American Mastodons Suffered from Chilly Climate Change Before Humans Arrived

Researchers may have a new timeline when it comes to when ancient, massive mastodons roamed the Earth. They've taken a closer look at fossil age estimates based on new radiocarbon dates and have found that the Arctic and Subarctic were only temporary homes to mastodons when the climate was warm.

Researchers have long known that the extinct relatives of elephants, mastodons, preferred forests and wetlands abundant with leafy food. Yet previous age estimates of American mastodon fossils indicated that these animals lived in the Arctic and Subarctic when the area was covered by ice caps. Obviously, something wasn't quite right.

"Scientists have been trying to piece together information on these extinctions for decades," said Ross MacPhee, one of the researchers, in a news release. "Was it the result of over-hunting by early people in North America? Was it the rapid global warming at the end of the ice age? Did all of these big mammals go out in one dramatic die-off, or were they paced over time and due to a complex set of factors?"

The American mastodon was widespread between 10,000 and 125,000 years ago. It roamed across continental North America and even in the tropics of Honduras and the Arctic coast of Alaska. These massive creatures relied on woody plants and lived in coniferous or mixed woodlands with lowland swamps. This means that it's unlikely they could have survived the last full-glacial period.

In order to find out why dates didn't match up, the scientists used two different types of precise radiocarbon dating on a collection of 36 fossil teeth and bones of American mastodons from Alaska and Yukon, the region known as eastern Beringia.

It turns out that all of the fossils were far older than previously thought. Most surpassed 50,000 years, which is the effective limit of radiocarbon dating. This indicates that mastodons probably only lived in the Artic and Subarctic for a limited time around 125,000 years ago, when forests and wetlands were established and the temperatures were as warm as they are today. Not only that, but this also seems to indicate that climate played a large role in the mastodon extinction.

"We're not saying that humans were uninvolved in the megafauna's last stand 10,000 years ago. But by that time, whatever the mastodon population was down to, their range had shrunken mostly to the Great Lakes region," said MacPhee. "That's a very different scenario from saying the human depredations caused universal loss of mastodons across their entire range within the space of a few hundred years, which is the conventional view."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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