The complete lower dentition of a new species of the basal anthropoid genus Eosimias shows a combination of primitive and derived traits unknown in other living or fossil primates. Although certain dental traits are decidedly more primitive in Eosimias than in other basal anthropoids, numerous derived aspects of jaw and dental morphology support the anthropoid affinities of Eosimiidae. Eosimiids document an early structural phase in the evolution of higher primates. Phylogenies that derive early anthropoids from cerca-moniine adapiforms are inconsistent with eosimiid anatomy. Because early fossil anthropoids are known from both Asia and Africa, the fossil record is presently insufficient to specify the continent on which this clade originated.