But at the close of the ice age, about 13,000 years ago, most of the megafauna vanished — an extinction attributed to both climate change and the appearance of efficient Stone Age hunters. With them went the largest predators, allowing the smaller grey wolves to fill the vacant niche, which put them in competition with the largest coyotes. That conflict, as well as the loss of large herbivores, caused coyotes to shrink in stature. Within 1,000 years of the Pleistocene extinctions, coyotes had reached the same size as in most present-day populations.
Now, they're going through a whole new set of changes as they adapt to the modern landscape of North America. Genetic studies show that some coyotes are even interbreeding with dogs, which could lead to a different sort of hybrid animal. Researchers are struggling to keep up with the animals and their impacts as they lope into more new regions.
“Invading a landscape emptied of wolves may trigger a whole new pathway in terms of the coyote's evolution,” says Bill Ripple, an ecologist at Oregon State University in Corvallis. “And the coyote's arrival will have unpredictable effects on other species in the ecosystem.”