mitton horse teeth

Caption: Fossilized horse teeth—a molar and an incisor with some enamel remaining—from approximately 13 million years ago  (made you look!) Serendipity struck while I was doing research on the limber pines at Pawnee Buttes, near the junction of the boundaries of CO, NB and WY. While on a break, I found shade and a soft seat on a pile of sand eroded from a tall cliff. I was sifting the soft sediment with my left hand when my fingers encountered something hard just below the surface. I extracted it and found myself staring at a fossilized tooth, an incisor that retained some of its enamel. A few minutes later I found a molar. These were from an ancestor of modern horses that lived 13 million years ago (mya). My lucky find of fossil teeth reminded me that horses were native to North America (NA), but their history has some intriguing twists and turns during their migration around the world. The family Equidae, which includes horses, zebras and asses, evolved in NA during the Eocene Epoch, 54 mya. The genus Equus, including the horse, Equus ferus, evolved during the Pliocene, between 4.5 and 4.0 mya in NA. During glacial periods, accumulation of ice on land lowered sea level to the point that an enormous expanse of land called Beringia connected current day Siberia and Alaska. Approximately 4 mya horses spread across NA and some populations migrated across Beringia to Asia and then to Europe. As recently as the Pleistocene Epoch (2.5 mya to 11,700 ya) the family Equidae […]