Time detective tackles a mammoth mystery

Mammoth teeth from the Old Crow area have made a splash in the news lately.

By Claire Eamer

Mammoth teeth from the Old Crow area have made a splash in the news lately. In some clever scientific detective work, University of Western Ontario graduate student Jessica Metcalfe used them to learn about the maternal behaviour of animals that have been extinct for thousands of years.

Metcalfe discovered that woolly mammoths living in the Old Crow area as much as 150,000 years ago raised their young quite differently from their modern relatives, elephants. Elephant calves start eating some solid food as early as three months, but woolly mammoth calves lived almost entirely off their mothers’ milk for as long as three years.

Nursing their babies for so long was a drain on the mother mammoth’s energy reserves. However, sticking close to mom was an advantage for the calf in a land where night-hunting scimitar cats and other predators were a constant threat. Also, the nursing calves had a steady supply of food, even during the long, dark months of a northern winter.

But how can you deduce intimate details of mother-child behaviour from ancient teeth? And how does an Ontario researcher end up with Yukon mammoth teeth?

For Metcalfe, it began with people. Her Master’s degree involved studying stable isotopes in the bones and teeth of ancient Mayans from Belize to determine what people ate. Stable isotopes are particular forms of elements, such as carbon, that don’t decay over time and show up in the same proportions in dead tissue as in living tissue. Those proportions reflect what the living person ate and drank, so measuring them provides information about ancient diets.

It works for animals too, so when Metcalfe was looking for a doctoral research project, her supervisor suggested applying the same technique to mammoths.

Metcalfe knew nothing about mammoths, but she was intrigued by the idea and started researching mammoths. “It looked interesting, and there was a lot of potential for different kinds of projects. The problem was getting samples!”

She needed access to a large collection of mammoth remains to find the answers she was looking for, so in 2006 she started searching for such a collection. It was a slow process, Metcalfe says, because she didn’t know exactly who to contact. “It was the first time I had done something like this. I didn’t get a lot of responses at first.”

Then she struck gold – Yukon gold. Her request for information passed from hand to hand until it reached Yukon government archaeologist Greg Hare. He passed it on to Yukon palaeontologist Grant Zazula, and the project took off.

“Grant was unbelievably helpful,” Metcalfe says. He asked about her work, suggested potential contacts for samples, and ultimately invited her to the Yukon to look over the Yukon Government’s collection. She arrived in November 2008.

“The palaeontology collection was amazing! I was like a kid in a candy store looking at all those fossils.”

Metcalfe had intended to use adult mammoth teeth to study regional differences in climate and diet. “But when I saw the amazing collection of baby teeth, I realized there was great potential for a nursing/weaning study. If I hadn’t been to visit the collection in person, this study never would have happened.”

Adult mammoth teeth are huge, Metcalfe says: as much as 30 cm long and 10 cm wide, or about as big as a man’s boot, size large. “It’s incredible to hold them in your hand and know that 40,000 years ago or more, they were in the mouth of a living elephant (mammoth).”

She spent several days carefully shaving off samples from different parts of the teeth. “I did my best to do it in the least damaging way possible, but it had to be done in order to get material for the study.”

In the end, Metcalfe had samples from 50 individual mammoths. The study of nursing patterns is based on 22 of the samples, all from the Old Crow area. The rest – teeth from the Klondike and Herschel Island – will be used in another chapter of her thesis and in another scientific paper, still to appear.

Teasing information out of the teeth is a laborious process. First, Metcalfe had to clean the samples, removing any dirt that might contaminate the results. Then she ground them by hand, with a mortar and pestle, and put them through a chemical purification process. The result, for the organic bits of bone and teeth, was a gelatin called collagen.

“It’s the same stuff used in baking,” she explains, “just from mammoths instead of cows or pigs.”

To measure stable isotopes of carbon, nitrogen, and oxygen, she weighed a tiny amount of collagen and burned it or reacted it with acid to produce gases containing the elements. A mass spectrometer then measures the relative amounts of the isotopes in the gases. The process is automated, but the machines are “finicky” and need to be monitored, she says.

“Basically, you sit beside a machine all day, watching a computer screen and recording results as they come up. It sounds boring, but is actually exciting, because all the work of sampling, cleaning, grinding, purifying, weighing, etc. has led up to this moment: actually getting numbers out of a machine!”

The work was worthwhile. The numbers Metcalfe teased from ancient teeth are shedding new light on ancient animal behaviour, as well as on extinction patterns and the impact of past climate change. The information might even help us predict how the current changes in climate could affect modern animals.

For more information, contact Jessica Metcalfe at jmetcal5@uwo.ca.

The Your Yukon column is co-ordinated by the Northern Research Institute at Yukon College. This column is sponsored by the CircumArctic Rangifer Monitoring and Assessment Network. A full list of funders and all past articles are available at www.taiga.net/yourYukon.

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