View Full Version : Overkill, glacial history, and the extinction of North America’s Ice Age megafauna

11-09-2020, 10:42 PM
Overkill, glacial history, and the extinction of North America’s Ice Age megafauna (https://www.pnas.org/content/early/2020/11/03/2015032117)
David J. Meltzer
The end of the Pleistocene in North America saw the extinction of 38 genera of mostly large mammals. As their disappearance seemingly coincided with the arrival of people in the Americas, their extinction is often attributed to human overkill, notwithstanding a dearth of archaeological evidence of human predation. Moreover, this period saw the extinction of other species, along with significant changes in many surviving taxa, suggesting a broader cause, notably, the ecological upheaval that occurred as Earth shifted from a glacial to an interglacial climate. But, overkill advocates ask, if extinctions were due to climate changes, why did these large mammals survive previous glacial−interglacial transitions, only to vanish at the one when human hunters were present? This question rests on two assumptions: that previous glacial−interglacial transitions were similar to the end of the Pleistocene, and that the large mammal genera survived unchanged over multiple such cycles. Neither is demonstrably correct. Resolving the cause of large mammal extinctions requires greater knowledge of individual species’ histories and their adaptive tolerances, a fuller understanding of how past climatic and ecological changes impacted those animals and their biotic communities, and what changes occurred at the Pleistocene−Holocene boundary that might have led to those genera going extinct at that time. Then we will be able to ascertain whether the sole ecologically significant difference between previous glacial−interglacial transitions and the very last one was a human presence.

11-13-2020, 04:14 PM
I keep wondering about the extinction of large mammals in South America. Mostly I'm interested in the mastodons/mastodon-like species (likely more than one).

11-15-2020, 08:59 PM
The images we are getting are of a wave of ancient humans mowing down all big beasts in their path, rapidly cutting down all of the big ones.
There is a similar loss of megafauna in Australia around about the time of arrival of humans, and what happened is also highly contested.
And contrary to our sometime vision, the timeline is often much longer.
And extinction might occur from the odd kill here and there, or denial of contested resources - to add to the other factors and just nudge a species into extinction.
Some of the sort of complexity that can arise is shown in a paper from last year by Saltre et al https://www.nature.com/articles/s41467-019-13277-0

I think what we are finding in Australia is that it can take a lot of detail to work out what might have been happening: a simplistic solution may or may not work.
And that is without allowing that different regions may have had slightly different things going on.
What we certainly know is that it is an interesting field for research.
Look forward to seeing more coming out of the Americas.

12-05-2020, 01:03 AM
It could have been a combination of factiors. Overkill just being one of them, some species probably went extinct due ecological changes and loss of habitat.

12-05-2020, 03:01 PM
lets look at Africa as an example for some of these theories. People have been living with large mammals since the beginning of human history. no glaciers but significant changes in climate which created the Sahara desert. Elephants, Hippopotamus, Rhinoceros, Giraffes, are all large, relatively slow moving herbivore mammals that produce limited offspring, yet they've lived beside man for millennia. couple that with the fact that Africa had/has the climate for year round plant producing foods. I am not saying early Africans were farmers, but the growing season is not limited by cold weather only warm weather drought. now look at North America. large relatively slow herbivore mammals that produce limited offspring in a colder climate where plant food is limited, AND the introduction of man.

to me it just makes sense. cold climate and large mammals survive in small numbers until man hunted them. warm climate and large mammals survive in larger numbers where man has additional options for food.