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Arctic mammoths may have nursed longer than elephants because the long winter nights made it more important for infants to stay near their mothers to avoid predators, researcher Jessica Metcalfe suggested. These mammoth models are displayed at the Neanderthal Museum in Mettmann, Germany. ((Martin Meissner/Associated Press))

Baby woolly mammoths in the Yukon were nourished exclusively on their mother's milk for two years, much longer than elephants exclusively nurse their young, a new study has found.

The dependency on nursing may have hastened the extinction of the giant tusked mammals 10,000 years ago, suggested Jessica Metcalfe, the University of Western Ontario researcher who led the study published in December in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

"Woolly mammoths may have been more vulnerable to the effects of climate change and human hunting than modern elephants," said Metcalfe, a PhD student working with earth sciences professor Fred Longstaffe, who co-authored the paper.

She noted that producing milk and nursing an infant requires a lot of energy from the mother, something that might be especially hard on mother mammoths during the Arctic's long winter months.

Metcalfe and another co-author, Grant Zazula of the Yukon Paleontology Program, studied the teeth of infant and adult mammoths that lived in Old Crow, Yukon, north of the Arctic Circle, about 150,000 to 40,000 years ago.

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An analysis of adult (such as A and D) and infant (B and C) mammoth teeth showed that baby mammoths didn't start solid foods until they were at least two years old. ((University of Western Ontario))

The researchers analyzed chemical elements in the teeth, including carbon, nitrogen, oxygen, calcium, barium and strontium. In some cases, they compared the amounts of different isotopes — multiple versions of an element with different atomic masses. Some of the ratios in teeth are known to change depending on the animal's diet.

Based on the analysis, they concluded that baby mammoths didn't start eating solid foods such as plants before they were two years old, even though elephants start solid foods at three months of age.

Mammoths may have nursed exclusively for longer because the long winter nights made it more important for infants to stay near their mothers to avoid predators, Metcalfe suggested. It also meant edible plants were less available.

To test that hypothesis, scientists will need to examine the teeth of mammoths that lived closer to the equator and see whether they started their young on solid foods sooner, the paper said.

Metcalfe added that research into mammoth adaptations and behaviour will not only help scientists understand how they became extinct, but could also help predict how modern day mammals might respond to climate change.