Nothing kills a beautiful theory faster than an ugly fact, to paraphrase Thomas Huxley. But what happens when you have three competing theories and two new facts that point in opposite directions? Welcome to the increasingly confusing picture of what happened to the mammoths and mastodons of North America, along with the other dominant mammal species of the late Pleistocene.

Tony Flanders

For a number of years, scientists have been debating over two possible culprits that might explain the big die-off of megafauna. One is severe climate change, brought about by the onset of the Younger Dryas global-cooling event. Another is overhunting by a newly arrived human population in North America known as the Clovis culture. More recently, a third hypothesis claims that a comet impact or airburst over the Laurentide ice sheet triggered the changes that caused the animal population collapse (see my article in the September 2009 issue of Sky & Telescope.

All of these scenarios, or any combination of them, hinge on the fact that the big mammals died off rather abruptly starting around 12,900 years ago. This matches the onset of the climate change and comes right after Clovis appears on the scene. It also coincides with evidence that appears to support the comet hypothesis, including lots of tiny “nanodiamonds” that proponents say may have been generated in the impact and subsequent fires.

Until now, the debate has revolved around what happened. Now there are new questions about when it happened.

Early exit or long goodbye?

Barry Roal Carlesn, University of Wisconsin-Madison

In a new paper in the journal Science, Jacuelyn Gill and others suggest that megafauna were in decline well before the 12,900 date. Gill, a doctoral candidate at University of Wisconsin, looked for spores of the fungus Sporormiella, known to grow in the dung of large herbivores. Those spores start to disappear from sites in New York state and Indiana between 14,800 and 13,700 years ago, suggesting an early disappearance for the mastodon.

But wait. Another recent paper by Neal Woodman and others in Quaternary Research finds that a mastodon skeleton discovered in Indiana in 1976 (and now on display at the Cincinnati Museum of Natural History) was dated incorrectly. A new analysis by the Smithsonian researcher finds that the mastodon was alive about 10,055 years ago.

Granted, one mastodon doesn’t make an entire population. But it can’t have been the only one. This means that some of the megafauna survived for thousands of years after they were supposed to have disappeared at the onset of the Younger Dryas, and long after the early decline suggested by Gill.

The commentary accompanying the Gill paper suggests that both the climate change and the impact hypothesis ideas are dead. Instead, the suggestion is that overhunting by paleo-Indians, already established in North America before the Clovis people arrived, is responsible for the early decline.

These conclusions seem premature. What can be said, based on the Gill paper, is that at least some local populations of megafauna were in trouble before the Younger Dryas, for reasons that remain unclear. From the Woodman paper we can infer that some other populations survived well after. And we know already, that an awful lot happened in between — which may or may not have included a comet impact.

It’s ironic that this picture is so confusing when the extinction of the dinosaurs by a large asteroid 65 million years ago now seems quite clear. But this is partly an effect of distance. If we could have visited Earth 12,900 thousand years after the dinosaurs went extinct it’s likely we would have found all kinds of interesting evidence, no longer available, that would have complicated the picture. The loss of the megafauna is both intriguing and hard to understand because it is so recent and there are so many more pieces of the puzzle to play with.

The only solution, as Woodman points out, is even more information. He suggests that mammoth and mastodon fossils in museums around the world should be looked again and redated if necessary to improve consistency in the data. There’s still more work to be done in sampling the environment too.

This debate is far from over. Like North America at the end of the ice age, it’s just getting warmed up.

Ivan Semeniuk is host of the podcast The Universe in Mind and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.


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Richard Firestone

November 23, 2009 at 2:49 pm

The paper by Jacqueline Gill in Science fails to address earlier evidence published by Davis and Schafer (Palaeogeography, Palaeoclimatology, Palaeoecology 237 (2006) 40–50). They state that "In several sites in the western United States, a precipitous decline of Sporormiella percentages after ca. 10,800 radiocarbon yr B.P. (12,900 years ago) marks a decline of herbivore density, probably associated with the North American megaherbivore extinction." It is deceptive to present such a broad theory for the extinction of the megafauna when previous work on the same subject directly refutes it. Gill et al failed to comment on this although they were aware of the Davis paper. The fungus argument is interesting and perhaps relevant on a local scale but fails to address a massive body of other evidence that the megafauna suddenly disappeared 12,900 years ago. Gill et al attempt to predate the extinction to before the arrival of the Clovis people begging the question of why they were such voracious hunters of mammoths if few were to be had. The Clovis style points suddenly disappeared 12,900 years ago along with the mammoths and whatever cause you may choose for this event you can't change the calendar for when it happened.

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Richard Carroll

November 23, 2009 at 8:28 pm

Enjoyable to hear the push-pull of competing ideas. Informative comment by R. Firestone.

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November 24, 2009 at 9:13 am

What an excellent example of good science writing! We could sure use more of it.

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November 26, 2009 at 10:55 am

Folks need to be reminded that reported (Dec/07) mammoths lived on Wrangel during the time of Sesostris I, middle kingdom Egypt during the 12th dynasty or about 1991 B.C. I did not see references here to these reports. Some may find Michael Oard's reports in the Journal of Creation (JOC) interesting too for an alternative view of earth history.

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Stan Kerns

November 27, 2009 at 9:55 am

This theory has always struck me as odd in that elephants--at least until fire arms--have done quite well living in Africa the home of our species--if we didn't kill them off there I doubt we did in America either. Also in Asia--man and elephants have coexisted for a very long time.

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November 27, 2009 at 2:49 pm

It is so interesting to read articles like this - but it all puts me in mind of current climate change concerns. Why now, in 2009, is climate change being blamed on human activity, when it has all happened before, time and time again, with no human activity at all?
Why are modern scientists all (apparently according to the media and government spin) now on this band-wagon? I live on an Island in the UK which 10,000 years ago was joined to mainland Britain - the result of climate warming and rising sea levels then - but again, nothing whatsoever to do with any human activity. What would have happened if we had had all these scientists and their computer modelling back in those days, oh boy! Still, one thing, it is very clever that governments can now tax naturally occuring climate change, very clever indeed. Bring back the mammoths!

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November 28, 2009 at 12:07 am

The Gill et al. paper is quite suggestive, but probably extrapolates too broadly from the limited data. Semeniuk is correct: the study seems to document a local reduction only. Coupled with Firestone's comments above, it appears that, rather than trying to "change the calendar" for when the extinction event took place, Gill et al. have demonstrated that megafaunal populations in North America (not Wrangel Island, which is in Russia and so not pertinent to this discussion) were responding to different pressures, in different areas of the continent, at different times. And that's a fascinating insight, as it suggests a much more complicated extinction event than many have previously suggested. What goes unmentioned is an exciting avenue of research posed by Gill et al.: can similar reductions in Sporomiella also be observed in sediments deposited during earlier periods of climate change? Those data would be critical in correctly assessing what happened in North America at the end of the Pleistocene - and interpreting what may happen in our own future. Climate change today is increasingly impacted by human activities; ice cores going back over 600,000 years indicate that our present day climate is warmer, and warming faster, than at any previous point during that time span, and not in a manner predicted by any earlier trends. Understanding how organisms responded to climate change at the end of the Pleistocene may therefore shed light on what can happen to biological communities today and in the future.

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November 28, 2009 at 10:48 am

Indeed the story of Wrangel Island needs to be told as well as reports like David Swift of CMI published.

[Mammoth among the pharaohs?

by Dennis Swift

A mammoth in an Egyptian painting? Surely not—haven’t we been told in textbooks that mammoths definitely died out some 9,500 years ago?

The fact is, however, that at least a dwarf type of mammoth must have been around some 1500 years before Christ, even by conventional dating...]

The larger question concerns just when mammoths became extinct on earth as well as why. The Rakh-Mara tomb is one of the largest of the 18th Dynasty and adds evidence against the conventional Stone Age stories we commonly are told about the disappearance of mammoths. The idea that mammoths in North America were extinct some 13,000 or so years ago yet lived on Wrangel Island during the middle kingdom of Egypt and tomb paintings of possible mammoths from the 18th dynasty pharaohs, does not add up.

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Ted D.

December 1, 2009 at 10:03 am

Maybe the mamoths of North America were particularly tasty. The paleo-Texans probably made some killer barbeque with them, and sold out quickly. Makes me wish for a time machine!

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Dennis Cox

July 10, 2010 at 9:44 am

I Wonder how many would be surprised to learn that the Younger Dryas impacts were caused by the impacts of the high velocity particles, and fragments, of the Taurid Progenitor, not long after it's total break up. Or that the planetary scarring of the event is the product of multiple airburst, thermal atmospheric, geo-ablative effects. Not single bolide, ballistic/kinetic shock effects.

The YD impact hypothesis can be proven conclusively by positive identification the blast effect materials. And those blast effected materials are not craters. The event didn't smash the ground. The tens of thousands of hyper-thermal, supersonic, impact down-drafts flash melted, and ablated,it.

But the Earth sciences are all founded on the unquestioned 19th century assumptions of Sir Charles Lyell. Namely,the assumptions of uniform, and gradual, geologic change. And the founding principle that 'The present is the key to understanding the past'.

The simple, empirical fact, is that it isn't. The short period of time called 'written history', gives us no clue of the level of violence which has visited this planet, during human times, in the geologically recent past. But because of those unquestioned 19th century assumptions, all of the extensive, and pristine, planetary scarring of the most violent impact event in 65 million years, has been mis-defined as ancient Volcanogenic. And mis-dated by orders of magnitude.

Founded on the outmoded, and unquestioned, 19th century assumptions of standard Uninformitarian landform theory, the Earth sciences are like blind scholars studying an elephant they can't even imagine. And the elephant is in the room with them.

Dennis Cox

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