National Geographic : 2009 Feb
shepherd. ey re a mixture of breeds that made it out onto the range over the centuries (many during the Great Depression), their stock en- hanced by deliberately released draft, Thor- oughbred, Morgan, and Arabian stallions, with the weaknesses of each pureblood salted out of it and the instinct for survival whetted with each successive generation. I was hun- kered down on a butte near Rock Springs, northwest of where the BLM had caught Dot, to watch horses being rounded up. "Don t move, don t talk," I d been warned, "or the horses might startle away from the corrals." Wild horses are acutely attuned to dangers in their environment, chief among them humans. I tucked my chin against my chest and folded my arms. e ever restless Wyoming wind was loaded with winter intentions, and the water in the troughs in the corrals below had frozen inches thick. A helicopter pilot contracted by the BLM swept out across the plains, herding groups of horses into a canyon below us. e canyon shrank into a camou aged burlap chase, at the mouth of which a "Judas" horse was released, leading its wild cousins into a metal corral, where yesterday s wild horse catch was already waiting. At the gate, the pilot tipped his blades at a few balking horses, which shocked forward into the cloud of dust. e gate was slammed shut, and a handful of young cowboys, quick as cats, spilled over the fences into the midst of the herd. e helicopter went back out for more horses. Inside the corral the cowboys separated the stallions from the mares, the foals from all the others. Within an hour 40 to 50 horses had been skillfully processed. Onohippidium Hipparion Equus Equus Equus Equus Equus Equus Sinohippus Hipparion (Old World) Astrohippus Hippidion 10 1 Dinohippus Pliohippus Begins migrating to South America two million years ago via the Panama land bridge. Begins migrating to the Old World three million years ago via the Bering land bridge. An Equus species resembling the modern horse appears some 1.6 million years ago. By about 10,000 B.C. it is extinct in the New World. Hunting by humans, disease, and climate change likely contributed. The genus survived in Africa and Eurasia. The modern horse, Equus caballus, arrives on the New World mainland with the Spanish in 1519.