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An illustration of a wooly mammoth.

Woolly mammoths roamed the northern steppes for at least 300,000 years before they died off.

ILLUSTRATION BY SCIENCE PICTURE CO., CORBIS

Dan Vergano

National Geographic

Published February 5, 2014

Grasslands suddenly spreading across the Arctic about 10,000 years ago helped killed off the woolly mammoth and other prehistoric mammals, suggests a study of ancient Arctic vegetation.

Climate warming after the Ice Age, prehistoric hunters, and even a comet impact have been proposed as reasons for the extinction of the mammoth, woolly rhinoceros, and other oversized "megafauna" that once inhabited Siberia and North America's far northern plains. (See also: "Can Purported Mammoth Blood Revive Extinct Species?")

The new DNA analysis of Arctic vegetation over the past 50,000 years, published in Nature by a team led by Eske Willerslev of the University of Copenhagen, offers a new wrinkle on the climate-warming theory: The great beasts vanished because they weren't getting enough of the right food.

Some 10,000 years ago, the researchers found, the flowering, broad-leafed plants known as forbs—including sagebrush, yarrow, mums, and tansies—disappeared from Arctic steppes, which became more dominated by grasses. That vegetation change was "a likely key reason for the decline and extinction of many megafuana species," Willerslev says, by email.

DNA Detectives

The new theory is surprising because mammoths were thought to thrive on grass. The Nature study challenges a long-held picture of a grass-covered "mammoth steppe" covering the polar regions of Europe, Asia, and North America during the last Ice Age.

In the study, the team sampled permafrost cores dating back to 50,000 years ago from 17 locations in northern Russia, Canada, and Alaska. They found that DNA signatures in the cores indicate that the flowering species, and the tiny roundworms associated with them in the soil, once predominated over grasses on the ancient steppes.

What's more, the mammoths and other beasts seem to have favored those forbs. Willerslev and colleagues analyzed 18 preserved samples of stomach contents and scat from mammoths, woolly rhinos, horses, reindeer, and elk. They found that flowering species were a large part of the animals' diet.

The forbs could have been a key source of protein, Willerslev says, and they may have been easier to digest than grass. Previous research had missed that component of the mammoths' diet, he and his colleagues argue, because those studies relied on pollen counts to estimate past Arctic vegetation. Grasses produce abundant pollen, so such studies gave a misleading picture of the makeup of the steppes.

"I think this is (a) preliminary conclusion," says Sergey Zimov, director of Russia's Northeast Science Station, who was not part of the study. He notes some overlap of the DNA results showing forbs flourishing after the Ice Age, and the limited number of prehistoric animal remains involved in the work.

Farewell to Flowers

When the last Ice Age reached its peak around 20,000 years ago, the diversity of all plants in the Arctic declined, but flowering plants continued to dominate over grasses. The warming that ended the Ice Age, however, also brought a wetter climate that was more friendly to grasses. "This is the likely reason for the vegetation change in the Arctic into a system dominated by shrubs and grasses we see today," Willerslev says. Indeed, much of the ancient steppe has given way to mossy tundra.

The herds of mammoths and other megabeasts had probably also helped maintain the steppe they lived in, whether it was dominated by grasses or, as the new research suggests, by forbs. Grazing and trampling of vegetation allowed new seedlings to take root, and manure fertilized the plants. Human hunters, by reducing the population of mammoths, may thus have helped complete the vegetation transition that climate change began.

"There are dangers in making broad generalizations about herbivore diet," says paleobotany expert Robert Crawford of Scotland's University of St. Andrews. Forage conditions in winter and local conditions for fodder across the Ice Age Arctic have to be examined more closely in more studies, he suggests, before forbs would look like an answer to the mystery of the mammoth.

Zimov, a founder of the "Pleistocene Park" effort to recreate Siberia's Ice Age steppes, agrees that the numbers of mammoths, bison and horses once seen in Siberia would have completely transformed the landscape. But he suggests that the ancient range of these creatures extended from Spain to China to North America, making it unlikely that climate change alone could have changed their habitat enough to wipe out the species.

Woolly mammoths had roamed the northern steppes for at least 300,000 years before they died off. In parts of Alaska, at least six times more animals—such as mammoths, horses, and bison—lived in the region during that era than live there today. A last, isolated population of mammoths is thought to have finally gone extinct on Siberia's Wrangel Island about 3,700 years ago.

Follow Dan Vergano on Twitter.

26 comments
E. Follett
E. Follett

If only ancient humans had done more to reduce their carbon footprint... 

Owen Busse
Owen Busse

I think they evolved into elephants.

JORGE JUNIOR
JORGE JUNIOR

Too bad they´re gone.Amazing animals. 

Richard R.
Richard R.

The effect of global climate change on Pleistocene megafauna.  

Arif Santoso
Arif Santoso

Mammoth extraordinary animals, if they live up to the present time the earth's ecosystems are now definitely different than it is today.

Jacob Stephens
Jacob Stephens

It always annoys me when people try to find new ways on how certain animals became extinct.  People the answer has been sitting right in front of us for so many years..... ALIENS KILLED OFF THE MAMMOTHS. That is the only possible explanation for this.  How could grass kill something that is 1000000X its weight!? That's outrageous! Of course I didn't actually read this article because I am a lazy bum but seriously that is impossible for grass to kill mammoths.  Aliens, aliens, aliens.  That is the answer to everything.  They came down in there fancy little UFO things and one by one, zapped the crap of the mammoths until they died.  I don't know about you all, but personally I'm scared that us humans will be next!  So stay alert and ALWAYS ALWAYS ALWAYS use the buddy system when walking on the streets so you don't get zapped next by them pesky, mammoth killing aliens.  Thank you for reading this and I hope you trust my CORRECT theory on how mammoths went extinct.   


-js

Fritz Reynolds
Fritz Reynolds

This is a really interesting study, and I'm glad it's getting some coverage in the media outside of academic journals, but it's unfortunate that the person who wrote this article apparently doesn't understand the very basic vocabulary that the authors of the study used to describe their findings in the abstract. "Forbs" are defined as "non-graminoid herbaceous vascular plants." The word "herbaceous" indicates that forbs are not woody plants, as opposed to shrubs and trees, which are woody plants. Perhaps this simple error could be corrected?

Tochukwu Ezeokafor
Tochukwu Ezeokafor

It is interesting to know that such a mega beast like the Woolly Mammoth would graze majorly on flowering plants over and above grasses. One would have expected such a beast to evolve in the course of time, and probably, escape extinction by grazing on any available plant or grass.


Eric Harmon
Eric Harmon

Yet again they don't really know, yet they act as if they did.  Yes, there is not bias in science.  Just like they weren't swayed by politics, money and fame to create weapons of mass destruction.  I have a question.  If we had many "human" like ancestors how come we are the only ones.  Are we similar to apes, yes.  But not like similarities between ape species, or finches that Darwin used, or dogs, cats, fish (of which there is a great variety yet they all exist the same way).  There is not a single upright walking hominoid other than us on Earth.  Why?  Don't you think the human evolutionary tree would have more branches in the current world just like other animals do?  There is not another hominid on Earth existing today.  And no Im not a creationist, I actually studied geology.  But I don't by the billions of years either because humans supposedly existed for millions of years then in the span of a few millennia created language, writing, math, great buildings and cities, complex social structure, art, warfare, clothing, metalwork and jewelry.  There has always been a inherent, subconscious need for religion.  You don't see that in apes.  Yes a few groups use sticks as tools and they have social structure but don't you think there would be many more advanced groups not animals with sort of human habits?  And if you cite different races well there is no agreement on their origins. One theory is that well all came from common ancestors beginning in Africa (sounds a lot like the bible) another is that many "sprang" up in different places.  Yet we all share a common "human" gene sequence.   

Joshua Oyer
Joshua Oyer

Cavemen in their SUV's?   Really though I've only heard 2 decent theories. 1) climate/habitat changes and 2) Hunting by early men.  But I wasn't there, so I don't know.

sdgsadgasd sdgsadghsadf
sdgsadgasd sdgsadghsadf

"but flowering plants continued to dominate over grasses. '


You guys do know grasses are also angiosperms and are thus flowering plants right?

TJay Jonnson
TJay Jonnson

Nope, they were wiped out by a worldwide flood.

Andrea Padonou
Andrea Padonou

@Jacob Stephens  yup. i am scared of plants and such as well...and NO way an asteroid killed dinosaurs...and this guy, ehm...ehm...aaahh...darwin, yep, he was totally wrong as well. so, please, you marsians, take me away, and then drop me in the US, where everything is possible.....woooahahhaahah....drool   drool....

Jacob Stephens
Jacob Stephens

@Fritz Reynolds I can guarantee you that Dan Vergano is way smarter than you so don't hate on his style bro.  Dan the man is killing it with this study so back off because I always got my boy's back.

ML Jones
ML Jones

@Tochukwu Ezeokafor  grass is one of the hardest things to digest in the plant kingdom. its why humans cant eat grass. even cerals we eat the kernals of the food not the stalks and we still dont digest it that well.

Kelly Clark
Kelly Clark

@Eric Harmon When you studied geology did you flunk out?  I am also guessing you no next to nothing about other hominid species. Take some time to understand where we are in understanding the evolution of the hominids before you preach whatever it is you are preaching. Our understanding of human evolution is more advanced than you think. There are actually a few good articles on the NatGeo website on this very subject...

Brendan Millar
Brendan Millar

@Eric Harmon

Hey you want to see how closely related to chimps the human race is: check this link out: http://world.time.com/2014/02/05/central-african-republic-lynching-samba-panza/?iid=gs-main-belt  


The only difference is that these chimps where clothes and carrying Ak47s. 

Humans have a carnal instinct to destroy, and also create, religions where used as tools to control. Hidden  in the beauty of mosques temples  and cathedrals is a cooperation, with promises of a better place if you follow their rules. 

"In the span of a few millennia humans created" no, Humans have been coming up with ideas all along out of need, the need to provide for their families, the need to communicate their desires, fears, beliefs and ideas,  the need to attract a mate, the need to survive. The underlying factors are the same but just evolve over time, sometimes in leaps and bounds. There is no destiny, nothing is written  everything starts with an idea.

craig hill
craig hill

@Eric Harmon  Anyne who says right out of the chute there "is no basis in science", as in zero, nada, tells me there is no basis to continue reading his drivel. The rest of you can waste your time as you please,

Lewis Crump
Lewis Crump

My ancesters were there... Mammoth tasted Good!

Charlie Petit
Charlie Petit

Sdgsadgasd - Dan's story on first ref explicitly referred to forbs as flowering, broad-leafed plants. He never said grasses don't flower. This is a solid account hw wrote. No need to nit pick for gotchas among such minor matters.

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