Johns Hopkins paleobiologist Steven Stanley has sleuthed out clues to the evolution of horses, coming up with a new solution for an enduring mystery: What caused the extinction of many equine species and other mammals 6 million years ago?

Like the protagonist in an evolutionary detective thriller, Stanley pursued a hunch that apparently had never occurred to other scientists. His long shot hit a bull’s-eye, enabling Stanley to learn how shifting climate and changing vegetation likely altered the fate of horses in North America millions of years ago.

Stanley, a professor in the Johns Hopkins Department of Earth and Planetary Sciences, pieced together the findings of other scientists and connected those data in a way no other researchers had done previously. When taken together, the data paint a picture of how Earth’s changing climate and vegetation may have been directly involved in the dramatic evolutionary trends of horses and other animals.

The time was marked by the largest extinction rate of North American mammals in the last 30 million years; about 60 genera, containing numerous species, perished