Extinction sucks. Only yesterday, in geologic terms, did mastodons, sabercats, giant ground sloths, and their charismatic Ice Age contemporaries roam North America. Humans even encountered these beasts, but I was born about 10,000 years too late to see the Pleistocene menagerie. I just missed some of the most wonderful mammals ever to tread the continent.

When 18th-century scientists began to scrutinize the bones of these Pleistocene megamammals, though, extinction had not yet been universally recognized as a reality. By the hand of God or the balance of nature, every creature was believed to have a perpetual role to play on the Earth’s stage. Remove even one species from that order, and the whole theater might crumble with it. No surprise, then,