The evolution of high dental complexity in the horse lineage

The horse lineage (family Equidae) represents one of the clearest acquisitions of complicated derived dental morphology from a more generalized ancestor. Here we investigate the change in dental complexity (orientation patch count rotated, OPCR) during the evolution of key members of this group. A clear linear increase in dental complexity over evolutionary time is apparent when complexity is measured at high resolution (125 to 175 rows per tooth). The taxa examined also show a linear scaling of OPCR with varying resolution. The slope of this relationship is also a key distinguishing factor among taxa, designated as OPCRS. We found that successive increases in dental complexity are due to the addition of finer-scale morphological features. The study sets the scene for a more detailed investigation into additional members of the Equidae.