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Yellowstone wolf teeth lead to extinction theory

by Ace Damon
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Billings, Mont. "It may be a tale only dentists can appreciate, but the teeth of dead Yellowstone wolves have been helping scientists understand predators' lives for over 11,000 years."

Within the Yellowstone Research and Heritage Center, there is a collection of 160 Yellowstone adult wolf skulls. In examining skulls, along with other collections from around the country and around the world, UCLA professor of ecology and evolutionary biology, Blaire Van Valkenburgh and her colleagues theorized a relationship between the shrinking prey available and how large canines consume wildlife.

The theory is based on cracked and broken wolf teeth and the number of prey available to predators, along with how much of their deaths predators consume. In Yellowstone, for example, biologist Doug Smith said researchers would evaluate wolf slaughter sites to examine the number of bones present.

"When wolves aren't so hungry, they don't chew their long bones so much," he said.

"This is in line with other indicators of how well they are eating."

For example, in Yellowstone, the ratio of moose to wolves was over 600 to 1 when wolves were reintroduced in the park in 1995. Since reintroduction, 90% of wolves' diets are moose.

With many moose in the landscape, wolves flourished initially. But hunting gradually became more difficult, as the number of moose decreased to about 100 to 1.

In examining Yellowstone's wolf skulls, Van Valkenburgh saw that in the first 10 years after their reintroduction, wolves rarely cracked their teeth. But in the next decade, when the moose population declined, the number of broken wolf teeth doubled, including the larger teeth wolves use when hunting and chewing.

As moose were getting harder to find and kill, broken teeth were probably the result of wolves consuming more carcasses, including chewing bones for additional bone marrow food, theorized Van Valkenburgh and his colleagues. This resulted in more cracked and broken wolf teeth.

"Broken teeth can't heal, so most of the time carnivores don't chew bones and risk breaking their teeth unless they have to," Van Valkenburgh said in a UCLA press release.

Smith said that while Yellowstone wolves have suffered more broken teeth, 90% are still in good condition. One thing he noticed when looking at wolf skulls is that about half have misaligned teeth.

"They often wear clothes that are indicative of a misaligned bite," he said. "I'm sure it's because they get kicked in the face all the time (when they chase after bison and elk). They always deal with it. Wolves are tough."

He noted that being kicked in the head by prey is a major cause of wolf death in Yellowstone.

So how does this relate to ancient predators during the Pleistocene, a time that stretched from 2.5 million years ago to about 11,700 years ago?

In the 1990s, Van Valkenburgh and other scientists examined the skulls of Pleistocene predators – such as terrible wolves and saber-toothed cats – that were taken from California's La Brea Tar Pits. These animals had rates of broken teeth that were two to four times higher than in modern animals.

"Our new study suggests that the cause of this dental fracture may have been more intense competition for food in the past than in today's large carnivorous communities," Van Valkenburgh said in a press release.

As large plant eaters, such as giant sloths, mammoths and mastodons, declined in the Pleistocene, their predators had to grind more bones to get the nutrition they needed. Why the great herbivores and their predators went extinct was debated, although human hunters and climate change are two of the prime suspects.

With the loss of their main prey, the ferocious Pleistocene predators – animals that in some cases were twice as large as today's tigers, African lions and spotted hyenas – were also extinct.

Van Valkenburgh's theory of dental problems also manifested itself in other wolf populations. She also examined 64 adult wolf skulls from Isle Royale National Park on Lake Superior and 94 Scandinavian skulls, collected between 1998 and 2010. She compared them to the skulls of 223 wolves that died between 1874 and 1952, from Alaska, Texas, New Mexico. , Idaho and Canada.

The pattern was similar for Isle Royale wolves, which mainly attack adult moose – with moose numbers set at about 55 to 1, the wolves had many broken and worn teeth. Royal Island wolves had high frequencies of broken and heavily worn teeth, reflecting the fact that they consumed about 90% of the bodies of the moose they killed.

The teeth of the Scandinavian wolves told a different story. The ratio of moose to wolves is almost 500 to 1 in Scandinavia, so Van Valkenburgh found few broken teeth among the wolves.

"Wolves could easily find moose, not eat bones and move on," she said.

Van Valkenburgh believes his findings apply beyond gray wolves to other large carnivores – such as lions, tigers, and bears – and that looking at the teeth of large predators can help scientists understand if lack of prey is one of their problems.

"We want to understand the factors that increase mortality in large carnivores that in many cases are almost extinct," she said. "Getting good information on this is difficult. Studying dental fractures is one way to do this and can reveal varying levels of food stress in large carnivores."

Co-authors of the study were Rolf Peterson and John Vucetich, professors of forest resources and environmental sciences at Michigan University of Technology; and Smith and Daniel Stahler, wildlife biologists at the National Park Service.

The research was funded by the National Science Foundation and National Park Service.

Yellowstone Heritage and Research Center, located near the Roosevelt Arch in Gardiner, is open from Monday to Friday from 8 am to 5 pm to view temporary exhibitions in the lobby.

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