A split mammoth tusk. Image: JR Ancheta/University of Alaska Fairbanks
Researchers told the tale of an ancient mammoth with its tusk, saying it had travelled far enough in its life to circle the Earth twice over.
What could scientists discern about the life of a woolly mammoth using an intact ivory tusk alongside the teeth of hundreds of dead rodents? Maybe some of the weather conditions it might have faced or perhaps battles it had fought? And where do the teeth come in?
According to new research from the University of Alaska (UA) Fairbanks, a tusk’s material is enough to piece together a picture of the beast’s entire life – a story of an incredibly mobile animal that travelled enough ground to circle the Earth twice over.
Rather than tracing the history of the species, this research tackled the story of one mammoth using isotope analysis to examine its tusk. The researchers then matched these isotopes to those found in rodent teeth from across Alaska.
“It’s not clear-cut if it was a seasonal migrator, but [the mammoth] covered some serious ground,” said UA Fairbanks researcher Matthew Wooller, co-lead 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.”
Featured in the journal Science, the research reconstructed the entire 28-year-long life of this woolly mammoth in Alaska. The subject of analysis was a 17,000-year-old fossil from the UA Museum of the North.
Starting out, the scientists already had some information. The fossil was originally found in Alaska’s north slope, which is located above the Arctic Circle. This provided the location of its death. There was far more to be learned from what remained, however.
A tusk’s tale
The key to unlocking the creature’s whole life story lay in what was preserved in the tusk. Not unlike the trunk of a tree, a mammoth’s tusk is built up with layer upon layer. When the tusk is split lengthwise, the growth bands resemble stacked ice cream cones, creating a lifetime record of the mammoth.
“From the moment they’re born until the day they die, they’ve got a diary and it’s written in their tusks,” said 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.”
A close-up view shows a split mammoth tusk at the Alaska Stable Isotope Facility. Blue stain is used to reveal growth lines. Image: JR Ancheta/University of Alaska Fairbanks
The tusk layers contained strontium and oxygen isotopes, with different layers corresponding to different times in the mammoth’s life.
Next is where the rodents come in. As teeth are durable, it was possible to get samples from across Alaska of rodent teeth. Since these rodents don’t travel far in their lifetime, it is possible to match the strontium and oxygen in the teeth to certain geographic areas.
This allowed researchers to create a map predicting isotope variations across Alaska. This map was then used to assign a time and place to the 400,000 microscopic data points analysed using a laser from the ivory tusk.
The researchers created an estimate of the average distance the woolly mammoth travelled each week, accounting for geographic barriers and the animal’s likely behaviours. The researchers could also tell that the mammoth was male – an essential piece of information in guessing aspects of the tusk’s history.
A woolly mammoth’s life
Take the fact that there was an abrupt shift in the tusk’s isotopes when the mammoth was around 15 years old. By looking at the behaviours of modern elephants, the researchers inferred that the mammoth had likely been kicked from its herd – something that often occurs to male elephants.
There was also a spike in nitrogen isotopes at the end of the creature’s life. Spikes like these usually happen when a mammal is starving, suggesting an unfortunate end for the woolly beast.
“It’s just amazing what we were able to see and do with this data,” said co-lead author Clement Bataille, a researcher from the University of Ottawa who led the modelling effort in collaboration with Amy Willis at the University of Washington.
The researchers emphasised that the study could prove relevant in today’s world as many species adapt their patterns and behaviours in a changing climate.
“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,” said Wooller. “Trying to solve this detective story is an example of how our planet and ecosystems react in the face of environmental change.”
