Authors: Matthew C. Mihlbachler, Florent Rivals, Nikos Solounias, Gina M. Semprebon
The evolution of high-crowned molars among horses (Family Equidae) is thought to be an
adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief
of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion.
We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global coolingand associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse paleopopulations had highly variable amounts of
dietary abrasion, suggesting that selective pressures for crown height may have been weak much of the time. However, instances of higher abrasion were observed in some paleopopulations, suggesting intervals of stronger selection for the evolution of dentitions, including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned