A study of North American dog fossils as old as 40 million years suggests that the evolutionary path of whole groups of predators can be a direct consequence of climate change.
"It is reinforcing the idea that predators may be as directly sensitive to climate and habitat as herbivores," said Christine Janis, professor of ecology and evolutionary biology at Brown University.
The climate in North America's heartland around 40 million years ago was warm and wooded.
The species of the time, fossils show, were small animals that would have looked more like mongooses than any dogs alive today and were well adapted to that habitat.
Their forelimbs were not specialised for running, retaining the flexibility to grapple with whatever meal unwittingly walked by.
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But beginning just a few million years later, the global climate began cooling considerably and in North America the rocky mountains had reached a threshold of growth that made the continental interior much drier. The forests slowly gave way to open grasslands.
Researchers examined the elbows and teeth of 32 species of dogs spanning the period from 40 million years ago to two million years ago.
They saw clear patterns in those bones at the museum: At the same time that climate change was opening up the vegetation, dogs were evolving from ambushers to pursuit-pounce predators like modern coyotes or foxes - and ultimately to those dogged, follow-a-caribou-for-a-whole-day pursuers like wolves in the high latitudes.
"The elbow is a really good proxy for what carnivores are doing with their forelimbs, which tells their entire locomotion repertoire," Janis said.
While the herbivores of this time were evolving longer legs, the predator evolution evident in this study tracked in time directly with the climate-related changes to habitat rather than to the anatomy of their prey species.
After all, it was not advantageous to operate as a pursuit-and-pounce predator until there was room to run.
"There is no point in doing a dash and a pounce in a forest. They'll smack into a tree," Janis said.
The study was published in Nature Communications.
