that the combination of human activities, either directly by hunting or indirectly by modifying ecosystems along with the climate effects made it more stressful on the whole system. There may be no one cause. The meteorite may not have been the sole cause of the dinosaurs' demise either, but it was part of the story. Can't pin it on humans, at least.

In Australia, the ecosystem was probably close enough to the edge that the burning introduced by the first Aborigines was all that was needed to cause desertification in the outback. The lack of forests seems to have caused the rains to fail in ways they didn't in previous glacials or interglacials, as Miller points out. Something of that nature could have happened elsewhere, as in the Great Plains of North America, but with greater rainfall (the Gulf of Mexico continues to provide moisture) the result might have been more an eastward expansion of the grasslands than desertification, which by itself may not have been enough to push grazers over the brink of extinction. There has been no documentation of any such effect that I'm aware of, however. Add interglacial warming and human predation (which seems to have been particularly heavy in the Clovis period) and you have a combination of stressors that might do the job. Something did, and that's certain, but was it one, two or three causes? I'm not sure. Just the interglacial warming by itself should just cause herds to migrate unless there was something really odd about the last one. It might be hard on them, but at least some should make it. I'm aware of Cal King's heat stress hypothesis, but what's the evidence that previous interglacials were less abrupt?

In Eurasia, something similar might have happened, but I'm less certain of the timing. In Africa, nothing much seems to have occurred other than the formation of the Sahara. The megafauna aren't doing too well there at the moment though, but we know who's responsible in that case.

However, there was a medium megafuana extinction event in which most species of elephant and hippo and all tigers died out, as well as shivatheres and several other large beasties. This was about fifty thousand years ago.

If you take the lattitude of Antioch as a line, you will notice that everything above it the elephants died out completely, and below it, they survived.

There were elephants in Syria and Israel until 3000 BP[1000 BC]. Lions in Greece and Anatolia until about the same time[further east, Asian lions thrived until this century].

Why Asian Elephants in africa and mammoths in Europe and north asia died out while they didn't in India and SE Asia is a mystery.

eric l.

That's interesting. Do you have any sources for it?

On 29 Aug 1999, ELurio wrote:

Most books on the subject will mention something about West Asian elephants.

Elephas riccii is mentioned several places. African tigers were mentioned in an old book on African wildlife by Louis Leakey.

Shivatheres are mentioned in many books on the subject of mammal

to the original thread, I was thinking that this zone of habitation might explain why there was a 'line' which divided certain animals from extinction, depending upon whether they were above or below that line.

Seems logical, at any rate.