Scientists track signs of Alaska's ice age wolves

Researchers say 'highly carnivorous' subspecies followed prey into oblivion

Posted: Wednesday, July 04, 2007

ANCHORAGE - Alaska used to be home to a previously unknown and "highly carnivorous" subspecies of ice age wolf with jaws so powerful it could snap a mammoth's thigh bone in two.

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Isolated from other wolves by a southern ice sheet, the "Eastern Beringia wolves" that roamed central Alaska more than 12,000 years ago were genetically different from any wolves that exist today, a Smithsonian-led team of scientists has discovered.

When the bison, musk ox, mammoth and other super-sized mammals they preyed upon either disappeared locally or went entirely extinct as the ice age ended, all the wolves in Alaska died off too, leaving no modern descendants.

So says a study due to be published in Current Biology that provides new insights about modern wolves, which now appear to have arrived in Alaska much later than previously believed. It also shows how highly specialized mammals might be particularly threatened by climate change.

For the past 10 years, the research team has measured the skulls and examined the DNA of wolf remains that lay buried for millennia in permafrost near Fairbanks until Gold Rush-era miners dug them up. That such fossils aren't related to modern wolves "was quite a surprise," lead researcher Jennifer Leonard says.

Also surprising were skull and tooth comparisons between the ancient Alaska carnivores and other ice age wolves that lived in California in the late-Pleistocene epoch and resembled the northern gray wolves of today.

The carnassials (the big side teeth that wolves use for sheering meat and bone) were significantly larger in the Alaska specimens, which also had a wider head that provided more room for jaw muscles.

"It had evolved to have a stronger bite," Leonard said, speaking by telephone from Stockholm, Sweden, where she now teaches at Uppsala University.

Tale of teeth

The teeth of the Eastern Beringia wolves (so-named because they populated the broad Bering Land Bridge that once joined Siberia to Alaska) also were more cracked and broken, indicating that such wolves were habitual bone-breakers.

"We think they were probably eating their prey more completely by doing a lot more bone-cracking," Leonard said. "If you're really hungry, it's worth cracking the bones to eat the marrow."

The tooth wear could also indicate that such wolves preferred to chew on very large animals, whether they hunted them down themselves or found the remains left by other carnivores, including such contemporaries as the now-extinct North American lions, saber-tooth tigers and short-faced bears of ice age days.

Included in that diet were musk ox, horse, caribou and bison, Leonard said.

But when their preferred prey began to die off about 12,500 years ago -- due to a warming climate, the new pressure of human hunters or some other reason not yet known -- the Alaska wolves began to quickly decline. Of the 56 specimens the team studied, only one died more recently than 12,000 years ago, according to carbon- and nitrogen-isotope dating techniques.

"It was a really lonely animal," Leonard said.

Surprise follows 100-year wait

None of the wolf specimens was dug up recently. Nearly all were found in the early 1900s by gold miners probing the frozen soil around Fairbanks.

The fossils were soon acquired by the American Museum of Natural History in New York City, whose scientists identified them as wolf bones dating back to the late-Pleistocene (the end of a 1.8 million-year period of serial glaciations that culminated about 10,000 years ago), then placed in drawers.

Over the next century they barely stirred - until 10 years ago, when Leonard, then a graduate biology student at UCLA, decided to check out the wolf bones as part of her doctoral thesis on evolutionary changes in vertebrate populations.

There, Leonard and other researchers measured and dated an ever-growing assortment of ancient Alaska wolf bones. They extracted mitochondrial DNA from the samples and compared the genetic sequences with those of modern wolves around the world.

There was no overlap. All of the genetic signatures of the ancient wolves differed from the modern ones. That wasn't the team's expectation.

"We thought possibly they would be related to Asian wolves instead of American wolves -- because North America and Asia were connected during that time period," Leonard said in a Smithsonian Institution press release announcing the discovery. "That they were completely unrelated to anything living was quite a surprise."

Implications for polar bears

Previously, biologists assumed that the wolves that populated Alaska during the last ice age survived the end-Pleistocene extinction intact. The Smithsonian research (joined by other scientists at UCLA, Uppsala and the University of California at Santa Cruz) shows they didn't.

Instead, Alaska must have been wolfless for a while, until descendants of distant cousins that survived the ice age in southern latitudes eventually recolonized the north.

The discovery may also shed light on how highly specialized mammals, such as polar bears -- now threatened by melting sea ice -- can die off when they no longer find the kinds of food their bodies were designed to harvest.

For the ice age wolves of Alaska, the fatal subtraction might have been the horses and super-sized caribou that eventually disappeared from the north. For today's polar bears, it might be the all-important ringed seals, lost to retreating ice floes.

"That's a good example," Leonard said. "The polar bear is clearly a very specialized bear."



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