Paleontology: Overkill, Not Overchill

What ever happened to the saber-toothed tiger, the dire wolf, the mammoth, the giant beaver, and more than 100 other species of large mammals that once inhabited North America? All that paleontologists know for sure is that about 10,000 years ago, as glaciers retreated northward into Canada during the Late Pleistocene epoch, these animals suddenly became extinct. Their demise, many scientists believe, was caused either by sudden climatic change —which upset their breeding season and produced a lethal sterility—or simply by winter weather, which ironically may have become increasingly severe as...

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