Where did all the mammoths go?

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15,000 years ago, mammoths, sloths, mastodons, and their giant friends were lumbering around North America, munching plants and admiring each other's tusks. (Except the sloths--no tusks there.) Then, something killed them all off. In Last Extinction (watch online), which premiered last spring, NOVA took on the headline-grabbing hypothesis that a comet wiped out the beasts. But a new study of ancient dung fungus (who said science was glamorous?) suggests that the behemoths were on their way out the door thousands of years before the alleged comet slammed it behind them.

Here's the evidence for the comet: A 12,900-year-old layer of organic material speckled with telltale impact markers like iridium, titanium, and nanodiamonds. But when a team of scientists went digging in the ancient sediment under Appleman Lake in Indiana, they found that the mammoth-dung-loving fungus Sporormiella started disappearing 14,800 years ago, and was almost gone just a thousand years later. Their conclusion: Mammoths and Company were gone long before the comet came on the scene.

Scientists have been debating the fate of the megafauna for decades, and the crossfire is sure to continue. Next stop: The American Geophysical Union conference in December, where the comet camp will duke it out with the comet skeptics. Stay tuned for more!

Image: Mastodon restoration by Charles R. Knight (1897)

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