They found the oldest bones to be just 650 years old. Worthy and colleagues confirmed their findings using a completely independent line of evidence, by dating 150 tree nuts from other sites, which were attractive food for ancient rats. "Some of the tree seeds are nearly a centimeter long and you can clearly tell whether they've been chewed by a rat or not," he said. Grooves in the nut match the width of the teeth of the rats, said Worthy, which were the only gnawing mammal in New Zealand at the time. "The seeds that were not chewed extended in age back to 3,000 years ago, but there was no evidence of rats prior to about 650 years ago." Worthy said the findings suggest Holdaway's dates were wrong due to errors in radiocarbon dating. At the time, he said, radiocarbon dating was not capable of accurately date small amounts of material, which is all Holdaway had. Worthy said the "cleaner technology" being used today, together with the more numerous samples of bones and confirmation from the chewed nuts all adds up to a more convincing argument. The date humans -- and rats -- arrived in New Zealand is also relevant to debates over conservation policy. New Zealand's fauna is threatened by rats and more recently introduced mammals requiring management by conservation authorities. But, Worthy said, these authorities have adopted Holdaworthy's dates, which suggests destruction of New Zealand fauna by rats occurs slowly. The latest paper confirms that destruction can happen quite quickly and should emphasize the urgency of controlling fauna destruction by such animals. Related Links: |
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