 Recently a close relationship with Periptychidae has been suggested.This would make pantodonts crown-group ungulate placentals and not related to cimolestids at all.Genera from North America tended to be large and robust, starting with "Pantolambda" and "Caenolambda" in the Middle Paleocene epoch, and later in the epoch started to get larger, with "Barylambda" as the largest Paleocene form of pantodont.