Ice Age horses and bison help protect modern Arctic tundra | Polarjournal
Fossil teeth from extinct steppe bison and wild horses provided scientists with clues as to why these large grazers became extinct in the Arctic. Photo: Andrew Higley/UC Creative + Brand

In the ice-age mammoth steppe, which shaped the landscape of what is now northern Canada, northern Europe, Alaska and Siberia between 2.6 million and 12,000 years ago, species diversity was much higher than in today’s Arctic. Large mammals such as mammoths, bison, wild horses and also bears, sloths and cave lions roamed the steppes and grasslands. In addition, much larger populations lived in the Arctic at that time, with a total of six to ten times as many animals as today. They all apparently found enough food to coexist. Researchers at the University of Cincinnati wanted to know more about how prehistoric horses and bison fed and examined the teeth of fossil specimens in a recent study published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

Horses and steppe bison were among the most common large mammals living in what is now Alaska between 40,000 and 12,000 years ago. Climate change, human hunting, or a combination of both led to their extinction. Abigail Kelly, a doctoral student at the University of Cincinnati and lead author of the study, made dental impressions of fossil specimens of the two species provided to her by the University of Alaska Museum and analyzed the wear marks on the teeth for clues about the animals’ diet.

“In the Pleistocene, the diversity of wildlife was so much greater than it is today. It looked completely different. A key question is why the Arctic today is so depauparte by comparison.”

Joshua Miller, assistant professor at the University of Cincinnati
PhD student Abigail Kelly made impressions of the fossil teeth and examined their wear marks. Photo: Andrew Higley/UC Creative + Brand

Depending on what kind of food the animals prefer, their teeth show different signs of wear. For example, the teeth of grazers wear down particularly badly because grasses contain silicic acid, which abrades the enamel and dulls the teeth. Under the microscope parallel scratches can be seen, caused by silica crystals. In contrast, animals that tend to eat leaves from trees, herbs, and shrubs have fewer microscopic scratches and sharper teeth.

A comparison of the fossil teeth with those of prairie bison and horses living today showed that the Ice Age animals apparently fed on less abrasive plants than modern ones, whose teeth showed greater signs of wear. This suggests a varied diet of broad-leaved, herbaceous plants in prehistoric bison and horses, which in turn suggests that vegetation was more diverse then than now.

Left image: Wild horses still live in parts of the U.S. today, helping to keep the landscape open. Right image: Wood bison calf at the Alaska Wildlife Conservation Center. Wood bison have been reintroduced to Alaska since 2015. Photos: Michael Miller

Bison and horses probably used the landscape’s resources in different ways, what biologists call “niche partitioning.”
“It seems that the diets of bison and horses were not that different. They ate similar structured diets,” Miller said. “But their physiology is very different. Bison are forestomach fermenters that digest food differently than large intestine fermenters like horses. So there’s a possibility that the species get different amounts of nutrients from the same diet.”

The study’s findings have critical implications for the reintroduction of wood bison, descendants of extinct steppe bison, to Alaska, according to Tom Seaton, a biologist with the Alaska Department of Fish and Game and co-author. The analysis opens important perspectives on how different populations of herbivores coexisted in the Alaskan landscape thousands of years ago, he said. This would allow biologists to better understand the needs of wood bison and promote their reintroduction accordingly.

Joshua Miller and Abigail Kelly of the University of Cincinnati collaborated on the study. Photo: Andrew Higley/UC Creative + Brand

However, it is not clear from the study that large mammal loss is generally blamed as a cause of plant diversity decline, as a 2018 study found (Koerner et al. 2018, Nature Ecology and Evolution). Therefore, it stands to reason that modern species poverty in the Arctic is also linked to the disappearance of large grazing animals.

At any rate, this is evidenced by the success of the “Pleistocene Park” project, which since 1996 has (re)introduced large grazing animals such as wisent, horses, cattle and bison to a 144-square-kilometre area in the Republic of Sakha in Russia’s Far East in order to preserve the permafrost. Currently goats and camels are on their way to the park to support the already existing species in their task. The goal of the project is to convert the entire area into “highly productive steppe tundra” by 2029 and to establish 3,000 animals.

If Russia and North America succeeded in permanently reintroducing a diversity of large grazing animals, this would be a major contribution to climate protection. Their presence helps to compact the permafrost and freeze it deeper in winter, which also considerably slows down the release of methane that has an impact on the climate.

Julia Hager, PolarJournal

Link to the study: A. Kelly et al. 2021. Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 572. Dietary paleoecology of bison and horses on the mammoth steppe of eastern Beringia based on dental microwear and mesowear analyses.

Link to the Pleistocene Park website: https://pleistocenepark.de

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