Megafaunal Extinctions and Preclovis

Faithful reader Norah writes: "I read in the paper this week about the disappearance of woolly mammoth and other large-bodied animals at the end of the Ice Age, and how the disappearance happened earlier than first thought. How does this affect what we understand about pre-clovis? Is this support for the presence of humans in North America before Clovis?"

Excellent question, Norah! The news stories came out of a study published in Science magazine last Thursday. The paper Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America provided a new wrinkle on the way we understand how megafaunal extinctions happened at the end of the pleistocene; but I'm afraid, not much support for pre-clovis occupations of North America.

Megafaunal Extinctions and Clovis

Mastodons eating black ash trees. Image Courtesy Barry Roal Carlsen, University of Wisconsin-Madison

At the end of the ice age, between 18,000 and 12,000 years ago, 34 megafauna—animals with bodies larger than, say, a big dog—went extinct. Mammoths, camels, dire wolves, horses, a whole range of big-bodied animals used to run around North America, and that whole range disappeared at roughly the same time. The reasons scholars have theorized about why the animals died out have included human predation, climate change, and most recently, a cometary impact on the Canadian ice shield. But evidence from lake sediments in a small kettle pond in Indiana have thrown a new wrinkle into those theories.

What the study by Jacquelyne Gill and colleagues reported in Science last week did was examine the evidence for a specific set of plant communities demonstrated by the presence for pollen in a kettle pond called Appleman Lake, Indiana. That's a pretty standard technique: scientists use sediment cores (essentially a narrow hollow tube pushed into the bottom soil in a waterbody to extract a sample) to look at the contents of lakes pretty regularly. Lakes accumulate plant and other material from runoff and the material is usually laid down in neat layers. Gill et al.'s study focused on pollen from Sporomiella, a type of fungus that lives in animal dung. The theory goes that if there's a lot of large animals around, there will be a lot of dung, and a lot of Sporomiella; and if not, there won't be. Thus, Sporomiella can be used as a fairly imprecise measure of the number of herbivores who could have been producing dung.

Animal Dung and Moss

The other pollen brought up with the core along with the Sporomiella indicated two shifts in vegetation beginning 14,800 years ago and then again 13,700 years ago. That's a little weird, because although the shift in vegetation wasn't unexpected, the timing is. Normally you would think of vegetation shifts happening when climate shifts occur, or shortly after they start. What Gill and colleagues are saying is that the vegetation shift happened before the Younger Dryas cooling period, long thought to be the engineer for vegetation change.

There is also, interestingly enough, a peak in charcoal starting at 14,300 years ago, and then again at 10,700 years ago. That means there was some fairly substantial amount of burning. Could that be human-engineered? Gill and her colleagues only mention preclovis sites in southeastern Wisconsin—and not by name (or by "preclovis", for that matter). She is referring to four mammoth bone sites in Wisconsin (Hebior, Mud Lake, Shaefer and Fenske), and those are still somewhat controversial.

But, even if there really is preclovis, and I'm inclined to think so, there are only about 50 sites identified so far, and they weren't by any means exclusively big game hunters—in fact, preclovis have been described as hunter-gatherer-fishers. It's very unlikely that a population density of that level would have been able to impact so many species in such a short time. Could prairie fires have been engineered by humans? Well, that's possible—but that might have happened with lightning strikes as well.

Interesting Things to Ponder

The study does suggest, interestingly enough, that Clovis people, the quintessential big game hunters, didn't start big-game-hunting until well after most of the megafauna disappeared. Hmm.

So, what killed the megafauna? We still don't know. But it was probably a combination of things, and it probably included climate change, human predation, and maybe even that old comet; and maybe some other reasons we haven't figured out yet. What we do know is that the megafauna began disappearing about the time people arrived in the Americas, we just don't know why yet.

Timing is, After All, Everything

A timeline of events; all dates calibrated from radiocarbon dates.

• ~15,000 BP (calendar years before present), glaciers begin to retreat from Wisconsin
• ~14,800-14,100 (theoretical) earliest dated preclovis sites in southeastern Wisconsin (Hebior, Schaefer, Fenske, Mud Lake)
• ~14,800 Appleman Lake (AL): Sporomiella declines
• ~14,500 Bølling-Allerød warming period begins
• ~14,300 (AL): charcoal becomes common, with intermittent peaks
• ~14,100 (AL): charcoal deposits peak
• ~13,700 (AL): Sporomiella drops below 2% and never recovers
• ~13,700 (AL): non-analog plant communities develop
• ~12,900-11,600 Younger Dryas cooling period
• ~12,900 earliest Clovis sites
• ~12,500 (theoretical) comet explodes over Laurentide ice sheet
• ~12,500 Clovis disappears
• ~11,900 (AL) non-analog plant communities disappear
• ~11,500 megafauna gone
• ~10,700 (AL) steep increase in charcoal
• ~10,000 glaciers completely out of the United States and southern Canada

More Information
Related Topics

• Megafaunal Extinctions
• Preclovis Culture
• Sediment Core Analysis
• Nano-Diamonds and Clovis Sites

Academic References

Gill, Jacquelyn L., et al. 2009 Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science 326(5956):1100-1103.

Johnson, Eileen 2007 Along the ice margin—The cultural taphonomy of Late Pleistocene mammoth in southeastern Wisconsin (USA). Quaternary International 169-170(World of Elephants 2: Selected papers from the 2nd Congress, Mammoth Site of Hot Springs, 2nd World of Elephants Congress):64-83.

Raper, Diana and Mark Busha 2009 A test of Sporormiella representation as a predictor of megaherbivore presence and abundance. Quaternary Research 71(3):490-496.

News Stories

• Dung Fungus Provides New Evidence in Mammoth Extinction, Wired Science
• New Data Shed Light on Large-Animal Extinction, Nicholas Wade in the NYT
• Fungus Provides Clues To North American Extinctions, NPR
• Mammoths and other megafauna dwindled for centuries, Knight Tracker