Some of the world's last remaining woolly mammoths literally died of thirst, according to a new study published in the Proceedings of the National Academy of Sciences. The ancient animals were still living on a small island off the coast of Alaska until about 5,600 years ago—or 5,000 or so years after most woolly mammoths had died off, the Alaska Dispatch News reports. The study concludes it was a lack of fresh water that finally did in the holdouts on St. Paul Island. According to the BBC, rising ocean levels at the end of the Ice Age not only shrank the woolly mammoths' island home, but inundated freshwater reservoirs with seawater.
The study's author, Russ Graham, tells the Guardian there were probably only two watering holes left for the mammoths at the end, and those were shallower and saltier than before. The problem was exacerbated by more mammoths crowding around fewer water sources, trampling vegetation and eroding sediment into the water. Modern elephants can drink more than 50 gallons of water per day; woolly mammoths would likely have needed even more to keep their hairy bodies cool in a warming climate. With little fresh water left, the St. Paul mammoths were likely killed off by heat stress and dehydration. A professor at the Swedish Museum of Natural History says the study likely makes the mammoths' demise the "most well-described and best understood prehistoric extinction event." (A Michigan farmer was shocked to discover a giant mammoth on his property.)