Samwik. That link provides enough reading for a year!

Mike asked:

"Migration routes for horses?"

From the information I have collected over the years: three-toed horses (genus Hipparion) left North america via the Bring bridge 5-7 million years ago. The first Equus (one-toed horse) left later, 2-3 million years ago. True horses didn't come out, so to speak, until about 1 million years ago. As to the extinction of horses in North America, we've been down that road before. I haven't changed my mind.