Pushes back their evolution to 4M years ago
                                
                                
                                    (Newser) -
                                    Woolly mammoths, saber-toothed tigers, and... horses? According to research using the oldest DNA ever found, horses have been trotting around for millions of years—about 4 million, to be exact. The study, published in  Nature , explains how scientists used DNA from a 700,000-year-old horse foot bone found in Canada'...