According to climate change research, the North American heartland’s climate began cooling about 40 million years ago and the researchers in the Brown study found that the cooling had a direct result on the evolution of the native species in that time period:
The climate in North America’s heartland back around 40 million years ago was warm and wooded. Dogs are native to North America. 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 specialized for running, retaining the flexibility to grapple with whatever meal unwittingly walked by.
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.
Did this transition affect the evolution of carnivores? To find out, Figueirido and the research team, including Jack Tseng of the American Museum of Natural History in New York, examined the elbows and teeth of 32 species of dogs spanning the period from ca. 40 million years ago to 2 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.
How do the changes in the elbows and teeth of dogs help us understand their evolution? The fascinating answer is on the next page…