Some 17,000 years ago a male woolly mammoth, gaunt and weak from a winter of starvation, perished on Alaska’s North Slope, a mountainous, coastal region within the Arctic Circle.
Now, scientists studying the mammoth’s remains have been able to recreate its astonishing lifetime journey through isotopic analysis of its gargantuan tusks, revealing that the creature was prolifically mobile: in its 28 years of life, the mammoth covered enough of Alaska’s ranging wilds to circle the Earth twice over.
Until now, little has been known about the movement patterns of woolly mammoths, and the new study, out today in the journal Science, offers an unprecedented window into the lives of one of prehistory’s most charismatic creatures.
“It’s not clear-cut if it was a seasonal migrator, but it covered some serious ground,” says University of Alaska (UA) Fairbanks researcher Matthew Wooller, senior author of the paper. “It visited many parts of Alaska at some point during its lifetime, which is pretty amazing when you think about how big that area is.”
This extraordinary discovery was made possible because the tusks of mammoths grew daily, layer-by-layer, creating a chronological record of their entire lives. From these growth rings, the isotopic signatures of particular regions – the isotopes the creature consumed in abundance from food in the region – could be extracted.
“From the moment they’re born until the day they die, they’ve got a diary and it’s written in their tusks,” says Pat Druckenmiller, a palaeontologist and director of the UA Museum of the North. “Mother Nature doesn’t usually offer up such convenient and life-long records of an individual’s life.”
Researchers were able to match the isotopic signatures from each layer of the mammoth’s tusks to maps that predict isotope variations across Alaska. These maps were created by analysing the isotopic contents of the teeth of various Alaskan rodents, each of which has a limited geographic range. After taking geographic barriers into account and the average distance travelled each week, researchers used a novel spatial modelling method to chart the likely routes the mammoth took over the course of its life.
Read more: Ancient mammoth DNA
Meanwhile, ancient DNA preserved in the body allowed the team to identify it as a male, genetically related to the last population of its species to live in mainland Alaska. These insights informed the reconstruction of the creature’s life course: for example, a rapid shift in the isotopic structure in the tusks at around age 15 likely coincided with the mammoth being kicked out of its herd, mirroring a pattern seen among some modern-day male elephants.
The isotopes also held the key to understanding the mammoth’s frosty demise: nitrogen isotopes spiked during the final winter of its life, which is a hallmark of starvation in mammals.
“It’s just amazing what we were able to see and do with this data,” says co-lead author Clement Bataille, a researcher from the University of Ottawa.
Wooller says understanding patterns of movement in the deep past may help inform understandings of species adaptation to climate and ecological change in the present.
“The Arctic is seeing a lot of changes now, and we can use the past to see how the future may play out for species today and in the future,” says Wooller. “Trying to solve this detective story is an example of how our planet and ecosystems react in the face of environmental change.”