How an elephant's teeth can help us track animal movements

Misha was a beloved zoo elephant that lived a long and well-documented life. When she passed away in 2008, her remains provided an unexpected opportunity for scientists studying how large animals move across landscapes.

Researchers from the University of Utah have developed a method that uses strontium isotopes in tooth enamel to track animal migration.

This technique could help scientists understand the movements of extinct species like mastodons and mammoths. It may also aid conservationists in tracing the origins of modern wildlife, including victims of the illegal ivory trade.

Unlocking history through elephant teeth

Strontium, a naturally occurring element, accumulates in teeth and bones as animals eat and drink.

Since different geographic regions have distinct isotope signatures, analyzing strontium ratios can reveal where an animal has lived.

“Our study not only adds to our understanding of how tooth enamel records an animal’s Sr isotope exposure, but also helps to reconstruct animal migrations from Sr isotope analysis,” said lead author Deming Yang.

“It can be applied to studies of paleobiology, to answer how megaherbivores migrated in the past. It can also be applied to studies of modern conservation and forensics, to trace the origins of illegal ivory trade and other forms of wildlife trafficking.”

Misha, a female elephant, was acquired by Salt Lake City’s Hogle Zoo in 2005. Before that, she lived at Six Flags Discovery Kingdom in Vallejo, California. Her well-documented history made her an ideal subject for testing this method.

The science behind strontium tracking

Strontium behaves like calcium in the body, incorporating into bones and teeth over time. The isotope 87Sr is radiogenic, meaning it is formed by the decay of rubidium, an element with a half-life of over 49 billion years.

While 87Sr levels increase over time, other strontium isotopes remain stable. This means that different regions have unique isotope ratios, which animals absorb through their diet.

“As animals eat and drink, they pick up this environmental signature and store it in their teeth, preserving a series of environmental exposures like historic archives,” noted Yang.

“We use other elements, but in this case, we’re focusing on strontium, which has proven to be really useful because of its strong link to geology,” said study co-author Gabe Bowen.

“Ultimately it comes down to where that element comes from, how the animal gets it into their body and from what sources.”

Tracking an elephant’s past with teeth

When Misha passed away, Professor Thure Cerling saw an opportunity. He reached out to Hogle Zoo for permission to recover her teeth before burial. The detailed veterinary records of Misha’s life allowed scientists to compare her tooth enamel’s isotope signatures to her known movements.

As a postdoctoral researcher, Yang led the effort to analyze Misha’s tusk and teeth to see how well they recorded her past environments.

The experts used laser ablation to sample different layers of enamel and tusk. They then measured the samples with a mass spectrometer to determine their strontium isotope composition.

Movement recorded in tooth enamel

“It’s a very simple movement history. She lived in one location for a decade or more, and then moved here [to Salt Lake City], and we know the date of that move,” Bowen said. “We don’t have a lot of opportunities to see these kinds of natural experiments.”

The researchers found that the innermost enamel layer provided the most accurate record of isotope exposure, making it the best location for sampling.

Study co-author Diego Fernandez is an expert in the Department of Geology and Geophysics who operates the university’s mass spectrometry lab.

“We determined the strontium isotopes from the top to the bottom of the tooth in different parallel lines and those represent different times in the growth of Misha,” said Fernandez. “It captured the time where Misha was moved from California to Utah.”

A learning experience

Undergraduate student Katya Podkovyroff assisted in refining lab procedures for analyzing bioapatite, the mineral that makes up enamel and bone.

“It was in this lab where I got my first hands-on experience with scientific research, and I immediately fell in love. One of the most thrilling aspects of the job was learning that each sample carried a history, a mystery waiting to be unraveled through chemical signatures,” said Podkovyroff, now a graduate student at the University of Oregon.

“This research was both exciting and challenging: sampling ivory required extreme precision, as even minor contamination could alter results, and isotope purification is a meticulous and time-consuming process,” she continued.

“The most rewarding aspect of this project was its broader implications beyond a single case study: it has applications in modern conservation efforts, with the ability to trace the origins of illegal ivory trade.”

Beyond elephant teeth

The success of the method used to analyze Misha’s teeth suggests that similar analyses could be applied to fossils, helping scientists learn how ancient animals migrated.

The technique could also play a role in conservation, identifying where modern animals come from and helping to track illegal wildlife trade.

By using nature’s own chemical records, such as those found in elephant teeth, researchers are gaining a clearer picture of the past while providing valuable tools for protecting animals today.

The full study was published in the journal Communications Biology.

Image Credit: Brian Maffly, University of Utah

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