As Earth Warmed, Ancient Mastodons Headed Far North

Digital painting of three American mastodons (Mammut americanum) under aurora borealis in Beringia. (Art by Julius Csotonyi)

(CN) — Since the discovery of a fossilized tooth by a Dutch tenant farmer in 1705, the American mastodon has been shrouded in mystery. Twenty-four years later, French soldiers in what is now Kentucky found the first bones, and soon similar teeth were discovered in South Carolina where enslaved Africans supposedly identified them as similar to the teeth of African elephants.

Today, when people imagine mastodons roaming the earth, they often think of hairy elephant-like creatures wading through heavy snow and icy wind before being hunted to extinction by Clovis hunters.

But a study published Tuesday offers evidence that this extinct forest-dwelling species routinely migrated to the upper latitudes of North America, lured by new vegetation during periods of interglacial warming during the Pleistocene, 2.5 million to 11,700 years ago.

“Our evidence supports the hypothesis that these animals were not there during frigid, cold kind of glacial periods that we envision when mammoths were roaming around, but probably more likely during these warmer interglacial periods where we had temperatures very similar to what we have today,” stated lead researcher Emil Karpinski of McMaster University in Ontario, Canada.

American mastodons (Mammut americanum) lived in wooded and swampy habitats across the Americas. Their remains have been recovered across a vast region stretching from “the Central American subtropics to the Arctic latitudes of Alaska and Yukon,” according to the study published in the September edition of Nature Communications.

Like other keystone species, mastodons served an important role in the integrity and diversity of its habitats.

Periods of warming and cooling global temperatures over the last 800,000 years led to the periodic expansion of an ice sheet that covered about half of North America. But scientists were unsure of how this important species responded to these fluctuations, which occurred during a time when climate change brought great upheaval as glaciers advanced and retreated and global sea levels rose and fell.

Until now.

Using fossil bones and teeth of American mastodons collected from museums, universities, and government institutions across North America, Karpinski and 18 colleagues sequenced the mitochondrial genomes of 33 specimens. Their research revealed five distinct groups, or clades, of mastodons, of which two groups originated from Beringia — a region that historically joined Russia and North America.

Interestingly, researchers found no overlap in the ages of the Beringia specimens, suggesting that the two clades migrated to the region independently during warmer periods when forests and wetlands flourished.

In addition, researchers discovered that the northern clades had lower levels of genetic diversity than that groups south of the continental ice sheets. This finding suggests that similar northward population expansions of moose and beaver today are vulnerable if more genetically diverse southern populations are eventually lost.

“The question has always been: why? Why have these major animals who were successful for millions of years across multiple continents all of a sudden just disappeared?” stated study co-author Hendrick Poinar of the McMaster Ancient DNA Center. “And if you look at the timeline of that extinction, it’s almost instantaneous from a geological perspective.”

What scientists don’t yet know is why the American mastodon and other species that had successfully migrated north on numerous previous occasions were unable to do so during the last warming period before their extinction. Were they already in severe decline when the ice age ended? And what does this indicate about current species pushed to the brink of extinction by climate change?

While those questions remain unanswered, Karpinski and his colleagues hope their research expands understanding of potential ecological responses of present-day species to global warming.

Mastodon fossil on display at the American Museum of Natural History. (Photo courtesy AMNH)
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