Ancestors of dogs living in north America 40 million years ago resembled small mongooses and, like cats, were ambush predators.
A few million years later the thick forests that once covered the continent began to give way to grassland as conditions became cooler and drier.
The change led to a transformation in dogs, turning them into animals that no longer surprised their prey but chased them down.
Their evolutionary transition was tracked by scientists who examined the elbows and teeth of 32 species of dog that lived from 40 million to two million years ago.
Professor Christine Janis, from Brown University in the US, who led the study, said: “The elbow is a really good proxy for what carnivores are doing with their forelimbs, which tells their entire locomotion repertoire.”
Cats have elbows that allow their front paws to swivel for grabbing and wrestling prey.
Dogs were once made the same way, but then developed a structure that always pointed downwards and was specialised for endurance running.
Dog evolution correlated directly with climate-related changes rather than new physical traits in their prey, such as longer legs.