And with another cold snap upon us following the polar vortex, this winter may feel like an ice age in certain parts of the country. Our next story takes us back to the beginning of that actual chilly period, with a look at new research published in the journal Nature. It's about what woolly mammoths and other prehistoric creatures ate, and how some little plants could have meant the difference between life and death. Here's NPR's Geoff Brumfiel.

GEOFF BRUMFIEL, BYLINE: Around 50,000 years ago, the arctic looked a lot different than it does today. It was a vast grassland, kind of like a prairie. But Eske Willerslev, a researcher at the University of Copenhagen, says you would have seen a lot more animals.

ESKE WILLERSLEV: There would be elephants in the form of woolly mammoth. There would be rhinoceros in the form of woolly rhino. There would be horses, bison, but also reindeer, and there would even be lions and possibly hyenas running around.

BRUMFIEL: Willerslev is a very particular kind of researcher. He learns about the past by analyzing ancient samples of DNA. His favorite place to get these samples is from frozen Arctic soil.

WILLERSLEV: It's the perfect environment for conducting this type of study.

BRUMFIEL: He and his collaborators took hundreds of frozen soil samples from modern-day Alaska and Siberia. The goal was to learn more about what mammoths and other creatures ate. The group analyzed the DNA from plants in the soil, and they found that the Arctic wasn't just grassland. There was a whole 'nother class of plants growing at the time. They were similar to dandelions. They had flowers, and they were everywhere.

WILLERSLEV: I'm pretty sure it would have been a beautiful landscape, because of all these flowering plants.

BRUMFIEL: So, that's what was growing, but was it on the mammoths' menu? To find out, Willerslev also analyzed poop from frozen woolly mammoths and rhinos found in Siberia. He didn't actually handle the poop, by the way. He left that to his foreign colleagues.

WILLERSLEV: Well, that was the Russians. So, that was their job to kind of deal with the feces.

BRUMFIEL: But he did analyze the DNA in the feces.

WILLERSLEV: And to our surprise, it turned out that the dominate source food that these animals were eating were, in fact, the flowering plants, and not so much the grasses that everybody thought were so important.

BRUMFIEL: The little dandelions weren't just pretty. For prehistoric vegans like the woolly mammoth, they were an essential source of protein. But then something happened. Twenty-five thousand years ago, the glaciers pushed south. When they finally retreated, the flowers never grew back. Around the same time, the mammoths and rhinos disappeared, too. Willerslev thinks the disappearance of the tiny flowers could have been the cause of the giants going extinct.

WILLERSLEV: The vegetation change could have most likely have been pretty devastating.

BRUMFIEL: But not everyone sees the relationship between disappearing flowers and disappearing mammoths the way he does. Daniel Fisher is a paleontologist at the University of Michigan. He says the new work shows both vanished around the same time, but he also studies mammoth poop.

DANIEL FISHER: Oh, it smells green and like a sort of a fresh hay field. I mean, a little more pungent than that.

BRUMFIEL: And it makes great fertilizer. So, maybe it was the other way around: the flowers needed the mammoths' poop to grow. So, when the mammoths started to disappear...

FISHER: The ongoing process of extinction could have been a factor in changing plant communities, rather than the changes in the plant communities driving the ongoing extinction. We really don't know.

BRUMFIEL: So, if it wasn't the flowers, what was causing mammoths to disappear? Fisher suspects it was us. We were around, and while the mammoths were eating the flowers, we were eating the mammoths. Geoff Brumfiel, NPR News.

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