Focus on Arts and Ecology

Genetic material collected from permafrost shows northern part of the island was once a lush forest, home to poplar trees and other surprising organisms. 

By Ewen Callaway, December 7, 2022

The northeastern tip of Greenland is a lonely, barren place, home to the odd hare and musk ox, and few plants. Two-million-year-old DNA sequences — the oldest ever obtained — recovered from frozen soil suggest that the region was once home to mastodons and reindeer that roamed a forested ecosystem unlike any now found on Earth.

“No one would have predicted this ecosystem in northern Greenland at this time,” says Eske Willerslev, a palaeogeneticist at the University of Copenhagen who co-led a study published on 7 December in Nature describing the ancient-DNA findings1.

“It’s pretty awesome,” adds Love Dalén, a palaeogeneticist at the Swedish Museum of Natural History in Stockholm who was not involved in the study. “Not in a million years would you expect a mastodon up there.”

In 2021, Dalén’s team obtained partial genomes from million-year-old mammoth remains from Siberia, shattering the record for ancient-DNA preservation2. But Dalén and other scientists suspected that although DNA degrades into ever-shorter fragments over time, even older sequences could be recovered and interpreted — if the right samples could be found.

As it turned out, some of those samples had been sitting in a freezer in Copenhagen since 2006, when Willerslev visited northern Greenland looking for ancient human remains. While there, the team collected sediment from the region’s Kap København Formation, a 100-metre-thick deposit of frozen mud and sand that built up around 2 million years ago.

Over the years, Willerslev and his team periodically tested the Kap København sediment, as methods for extracting and sequencing ancient DNA improved. A couple of years ago, they got their first success. All told, they sifted through more than 16 billion DNA fragments — many from modern microorganisms that had contaminated the samples — to identify shards of authentic ancient DNA. “It’s a massive sequencing effort,” Willerslev says.

Surprise appearance

When the team matched these sequences to databases of genomes from modern plants and animals — which sometimes differ substantially from those of the organisms’ ancient relatives — a snapshot emerged of Kap København two million years ago. Greenland was much warmer then, but the researchers did not expect the DNA sequences to reveal forests of poplar, spruce and yew trees such as those now typically found at much lower latitudes, alongside sedges, shrubs and birch-tree species that still grow in Greenland.

Kap København’s animal life, detailed in sequences probably from reindeer and mastodons — extinct relatives of elephants — as well as rodents, geese and rabbits, held even more surprises. “Reindeers, according to palaeontologists, should not have survived; they shouldn’t even exist at that time,” says Willerslev. Mastodons were thought to have lived in North American forests, and their remains have never been found in Greenland.

“You would have expected such gigantic animals to be hard to miss in the fossil record,” says Ludovic Orlando, an ancient-DNA specialist at the Centre for Anthropobiology and Genomics of Toulouse in France. Such findings show the potential of ancient sedimentary DNA to yield surprising insights about past ecosystems.

Willerslev thinks his team’s work could say something about how future ecosystems will respond to climate change, as well. “In these organisms is an ability to adapt in composition and in range that we don’t understand and we can’t predict,” he says.

References

(Sources: Nature)