英语听力：探索发现 2013-02-08 猛玛象进城记 Mammoths to Manhattan—5

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Camels survived for millions of years in North America, but disappeared around the same time as the mammoths. Wild horses first evolved here and became dominant² grazers. Yet they, too, vanished soon after the Ice Age ended. But there’s little evidence to suggest that humans hunted horses or camels. This seems to go against the hunting argument. 

 

So what else would have triggered such large-scale extinctions? 

 

The other major possibility is climate change. The end of the Ice Age was a turbulent, erratic³ period. In some areas, rain patterns were shifting, bringing moisture back to dry landscapes and turning grassland⁴ into forest.

 

Other regions of the continent were plunged⁵ into prolonged periods of draught⁶. For grazers such as horses, this led to a massive change in habitat, one they were not flexible enough to overcome. 

 

As the land dried out, many grass eaters disappeared. We may never know for certain what killed off most of the larger animals at the end of the Ice Age. We do know that there was a time of coincidence—people were arriving just as the climate was in a state of change. Both may have played their part. Whichever was responsible, more than 70 species vanished for good, but some large animals did survive and still live here today.

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