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American Mastodons Made Warm Arctic, Subarctic Temporary Home 125,000 Years Ago

Reconstructed image of an American mastodon, the ground sloth, the flat-headed peccary, and the western camel in a hilly green scrubby setting 125,00 years ago.
Some 125,000 years ago, during a warm interval known as the last interglaciation, megafaunal mammals were able to penetrate parts of northern North America that had previously been covered by massive ice sheets. In this reconstruction, in addition to the American mastodon (Mammut americanum), illustrated is Jefferson’s ground sloth (Megalonyx jeffersonii), the flat-headed peccary (Platygonus compressus), and the western camel (Camelops hesternus). 
© George "Rinaldino" Teichmann

Existing age estimates of American mastodon fossils indicate that these extinct relatives of elephants lived in the Arctic and Subarctic when the area was covered by ice caps—a chronology that is at odds with what scientists know about the massive animals’ preferred habitat: forests and wetlands abundant with leafy food. In a paper published this week in the Proceedings of the National Academy of Sciences, an international team of researchers is revising fossil age estimates based on new radiocarbon dates and suggesting that the Arctic and Subarctic were only temporary homes to mastodons when the climate was warm. The new findings also indicate that mastodons suffered local extinction several tens of millennia before either human colonization—the earliest estimate of which is between 13,000 and 14,000 years ago—or the onset of climate changes at the end of the ice age about 10,000 years ago, when they were among 70 species of mammals to disappear in North America.