The last mammoths to stomp on Earth lived on Wrangel Island in the Arctic Ocean. This isolated population lived for thousands of years after most mammoths were gone, but when extinction finally came, it happened quickly. New evidence may finally explain what happened to these stubborn holdouts.
Research published in Quaternary Science Reviews is shedding new light on the last population of woolly mammoths and the possible reasons for their extinction.
Chemical analysis suggests the mammoths’ habitat on Wrangel Island was in decent shape when they finally disappeared some 4,000 years ago and was therefore an unlikely reason for their extinction. Rather, the new research, led by Laura Arppe from the University of Helsinki, suggests prolonged isolation on the island made the mammoths genetically weak, making them vulnerable to extreme weather. Other factors, like poor access to fresh water and human predation, were cited as other possible reasons for their demise.
During their impressive reign, woolly mammoths occupied a territory extending from Spain to Beringia and into North America. Mammoths thrived for hundreds of thousands of years, but something changed between 15,000 and 10,000 years ago that led to their extinction. Scientists aren’t in agreement as to why mammoths went extinct, but the end of the last ice age and the resulting loss of habitat, plus over-hunting by humans, probably had a lot to do with it.
Map showing the locations of mammoth remains used in the new study (1 ka = 1,000 years). (Image: L. Arppe et al., 2019)
By around 10,000 years ago, the mammoths were gone – save for two isolated populations: one on St. Paul Island off the southwest coast of Alaska and one on Wrangel Island in the Arctic Ocean off the northeast coast of Siberia. Incredibly, these mammoths, who were stranded by rising sea waters, survived for thousands of years, but they too died out. The mammoths on St. Paul were gone by 5,400 years ago, and the population on Wrangel wrapped things up around 4,000 years ago. And that was it – the woolly mammoths were officially done.
That mammoths were still around on Wrangel Island some 4,000 years ago is pretty amazing. That’s well into the Holocene period, somewhere around 6,000 to 7,000 years after mammoths disappeared from Siberia, Beringia, and North America, and a few hundred years after the Ancient Egyptians built the Great Pyramid at Giza. That said, the extinction of the Wrangel mammoths was “fairly abrupt” and “without signs of prior decline of the population,” according to the new paper.
The purpose of the new study was to figure out what happened to the Wrangel Island mammoths and why things turned sour for them so quickly. To that end, the researchers conducted an isotopic analysis of mammoth remains, which they did to gain a better understanding of the ecology at Wrangel Island at the time of the mammoth extinction. This analysis involved carbon, nitrogen, and sulfur isotopes, and it showed what the mammoth diet was like at the time.
In total, the researchers analysed 77 mammoth specimens from Wrangel Island, Beringia, and the lower latitudes of Eurasia, along with the remains of mammoths from St. Paul Island. These specimens dated from 40,000 to 4,000 years ago.
Data gleaned from the Wrangel mammoths suggests their island habitat was just fine at the time of their extinction. Consequently, the suggestion that these mammoths went extinct because of gradual environmental degradation, and the subsequent reduction in the quality and quantity of their food, does not hold up to the new evidence. Something else must have happened.
That “something else” may have something to do with their extended isolation on the island.
Recent genetic research into the Wrangel mammoths shows they lacked genetic diversity and were susceptible to inbreeding – factors that possibly “made the population more vulnerable to extinction,” the authors wrote in the new paper. Compared to their 40,000-year-old Siberian forebears, the Wrangel mammoths exhibited a significant number of gene deletions, retrogenes, and other genetic anomalies which, “although not lethal,” may have diminished the “survival capacity of an already struggling population,” according to the paper.
Importantly, geneticists have linked many of these gene deletions to the mammoths’ ability to metabolise fat – an observation corroborated in the new study. Carbon isotopic analysis of the Wrangel mammoths showed stark differences between the fats and carbohydrates in the diets of Wrangel mammoths compared to their earlier Siberian counterparts. This suggests the Wrangel mammoths were less adapted to tolerating extreme cold conditions.
“We think this reflects the tendency of Siberian mammoths to rely on their reserves of fat to survive through the extremely harsh ice age winters, while Wrangel mammoths, living in milder conditions, simply didn’t need to,” explained Arppe in a University of Helsinki press release.
Rock weathering was another factor raised in the new paper. The increased precipitation on Wrangel Island during the Holocene caused toxic chemicals, such as sulfide, base metals, copper, and antimony ores, to be flushed out from the rocks on the island’s central mountains, which the researchers observed as traces of sulfur and strontium in the mammoth remains. Poor access to clean fresh water didn’t cause the mammoths to go extinct, but like their diminished DNA, it certainly didn’t help, according to the paper.
Despite these hardships, there’s no evidence to suggest the Wrangel mammoths suffered gradual population declines. As noted, their disappearance happened quite suddenly. To explain their quick extinction, the researchers argue that this genetically weakened population – one possibly made even weaker by poisoned water – was likely killed off by an extreme weather event.
One possibility is a phenomenon known as rain-on-snow, in which an impenetrable frozen layer of snow makes it impossible for herbivores to graze on plants underneath (as a relevant aside, this actually happened on the Norwegian archipelago of Svalbard this past winter, killing more than 200 reindeer). A single rain-on-snow event might have been the straw that broke the camel’s back on Wrangel Island, reducing the mammoth population to an irrecoverable degree.
The notion that humans contributed to the extinction of the Wrangel mammoths was deemed unlikely by the researchers, but they did not it out.
The earliest archaeological evidence of humans on Wrangel Island dates to around 3,650 to 3,350 years ago, which is several hundreds of years after the mammoths were gone. These humans survived by hunting marine mammals and geese, and there’s no evidence they hunted mammoths. That said, the “idea of prehistoric hunters visiting the island and encountering mammoths cannot be excluded on simple grounds of absence of archaeological evidence, as probabilities of finding such evidence is low,” the authors wrote, adding that future research should focus on this possibility.
Regardless, the end of the mammoths was all but assured by this point. With the ice age firmly in the rear-view mirror and much of the Mammoth Steppe replaced by lush forests and marauding humans, these majestic beasts bid farewell to a world that no longer had a place for them to live.
Featured image: Juha Karhu