Close up of mastodon tusk with numbers marked on it
American mastodons, like the adult male who bore this tusk discovered in Northern Indiana, would travel hundreds of miles, likely as part of an annual migration to breeding grounds. The markings on the tusk indicate where isotope samples were retrieved.
Jeremy Marble, University of Michigan News

It can be hard to discern the daily lives of extinct species just by looking at fossils, but studying isotopes within their ancient bones can help paint a broader picture. According to a new study published Monday (June 13) in PNAS, American mastodons (Mammut americanum) migrated great distances throughout the year. To uncover this, researchers analyzed isotopes of strontium and oxygen along the length of a tusk from a 34-year-old male mastodon from the Indiana State Museum, which museumgoers affectionally call “Fred.” These isotopes occur in different proportions based on an area’s geology and the time of year, and they get incorporated into mineralized tissues, so they can serve as markers for the habitats animals were in when their bones grew. The recurring patterns of isotopes in the tusk suggested the animal traveled great distances on a regular basis, particularly once it hit adulthood. It ultimately died in what is now northern Indiana after being impaled by another mastodon’s tusk. Based on the isotopes present when it died, the researchers deduced that the animal was at its breeding grounds, and presumably lost its life fighting for a mate.