What finished off the woolly mammoth? Well, mostly, it was the same thing behind most extinctions—humans. But one mammoth population, living on Alaska's St. Paul Island, managed to survive another 4,000 years after we’d done our worst, only to disappear spontaneously.
Until now, the reason for the demise of this mammoth population was a mystery, but a new study posits that the St. Paul Island mammoths ran out of freshwater thanks to climate change and died of thirst.
St. Paul Island remained untouched by humans until Russian whalers landed there in 1787, so the mammoths there died off by themselves, without our help. Other mammoth populations had migrated north as temperatures rose, and around 14,000 years ago, St. Paul Island became isolated by the rising sea level. This isolation protected the mammoths while humans hunted mainland mammoths to near extinction (one other group of mammoths outlived the St. Paul Islanders, but were finished off by us).
So Russ Graham of Pennsylvania State University and his team set out to discover just what killed the St. Paul Island mammoths.
If you get frustrated trying to find your misplaced phone charger, or when pairing your socks, then paleontology isn’t for you. The team painstakingly searched the island, gathering bone fragments from caves and taking core samples from lake beds. These core samples were tested "for four proxies that previous research has correlated with the presence of large animals, including ancient DNA and certain types of fungal spores," writes the Smithsonian’s Rachel Nuwer.
These samples also gave the history of the amount of phytoplankton, water fleas and other indicators of freshwater levels, allowing the researchers to piece together a timeline of the demise of the mammoths on St. Paul Island.
The problems were manifold. First, the lakes shallowed and became more turbid some time between between 7,850 and 5,600 years ago. The increased turbidity could have been caused by the mammoths congregating around the remaining waters and causing them to muddy. At the same time, rising sea levels caused salt water to seep into the ground, tainting the freshwater supplies.
And finally, the mammoth itself is a thirsty animal. Rachel Nuwer again:
The mammoth’s physiology—including thick hair impermeable to water, a body adapted to retain heat and the need to drink 70 to 100 gallons of water per day—made the animal less able to weather the drying landscape.
All these factors combined to wipe out the last of the St. Paul Island mammoths.
The parallels to today’s climate change are obvious, but the new research also raises a few points that have been less considered. For example, the "salt wedge"—the ingress of saltwater into the ground as sea levels rise—hasn’t been well studied. We have focused more on the loss of land to the sea.
Obviously, we’re not woolly mammoths—those huge hairy beasts couldn’t escape their island, nor could they go to war to secure freshwater supplies, but we can still learn from them. One of the surprise findings of the study was that "isolated megafaunal populations can survive thousands of years after habitat fragmentation." That is, even a population of oversized herbivore can keep going long after climate change has spoiled its habitat. Then again, the mammoth’s world changed over a long period, whereas we’re clearly already experiencing the beginnings of an accelerated change. Our world is likely to get pretty bad, fairly soon, and while that happens, we need to remember how important it is to protect our precious freshwater supplies.
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