Notharctinae is an extinct subfamily of primates that were common in North America during the early and middle Eocene (55-34 million years ago).

Notharctines became extinct in the middle Eocene, most likely because of a combination of factors including climatic change and competition with other North American primates.

One of the diagnostic features of this subfamily is that later species acquired a hypocone, or an extra cusp on the upper molars, from the postprotocingulum, instead of the lingual cingulum (a shelf on the margin of the tooth at the side of the tongue) as in cercamoniines.

The earliest widely accepted adapiform was the European cercamoniine Donrussellia, though recent finds of additional species may soon show otherwise.

After surviving the Atlantic crossing, more advanced species of Cantius gradually got bigger and developed larger mesostyles and hypocones, which go along with the switch from a primarily frugivorous diet to a folivorous one.

Though some scientists believe that members of the adapiform radiation gave rise to simians because of the long list of dental and cranial similarities including a fused mandible, loss of paraconids, and large, sexually dimorphic canines, normally the European cercamoniines are the specific subfamily cited.