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Giant Prehistoric Bears Evolved to Fill Scavenger Gap

Ancient bears evolved to become giants so they could scavenge prey killed by others, a new study suggests.

Ancient bears evolved to become giants so they could scavenge prey killed by others, a new study suggests.

The findings, published in the Royal Society journal Biology Letters, found that short-faced bears weighing over a tonne evolved independently in North and South America.

"We think their large size was a particular advantage that let them exploit carcasses from other predatory species," said evolutionary biologist Dr Kieren Mitchell from the University of Adelaide, who was lead author on the new paper.

Bears And Wolves Feasting Together On Dead Whale: Photos

Dr Mitchell said giant bears from the Tremarctinae group were among the largest land-based carnivorous mammals that ever lived. The bears roamed the grasslands and open woodlands of the New World from about 2.5 million years ago to about 12,000 years ago.

The animals strode around on their long legs, eating whatever they could find, but the shape of their teeth suggests they were better adapted for eating meat than plants, he said.

At the time the giant bears lived there would have been lots of large herbivores, such as bison and mammoth in North America, and horses and giant ground sloths in South America.

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There would also have been specialized predators like wolves, lions and sabre-tooth cats, but there would have been no specialized scavengers, Dr Mitchell said.

"This opened up a bit of a gap that looks like the bears took advantage of separately in North and South America."

By turning into giants, the bears could spot vultures circling and quickly get to any newly-killed prey and get a meat meal without the risk and energy of having to do their own hunting.

"They could just get anything out of the way that was there originally, and just tuck in," Dr Mitchell said.

Penis Bones Show Size Mattered To Ancient Bear

The giant bears in North America belonged to the genus Arctodus while in the South America it was the genus Arctotherium.

Both were members of a group, which today has only one living member - the much smaller and largely vegetarian Andean spectacled bear (Tremarctos ornatus).

To shed light on the evolution of the giant bears, Dr Mitchell and colleagues compared the mitochondrial DNA of Arctotherium and Arctodus bears with the DNA of the living spectacled bear.

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This included DNA extracted from a femur of a giant bear found in a cave in Chile and DNA from the largest species of North American giant bear Arctodus simus.

The genetic analysis showed the South American giant bear was more closely related to the modern bear, even though it looked more like the North American giant bear, indicating the two extinct species evolved independently as an adaptation to exploit a similar ecological niche.

Article first appeared on ABC Science Online.

The big bears weighed more than a ton and were as tall as a human when on all fours.

When a dead whale washes ashore, it's a meaty bounty for whatever carnivores happen to find it. Researchers were surprised to find brown bears and wolves, two predators that don't usually get along, sharing a whale carcass for more than four months. And they have the photos to prove it. On May 5 2010, a 41-foot dead humpback whale washed onshore in Alaska's Glacier Bay National Park. Once the carcass was discovered, researchers Tania M. Lewis of the

National Park Service

and Diana J.R. Lafferty of the

Carnivore Ecology Laboratory

at Mississippi State University deployed a few camera traps nearby to see how the massive beast would be consumed. One camera took a photo every 15 minutes for 90 days. The second one was triggered by a motion sensor. Together, the researchers had more than 10,000 photos to pore over. Those photos allowed Lewis and Lafferty to document, for the first time, the interactions among the scavengers that fed on the corpse, led by the two magnificent carnivores seen in the photo above: brown bears and wolves.

For four months, the carcass provided a rich source of meat for both carnivores. Altogether, between half and three quarters of the flesh and blubber was consumed by bears, wolves, and bald eagles before the carcass floated away in early September. The bears and wolves continued to visit occasionally for two years, gnawing on the remaining bones and scraps of blubber through at least November of 2012. Lewis and Lafferty published their findings recently in the journal

Ursus

. Here, a brown bear's face is covered in blubber.

Brown bears are usually solitary, though they do occasionally aggregate around especially large food sources, such as dead whales and large salmon runs. What's uncommon, however, is to see brown bears sharing with other carnivores. They usually drive away other predators, including black bears and polar bears. That's why it's so interesting that this carcass was repeatedly visited by a pack of wolves.

"We saw little evidence of aggression between species—no instances of wolves attempting to displace brown bears and few instances of brown bears displacing wolves," Lewis and Lafferty wrote. "... Brown bears were present in more than 50 percent of the photos with wolves, indicating some level of tolerance. Smith et al. (2003) documented brown bears and wolves feeding and traveling together on several occasions at abundant salmon streams in Alaska. We observed similar tolerance between multiple brown bears and 7 members of a wolf pack sharing a humpback whale carcass and exhibiting similar diel patterns for [more than] 4 months. Our results provide supporting evidence that the frequency and severity of bear–wolf conflicts may decrease at large-magnitude food resources."

Lewis and Lafferty suspect that the sheer abundance of meat and blubber offered up by the lifeless giant allowed the bears and wolves to coexist relatively peacefully. In fact, three of the photos they retrieved from their camera traps revealed bears and wolves feeding nose-to-nose. Here, five bears are caught feeding together, an infrequent occurrence.

"Brown bears were present in 50 percent of the photos with wolves, indicating some level of tolerance," Lewis and Lafferty wrote. The unusual aggregation of both predators provided tourists with excellent wildlife viewing opportunities.

This article originally appeared on

io9.com

.

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