Scientists decipher ivory information and recreate the life of a mammoth

For the first time, scientists deciphered a chemical in an ancient tusk, revealing an unprecedented rich prehistoric biography.

Written by: ZACH ST. GEORGE

Cracked mammoth tusks (foreground) are placed in the Alaska Stable Isotope Research Laboratory at the University of Alaska Fairbanks. In the background, researcher Karen Spaleta prepared a fragment of mammoth teeth for isotope analysis that will uncover the full life history of mammoths. Photo by JR Ancheta, University of Alaska Fairbanks

Ivory records the story of the mammoth's life. Teeth erupt from the mammoth's gums, after which the cells continue to divide, even every day.

"The tip of the tusk belongs to the young mammoth," says Matthew Wooller, an ecologist at the University of Alaska's Fairbanks, "and at the bottom tells the story of the mammoth's later years." Everything in between condenses the mammoth's life. "Ivory records the travels, diets and even deaths of their masters. The concept is simple, the difficulty is to obtain the chemical composition of ivory and explain it.

The research team led by Wooller is doing just that. They analyzed the tusks of a mammoth that lived about 17,000 years ago and found details of its activity from birth to death. The team also traced the mammoth's footprints over the 28 years of the Alaska Ice Age, marking the first time scientists have reconstructed the mammoth's life history in such detail.

The study, recently published in the journal Science, provides clues about how mammoths live, including their possible interactions with humans. The work may also help explain why these iconic animals eventually went extinct and how today's large mammals would cope with a steadily warming world.

Larisa DeSantis, a paleontologist at Vanderbilt University, said researchers have recreated the life of mammoths as much as possible, just unable to "go back in time and put a GPS collar on the mammoths." DeSantis was not involved in the study.

"Just reading this paper makes me feel like Jane Goodall, a globally acclaimed zoologist, looking at these animals."

Analyze the tusks of mammoths

I met him in Wooller's office in the summer of 2018, when he was the head of the Alaska Isotope Research Laboratory. Isotopes are different nuclides of the same element with the same number of protons and different numbers of neutrons, with slightly different atomic masses. In recent years, scientists have used isotopes to reconstruct the diet of ancient humans, cracked unsolved murders, and even determined drug smuggling routes.

"It's a thriving industry," Wooller said.

Wooller later wrote in an email that his name bore striking resemblance to his latest research subject. ("We call it the Wooller mammoth," jokes Florida-based paleontologist Gregory Erickson, co-author of the paper.) But it's just a resemblance of name; Wooller's hair and face are cleanly groomed, his glasses are well-worn, and he has a pure British accent.

He led me out of the office and across the hallway to the lab. Lab coins hang gas cylinders, bones and cuticle fragments. On the black lab bench in the center of the room was a mammoth ivory, about 1.7 meters long, thicker than my arm. It split longitudinally from the middle, like a long spiral of hot dog bread.

Wooller explains that ivory has a very pronounced inner layered structure that looks like a stack of ice cream sugar cones, but on its outer layer, the division between layers is irregular. To capture the full chemical record of ivory, the team needed to take samples from the ivory center. The first challenge of the project was to saw the curved, 22-kilogram tusks with a band saw. "We broke a couple of saw blades," he said.

After sawing the ivory apart, the team cut out wedge-shaped sections from its center, each 5 centimeters long, which were stuffed into a machine on one side of the lab. The machine, known as a laser-ablative multi-receiver inductively coupled plasma mass spectrometer, uses a laser to vaporize or melt tiny materials. The atomic mass of the resulting chemical is then analyzed.

The machine can read several isotope readings within every centimeter, providing details that other methods cannot provide. Slowly, its laser made a dotted trajectory on the ivory, combing through the chemical cues in the fragments of the ivory.

"It's like chemical GPS"

Strontium isotopes are at the heart of this research. Animals obtain strontium from plants that eat them, and plants absorb strontium from underground rocks. Different geological regions have different strontium isotopic features. Although Alaska's climate has changed dramatically since the Pleistocene, its geological structure has not changed. When a mammoth feeds on land, the strontium sealed in its tusks becomes its travel record. Ivory is "like a chemical GPS," says Wooller, a GPS with 340,000 entries.

"This is ultra-high-resolution data, like using a laser to observe the daily strontium isotope on the ivory of a mammoth," said study co-leader Clément Bataille, a geochemist at the University of Ottawa.

To link strontium's data points to actual locations on the map, Wooller's team also utilized modern Alaskan voles. The University of Alaska Museum of the North has a large collection of such small herbivorous rodents. They tend not to go very far, so the strontium in their teeth is a good representation of the geological area in which they live. "These little voles are like citizen scientists," Wooller said. "They're taking samples of the local situation."

Bataille and Juliet Funck (then Doctoral students in Wooller's lab) used data from voles to map strontium in Alaska. Bataille then built a model that correlates data points on ivory with maps. Wooller notes that the model takes into account certain physical realities, such as mammoths that can't fly or climb cliffs, "so certain landscapes can be excluded." Bataille traced the mammoth's footprints from the site of its death, gradually going back to the origin of the mammoth.

Just reading this paper, I felt like Jane Goodall was looking at these animals.

As Wooller and colleagues struggled to trace the mammoth's tracks, Beth Shapiro and Katie Moon of the University of California, Santa Cruz, extracted ancient DNA fragments from mammoth fossils to understand their sex. They also used radiocarbon dating to determine the century in which it was born.

At Florida State University, Erickson analyzed the tiny stripes of ivory teeth that are caused by seasonal changes, even daily activities and sleep cycles, that can mark the year, month, and day of a mammoth's lifetime. The combination of details transforms the chemicals contained in ivory into an unprecedentedly rich ice age biography, a story of family, migration and early death.

Follow in Kik's footsteps

The team nicknamed the mammoth Kik, a male mammoth born in what is now northeastern Alaska before 17,100. It was born at a time when the last ice age of the Pleistocene had just begun to decline. There is a vast plain between Alaska and Russia, and glaciers cannot form because they are too dry. Scientists debate exactly what the area looks like, and the large number of fossils found here (bison, mammoths, reindeer, horses, musk oxen and lions) suggests that it is like the Serengeti in the cold region. The land was covered with grass, rush grass and artemisia shrubs, which scientists now call the "mammoth prairie."

Kik spent the first few years of his life in a small place south of the Brooks Mountains in the interior of Alaska. It was weaned at the age of two, and isotopes of carbon and oxygen recorded this dietary change. In the following years, its scope of activity expanded. It seems to like to spend the winter in the lowlands and summer in the foothills — perhaps to avoid insect bites, Wooller said.

It moves back and forth, and its migration patterns reflect the movement of modern African elephants. Scientists have long speculated about this. "We used the elephant's activity to speculate on what mammoths might do in this land," he said. "But until now, there has been no evidence.

Kik's experience is likely to reflect the situation of modern elephants on the other hand: "When it was a young mammoth, it could have been a member of the herd," Wooller said. The mammoth must have spent her childhood with its mother, and probably with a large group of other females and juvenile mammoths. In fact, tracking a young Kik also means tracking the herd of elephants where it is located.

When Kik was 16 years old, its trajectory suddenly changed. In fact, when male African and Asian elephants reach sexual maturity, they will leave the herd to wander, either alone or in small groups with other male elephants. The same goes for Kik. It began to travel further afield, through the pass on the western edge of the Brooks Mountains to the northern slopes of Alaska, a road that is still necessary to migrate reindeer herds to this day.

"They used to migrate with mammoths," Wooller said. "I think it was a neat scene."

The last isotope the team studied revealed the outcome of Kik's story for us. In the summer of the year he was 27, the nitrogen isotopes in his teeth began to change. Different foods produce different nitrogen isotope characteristics, and Kik's nitrogen isotope has become similar to that of carnivores since that summer. For herbivorous mammoths, this can only mean one thing: Kik is consuming himself. It is enduring hunger.

Daniel Mann, a Quaternary scientist at the University of Alaska at Fairbanks, said that sometimes older elephants starve because their teeth are too worn to use. But Kik is still relatively young, and the tusks were found next to fragments of mammoth skulls, and scientists can examine the teeth to see if they're in good condition. "I suspect it was hurt in some way," Mann said of the mammoth.

In the fall of its last year, Kik set out from today's Seward Peninsula in Alaska to the northeast side of the Brooks Mountains. It stopped there and wandered throughout the winter in a dune area west of the Colville River. Then, in late winter or early spring, it comes to the edge of a shallow canyon carved by a tributary of the Colville River (Kikiakrorak River for short), which is where its life ends and where it has been resting for 17,000 years.

Ancient clues foreshadow future catastrophes

"For a single animal, it's pretty amazing to have a dataset like this." Grant Zazula, a paleontologist in the Yukon, said he was not involved in the study. "This will really open up several opportunities for new projects in Alaska and the Yukon, where there is a very rich collection of fossils to study."

Isotopic studies also help solve one of the biggest mysteries about mammoths: why they went extinct. Many scientists believe that in the late Pleistocene and early Holocene, human hunters were responsible for the extinction of mammoths and many other large mammals. Proponents of this "over-hunting" hypothesis argue that even a small percentage of people may kill this slow-breeding mammal. Other scientists argue that climate change plays a bigger role in species extinction.

Wooller said that while Kik's story doesn't address the debate, it does point to the possible effects of human predation and climate change.

The earliest definitive evidence of human existence in the region occurred about 14,000 years ago, thousands of years after Kik's death. Archaeologists have debated fiercely about when humans arrived in North America, but mammoths didn't become extinct on the alaska continent until about 13,000 years ago, so it's likely that mammoths and humans coexisted there for more than 1,000 years.

North American bison and Canadian red deer appear to have been preferred targets for hunters, said study co-author Joshua Reuther, an archaeologist at the Museum of the North. The fact that Kik follows a fixed migration route suggests that mammoths may also be a very attractive target. "Social animals are more reliable than solitary animals like moose," he said.

In the thousands of years after Kik's death, mammoth grasslands slowly grew with trees, which narrowed mammoths' preferred habitats, limited their movements on the land, and may even force them closer to new dangerous predators. It also hints at the pressures that modern animals may face, as climate change can cause a sudden shift in ecosystems. Scientists say Alaska's changing climate has led to changes in the activities of the reindeer, the mammoth's ancient migration partner.

"We live in a world where both humans and climate change have an impact on animals," DeSantis said. "If this is a lethal combination of factors that led to the extinction of large animals that occurred in the Pleistocene, then we really need to be cautious."

(Translator: Strange Flowers Blossom)