科学美国人60秒:Humans off the Hook for Alaskan Mastodon Extinction

It’s long been thought mammoths and mastodons rambled over North America’s arctic and subarctic realms between 75,000 and 100,000 years ago, and were made extinct by hungry new arrivals on the scene: human beings. But new evidence indicates mastodons probably roamed the region as far back as 120,000 years ago—and they were gone before the first people showed up.

“For at the least the story of the mastodon, we now know for what we call Beringia—Alaska, parts of Yukon and over into northeastern Asia—they were wiped out in those areas for things that had nothing to do with humans, because they all died out before there were humans there.” Pat Druckenmiller is the Curator of Earth Science at the University of Alaska Museum of the North. “Humans could not have been part of the story and that’s pretty interesting.”

The research is in the Proceedings of the National Academy of Sciences. [Grant D. Zazula et al, American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change]

Druckenmiller and co-authors were led to these conclusions after colleagues at the Yukon Paleontology Program in Canada decided to redate nearly 40 specimens, because American mastodons are often mistaken for their much hairier wooly mammoth cousins, who hung around the area later.
 
“A mammoth and a mastodon can be immediately distinguished on the basis of their teeth, their big cheek teeth.” The surface of a mammoth tooth looks like a washboard, perfect for grinding grasses that grew during the last ice age. But mastodon teeth have much lumpier, bumpier cusps: ideal for chewing twigs and leaves.
 
“People in the past when they found these teeth and bones, they put glue and other kinds of strange things on them, and that glue can mess up the dates, gives you a wrong date. In fact, it gives you a date that’s too young.”
 
The new dates corroborate what mastodon teeth show: They ambled over Beringia when the region was warmer and forested, long before mammoths and earlier than humans. So, if humans didn’t wipe out the mastodon, what did? That mystery remains for scientists to sink their teeth into.
 
—Emily Schwing