Who Killed Woolly?

New studies suggest that Stone Age hunters may have driven dozens of huge creatures to extinction

Hard as it may be to imagine, 20,000 years ago--when the last Ice Age reached its climax--much of North America looked like something out of Africa's teeming Serengeti Plain. Roaming through grasslands and forests were mammoths and mastodons with huge, curved tusks, ground sloths the size of rhinos and bison with sharp-tipped horns that measured more than 6 ft. from tip to tip. Bear-size beavers roamed the forests. Large-headed llamas grazed in rocky meadows. And giant armadillos maneuvered across the landscape like living armored tanks.

Stalking these massive creatures were predators of equally awesome aspect: muscular jaguars, saber-toothed cats and thick-bodied...

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