The answer, of course, was the Ice Age. That was what exterminated the former horses of the Americas, and a number of other previously successful mammals. Nor were extinctions limited to the New World. On the contrary, in different parts of the earth (for different reasons and at different times) the long epoch of glaciation witnessed several quite distinct episodes of extinction. In all areas, the vast majority of the many destroyed species were lost in the final seven thousand years from about 15,000 BC down to 8000 BC.
