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Eight million years ago, a shift in the climate caused more barren, open landscapes to spread across the globe. And without the cover of trees, large animals grouped together for protection. 
This, the scientists say, was when wild dogs started to work together, teaming up to drive big prey out of the herd. The Colombian team examined the skulls of more than 300 dog species, building a timeline that revealed how their jaws and teeth hadevolved. 
This revealed that the wolves from which our domestic dogsdescend  started to change when they began to hunt in packs. From then on, the  dogs with the biggest teeth and most powerful jaws were most likely to  succeed in overpowering their prey, so they passed their 'hypercarnivorous' genes on to the next generation. 
The researchers say that this is what's given our pet dogs such good evolutionary reasons to really enjoy chewing on bones.