Eurasian Pleistocene Extinctions & Ecological "Overkill"

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The skeleton of an Irish Elk (Megaloceros giganteus) at the AMNH.


Blogging on Peer-Reviewed ResearchDiscussions of mass extinctions nearly always give rise to heated debates as to the mechanism(s) behind the disappearance of so many taxa in a short amount of time, and one of the most active debates still surrounds the extinction of Pleistocene megafauna. All over the world the extinction of large animals appears to be correlated with the movements of our own species, Homo sapiens, into new territories. Disease and climate change have their own parts to play, the "Overkill Hypothesis" is perhaps the most popular explanation for the extinction of Pleistocene megafauna. A new study by Pushkina and Raia, however, suggests that in Eurasia the role of our own species in extinction was diminished.

Utilizing data from published literature and databases, the two authors found that while the territories of humans overlapped that of extinct megafauna, the overlap was not total. Indeed, the megafauna appeared to prefer colder regions than humans and other more common species, and a comparison of paleontological sites (sites where there were no human remains or artifacts) and archaeological sites (sites with human remains and artifacts present) across the range of human habitation showed that large, extinct mammals were not very common in temperate areas occupied by humans. In fact, with the exception of one species (the steppe bison, Bison priscus), the fauna most commonly found in association with humans were extant taxa. Indeed, contrary to what might be intuitively expected, humans seemed to prefer medium-sized prey within their range, perhaps causing a co-evolution of the species that were being hunted.

Still, some representatives of the Eurasian megafauna did overlap in range with humans, and there are some important questions as to how those species interacted with earlier representatives of our own. Species naivety is sometimes invoked to explain the Pleistocene megafauna extinctions, the large animals being unfamiliar with earlier humans and their hunting abilities, an ignorance that led to their demise. Recent ecological studies have revealed that prey species can quickly adapt (or re-adapt) to the presence of predators, though, and it appears that humans had a more important relationship with smaller, extant prey than larger species that ultimately went extinct. The researchers explain the implications of the trend this way;

Intuitively, the relative rarity of remains of extinct species in many archaeological sites could simply reflect a situation in which remains of these heavy animals were seldom brought back to any human site. Yet, the extinct large mammals were equally rare in paleontological sites at similar latitudes. This latter observation indicates that the rarity of extinct species within human ranges (and not just in archaeological sites) was a real ecological phenomenon, and strongly argues against the notion that humans were responsible for their demise. Our data suggest that if a direct avoidance of humans by these species via gathering in northern areas was possible, it was not due to human overexploitation in the south.

But what about the steppe bison? They were a large species that did go extinct, and as with the more recent elimination of bison in North America, humans seemed to be a direct factor in the demise of the steppe bison, as well. The prevalence of steppe bison remains seem to increase at archaeological sites and decrease at paleontological sites, increasing human populations and better hunting technologies causing humans to have a bigger effect on bison populations;

In our study too the extinction of the steppe bison appears to be related to humans. Human subsistence activities in Siberia heavily relied on bison, reindeer, and horse during the Late Paleolithic... The commonness of the extinct bison and surviving ungulate species (reindeer, horse, saiga, and red deer) in archaeological sites strongly indicates their intensive utilization by humans, especially during the Weichselian glaciation or the late Middle and Late Paleolithic. This can be related to increased population density (archaeological sites outnumber paleontological sites for the first time during the early and middle Weichselian) and to improving hunting technologies, such as the appearance of the microblade-producing populations of highly mobile hunters across Siberia after the LGM who concentrated on a single prey species of large or medium size... The microblade technology appeared with the exploitation of smaller less gregarious species probably because the big game species were disappearing... Overall, it appears that humans were generalized, albeit effective, predators and efficiently concentrated on the most abundant prey species, most of which survive today.

Still, for the majority of other extinct species mentioned in the paper ("the
woolly mammoth, Mammuthus primigenius; the woolly rhinoceros, Coelodonta antiquitatis; ... ; the musk ox, Ovibos moschatus; the straight-tusked elephant, Palaeoloxodon antiquus; Merck's rhinoceros, Stephanorhinus kirchbergensis; the narrow-nosed rhinoceros, Stephanorhinus hemitoechus; the aurochs, Bos primigenius; the giant deer or Irish elk, Megaloceros giganteus; the Pleistocene ass, Equus hydruntinus; cave hyena, Crocuta crocuta; cave lion, Panthera leo; and cave bear, Ursus spelaeus") humans had a less substantial impact. While humans may have had a more important role in the extinction of megafauna in other parts of the world during the Pleistocene, in Eurasia it seems that something else was at work. The authors of the part posit climate change, but very little about climate change and how it correlates to the data is covered.

The findings of the authors are consistent with the idea that the overkill hypothesis is not a very good fit for the extinction of megafauna in Pleistocene Eurasia, but what exactly did happen still requires resolution. Indeed, I would imagine that the extinctions occurring in the Pleistocene were triggered by varying mechanisms depending on the region, and selecting hunting, disease, climate change, etc. as the answer for global megafaunal extinctions is taking an approach that is far-too narrow to do justice to understand what happened.

[Hat-tip to Greg Laden.]

PUSHKINA, D. (2008). Human influence on distribution and extinctions of the late Pleistocene Eurasian megafauna. Journal of Human Evolution DOI: 10.1016/j.jhevol.2007.09.024

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Very interesting. I've always been a bit critical of the overkill hypothesis, because there's just no way to be sure it's right. I also find it difficult to believe that early man could wipe out an entire species via hunting. I wonder if we could do that today with the enormous caribou herds on the North Slope.

I'd say the case for humans as a major driving force behind megafaunal extinction is probably strongest for islands like New Zealand, Madagascar, Caribbean, and Australia, and for North America, but pretty weak for Africa, followed by temperate Eurasia. Although I have to admit, the fact that (sub)species as widely distributed as the lion, spotted hyena, woolly mammoth and steppe bison actually managed to become extinct seems to hint at a true ecological disaster that struck swiftly and rapidly spread throughout the range of these animals. It is plausible to think that many of these creatures would have been just as numerous and widespread as extant species such as red deer, reindeer, wild boar, lynx, wolf and brown bear.

I'm not sure if the idea that extinct megafauna did not overlap much with humans is a viable one; after all, both forest and steppe species were impacted, and both habitats have their fair share of survivors and casualties.

While I strongly feel that climate would likely have played a major role in the case of the temperate Eurasian megafauna (besides also causing the range of many extant species to shrink; amongst them leopard, striped hyena, dhole, hippopotamus, onager and saiga), I still somehow have this nagging feeling that human activity cannot be discounted just yet.

A new thought just came to me; I wonder if the authors of this paper discussed Neanderthals? You could think of them as Pleistocene megafauna...

I know that humans have also been blamed for the North American megafauna extinctions, and that the explanation has also been called into doubt.

Have there been any new developments in that area? If I recall correctly, the thinking was that the great extinctions happened thousands of years before the humans were thought to have arrived.

By Caledonian (not verified) on 28 Jan 2008 #permalink

Hai; The paper doesn't make explicit reference to Neanderthals as far as I can remember. The authors did say that humans did have some effect on the megafauana that ultimately went extinct, but that it was not as drastic as elsewhere.

Caledonian; The NA extinctions have been among the most controversial, although admittedly I haven't kept up with every paper. The latest development that may have some bearing on the issue is the discovery of evidence for the impact of a bolide about 13,000 years ago. As you would imagine this is still controversial, but it'll be interesting to see what turns up as more studies are undertaken.

As it happens, evidence for the 'Magic Bolide' is a little shaky. Pinter and Ishman wrote a brief, highly skeptical response to the Firestone et al. paper in GSA Today. They identified a number of the mega-tsunami features as ordinary parabolic dunes, aligned with the prevailing wind direction. The iridium and microdiamond concentrations found in 12.9-ka sediments can be explained by a non-apocalyptic shower of space grit. Most damning, the megafauna extinction in NA did NOT take place all at once at 12.9-ka. I have, taped to my desk, a list of last known occurrences of NA megafauna, correct as of a couple of years ago:

33.8-ka: Alces latifrons
22.0-ka: Bison latifrons
20.0-ka: Arctodus pristinus
13.0-ka: Arctodus simus, Acinonyx trumanii
12.0-ka: Equus lambei
11.0-ka: Dasypus bellus, Glyptotherium texanum, Panthera leo atrox, Homotherium serum, Mammuthus primigenius, Camelops hesternus, etc.
10.0-ka: Megalonyx jeffersoni (and most other sloths), Holmesina spetentrionalis (and other pampatheres), Mammuthus columbi (I shed a tear for you), Equus scotii, Casteroides ohioensis, etc.

Note that quite a few of these predate the '12.9-ka' bolide, and a LOT of them came considerably later. Also, unlike Eurasia, there is no shortage of NA mammoth and mastodon kill sites. A short list:

Colby Site -- WY
Lane-Furgeson Site -- SD (Not far from the Mammoth Site natural trap)
Lehner Site -- AZ
Domebo Site -- OK
Murray Springs Site -- AZ
Dent Site -- CO
Coates-Hindes Site -- TN
Adams Site -- KY
Page-Ladson Site -- FL
etc.

Early NA humans certainly hunted very large game, even if their Eurasian counterparts didn't. That said, while overkill is a better explanation for the megafauna extinction out here, it isn't perfect -- there aren't many (any?) sloth or papathere kill sites, for example.

Anyway, I hope this helps.

"I also find it difficult to believe that early man could wipe out an entire species via hunting"
I think pretty much every island in the Pacific proves you wrong on that one...

And they damn near got Steller's Sea Cow, iirc. It vanishes from most of its range soon after humans show up, surviving in only the one place (until a ship wrecks there and, well, you know the rest). Being easy to kill and good to eat (according to the firsthand accounts), it's not hard to see why.

having read once about the inuit method of hunting polar bear,they would curve a sharpened pliable bone around in a tight ball and freeze it in a ball of bait. Polar bear comes along swallows the bait and when it melts inside springs open and punctures the stomach,in a few days dead bear.Humans sitting around a campfire late at night could devise many simple effective ways to kill game besides spears and clubs.Surely fire, possibly poisons,traps etc. They surely killed not just for meat but also for skins,fur,antlers ,horns and just for bragging rights.I've often thought every paleontologist should be accompanied by an indigenous hunter,trapper for their expertice in animal/human interactions.some of the theorys I've heard coming from paleontologists would be laughed at I'm sure around a hunter/gatherers campfire.I think the overkill hypothesis is the simplest explanation as time and again when we show up large animals are soon gone.

By Dan Aites (not verified) on 12 Jun 2010 #permalink