Back when the Arctic was a swamp — about 53 million years ago — it was home to a flightless bird with a head the size of a horse’s. This strange creature is described in a recent study from the journal Scientific Reports.

Researchers don’t have all that much to go on: Their study is based on a single toe bone found on Ellesmere Island back in the 1970s. But they say it’s a perfect match for toe bones from a bird known as Gastornis that lived in what's now North America around the same time period. In fact, many scientists have classified it as such since it was first found — but this is the first time the toe has been analyzed closely.

Gastornis was a big bird with an even bigger head, dwarfing the head-to-body ratio of most similar birds. There’s a long-standing debate on what they ate: Those massive heads boasted mighty powerful jaws, which led many scientists to classify them as ferocious predators. But a lack of other physical traits associated with hunting has led others to classify them as herbivores who chomped on sturdy nuts and seeds.

Quick side note: The news release on this bird — and, as a result, a lot of media outlets — keep calling it a "vegan." Animals are either herbivores, carnivores or omnivores. They don't sit around making cheese, so if they eat nuts and seeds and don't eat meat or prey upon the eggs of other animals, they're herbivores. Sorry, vegans! 

Another bird previously found in North America — Presbyornis, which looked like a duck with the long legs of a crane — now has a confirmed presence in the Arctic, as well. The evidence is again quite scant, coming only from a single upper-wing bone found at the same time as the Gastornis toe. But a close examination suggests that the wing belongs to a bird from this group.

"I couldn't tell the Wyoming specimens from the Ellesmere specimen, even though it was found roughly 4,000 kilometers (2,500 miles) to the north," study co-author Thomas Stidham of the Chinese Academy of Sciences said in a statement.

The researchers aren’t sure how the birds got to be in both places. The Arctic was quite warm 53 million years ago — similar to cypress swamps found in the southeastern United States today — but living above the Arctic Circle still meant very little sunlight, with months-long stretches in the dark. It's possible that these birds and others dealt with the dark months by migrating south. There are modern birds that spend their entire year in the Arctic today, even given its chilly weather. But there are many more that fly south to escape the dark.

As the climate shifts, the researchers suggest in their study, it’s possible that this kind of migration will become more common again. Perhaps more species of birds will be able to thrive in the average temperatures of the Arctic Circle, but will still need to seek sunnier shores come winter. That kind of movement will affect ecosystems in both the Arctic and in the areas these birds fly to for their winter holiday.

"Permanent Arctic ice, which has been around for millennia, is on track to disappear," co-author Jaelyn Eberle of the University of Colorado said in a statement. "I'm not suggesting there will be a return of alligators and giant tortoises to Ellesmere Island any time soon. But what we know about past warm intervals in the Arctic can give us a much better idea about what to expect in terms of changing plant and animal populations there in the future."

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