This photograph compares upper teeth of the earliest known horse, Sifrhippus, at its larger size during lower temperatures, top, with teeth from the same horse after it shrank as a result of higher temperatures about 56 million years ago. University of Florida researcher Jonathan Bloch co-authored a study appearing in Science Feb. 24 documenting this phenomenon using fossils from the Cabin Fork area of the southern Bighorn Basin in Wyoming.
University of Florida photo taken Feb. 1, 2012, by Kristen Grace