![]() ![]() And in each case, the sloths disappeared soon after humans first arrived, the team reports online this week in Proceedings of the National Academy of Sciences. Although global warming could have played a part in the North American extinctions, climate was relatively stable during the final years of the island dwelling sloths. Using carbon dating, they found that while large sloths on the North American continent died off around 11,000 years ago, sloths in South America survived until 10,500 years ago, and some on the West Indian islands lived until 4400 years ago. In the new study, biologist David Steadman of the Florida Museum of Natural History at the University of Florida in Gainesville, Paul Martin of the University of Arizona in Tucson, and colleagues studied fossilized sloth bones and dung from extinct species in North America, South America, and several West Indian islands. ![]() Untangling the two potential causes has proven difficult, and a dearth of archeological "kill sites" with man-made weapons and mammal bones together has forced scientists to rely on circumstantial evidence. But clouding the issue is the environmental upheaval that accompanied the end of the last ice age, and a few vocal scientists continue to argue that climate change was to blame. The most incriminating evidence is radiocarbon dating of tools and spear points that puts humans in the right place at the right time-with weapons. The idea that humans caused the large mammal extinctions in North America has gained steam in recent years. Scientists have been trying to solve this prehistoric whodunit for decades, and now, thanks to new radiocarbon dating, they're one step closer to fingering human hunters as the culprit. Around 11,000 years ago, saber tooth cats, woolly mammoths, giant ground sloths, and almost every other large mammal in North America went extinct.
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