Mammoth’s Rambling Life Mapped Out From Study of Its Tusks

Mammoth’s Rambling Life Mapped Out From Study of Its Tusks

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More than 17,000 years ago, a woolly mammoth known today as Kik wandered far and wide across Alaska during his 28 years of life.

When Kik was young, he spent most of his time in the Alaskan interior, a less mountainous area. Then, when he turned 15, his patterns of movement shifted, spending much more time to the north, where the Arctic Wildlife Refuge and National Petroleum Reserve are found today.

During some years, Kik migrated with the seasons. Other years, he largely stayed put in the same area all year around.

In the last couple of years of his life, his movement slowed, and he was confined to a smaller area above the Arctic Circle. At 28 when he died, Kik was still middle age for a mammoth.

This map of where Kik roamed during his life was pieced together by studying signatures of elements locked in one of his curving eight-foot-long tusks, and it provides insight into these hairy, elephant-like mammals.

“This is a better understanding how they behaved, what environment they used,” said Matthew Wooller, director of the stable isotope facility at the University of Alaska, Fairbanks and lead author of a paper published on Thursday by the journal Science that describes the findings.

The data could also play into the debate about the demise of the woolly mammoth after the end of the last ice age. Did early humans hunt them to extinction? Was it a changing climate that they could not adapt to?

“Our work kind of speaks to that a little bit as well by filling in a little bit of the jigsaw puzzle,” Dr. Wooller said. “When you’re trying to figure out what the causes of an extinction were, you need to know a little bit more about the behavior and ecology of the organisms involved.”

Most mammoths disappeared about 10,000 years ago — very recently, on evolutionary and geological time scales — and not all of the fossil remains have turned to rock. That allows DNA to be extracted from bones and sequenced, which helps answer broad-brush questions like how closely related mammoths in Alaska might have been to those in Siberia.

But the genetic information tells little about how a mammoth lived. Did it migrate with the seasons? Did it spend its youth in one region and its adulthood somewhere else?

By studying isotope signatures in Kik’s tusk, Dr. Wooller and his colleagues were able to answer those questions.

“If you were to take all those wiggly lines and straighten them out, it could have gone around the Earth almost twice,” he said.

The findings impressed Brooke Crowley, a professor of geology and anthropology at the University of Cincinnati who was not involved in the study.

“It’s rather amazing how much one can learn from little tiny bits of material from a now-extinct animal,” she said in an email. “I’m particularly impressed that the authors were able to track this individual mammoth’s movements for his entire life.”

To reconstruct Kik’s whereabouts, Dr. Wooller and his colleagues took advantage of the fact that tusks grow layer by layer — a structure that resembles stacked ice cream cones. The tip of the tusk poked out when Kik was a baby.

Pointing to the base of the tusk during a video call, Dr. Wooller said “This surface here is basically the day it died.”

In between was a record of essentially every day of his life. “If you zoom in with the microscope,” Dr. Wooller said, “you can see individual daily bands.”

In addition, Alaska possesses a rich diversity of rock formations, each with varying mineralogical fingerprints, which are reflected in the plants growing there. The researchers focused on strontium, an element that comes in four stable versions, or isotopes.

Thus, each day Kik munched on grass, which contained strontium levels reflecting that of the underlying rocks, and those same strontium levels were incorporated in that day’s layer at the base of the tusk.

Similar analysis techniques have been applied to teeth. But it was trickier to use them with a long, unwieldy, curved tusk. To get at the microscope tusk layers required a careful application of brute force.

Among the hundreds of mammoth tusks that have been found, Kik’s, excavated in 2010 near a river that gave him his nickname, were well-suited for this research. They were in good shape and both were recovered together.

“It’s pretty rare to find a pair of tusks,” Dr. Wooller said.

That and the presence of parts of his skeleton gave the scientists confidence that Kik had died where he was found, and that the remains had not been pushed there by a glacier or a flood. The bones allowed them to perform a genetic analysis that confirmed he was a male mammoth. The fact that there were two tusks made them less remorseful that they cut one of them in half.

“It’s fairly heavy,” Dr. Wooller said. “And you do a lot of thinking about it. Before you commit, you also practice.”

They cut apart what he called a “no data tusk” — one where there is no recorded information about where and when it was found and thus is of little scientific use. First, they sliced a tiny channel along one side. Then they marked points halfway around the tusk. With a big band saw — “It’s as tall as a person,” Dr. Wooller said — they cut the tusk in two, carefully guiding the blade between the channel and the marks on the other side.

Next, they cut Kik’s tusk.

“It took us most of the day to do it just to split the thing,” Dr. Wooller said. “Six of us and then a very, very large band saw.”

He added, “Even over the top of the noise of the band saw, what was nerve-racking was the sometimes quite loud pops and cracks,” he said. “We were thinking, ‘Augh, we’re going to destroy this thing. It’s going to fall apart by the time we get to the end.’ But it didn’t. It held up really, really great.”

After the tusk was cut in half, the scientists used a laser to knock off specks along the length of it for isotope analysis. From there, a computer program compared the strontium levels with a map of what is found in the rocks of Alaska and calculated the likeliest path that Kik walked. The scientists also looked at other elements like oxygen, nitrogen and carbon, which provided complementary information about the ecology.

At the time that Kik died, the world was still at the height of the last ice age, but the glaciers did not flow over most of Alaska then. Instead, the environment appears to have been dry, cool grasslands, perhaps similar to the steppes of Mongolia today. “It provided this wonderful environment for mammals to move around,” Dr. Wooller said.

Like some modern elephant species where juvenile males are kicked out of female-led herds at an age of 15 or 16, Kik might have similarly had to live a more solitary life.

“That was a really wonderful thing to find,” Dr. Wooller said. “In many ways, that was almost exactly the same as some of the behavior that we’d see in modern elephants.”

A spike in nitrogen isotopes was a distinctive signature that suggested starvation at the end of his life.

“Kind of cool to think that we’ve pinpointed not only its movement patterns but probably what caused its death,” Dr. Wooller said.

As to why Kik starved, perhaps a drought had withered the landscape or perhaps he had been injured in a fight, limiting his mobility.

Although Kik made his way around much of Alaska, it appears that he never went west, across the land bridge that then connected Alaska with Russia. That could suggest that the intercontinental crossing was not an easy path. “Some people believe that it was very, very wet and boggy and treacherous,” Dr. Wooller said.

Kate Britton, an archaeologist at the University of Aberdeen in Scotland who was not involved with the research, said scientists needed to be careful not to extrapolate the movements of Kik to the behavior of woolly mammoths as a species.

She noted that her research using similar techniques showed that members of the same species of modern-day caribou behaved in different ways — some migrating long distances with the change of seasons, others remaining in more confined regions — depending on where they lived, and information about the day-to-day life of animals was not found in their genes.

“We need these kinds of studies that give us this access to this direct information,” Dr. Britton said. “We can infer the behavioral ecology of extinct species.”

In future research, Dr. Wooller would like to saw and examine more mammoth tusks. Did patterns of movement change over the millenniums as the climate changed? Did female mammoths and their herds frequent different parts of Alaska?

He said what happened to the woolly mammoths as the world warmed at the end of the last age could also point to understanding animals living in Alaska today.

“We see polar bears and caribou are changing their biology and behavior in response to some of the warming,” Dr. Wooller said. “There are parallels that we can draw as well.”


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