Scientists say they have discovered why dogs love to eat meat and bones.
Ancient canines adopted pack-living about eight million years ago, to hunt larger prey, according to researchers.
The resulting evolution of their jaws gradually turned the ancestors of modern wolves, and ultimately our own pets, into "hypercarnivores".
Dr Joao Munoz-Doran presented the findings at the First Joint Congress for Evolutionary Biology in Ottawa, Canada.
He and his colleagues from the National University of Colombia have created a canine "family tree", piecing together the relationships between each of the more than 300 dog species.
"So we classified them as carnivores, hypercarnivores [animals that eat more than 70% meat] and omnivores [animals that eat meat and vegetation]."
The ancestors of modern wolves belong to this hypercarnivorous group.
The team's analysis showed that the skull features that now distinguish a wolf - strong jaw muscles and enlarged canine teeth - first started to develop when their ancestors 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: BBC News