Mastodon tusk reveals North America migration patterns

The mastodon’s fossil was first found on a farm in 1998 by Kent and Janne Buesching, who were mining for peat on their property. Archaeologists then excavated the Buesching mastodon’s remains. His skeleton, which is 9 feet (2.7 meters) tall and 25 feet (7.6 meters) long, has been studied since 2006.

A closer look at the mastodon’s skull showed he was killed when the tusk tip of another male mastodon punctured the right side of his skull. He died about 100 miles (160 kilometers) away from his home territory, according to a new study that was published Monday in the Proceedings of the National Academy of Sciences.

“The result that is unique to this study is that for the first time, we’ve been able to document the annual overland migration of an individual from an extinct species,” said first study author Joshua Miller, paleoecologist and assistant research professor of geology at the University of Cincinnati, in a statement.

Northeast Indiana served as a summer mating ground for the mastodons, and the study found that this solitary creature annually migrated north from his home during the winter months the last three years of his life. The ancient animal was around 34 when he died, the researchers estimated.

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“Using new modeling techniques and a powerful geochemical toolkit, we’ve been able to show that large male mastodons like Buesching migrated every year to the mating grounds,” Miller said.

Daniel Fisher, co-leader of the study, helped excavate the mastodon 24 years ago. He is a professor of paleontology at the University of Michigan, and director of the University of Michigan Museum of Paleontology.

Fisher cut a long, thin section from the center of the 9.5-foot-long (3-meter-long) right tusk. Like studying tree rings, analysis of the mastodon’s tusk revealed how he interacted with his landscape as an adolescent as well as during the last years of his life.

University of Michigan paleontologist Daniel Fisher stands with a mounted skeleton of the Buesching mastodon. Photo by Eric Bronson, Michigan Photography.

“You’ve got a whole life spread out before you in that tusk. The growth and development of the animal, as well as its history of changing land use and changing behavior — all of that history is captured and recorded in the structure and composition of the tusk,” Fisher said.

When he was younger, the mastodon stuck close to home with his female-led herd in central Indiana before separating and venturing out on his own — much like modern elephants. As a lone rover, the mastodon would trek for about 20 miles (32 kilometers) each month.

Analyzing the tusk

Migration was critical for the mastodons to find places where they could reproduce while living in harsh, cold climates. But it has been difficult for researchers to pin down their geographic ranges.

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Looking for oxygen and strontium isotopes within mastodon tusks is revealing some of that insight.

Mastodon tusks, like elephant tusks, have new growth layers that form near the center throughout their life. Information about when they were born can be found stored at the tip of the tusk, while their death is in the layer at the tusk’s base.

As mastodons munched on shrubs and trees and drank water, chemical elements from their meals became stored in the tusks as well.

The left half of the Buesching mastodon's right tusk bears numbers indicating specific layers. Photo by Jeremy Marble, University of Michigan News

Chemical analysis of tiny samples taken from different tusk layers of the Buesching mastodon correlated to geographic locations as the elements changed according to the landscape, as well as seasonal fluctuations. This data was put into a movement model developed by the researchers to essentially track when, where and how far he traveled.

“Every time you get to the warm season, the Buesching mastodon was going to the same place — bam, bam, bam — repeatedly. The clarity of that signal was unexpected and really exciting,” Miller said.

Next, the researchers want to study the tusks of other mastodons to see if they can make similar discoveries.

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