Mammoths are icons of Ice Age fauna, but little was known about their life. Now researchers have for the first time reconstructed the life path of a woolly mammoth that died 17,000 years ago in Alaska. The data obtained from the isotopes of its tusk revealed astonishing things: in the course of its 28 years of life, the mammoth wandered so much in Alaska that it could have circled the earth twice. After leaving its place of birth in the Yukon Basin, the adolescent animal expanded its forays into the entire region. The data also provide information about the end of the mammoth. Accordingly, it remained in a small area north of the Brooks Mountain Range for the last year and a half – and starved.
Mammoths were the heavier, shaggy cousins of our elephants today and perfectly adapted to the harsh conditions of the Ice Age. Up until about 20,000 years ago, woolly mammoths (Mammuthus primigenius) roamed the cold steppes of Europe, North America and Asia in large herds. Our ancestors portrayed these giants from the Ice Age in many of their cave paintings, as the mammoths were important prey for them. Much is known about the appearance and biology of these animals from numerous fossils found in permafrost, and scientists have also been able to obtain and analyze at least parts of the DNA of some mammoth specimens. Nevertheless, the Ice Age proboscis still hold some secrets. “Because the mammoths are now extinct, we know little about their way of life, including the size of their range or the extent of their migration,” explain Matthew Wooller of the University of Alaska at Fairbanks and his colleagues.
Isotopes in the tusk as a “diary”
For the first time, the team has succeeded in reconstructing the life of a woolly mammoth – from birth through adolescence and adulthood to early death at the age of only 28. This was made possible by the 17,000 year old remains including tusks of this mammoth, which were found in the far north of Alaska beyond the Arctic Circle. As with today’s elephants, the tusks of a mammoth grow slowly and accumulate annual rings in the ivory. “From the moment they are born until the day they die, they carry a diary with them inscribed in their tusks,” says Patrick Druckermiller of the University of Alaska Museum of the North. The ratio of the strontium isotopes 87Sr and 86Sr in the thin growth layers of the tusk reflect where the mammoth resided at different times in its life. Because the soils and plants have different isotope ratios depending on the region, the animal ingests the site-specific mixture with its food and stores it in the growing tusks.
For their study, the researchers split the mammoth’s 2.40-meter-long tusk and tested the isotope distribution using particularly high-resolution separation and analysis methods. The result was around 340,000 individual isotope measurements, which enabled them to trace the whereabouts of the woolly mammoth down to almost a week. In addition, Wooller and his team also analyzed the oxygen and nitrogen isotopes in ivory, because these can provide information about the climatic conditions and the condition of the mammoth. DNA analyzes had previously shown that the animal was a male.
Long walks and starvation
The isotope data shows: The mammoth was born in central Alaska in the depression of the lower Yukon River. The young animal wandered around with its herd in the following years in the plains of central Alaskan. Similar to today’s elephants, the herd of the little mammoth cub probably consisted of several adult females with their offspring, as the scientists explain. The migration area of the mammoth herd extended from the south side of the Brooks Range in the north to the coast of the Gulf of Alaska. At the age of around 16, however, the life of the young woolly mammoth changed abruptly, as indicated by a sudden change to significantly greater fluctuations in the isotope pattern. “This likely reflects the transition to reproductive age and the beginning of further migrations between central Alaska and the north side of the Brooks Range,” write Wooller and colleagues. Similar to elephants, young mammoth bulls separated from their herd when they reached sexual maturity and from then on moved around alone or in bachelor groups.
During its forays through Alaska, the mammoth covered astonishing distances: the distances covered in the course of its life correspond to almost double the circumference of the earth, according to the team. “It’s not yet entirely clear whether these mammoths were seasonal migrants, but in any case they got around,” says Wooller. But that changed in the last year and a half before the woolly mammoth’s death. According to the isotope data, the animal was only in a small area north of the Brooks Range during this time. “There it probably died of starvation,” the researchers report. This can be recognized by a significant increase in the nitrogen isotope 15N in the mammoth tusk and a corresponding decrease in the carbon-13 values. The isotope data also shows that the animal died in late winter or early spring – presumably emaciated from the cold season of the year, which was full of privation.
Source: Matthew Wooller (University of Alaska, Fairbanks) et al., Science, doi: 10.1126 / science.abg1134