Tusks of Siberian woolly mammoths suggests humans were more responsible for mammoth's demise than climate change
The cause of extinction of woolly mammoths has been a mystery over the years. It’s a longstanding debate among scientists whether it was the humans, the climate change or a multitude of factors that contributed to the killing of the giant mammal.
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But a new research suggests that humans were more responsible for the extinction of the animal rather than climate change. By collecting chemical samples from tusks of Siberian woolly mammoths, two paleontologists from University of Michigan found that hunting pressure accelerated maturation process in the mammoths and likely resulted in earlier weaning, a time when calf stops talking milk and ultimately drove them to demise.
"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.” Michael Cherney, a doctoral student in the U-M who is working alongside Daniel Fisher, director of the University Of Michigan Museum of Paleontology said.
Woolly mammoths disappeared from Siberia and North America about 10,000 years ago, at the end of the last glacial period. Many previous researches blamed both humans and climate change for the extinction of the animal but they were unable to determine the dominant factor of two. The new study is not conclusive either but it certainly opened a new window on this discussion.
"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.” Cherney said.
The study was made possible by the extensive collection of Siberian mammoth tusks that Daniel Fisher has collected over the past 20 years.
"We have known for about a decade that valuable information about weaning age could be extracted from these tusks," said Fisher. "But this is the first time we've had data from enough individuals, and covering a wide enough range of geologic ages, to show a pattern through time. This is a milestone in the development of our approach, and it shows that the extinction problem is solvable."
Researchers compared the isotopic composition of mammoths with a mother and calf pair of elephants at Toledo Zoo. The CT scans of tusks were taken to identify the annual growth pattern of mammoths and it was found that isotopic ratios from the calves' early years of life reflected the reduced contribution of milk to the overall diet. It is a sign of short-term nutritional stress and indicates that average weaning age decreased from 8 to 5 over a span of roughly 30,000 years leading up to the woolly mammoth's extinction.
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"The strength of life-history analyses for resolving the extinction debate rests in the knowledge that the age of final weaning is a life-history landmark that is expected to change differently in response to predation and climate-related nutritional stress," said Cherney. "Our analysis sets up a test of competing hypotheses, and our preliminary results are consistent with expectations under hunting pressure."