Pleistocene Extinction Event

Another mass extinction event took place at the end of the Pleistocene epoch (about 11,000) years ago. In this event, a variety of animals went extinct across North America. These were mostly large mammals like the saber-tooth tiger, woolly mammoths, and mastodons. Because of this mass extinction event, there are very few large mammals found in North America. This extinction happened in other locations around the world too, but not on such a large scale as seen in North America.

Why did these animals go extinct?

Scientists do not know the exact cause of this extinction event, but they have identified 3 hypotheses that may explain this extinction event: 1) Over-Hunting; 2) Climate Change; and 3) Hyper-Disease. Scientists do not know for certain if only one of these causes was responsible for the extinction or if it was due to a combination of causes.

1. Over-Hunting Hypothesis

Scientists hypothesize that the arrival of humans across the Bering Strait during the Pleistocene period may have caused this mass extinction. These early humans may have over-hunted the large animal populations they encountered in North America. If humans over-hunted one key species (like mammoths or mastodons) in the ecosystem, it would have implications for all the other organisms in the ecosystem, possibly leading to the extinction of many other species.

2. Climate Change Hypothesis

During the Pleistocene, the climate was changing dramatically over North America. North America's climate began warming up and the giant ice sheets that covered much of the continent began to melt. Scientists hypothesize that this change in climate caused fundamental changes to many of North America's ecosystems, which caused organisms to either adapt to new conditions, move to a new location, or die out. This change in climate also led to changes in the dynamics and interactions in ecosystems, as organisms began competing for limited resources.


Scientists hypothesize that early humans may also have brought new diseases with them to North America, highly contagious diseases that could spread from humans to animals very rapidly.

Uncertainties about these Hypotheses

Uncertainties exist about each of these hypotheses, which lead most scientists to believe that the extinction event that took place at the end of the Pleistocene was caused by a combination of one or more of the causes listed above.

For example, one issue with the over-hunting hypothesis is that scientists are not sure if human populations were large enough to hunt species to extinction. But if they altered the ecosystem enough, they still could have initiated the extinction event. Also, the Pleistocene period is characterized by fluctuations in climate, with ice sheets advancing (in glacial times) and retreating (in interglacial times) throughout this period of time. Therefore, scientists do not know for sure what would make these animals survive the other interglacial periods, but not the one at the end of the Pleistocene.




Sources
http://www.ucmp.berkeley.edu/quaternary/ple.html (fair use)
http://www.oercommons.org/courses/what-killed-the-mammoths-could-it-have-been-a-killer-plague (CC BY-NC-SA)
http://www.amnh.org/exhibitions/expeditions/siberia/ (fair use)