We might not be able to study a walking, breathing woolly mammoth in real life, but what if we could track its movements and get a sense of where it traveled, from its birth to its death? For the first time ever, scientists have done just that.
An international team of researchers published a paper this week in the journal Science that reveals the 28-year movement history of a male woolly mammoth. With exciting detail about where it roamed throughout northern Alaska, its seemingly favorite locations—as it returned time and time again—and where it eventually died, this paper offers unparalleled insight into an animal that lived approximately 17,000 years ago.
His movement, for the first two years of his life, was restricted to an area within the interior of northern Alaska. Between 2 and 16 years of age, when he was considered a juvenile, he started to move over a larger expanse of land. The authors believe this might reflect the movement of a herd, if mammoths had a similar social structure as today’s elephants. He began to travel considerable distances, however, when he matured at age 16 or so, and throughout his life, he often returned to specific areas within Alaska.
With an in-depth discovery such as this, it might be tempting to think these scientists had access to a complete woolly mammoth skeleton—lots of fossil material to help them form their hypotheses. But in truth, they had mere fragments: two complete tusks, parts of its skull, and some of its jaw with intact teeth.
But those scattered parts were enough. The team used a variety of scientific analyses to shed light on the travels of this ancient beast. Ancient DNA revealed its sex and its clade, a term meaning organisms with a common ancestor. The team sliced one entire tusk down the middle to both sample and examine it. To learn more about the mammoth’s migration, they used a neat trick called isotopic analysis.
Isotopes are like chemical footprints, and they are in everything around us. Being able to read those chemical footprints in their various forms can help us understand more about diet, for example, or where an animal roamed. Some isotopes reflect the geology of specific environments; some reflect the type of precipitation and season within an environment. All of us—animals and plants—ingest them and incorporate them into our bodies. Scientists, if they have the appropriate samples and tools, can “read” them. It’s a highly complex type of science, but one that is growing in popularity across paleontology and archaeology because it can reveal so many fascinating details.
The bulk of the work centered around one of the tusks. Proboscideans—mammoths, mastodons, elephants, and their relatives—are one of the rare types of animal uniquely suited for understanding an entire life history. Those histories are stored in their tusks, where daily growth increments, information about diet, seasons, and even pregnancy, can be read from the moment they are born to their death. It is therefore no surprise that the authors chose this as their starting point. What is surprising is how they went about doing it.
Matthew Wooller, co-lead and senior author of the new paper, is a professor at the College of Fisheries and Ocean Sciences and Institute of Northern Engineering at the University of Alaska Fairbanks. He is also director of the Alaska Stable Isotope Facility, which has a relatively new, high-tech instrument crucial to this study (its full name: a Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometer).
It’s not enough to have the technology. Understanding both how to set up the equipment and then knowing how to use it will impact the results. Co-authors Johanna Irrgeher and Thomas Prohaska are experts in isotope ratio analysis, and they helped Wooller and his team in the initial set-up. Obtaining accurate isotope ratio measurements, said Irrgeher, research scientist at Montanuniversität Leoben in Austria, is “still an art.”
Irrgeher reflected on the type of research typically done with this kind of technology: the study of ear bones in fish. Consider, for a moment, an ear bone in a fish versus a woolly mammoth tusk. “We took that same high-resolution micro-technology and applied it on a macro scale,” said Wooller.
Prohaska said he believes “you need to be crazy to be a good scientist,” and he means it in the best possible way: having the courage to think differently and to try things others might not even consider possible. He described the enormous size of this mammoth’s tusk—1.7 meters—and compared it to the very tiny space within the instrument they would be using to analyze it. He remembers thinking of his Alaskan colleagues, “You want to put samples of this tusk into a laser cell of this size?? You people are really crazy!”
“Mat [Wooller] really brought this research to a very high level,” Irrgeher said.
To help them understand where the mammoth traveled, the authors turned to strontium isotope geochemistry. Strontium isotopes, said Joshua Miller, paleoecologist and assistant professor at the University of Cincinnati who was not involved in the research, are “a geographically informative chemical marker sourced from the animal’s environment and local geology, and acquired by an animal as it eats and drinks.” In a nutshell, it’s almost like a tracking device. Strontium is in the ground; it is ingested by plants through their roots; herbivores eat the plants and therefore unknowingly ingest the strontium; the strontium is stored in the animal’s teeth (or, in this case, the tusk—which is actually a really long tooth); and then, thousands of years later, scientists can tell where the animal has been throughout its life.
To create the history of the mammoth’s life, they used something called isoscapes, which map the type of strontium found across a specific landscape. Two of today’s co-authors and others mapped the various kinds of strontium across Alaska by using the teeth of rodent specimens housed at the University of Alaska Museum Mammal Collection.
They began where the mammoth died, an area they suspect was close to where the fossils were found in 2010, and worked backward, tracing its route from death back to the moment of birth. They applied certain logical inferences when mapping the mammoth’s movement to the isotopic data. For example, they assumed “that this mammoth couldn’t fly,” Wooller mentioned in a video interview, smiling, and therefore couldn’t travel over impossible terrain such as cliffs or other “extreme topography.”
“This animal,” he continued, “was alive 17,000 years ago, pretty much at the height of the last Ice Age. A lot of people outside of Alaska assume that we were covered by ice during the Ice Age, but that’s not true. The majority of it was NOT covered by ice.”
“We never really knew what we were going to see as each tusk section came off the mass spectrometer,” Wooller recalled. “We were plotting it up in real time to say, ‘ah, look! It stopped for a while!’ And ‘oh, look! It’s headed up north again!’”
Remarkably, some of the mammoth’s most oft-traveled routes are used today by herds of caribou. Perhaps more interesting, some of these routes are not only close to locations where numerous other mammoth fossils have been found but to known sites of ancient humans. If all or even most mammoths in Alaska traveled as much as the one in this study, Wooller mentioned, this would have implications for potential contact with ancient humans when they later migrated to the area.
“The general areas regularly used by this mammoth are also used by the earliest Beringian hunters,” wrote co-author and archaeologist Ben Potter in an email, “focused on the Yukon river basin and northwest Alaska, with relatively few occupations in the southwest, south-central, and far eastern unglaciated regions. In other words, the habitat likely favored both species, mammoths and humans.”
But, for now, he wrote, “the exact nature of human-mammoth interactions remains tantalizingly ambiguous.”
Katy Smith, associate professor of geology and curator of paleontology at Georgia Southern University who was not involved in the study, is a tusk specialist. She wrote in an email, “I think this is an amazing level of insight—it’s certainly something I would like to know about every tusk on every proboscidean.”
Smith noted that paleontologists “can all do a lot of different things with the resources that we have,” whether that involves high-tech equipment or relying on more basic tools such as taking measurements and observing growth patterns in tusks, much like tree rings. It is, she said, “why science is a community. We all can bring our different skills and strengths to it.”
“I’m fascinated to see that mammoths act like modern caribou!” she wrote. “Seeing patterns of behavior in extinct animals repeated in extant animals really puts life back into the extinct forms. This study infers that mammoths were successful until the environment changed, something that we see time and time again for extinct—and extant—animals.”
“We often make these assumptions that these extinct animals behaved much like their living cousins do today,” Advait Jukar, Yale paleontologist who was not involved in the research, said in a video interview, “but there is no good way to test this unless we have direct evidence from the fossil record. And this [paper] is a great test of that.”
One of the more poignant aspects of the paper was the description of the mammoth’s death. According to nitrogen isotopes in the tusk, evidence suggests that he died of starvation in late winter or spring. The authors wonder whether a harsh winter, which may have frozen the snow, would have prevented access to the vegetation underneath.
“You can almost see the animal dying,” Miller expressed in a video interview. “You can really feel it. I mean, that kind of nitrogen excursion is really dramatic. To me, this suggests he may have even been suffering during the end of his life.”
Jukar, noting the relatively young age of 28 when this mammoth died, said that he would like to see more research on other mammoths to see “if there are periods in the geological past when these animals were dying younger in a particular part of Alaska, as it can add more nuance to our understanding of how the environment is affecting their population dynamics.”
“For the first time, we’ve learned something specific about the behavior of an extinct animal!” Beth Shapiro, co-author and paleogeneticist, wrote in an email. “With more data like this from other individuals, we will begin to tease out how behavioral patterns like movement changed as the environment changed and habitats shifted, or even as people became increasingly present on the landscape. These sorts of data sets bring us closer to really understanding how shifting climates and habitats impacted species and, perhaps, drove them to extinction.”
It took a multidisciplinary, international team over a year to interpret the migration of this one mammoth. One individual animal alone cannot offer insight into the eventual extinction of an entire species, but they hope this is a starting point. More than one author involved in this study mentioned the haunting connection of mammoth extinction to today’s troubling climate change.
“In Alaska, we are very, very aware of the impact and changes associated with climate change right now,” Wooller said. “We are already seeing the impacts on the movement and behavior of existing megafauna such as polar bears and caribou. I think our work can help inform how things may or may not change in the future in response to some of the big changes the Arctic is facing today.”