Mauricio Antón/Wikimedia Commons
- A remote island in the Arctic ocean northeast of Siberia was identified as the resting place of the world's last woolly mammoth population.
- A new study shows that these island mammoths outlived their North American and European counterparts by some 7,000 years, before going abruptly extinct.
- A genetic analysis reveals that these mammoths, on their isolated island, likely fell victim to inbreeding. This decreased the population's genetic diversity, and made them less able to adapt to possible natural disasters.
- The research shows that the last of these animals died out much later than scientists once thought, at a time when the Egyptians had already built the pyramids at Giza.
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About 4,000 years ago on a remote island in the Arctic, the last woolly mammoth died out.
Elephantine in shape and size, mammoths (official name Mammuthus primigenius) dominated the northern hemisphere during Earth's last ice age for nearly 90,000 years, before changing climates and human hunting drove them to extinction.
Scientists have uncovered mammoth skeletons and frozen carcasses everywhere from Spain to Siberia, and the understanding was that these creatures had wholly disappeared by about 11,000 years ago.
But a handful of mammoth populations survived on two tiny, isolated islands nestled between Russia and Alaska that were cut-off from the mainland by rising seas. Researchers think one of these refuges, name Wrangel Island, became the last mammoth hold-out; these tusked giants outlived their North American and European counterparts by some 7,000 years before going abruptly extinct.
That means mammoths as a species lasted far longer than scientists previously thought. When the last woolly mammoth kicked the bucket, the Great Pyramid of Giza had already been built in Egypt.
According to a new study, published in the journal Quaternary Science Reviews, the Wrangel Island inhabitants didn't die of the same causes as other mammoths. Rather, the study authors argue, the isolated animals started to inbreed, which weakened their genetic diversity. The weakened population was then unable to adapt to extreme weather events, which likely caused the mammoths' sudden, untimely demise.
A mysterious, 'fairly abrupt' extinction
Wrangel Island is about 86 miles northeast of Chukotka, Siberia, a 3,000 square-mile chunk of land in the Chuckchi Sea that broke off from Asia about 10,000 years ago. The population of mammoths that went along for the ride was seemingly spared the global extinction of their species, until about 4,000 years ago when they all disappeared.
Radiocarbon dating of skeletons from Wrangel Island showed that the mammoth population's extinction was "fairly abrupt" without any warning signs, according to the study authors.
But the reason behind this sudden die-off wasn't clear.
A previous study found that the mammoth inhabitants on the other similarly isolated island of St. Paul perished from environmental factors. That island, about 1,000 miles to the south of Wrangel Island in the heart of the Bering Sea, was only 42 square miles in size. By examining fossilized DNA, pollen, and spores, scientists discovered that the St. Paul mammoths had likely run out of fresh water as their tiny island dried up, before finally going extinct 5,600 years ago.
That story was reflected in the composition of the St. Paul mammoths' bones, which showed drops in certain types of elements just before the creatures went extinct.
Kirk McKoy/Los Angeles Times/Getty
Looking for clues inside mammoth bones
So the researchers behind the new study decided to look for the same telltale clues in the Wrangel mammoth bones to discern whether their island population had met the same fate.
They analyzed the collagen in 4,000-year-old mammoth bones and teeth from the island, and compared those results to bones from mammoths that had died in other parts of the world like Alaska and Siberia as old as 40,000 years ago.
The scientists were looking for drops in the levels of carbon, nitrogen, and sulfur isotopes in the bones — which would indicate changes in the mammoths' diets due to environmental changes.
Their results showed that the compositions of the Wrangel Island fossils, unlike those of their mainland counterparts, had not changed as the climate warmed 10,000 years ago when the ice age ended and almost all the other mammoths worldwide went extinct.
Juha Karhu/University of Helsinki
Even just prior to their extinction, the Wrangel Island mammoths' bones showed no signs of dietary or environmental stress — meaning these creatures died off in the middle of unchanging, if not propitious, ecological conditions on an island that wasn't affected by a changing climate.
In fact, the authors said their study shows that Wrangel Island "maintained environmental conditions suitable for a typical mammoth ecological niche ... possibly until the present day."
So if a changing environment didn't kill them, what did?
Given that it seemed unlikely the Wrangel Island mammoths died of thirst or climate change, the researchers sussed out other possible reasons behind the extinction.
It was unlikely that human hunting contributed to the sudden die-off, the authors wrote, because there's only a single site of human occupation on Wrangel Island, and archaeological evidence shows the campsite was used for hunting marine mammals and geese. Plus, the site is dated several hundreds of years or so after the last mammoth disappeared.
A previous genetic analysis of some of the Wrangel Island mammoths revealed that the creatures were interbreeding, which caused a severe loss in genetic diversity.
Another 2017 study revealed that the island population had shrunk 43-fold compared to previous mainland mammoth population sizes by the time it went extinct. The study also concluded the mammoths had accumulated "detrimental" genetic mutations that diminished the population's ability to survive disease outbreaks, famines, or natural disasters that could cull large numbers at once.
Courtesy of Giant Screen Films/Reuters
Ultimately, scientists still aren't sure what the smoking gun is, but "a short-term crisis" tops the list, the authors of the new study wrote.
"It's easy to imagine that the population, perhaps already weakened by genetic deterioration ... could have succumbed after something like an extreme weather event," Hervé Bocherens, a co-author of the study, said in a press release.
One of Bocherens and his colleagues' suggestions was a rain-on-snow event — during which an impenetrable layer of ice freezes on top of the snowpack — that prevented the mammoths from grazing on the vegetation they needed to survive.
In October 2003, a severe rain-on-snow event killed 20,000 musk-oxen on Banks Island in northern Canada, reducing the herd by 25%. Thousands of reindeer on present-day Wrangel Island have perished from similar icing episodes in the past century, according to a 2018 study.
"These events can be catastrophic to the population and appear to occur fairly often," Bocherens and his co-authors concluded.
Perhaps rain-on-snow killed off the last mammoth, too.