How Scientists Tracked the Movements of a 17,000-Year-Old Woolly Mammoth

Isotopes tell the epic tale of one ancient mammal’s odyssey across Alaska

The arctic woolly mammoth named Kik, one of the only Ice Age mammals whose life story is known in detail, was born approximately 17,100 years ago in the Alaskan interior, a region bounded by the Brooks Range to the north and the Alaska Range to the south. Back then, the area was a cold, dry grassland that extended across the Bering land bridge into Siberia, and all the way to western Europe. Paleontologists call this vast region the “mammoth steppe” after the largest animals that traversed it.

Adult male woolly mammoths reached a height of 12 feet at the shoulder, with a thick hide, shaggy coat and tusks up to 12 feet long. No predator could bring down an adult, but young mammoths, likely standing about four feet tall, were prey to scimitar-toothed cats. Kik and his herd-mates would have kept a wary eye on these predators, which weighed more than 500 pounds, with serrated canines that could bite through mammoth hide. Beringian lions were another threat; also on the landscape were steppe bison, giant short-faced bears and the gray wolves and brown bears we see today.

For the first two years of his life, Kik mostly stayed in the lower Yukon River basin, almost certainly in a matriarchal herd. Over the next 14 years, the juvenile’s range expanded dramatically. Still probably traveling with the herd, he made regular back-and-forth journeys across the 250-odd-mile stretch of steppe grassland between the Brooks Range and the Alaska Range. Sometimes he ventured to the eastern end of the Brooks Range. He also traveled to the Seward Peninsula on today’s west coast, a journey of more than 700 miles. Although the data suggests that for much of his life, he seldom covered less than ten miles in a day, we now know that over the course of his lifetime, Kik walked roughly twice the circumference of the earth—much farther than mammoths were thought to travel.

To be able?to track an Ice Age animal’s movements in such detail is a stunning milestone in paleontology. It began with a moment of inspired curiosity in the mind of?Matthew Wooller , an isotope scientist at the University of Alaska Fairbanks. In 2015 he was in his laboratory, watching one of his graduate students analyze fish otoliths—small ear bones that add a new layer every year and store chemical information about the fish’s life and habitat. “What if we did the same thing with a mammoth tusk?” thought Wooller, an expatriate Englishman with a shaved head and a crisp, upbeat manner. He was already interested in mammoths from studying their extinction on St. Paul Island in the Bering Sea. He compares a mammoth tusk to a diary written in ivory. “It adds a new layer every day, and the layers stack up on each other like ice cream cones,” he says. “The isotopes in those layers record where the animal was and what it ate that day.”

Isotopes are atoms of the same chemical element that have differing weights, because of a greater or lesser number of neutrons. “Think of isotopes as chemical signatures,” Wooller says. “They’re in the rocks, soil, vegetation and water, and creatures pick them up.” These signatures—or “fingerprints,” as they’re sometimes known among researchers—are specific to particular locations. Wooller knew that isotopes in elephant tusks can reveal migration routes. “Where does a mammoth move?” he says. “That was the main question I wanted to answer.”

He began the project in 2016 by crossing campus to the?University of Alaska Museum of the North , where 174 woolly mammoth tusks are stored on top of specimen cabinets in a lower level. He selected one that had been collected by the university’s researchers in 2010, near the headwaters of the Kikiakrorak River on Alaska’s North Slope. The mammoth’s jawbone, containing molars the size of a man’s shoe, was collected at the same site. Radiocarbon dating showed that the animal died 17,100 years ago, and genetic testing revealed that it was male. “We nicknamed him Kik after the Kikiakrorak,” says Wooller, who assembled a team of 16 scientists from four different countries to work on the study.

The most physically arduous task was splitting the roughly 50-pound tusk in two. “Six of us fed it through a huge band saw,” Wooller says. “The tusk has a double twist, so you’re constantly making adjustments, and it was cracking and popping like it was going to explode. It took us a whole day.”

Now, the split tusk lies on a laboratory table. Each half is five-and-a-half feet long, stained with blue dye to reveal its growth layers. “The tip of the tusk is the young mammoth, the base is the old mammoth, and everything in between is its lifetime,” Wooller says.

Wooller opens up a remarkable map on a screen. It shows the different regions of Alaska that Kik occupied during the different phases of his life, plus hundreds of his travel routes. Asked how the team managed to map Kik’s life in such detail, Wooller cites a surprising aid: “It’s amazing what voles can tell you. They’re like little citizen scientists.” Since voles have a small range and don’t travel, the isotopes in their teeth record site-specific information about where they lived—allowing Wooller to dig into the past with even more clarity.

In a lower?level of the University of Alaska Museum of the North, in the specimen cabinets beneath the mammoth tusks, sits an extensive collection of voles and other rodent specimens collected from all over Alaska. The museum’s director, a paleontologist named?Patrick Druckenmiller , who contributed to the Kik study, says strontium isotypes in these rodents’ teeth offered the key mapping aid. “[The] isotopic signature varies from place to place, depending on the underlying geology. Plants absorb strontium from the rock beneath the soil, and animals ingest it through eating plants.”

By analyzing the strontium values in 162 of these rodents, the team was able to build up a strontium map of Alaska. Clément Bataille at the University of Ottawa and Juliette Funck, then a doctoral student at Wooller’s laboratory, created the map. Even though it’s based on data from rodents in the modern era, the map is accurate for the Pleistocene, too, because the underlying rocks are the same. “Strontium values reflect bedrock geology, so they change very, very slowly, over millions of years,” Druckenmiller says.

Meanwhile Wooller and his colleagues were looking at the strontium and other isotopes in Kik’s tusk. Working their way from one end to the other, they cut five-centimeter wedges from the core, mounted them and fed them into a $830,000 scientific instrument called a Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometer. The National Science Foundation awarded a $580,000 grant to help the University of Alaska Fairbanks purchase this instrument, which now resides in a cavernous basement room. It’s the size of a minivan. “It’s down here because we were worried it would break through the floor upstairs,” Wooller says.