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Old August 21st, 2014, 08:22 AM   #1

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What caused the Pleistocene Extinctions?

You have to give credit to the 'Paleo-Indians' of North America. To modern eyes, their world was a living nightmare.

Pleistocene North America was home to a diversity of fauna comparable to the modern African Serengeti. There were several species of bison, as well as mammoths, camels, ground sloths, antelope, and a variety of horses and zebra-like equids. All of these animals must have commanded the respect of their bipedal neighbors, but it was the predators that made the Pleistocene look like a seething hell-hole. In addition to modern American bears, wolves, and felids, there were also dire wolves, Smilodons, American lions and cheetahs, and the short-faced bear.

What caused all of these animals to go extinct? Or, even more strangely, why didn't their modern counterparts go with them? What made a modern gray wolf more fit for survival than the dire wolf? Why did the American equids die out, when recent history shows just how 'horse-friendly' the American plains are?

One theory, at least in regards to the predators, is that early Indian nations deliberately persecuted them into extinction. If that's the case, again, why didn't they kill off the grizzly bears and gray wolves as well?

As with other mass extinctions earlier in the planet's history, there's a multitude of other theories - changes in climate and habitat, widespread diseases, or even natural disasters. Even this can't explain why Bison latifrons died out, but Bison bison virtually ruled the continent as recently as four centuries ago.

Perhaps some of these animals were too specialized. This theory makes sense in regards to Smilodon, in particular. It was probably an ambush predator (and the Great Plains would be unfriendly to such an animal), and its impressive fangs would have made it difficult to prey on smaller game.
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Old August 21st, 2014, 08:38 AM   #2

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I'd say there were a number of factors. Humans and climate change are the most likely culprits. The last glacial maximum saw glaciers extending well into the present-day midwestern U.S. Around the southern periphery of the glaciers would be extensive permafrost. The disappearance of those conditions surely created a major disruption in the food chain. The failure of glacial lakes probably caused extensive flooding over large areas as well. For animals unlucky enough to live in the path of that water, I'd expect widespread annihilation to both the habitat and the animals themselves.

Last edited by dreamregent; August 21st, 2014 at 08:41 AM.
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Old August 21st, 2014, 08:11 PM   #3

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I think the too specialized is a definite factor. There are others.
you have "climate change" -- some animals were just adapted better for the warmer climate and out competed the others.
you also have the "size matters" issue. A Columbia Mammoth is just that. A giant Bison is just that -- smaller bison need less food and less space per animal than the bigger version which means that it's easier to have enough numbers to maintain a genetically viable species (ie, no inbreeding). The same for dire vs grey wolf. A grey wolf, being smaller, doesn't need as much fuel to survive, so it's easier to maintain breeding packs when food is less plentiful. Having more numbers, it's easier to survive attempted extermination.

It may have been disease as well. Just as the arrival of the Europeans decimated the Native Americans, it may well be that the arrival of the Paleo Indians may have brought in disease that the native mammals of the Americas had no resistance to.
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