Around 20 million years ago, North America was mainly covered in woodland, yet transformation was afoot. As the climate changed, the trees and forests gave way to grasslands and savannahs, and eventually formed the prairies we know today. This change in climate is reflected, it turns out, in the hunting style and thus evolution of the myriad of dog species that stalked the landscape and habitats of the time.    

“People have thought that basically as soon as the herbivores got to be better runners, around about 20 million years ago, that the carnivores would follow suit,” explained Professor Christine Janis, who co-authored the study published in Nature Communications, to IFLScience. “But what we see is that the dogs' hunting style really changed in correlation with the habitat change, not so much with what the herbivores were doing.”

In order to track the change in hunting technique, and to work out these behaviors from fossil remains, the researchers had to start with the living. Janis and her colleague Borja Figueirido from Brown University began by analyzing the elbow joint, where the humerus joins the ulna and radius of “a bunch of living animals where we know the behaviour, and then we were able to get the correlates of how that relates to arm movement,” she explained.  

^{Two early dogs, Hesperocyon, left, and the later Sunkahetanka, were both ambush-style predators. As climate changes transformed their habitat, dogs evolved pursuit hunting styles and forelimb anatomy to match. Credit: Mauricio Anton/Brown University}

They were then able to collect the same data from 32 species of ancient dog spanning the period from around 40 million years ago to 2 million, and compare them with the living animals. From this, they were able to get an idea of how the ancient dogs moved and hunted. Basically, from looking at the elbow, the researchers could tell how much flexible movement the animal had in its forepaws.

Cats, for example, have very flexible elbows that allow them to rotate their paws and manipulate objects. Dogs, however, do not, which means that while they have increased their efficiency in running, they've had to sacrifice the ability to manipulate. The researchers found that when America was covered in forests, the dogs were mongoose-like, adapted to the woodland environment but not running. When the grassland opened up, the dogs evolved in sync, changing from ambush predators to pursuit-pounce predators. And when prairies later formed, they ultimately developed into long-distance predators that chase prey down, like what we see in wolves today.

This change was distinct and not in correlation with the evolution of herbivores, as was previously thought. Instead, Janis thinks that the herbivores evolved their longer legs around 20 million years ago, way before the dogs became pursuit hunters, in order to increase their stamina and efficiency when walking over long distances in the savannah while foraging for food. This new works adds to our knowledge of how species adapt to a changing climate, though unfortunately, the current warming of the planet is happening way too quickly for most animals to respond.