Simple spoonfuls of dirt extracted from Canada's permafrost provide rich new information and rewrite old views about the extinction dynamics, dates, and survival of megafaunas like mammoths, horses, and other long-lost living forms in the Yukon.

Researchers from McMaster University, the University of Alberta, the American Museum of Natural History, and the Yukon government present a 30,000-year DNA record of past environments derived from cored permafrost sediments extracted from the Klondike region of central Yukon in a new paper published in the journal Nature Communications.

Studying DNA Data

Researchers used McMaster-developed DNA capture-enrichment technology to isolate and reconstruct the fluctuating animal and plant communities at different time points during the Pleistocene-Holocene transition, a climatically unstable period 11,000-14,000 years ago when several large species such as mammoths, mastodons, and saber-toothed cats vanished.

To rebuild ancient ecosystems, they used small soil samples containing billions of minuscule genetic sequences from animal and plant species.

Related Article: Climate Change, Not Humans, May Have Caused Iconic Wooly Mammoth's Extinction

Changing Environment

The findings show that mammoths and horses were already in sharp decline before the climatic instability, although they did not go as quickly as previously assumed due to human overhunting. Indeed, DNA evidence indicates that both the woolly mammoth and the North American horse survived until as recently as 5,000 years ago, putting them into the mid-Holocene. This period began around 11,000 years ago and has lasted until now.

The Yukon ecosystem continued to change dramatically during the early Holocene. Grazing herds of mammoths, horses, and bison could no longer keep shrubs and mosses in control, and the "Mammoth Steppe" became overrun with them. Grasslands in northern North America do not thrive now, in part due to the lack of megafaunal "ecological engineers" to manage them.

"Through more subtle reconstructions of past ecosystems, the rich data provides a unique window into the population dynamics of megafauna and nuances the discussion around their extinction," says evolutionary geneticist Hendrik Poinar, a lead author on the paper and director of the McMaster Ancient DNA Centre.

This research builds on McMaster scientists' prior findings that woolly mammoths and the North American horse were likely present in the Yukon around 9,700 years ago. Better methodologies and more research have improved the previous results, bringing the date even closer to the present.

Tyler Murchie, a postdoctoral researcher at McMaster's Department of Anthropology and a primary author of the study, adds, "Now that we have these tools, we know how much life-history information is kept in permafrost."

"The amount of genetic data in permafrost is huge, allowing for a scale of ecological and evolutionary reconstruction that is unequaled by any technologies to date," he adds.

Mammoths and Horses

"While mammoths are extinct, horses are not," says co-author Ross MacPhee of the American Museum of Natural History. "The horse that roamed the Yukon 5,000 years ago is genetically connected to the horse species we have today, Equus caballus, making it a native North American animal that ought to be classified as such."

Scientists also emphasize collecting and archiving additional permafrost samples, which are at risk of disappearing forever as the Arctic warms.

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