Mammoth tusks grew daily from birth to death. They acted like a journal, continuously recording information about the individual’s health and environment. Prof. Bataille, who studies isotope variations in the environment, analysed the strontium isotopes (87Sr/86Sr) ratios in mammoth tusks to investigate the animal’s mobility.
Prof. Bataille and Prof. Matthew Wooller (University of Alaska Fairbanks) selected a pair of tusks from a mammoth named Kik, who was radiocarbon dated to have lived 17,100 years ago. Paleo-DNA analysis and assessment determined that Kik was male and 28 years old at his time of death. The team used large chambers with improved lasers to sequentially ablate sample along the tusk length, which were directly sent into a multi-collector mass spectrometer that provided high-resolution records of the strontium isotope variations in the tusk over time. These values were then compared to a map showing the abundance and variation of Sr isotopes in the environment around Alaska where this mammoth roamed.
“Strontium isotope patterns are really hard to model with regular algorithms,” explains Prof. Bataille. Consequently, he applied a new machine learning regression technique to spatially model Sr isotopes on landscapes. Prof. Bataille and Prof. Amy Willis (University of Washington) traced the mammoth’s mobility history from its place of death in Alaska by comparing the map and mass spectrometry records.
Kik’s extensive range of movement suggests that mammoths travelled quite a bit in response to climate and resource changes and/or sexual stimuli. In his early life, Kik used a series of core areas along large rivers that probably had abundant resources. However, at approximately fifteen years old, he started to display more erratic mobility, moving hundreds of kilometers in a few months. Interestingly, some of the regions habitually visited by Kik coincide with locations where numerous mammoth remains and early human settlements were observed.
These discoveries inform theories around the extinction of mammoths and other megafauna. The change in climate at the end of the last Ice Age replaced large parts of mammoth’s tundra habitat with boreal forest, fragmenting a once opened landscape, limiting mobility, diversity of resources and the mixing of population genetic biodiversity. Moreover, mammoth’s considerable mobility would have made them regular prey for early humans. After the last Ice Age, some mammoth populations were constrained to islands, where the inability to roam combined with generations of inbreeding contributed to their demise.
Studying the mobility and causes of extinction of ancient species helps us better understand current impacts of climate change and contributes to improving biodiversity conservation worldwide. It is devastating to imagine a world in which polar bears, elephants and other species will only be millennia-old extinct fossils displayed in museums.