Around 13,200 years ago, an 8-ton adult American mastodon (Mammut americanum) — nicknamed the Buesching mastodon — was killed when a rival punctured the right side of his skull with a tusk tip, a wound that was revealed to paleontologists when the animal’s fossilized remains were recovered from a peat farm near Fort Wayne in Indiana, the United States, in 1998. Using isotopic analysis of the individual’s tusk, a team of researchers from the University of Cincinnati, the University of Michigan and the University of Nebraska-Lincoln was able to track changes in landscape use between his teenage and adult years. They found that northeast Indiana was likely a preferred summer mating area for this individual, who made the trek annually during the last three years of his life, and may have been regionally significant for Late Pleistocene mastodons.
Mastodons, mammoths and modern elephants are part of a group of large, flexible-trunked mammals called proboscideans.
These creature possess elongated upper incisor teeth that emerge from their skulls as tusks.
In each year of their life, new growth layers are deposited upon those already present, laid down in alternating light and dark bands.
The yearly growth layers in a tusk are somewhat analogous to a tree’s annual rings, except that each new tusk layer forms near the center, while new growth in trees occurs in a layer of cells next to the bark.
The growth layers in a tusk resemble an inverted stack of ice cream cones, with the time of death recorded at the base and the time of birth at the tip.
Mastodons were herbivores that browsed on trees and shrubs. As they grew, chemical elements in their food and drinking water were incorporated into their body tissues, including the gracefully tapered, ever-growing tusks.
In the new study, University of Cincinnati paleoecologist Joshua Miller and colleagues analyzed strontium and oxygen isotopes in the growth layers of the Buesching mastodon’s tusk.
They collected 36 samples from the animal’s adolescent years (during and after departure from the matriarchal herd), and 30 samples from the animal’s final years of life.
Ratios of strontium isotopes in the tusk provided geographic fingerprints that were matched to specific locations on maps showing how strontium changes across the landscape.
Oxygen isotope values, which show pronounced seasonal fluctuations, helped the team determine the time of year a specific tusk layer formed.
According to the researchers, the Buesching mastodon died in a battle over access to mates at age 34. His original home range was likely in central Indiana.
Like modern-day elephants, the young male stayed close to home until he separated from the female-led herd as an adolescent.
As a lone adult, Buesching traveled farther and more frequently, often covering nearly 20 miles per month.
Also, his landscape use varied with the seasons, including a dramatic northward expansion into a summer-only region that included parts of northeastern Indiana — the presumed mating grounds.
“Every time you get to the warm season, the Buesching mastodon was going to the same place repeatedly,” Dr. Miller said.
“The clarity of that signal was unexpected and really exciting.”
The findings were published in the Proceedings of the National Academy of Sciences.
Joshua H. Miller et al. 2022. Male mastodon landscape use changed with maturation (Late Pleistocene, North America). PNAS 119 (25): e2118329119; doi: 10.1073/pnas.2118329119
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