An international research team has traced the astonishing life journey of an Arctic woolly mammoth, which in its 28 years in the Alaskan landscape covered a distance almost twice the circumference of the earth in its wanderings.
Scientists gathered unprecedented details of its life by analyzing a 17,000-year-old fossil from the University of Alaska’s Museum of the North. By generating and examining isotopic data in the mammoth’s tusk, they were able to match its movements and diet with isotopic maps of the region.
Few details are known about the lives and movements of woolly mammoths, and the study provides the first evidence that they traveled great distances. An overview of the life of the mammoth is given in the new issue of the journal Science.
“It’s not clear if this was a seasonal immigrant, but it covered some serious ground,” said University of Alaska Fairbanks researcher Matthew Wooller, senior and co-lead author of the paper. “He’s visited many parts of Alaska over the course of his life, which is pretty amazing considering how large this area is.”
Researchers at the Alaska Stable Isotope Facility, of which Wooller is director, split the 6-foot tusk lengthwise and used a laser and other techniques to generate about 400,000 microscopic data points.
The detailed isotope analyses they performed are possible because of the way mammoth tusks grew. Mammoths added layers every day for the rest of their lives. When the tusk was split lengthwise for sampling, these growth bands looked like stacked ice cream cones and provided a chronological record of a mammoth’s entire life.
“From the time they’re born until the time they die, they have a diary and it’s in their tusks,” says Pat Druckenmiller, paleontologist and director of the UA Museum of the North. “Mother Nature doesn’t usually provide such a convenient and lifelong record of a person’s life.”
Scientists knew the mammoth died on Alaska’s North Slope above the Arctic Circle, where its remains were unearthed by a team that included Dan Mann and Pam Groves of UAF, who are co-authors of the study.
The researchers pieced together the mammoth’s journey to this point by analyzing isotopic signatures in its tusk of the elements strontium and oxygen, which were matched to maps predicting isotopic variations across Alaska. The researchers created the maps by analyzing the teeth of hundreds of small rodents from across Alaska that are in the museum’s collections. The animals travel relatively small distances during their lifetime and represent local isotopic signals.
Using this local dataset, they mapped isotopic variation across Alaska and provided a baseline to track mammoth movements. Taking into account the geographical barriers and the average distance it travelled each week, the researchers used a novel spatial modelling approach to plot the likely routes the animal took during its lifetime.
Ancient DNA preserved in the mammoth’s remains allowed the team to identify it as a male related to the last group of its species to live on mainland Alaska. These details provided more insight into the animal’s life and behavior, said Beth Shapiro, who led the DNA component of the study.
For example, an abrupt change in its isotopic signature, ecology, and movement at about 15 years of age likely coincided with the mammoth’s sexual maturity, mirroring a pattern seen in some modern male elephants.
“Knowing he was male provided a better biological context in which we could interpret the isotope data,” said Shapiro, a professor at the University of California Santa Cruz and a researcher at the Howard Hughes Medical Institute.
Isotopes also offered a clue as to what led to the animal’s death. During the last winter of its life, nitrogen isotopes increased, a signal that may be a sign of starvation in mammals.
“It’s just amazing what we’ve been able to see and do with this data,” said co-lead author Clement Bataille, a University of Ottawa researcher who led the modeling effort in collaboration with Amy Willis of the University of Washington.
Learning more about the lives of extinct species satisfies more than curiosity, Wooller said. These details could be surprisingly relevant today, as many species adapt their movement patterns and ranges to the changing climate.
“The Arctic is going through a lot of changes right now, and we can use the past to see how the future might unfold for species now and in the future,” Wooller said. “Trying to solve this detective story is an example of how our planet and ecosystems respond in the face of environmental change.”
Report by Matthew Wooller, University of Alaska