Shift in weaning age supports hunting-induced extinction of Siberian woolly mammoths

http://www.eurekalert.org/pub_releases/2015-10/uom-siw100915.php

Public Release: 15-Oct-2015
Shift in weaning age supports hunting-induced extinction of Siberian woolly mammoths
University of Michigan

Chemical clues about weaning age embedded in the tusks of juvenile Siberian woolly mammoths suggest that hunting, rather than climate change, was the primary cause of the elephant-like animal's extinction.

Woolly mammoths disappeared from Siberia and North America about 10,000 years ago, along with other giant mammals that went extinct at the end of the last glacial period. Current competing hypotheses for the mammoth's extinction point to human hunting or climate change, possibly combining in a deadly one-two punch.

Despite decades of study, the issue remains unresolved and hotly debated. But two University of Michigan paleontologists may have found an ingenious way around the logjam.

U-M doctoral student Michael Cherney and his adviser, Museum of Paleontology Director Daniel Fisher, say an isotopic signature in 15 tusks from juvenile Siberian woolly mammoths suggests that the weaning age, which is the time when a calf stops nursing, decreased by about three years over a span of roughly 30,000 years leading up to the woolly mammoth's extinction.

Climate-related nutritional stress is associated with delayed weaning in modern elephants, while hunting pressure is known to accelerate maturation in animals and would likely result in earlier weaning, according to Cherney and Fisher.

"This shift to earlier weaning age in the time leading up to woolly mammoth extinction provides compelling evidence of hunting pressure and adds to a growing body of life-history data that are inconsistent with the idea that climate changes drove the extinctions of many large ice-age mammals," said Cherney, who is conducting the work for his doctoral dissertation in the U-M Department of Earth and Environmental Sciences.

"These findings will not end the debate, but we hope they will show people the promise of a new approach toward solving a question that, so far, has just led to divided camps," said Cherney, who is scheduled to present his findings Oct. 15 at a meeting of the Society of Vertebrate Paleontology in Dallas.

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