Bear-size beavers, mammoths, horses, camels and saber-toothed cats used to roam North America, but by 11,000 years ago most such large mammals had died off. To this day, experts debate what caused this late Pleistocene extinction: climate change, overhunting by humans, disease--or something else? Eric Scott, curator of paleontology at the San Bernardino County Museum in Redlands, Calif., suggests it was something else: namely, the immigration of bison from Eurasia.
Armed with data from his own ongoing excavations as well as from those dating back as far as the 1800s, Scott says that bison appeared in North America as early as 220,000 years ago and spread across the continent throughout the remainder of the Pleistocene, a time when climate change had made food and water scarce. He first formally suggested the idea last spring in the journal Quaternary International , speculating that bison may have won enough battles for food and water during that time to share the blame with climate change as the major cause of the large mammal extinctions.
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