4 November 2011 Last updated at 02:04

Ancient bear had the strongest bite

By Ella Davies Reporter, BBC Nature

Scanning the skull revealed meaty secrets

The largest bear that ever lived also had the strongest bite of any land mammal, say scientists.

Agriotherium africanum was a giant short-faced bear that became extinct five million years ago.

Reconstructions of the carnivore's skull revealed that it was well adapted to resist the forces involved in eating large prey.

By comparing the skulls of several species, scientists also found polar bears to have surprisingly weak bites.

The findings were published in the Journal of Zoology.

Dr Stephen Wroe from the University of New South Wales, Australia, and his team used CT scanners to create 3-D images of bear skulls. They scanned six species, ranging from a giant panda to a reconstructed fossil of A. africanum.

Using the computer generated models created by student Chris Oldfield, the researchers investigated how the skulls stood up to the forces that mimicked killing and feeding behaviours.

"Our analyses show that Agriotherium africanum had an enormously powerful bite - considerably greater than for the largest of living big cats, or any living bear," said Dr Wroe.

The extinct bear exerted the highest bite force with its large canine teeth. Of all the bears the team examined, its model showed the least strain through the skull when the researchers simulated the forces of biting an item of prey.

"Our analyses show that it had the most powerful bite of any known terrestrial mammal determined thus far," Dr Wroe told BBC Nature.

A comparison in skull stress for bears biting with their canines (a) A. africanum, (b) Asian bear, (c) black bear, (d) brown bear, (e) giant panda, (f) polar bear and (g) polar bear. Pink shows an area of high strain, while dark blue areas show no strain.

Results for another short-faced bear, the giant panda, were also notable; the animal's skull appeared to be well adapted to high levels of stress.

This might seem surprising for an animal with a diet strictly limited to plant material, but Dr Wroe pointed out that the panda had a large "grinding area" to chew through tough stalks of bamboo.

In comparison, A. africanum had the smallest grinding area of the bears analysed.

'Power to kill'

The researcher said that A. africanum may have been a "hypercarnivore" with an unparalleled level of meat in its diet for a bear.

"There has been considerable debate over the diet of A. africanum and other short-faced bears. Some have argued that these bears were more carnivorous than most living bears," said Dr Wroe.

"There can be no doubt that this beast had the power to kill almost anything it could get a hold of - it could also have chased any other predators off their kills; hence it could also have been a very effective scavenger."

"Its skull was well adapted to resist the forces that would have been generated under such extreme loads."

Fat-sucker

The study also revealed that the polar bear was a surprisingly "poor performer".

"It has a really surprisingly weak bite for its size - arguably the weakest among living bears," Dr Wroe told BBC Nature.

He pointed out that these huge carnivores tended to target relatively "easy-to-kill", blubbery prey, such as seals.

"It might be more correctly categorised as a specialised 'fat-sucker' than a real meat eater," he said.

The skull comparisons revealed that the polar bear had much shorter blade-like teeth for ripping flesh than the supersized A. africanum.

These extinct giants lived in Africa at the end of the Miocene epoch and into the Pleistocene - five million years ago - and measured up to 2.7m in length.

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