Evolution of Pelycodus
an early Eocene Primate from Big Horn Basin, Wyoming

    The chart documents the gradual evolution of the Eocene lemur-like primate Pelycodus into Notharctus over several million years as seen in a North American stratigraphic series. The horizontal scale is an index of molar tooth size. Each horizontal bar gives the mean (vertical bar), two standard deviations (thick horizontal bar) and range (thin horizontal bar) for the indicated number of skulls from a series of fossil deposits. The doubling of the index value from 1.0 to 1.4 indicates an approximate doubling in size. The inset photograph shows a reconstruction of Notharctus venticolis, the species in the upper right of the series]. [Diagram after Gingerich]