Woolly Siberian Mammoths Extinct Due To Hunting, Not Climate Change

Siberian woolly mammoths went extinct because of excess hunting, not climate change, according to a study at the University of Michigan.  

The chemical clues inside the tusks of the young mammoths revealed that they were still in their weaning age, researchers Michael Cherney, a doctoral student at University of Michigan and his adviser Daniel Fisher, the Museum of Paleontology Director, revealed in a news relase.

The weaning age is when an infant mammal is introduced to its adult life diet and gradually withdrawing the supply of its mother's milk.

Woolly mammoths and other giant mammals were wiped out from Siberia and North America 10,000 years ago, going extinct at the end of the last ice age. Human hunting and climate accounted as a one-two punch in the mammoth's extinction, according to the researchers. But, by examining juvenile Siberian woolly mammoths' tusks, the researchers found that the weaning age of the mammoths had decreased about three years over the course of 30,000 years, when the mammoths were heading for extinction. Climate change affected nutritional stresses also delayed weaning in the mammoths.

"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," Cherney said.

In their study, the researchers used a collection of Siberian mammoth tusks that were gathered over the last 20 years - about three dozen of them were juvenile tusks.

"We have known for about a decade that valuable information about weaning age could be extracted from these tusks," said Fisher. "This is a milestone in the development of our approach, and it shows that the extinction problem is solvable."

Fifteen mammoth tusks ranging between the ages three to 12 were analyzed. The three-year-old's tusk was about 10 inches long, while the 12-year-old's tusk was about 30 inches long. By using CT scans, Cherney was able to identify annual growth increments, which were comparable to a tree's annual growth rings, in the mammoths' tusks.

Radiocarbon dating, a method for determining the age of an object containing organic material by using the properties of radiocarbon, of the 15 Siberian tusks showed they existed about 40,000 years ago to about 10,000 years ago, according to the researchers.

Cherney and Fisher found that during the course of 30,000 years, the average weaning age decreased from age eight to age five among juvenile mammoths.

"I started studying tusks 30 years ago and realized early on that life histories are the key. Nobody else has used tusks, which are after all a record of life and growth, as a source of data in this way," said Fisher.

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