Ancient American pronghorns were built for speed

The fastest land animal in North America is the American pronghorn, and previously, researchers thought it evolved its speed because of pressure from the now-extinct American cheetah. But recently, that theory has come under fire. Now, a University of Michigan study examining fossilized ankle bones of ancient relatives of the American pronghorn has shown that the pronghorn was evolving to be faster more than 5 million years before the American cheetah appeared on the continent. The study is published in the Journal of Mammalogy.