What doomed mammoths on a remote Alaskan island?
Flying Puffin/Wikipedia Commons

What doomed mammoths on a remote Alaskan island?

Scientists may have finally solved the mystery of when—and why—the mammoths on a remote Alaskan island died out. Once a part of the Bering land bridge that joined Alaska to Siberia, St. Paul Island lies more than 450 kilometers from both the Alaskan mainland and the nearest Aleutian island. Carbon dating of the remains of woolly mammoths (Mammuthus primigenius, artist’s model shown) found there suggest the creatures lived on the island at least until about 6500 years ago. But there’s no guarantee that the most recent remains thus analyzed belong to the last mammoth to live on the island, of course. Now, scientists have scrutinized a 14-meter-long tube of sediment drilled from one of the largest lakes on the 110-square-kilometer island, a trove of information thought to have accumulated during the last 18,000 years. Several trends in the sediments’ contents—including near-simultaneous shifts in its pollen and plant remains, the DNA from ancient creatures that lived around the lake, and the spores of three types of fungi known to have thrived on the dung of ice age megafauna—all point to the survival of mammoths until about 5600 years ago, the researchers report online today in the Proceedings of the National Academy of Sciences. On the North American and South American mainlands, humans as well as climate change contributed to the extinction of megafauna such as saber-toothed cats, giant sloths, and woolly mammoths about 12,300 years ago, a recent study suggests. But because humans apparently didn’t discover St. Paul Island until the late 1780s, ancient hunters didn’t trigger the die-offs there, the team suggests. Instead, rising sea levels following the end of the last ice age shrunk the island, reducing the number of mammoths it could support. Lake water also grew shallower, cloudier, and slightly saltier about 7850 years ago, according to the data. Modern-day elephants need between 70 and 200 liters of freshwater each day, the researchers note, and woolly mammoths—encased in thick hair—likely needed more than that to combat overheating as Earth’s climate warmed.