Why dogs 'love' to gnaw on bones

10 July 2012 Last updated at 01:34 By Victoria Gill Science reporter, BBC Nature, Ottawa, Canada

Scientists have discovered why dogs love to eat meat and bones.

Living and hunting in groups coincided with a shift in dogs' diets, scientists analysing their ancestry found.

The animals adopted pack-living about eight million years ago in order to hunt larger prey, according to a team from the National University of Colombia.

The resulting evolution of their jaws gradually turned the ancestors of our domestic pets into "hypercarnivores".

Dr Joao Munoz-Doran from the university presented the findings from his study of at the First Joint Congress for Evolutionary Biology in Ottawa, Canada.

He and his colleagues have created a canine "family tree", piecing together the relationships between each of the more than 300 dog species.

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Canine facts

• Common canines: Foxes, wolves, jackals, coyotes and dingoes are all members of this well-known group
• Familiar faces: Wild canids are found on every continent except Antarctica
• Communication is key: Previous studies of dog evolution have revealed that calls were essential for forming social groups and hunting larger prey
• Pets' past: All domestic dogs are descendants of the grey wolf

This map of canine evolution showed approximately when each species evolved, and it allowed the scientists to understand how an animal's lifestyle and habitat was connected to the shape of its skull.

"We compared species that have very different diets," Dr Munoz-Doran explained to BBC Nature.

"So we classified them as carnivores, hypercarnivores and omnivores [animals that eat meat and vegetation]."

Examining the hypercarnivores, which include the domestic dog's closest relative, the grey wolf, showed that the animals' strong jaw muscles and enlarged canine teeth started to develop when the animals first began hunting in groups.

"We found a common evolutionary history for these traits," Dr Munoz-Doran explained.

"Eight million years ago was when [less forested, more] open habitats were spreading through Asia, Europe and North America.

"And when there are open habitats, the big prey group together. So there will be more eyes watching for a predator."

The only way that dogs roaming the open plains could snatch very large prey from a herd was to work together.

"And after many generations of this grouping behaviour, there are new selective pressures on their [skull shape]," said the researcher.

This pressure meant that animals with larger teeth and stronger jaws were more likely to succeed in hunting, and to survive to pass on their large-toothed, strong-jawed genes to the next generation.

"They developed strength in their muscles - especially the muscles that close their mouth," said Dr Munoz-Doran.

"And bones that are more resistant to bending, so they could support the mechanical strains of biting the prey.

"Over time, they became adapted to be 'hypercarnivorous'."

The researcher pointed out that domestic dogs had "very good evolutionary reasons to enjoy chewing a bone".

"They have the tools to do that," he told BBC Nature, "and they want to use their tools."

Source: http://www.bbc.co.uk/nature/18767817

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