An Early Oligocene age for the oldest known monkeys and rodents of South America

The Paleogene dispersals of monkeys and rodents from Africa to South America permanently and profoundly altered the composition of mammalian communities in the Neotropics, but the timing of these colonization events remains uncertain. Through a combination of geochronological analyses (detrital zircon dating of the Santa Rosa fossil locality in eastern Perú) and phylogenetic biochronological analyses (tip-dating age estimation of caviomorph rodents), we demonstrate that the oldest known primates and rodents of South America are unlikely to be older than Early Oligocene in age and are not Eocene in age as previously postulated. There are no grounds for rejecting the possibility of an earlier arrival for either clade, but at present the fossil record provides no evidence for earlier dispersals.