When did the last of the ground sloths disappear? The standard answer is “about 10,000 years ago”. That’s the oft-repeated cutoff date for when much of the world’s Ice Age megafauna – from mastodons to Megatherium – faded away. It’s nice and neat, falling just after the close of the last Ice Age and during a time when humans were spreading to new continents. In fact, it’s too clean a cutoff. The shaggy, ground-dwelling sloths that inhabited almost the entire span of the New World didn’t all topple over at once. They very last of their kind, both protected and made vulnerable by life on islands, were still shuffling 4,200 years ago.

Calling the time of death for any