Ancient horses crossed back and forth over land bridge

Ancient horses crossed back and forth over land bridge

UC contributes to First Nations study on movements of prehistoric horses

The horse originated in North America around 4 million years ago. As changing sea levels created land bridges between continents, the horse traveled into Eurasia and back.

The University of Cincinnati and an international team of 57 researchers - including 18 Indigenous scientists from the Lakota, Sqilx'w (Suknaqin/Okanagan Nation), Blackfoot and Dene' (Athabascan and Iñupiaq Nations) - reveal that inter-continental exchange of horse populations occurred in both directions.

This back-and-forth migration pattern continued as recently as the last glacial period between 50,000 and 19,000 years ago.

By combining cutting-edge analyses of ancient DNA and isotopes with traditional Indigenous scientific knowledge systems, researchers revealed new insights into how climate change affected horses and other large herbivores in the late Pleistocene Epoch.

Published in the journal Science, the study carries important lessons for biodiversity conservation in the face of today's ongoing climate and ecosystem shifts, researchers said.

UC Associate Professor Joshua Miller studies the jawbone of a prehistoric horse in his geoscience lab. Photo/Andrew Higley/UC Marketing + Brand

Horses' behavior, ecological roles and ability to adapt and move great distances have played an integral role in shaping the world views and scientific systems of many Indigenous peoples globally. Their actions have offered profound lessons to Indigenous communities that served as stewards over vast territories in the Americas for more than 20,000 years.

"We understand the Horse Nation to be a keystone species that, together with the other life forms with which it shares relationality, brings balance to the ecosystem," says Chief Harold Left Heron, a traditional Lakota scientist, knowledge keeper and leader from the Lakota Nation.

"Multiple scientific systems respectfully joined together in this study to offer critical knowledge that can be applied by each of us today in our respective communities around the world to preserve all life."

Wilson Justin, Athabascan elder

Dene' (Athabascan) traditional knowledge speaks of the Medicine Man Trail - a vital corridor that connected the American and Eurasian continents for thousands of years. Along this trail, horses, like all life, traveled freely, while mixing, contributing, reinforcing and learning from the natural systems that shaped their journey.

"This knowledge is held in our songs, stories and in the sciences and lifeways we carry. Singing the song of life ensures that the world is balanced and life can diversify and continue in a good way," said Wilson Justin, an Upper Ahtna/Upper Tanana Dene' (Athabascan) elder and knowledge keeper of the Alth'setnay clan.

Yvette Running Horse Collin takes samples from the bones of a prehistoric horse. Photo/Jacquelyn Cordova.

Reacting to change

UC Associate Professor Joshua Miller and Professor Brooke Crowley studied carbon and nitrogen isotopes that provided clues about horse diets across roughly 40,000 years and the environmental conditions in what is now Canada's Yukon Territory. They have used similar techniques to study caribou migrations in both recent centuries and past millennia, and the ecology and movements of long-extinct mammoths.

UC College of Arts and Sciences researchers Brooke Crowley and Joshua Miller contributed to an international study that examined the movements of prehistoric horses between North America and Eurasia. Miller has found ancient horse bones in the Arctic while looking for shed caribou antlers. "The toe bone of a horse sticks out. The only thing it could possibly be is an Ice Age horse, so it's fun to find," Miller said. Photo/Andrew Higley/UC Marketing + Brand

Tracking horse lineages

Today, the frozen soils of Alaska, Canada's Yukon and Siberia in Russia preserve a remarkable archive of fossilized bones from ancient horses and other large herbivores.

"DNA preserves best in cold environments," said Ludovic Orlando, director of the Centre for Anthropobiology and Genomics of Toulouse, a joint multidisciplinary research center supported by the French National Center for Scientific Research and University of Toulouse, France.

Domesticated horses spread across the globe with human societies. Researchers sequenced the genomes of 68 Late Pleistocene horse specimens from both the American and Eurasian continents dating back as far as 1 million years ago. The team included researchers from the territories from which the samples derive and delves deeper into intercontinental horse migrations, focusing on movements up to and during the peak of the last Ice Age.

Yvette Running Horse Collin, a Lakota scientist and director of Taku Skan Skan Wasakliyapi: Global Institute for Traditional Science, led the project's genome sequencing laboratory work and helped to ensure all Indigenous scientific protocols were applied and followed.

"Our work shows that, in North America alone, there was one distinct horse lineage south of the ice sheets, another across Alaska and the Yukon and even a third at the westernmost edge of Alaska," she said. "However, the natural migration patterns of our Horse Nation relatives show us clearly that today's geographic country boundaries and accompanying paleontological labels do not accurately define or capture the actual experience of the horse."

Wild horses roam free in South Dakota. Photo/Black Hills Wild Horse Sanctuary

Genomic research

Researchers traced the genes of the western lineage in North America back to Eurasia. It represents the easternmost spread of a horse population native to the Ural Mountains, one that extended across the Arctic and entered North America as sea levels dropped and a landmass connected Siberia to Alaska.

The study shows that horses crossed this land bridge many times from Eurasia to America between 19,000 and 50,000 years ago. It also reveals that horses traveled the opposite direction during earlier time periods, following coastal routes southward along the Pacific and reaching as far as northeastern China.

This population eventually left enduring genetic traces as far west as Anatolia and the Iberian Peninsula well into the Holocene Period.

The team also analyzed horses that lived in the Yukon during the post-glacial warming period as melting ice sheets gave rise to new environmental conditions.

"These horses lived within the ice-free corridor at a time when the landscape was transitioning from steppe-tundra to a much wetter ecosystem," said Clément Bataille, professor at the University of Ottawa, who coordinated the carbon and nitrogen isotope analyses. This shift proved less favorable to horse populations and their necessary ecosystems, leading to a significant demographic decline.

Jane Stelkia is an elder for the Sqilx'w, which is based on her people's traditional lands in Canada. She is a keeper of traditional science surrounding Horse Nation called the Snklc'askaxa and confirms her people's experience with the Medicine Man Trail and their ability to overcome great environmental and historical adversity together with and alongside the horse.

"In this study, Snklc'askaxa is offering us medicine by reminding us of the path all life takes together to survive and thrive as life moves and changes," she said. "It is time that we come together, again, to help life find the openings and points to cross and move safely."

Featured image at top: Jane Stelkia is a prominent Okanagan elder who helped researchers contextualize their findings about wild horses in North America and Eurasia. Photo/Little Pine Productions

UC Associate Professor Joshua Miller, pictured with a bronze mammoth outside the Geier Research Center, uses isotopic analysis to track the movements of animals across landscapes. Photo/Andrew Higley/UC Marketing + Brand

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