Mastodons, the giant lumbering cousins of mammoths and elephants, likely disappeared from Alaska and the Yukon long before humans arrived across the Bering Land Bridge from Asia, researchers said Monday.
Mastodons were once believed to have roamed the snowy Arctic region alongside the first human colonists some 13,000 to 14,000 years ago, but new evidence suggests they disappeared tens of thousands of years earlier and were not hunted to extinction.
Scientists now think that long-extinct mastodons probably only lived in the Arctic for a short time some 125,000 years ago, when forests and wetlands were present and the temperatures were warmer.
"The residency of mastodons in the north did not last long," said lead author Grant Zazula, a paleontologist in the Yukon Palaeontology Program.
"The return to cold, dry glacial conditions along with the advance of continental glaciers around 75,000 years ago effectively wiped out their habitats."
After long puzzling over how mastodons -- known for eating twigs and leaves -- survived in the snowy Arctic, scientists re-examined 36 bones and teeth from mastodons in museum collections.
Using new techniques that eliminated the potential for contamination by modern preserving materials, the team found that all the samples were far older than previously thought.
Researchers reported in the Proceedings of the National Academy of Sciences that most surpassed 50,000 years, about as far back as radiocarbon dating can go.
The American mastodon lived in an era known as the late Pleistocene, between about 10,000 and 125,000 years ago, throughout North America as far as tropical Honduras and the Arctic coast of Alaska.
"Mastodon teeth were effective at stripping and crushing twigs, leaves, and stems from shrubs and trees. So it would seem unlikely that they were able to survive in the ice-covered regions of Alaska and Yukon during the last full-glacial period, as previous fossil dating has suggested," said Zazula.
The findings indicate that humans were not to blame for the creatures' extinction some 75,000 years ago, as they had not yet crossed the Bering Isthmus from Asia.