On trail of mammoth using isotope patterns in a tusk

On trail of mammoth using isotope patterns in a tusk

Artist’s impression of mammoths observed by early inhabitants of Alaska. © Julius Csostonyi

The relationship between humans and mammoths in sight: Using isotope patterns in a tusk, researchers have reconstructed the life path of a North American mammoth cow and linked it to traces of human presence in the region. “Elma” migrated around 14,000 years ago to an area where most traces of early human settlement were found. The mammoth cow met its end at one of the campsites – presumably as a hunting victim. The results reflect that people specifically visited places where mammoth herds congregated, the researchers say. This in turn is an indication that they have at least contributed to the extinction of the proboscideans in the region.

They once roamed in large herds across the cold steppes of Eurasia and North America: the woolly mammoths (Mammuthus primigenius) were the cold-adapted relatives of today’s elephants. At the end of the Ice Age, however, their typical habitats shifted more and more north. But eventually they could no longer survive there either: their populations dwindled more and more until the last shaggy giants died out. What was the decisive reason for the end is considered controversial. Basically, it seems clear that the climatic conditions became less favorable for the animals. But humans could also have had a hand in it. Because our ancestors hunted the proboscideans, as various evidence shows.

The current study now focuses on one of the late distribution areas of the woolly mammoth: Alaska. It is assumed that the people who immigrated to North America from Siberia continued to coexist with the giants for at least another 1,000 years. The focus of the study by researchers led by Audrey Rowe from the University of Alaska in Fairbanks was the examination of a mammoth tusk that was discovered at the site of Swan Point in the interior of Alaska. It is one of the oldest known archaeological sites in Alaska: traces of campfires, stone tools and remains of hunted prey prove the presence of humans around 14,000 years ago. According to the dating, the tusk in the camp area also dates from this period. Remains of two other young mammoths were also discovered there.

DNA and isotope analyzes provide insights

For their study, the scientists extracted fossil DNA from the tusk and the remains of the other two animals from Swan Point. In addition, they recovered genetic traces from mammoth remains found at three other archaeological sites around Swan Point. The scientists also carried out an isotope analysis on the tusk. As they explain, layers form as tusks grow – similar to the annual rings of trees. The ratio of certain strontium isotopes in the layers can allow conclusions to be drawn about where the animal was at different times in its life. Depending on the region, water and food plants have certain isotope signatures, which can then also be found in the respective tusk layers. In addition, the team also examined the profiles of oxygen and nitrogen isotopes in the tusk layers, which can provide information about the animal’s diet and climatic environment.

As the scientists report, their results showed: The tusk belonged to a mammoth cow that had died in its early adulthood of around 20 years. They gave her the name Elma. The isotope profile showed that this mammoth was in good nutritional condition, the researchers report. Comparison of DNA sequencing results showed that Elma was closely related to the two cubs whose remains were discovered at the same site. The mammoths from the neighboring sites, however, apparently belonged to other mammoth groups.

Camp at a mammoth hotspot

The reconstruction of Elma’s life path based on the strontium isotope profiles in the tusk showed that the mammoth cow had traveled at least 1,000 kilometers during her life. She spent most of her life in a relatively small area in the eastern part of the Yukon River. However, she later went on a hike and covered the long distance to the interior of Alaska in just three years. There she met her end at Swan Point – together with the two young animals that presumably belonged to her herd.

The researchers now see their results as an indication that the Swan Point area was probably an ancestral meeting place for different herds of mammoths. “Our mammoth cow was in the region where most of Alaska’s archaeological sites are located. “It appears that early residents of the region established hunting camps in areas where mammoths frequented,” says Rowe.

The results also suggest that humans may have played a role in the regional extinction of mammoths in Alaska. Basically, it is clear that the climatic changes during the era worsened the living conditions for animals adapted to open vegetation: higher temperatures and precipitation led to the formation of forests in the region. “Climate change at the end of the Ice Age fragmented the mammoths’ preferred open habitat, which may also have restricted their range of movement, which benefited human hunters,” says co-author Potter from the University of Alaska at Fairbanks.

Source: University of Alaska Fairbanks, McMaster University, specialist article: Science Advances, doi: 10.5281/zenodo.8408732

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