Long before humans were teaching dogs tricks and feeding them kibble, wild dogs roamed the heartland of North America in search of prey. Now, those ancient dogs are teaching humans about important trends in the evolution of predators.

When scientists studied dog bones as old as 40 million years, they noticed changes in the elbows that suggest these prehistoric pooches underwent a radical change in hunting strategy. It seems that as the global climate cooled and forests transformed into grassy fields, dogs went from cat-like ambush predators to chasers similar to modern coyotes, according to a paper published in the journal Nature Communications.

"It's reinforcing the idea that predators may be as directly sensitive to climate and habitat as herbivores," study co-author Christine Janis of Brown University said in a statement. "Now we're looking into the future at anthropogenic changes."

The researchers looked at fossils of 32 species of dogs that lived in North America between 40 million and 2 million years ago, paying particular attention to their elbows. The elbow is especially telling because it indicates whether a predator relied more heavily on the ability to swivel their paws and grab prey or the ability to run for long distances on permanently downward-facing paws.

In a forest, there are simply too many trees in the way for wearing out prey with a long distance chase to be a viable strategy. While forests dominated the landscape, dogs tended to have swiveling elbows adapted for ambushing and then latching onto prey. Around the time that the global climate cooled and forests gave way to wide-open plains, more of the dogs' elbows locked their paws into the downward position so that they were always ready to run. 

The work suggests that "evolutionary arms races" between predator and prey are not the only source of evolutionary chance. Global climate change appears to have been an important evolutionary force even among major predators millions of years ago, and studies such as this one add to a growing understanding of the far-reaching impacts we can expect from the warming temperatures that the world is experiencing today.

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