Objectives: Undoubted fossil Cebidae have so far been primarily documented from the late middleMiocene of Colombia, the late Miocene of Brazilian Amazonia, the early Miocene of PeruvianAmazonia, and very recently from the earliest Miocene of Panama. The evolutionary history ofcebids is far from being well-documented, with notably a complete blank in the record of callitrichinestem lineages until and after the late middle Miocene (Laventan SALMA). Furtherdocumenting their evolutionary history is therefore of primary importance.Material: Recent field efforts in Peruvian Amazonia (Contamana area, Loreto Department) haveallowed for the discovery of an early late Miocene (ca. 11 Ma; Mayoan SALMA) fossil primatebearinglocality (CTA-43; Pebas Formation). In this study, we analyze the primate material, whichconsists of five isolated teeth documenting two distinct Cebidae: Cebus sp., a medium-sized capuchin(Cebinae), and Cebuella sp., a tiny marmoset (Callitrichinae).Results: Although limited, this new fossil material of platyrrhines contributes to documenting thepost-Laventan evolutionary history of cebids, and besides testifies to the earliest occurrences ofthe modern Cebuella and Cebus/Sapajus lineages in the Neotropics. Regarding the evolutionary historyof callitrichine marmosets, the discovery of an 11 Ma-old fossil representative of the modernCebuella pushes back by at least 6 Ma the age of the Mico/Cebuella divergence currently proposedby molecular biologists (i.e., ca. 4.5 Ma). This also extends back to>11 Ma BP the divergencebetween Callithrix and the common ancestor (CA) of Mico/Cebuella, as well as the divergencebetween the CA of marmosets and Callimico (Goeldi’s callitrichine).Discussion: This discovery from Peruvian Amazonia implies a deep evolutionary root of theCebuella lineage in the northwestern part of South America (the modern western Amazon basin),slightly before the recession of the Pebas mega-wetland system (PMWS), ca. 10.5 Ma, and wellbeforethe subsequent establishment of the Amazon drainage system (ca. 9–7 Ma). During the latemiddle/early late Miocene interval, the PMWS was seemingly not a limiting factor for dispersalsand widespread distribution of terrestrial mammals, but it was also likely a source of diversificationvia a complex patchwork of submerged/emerged lands varying through time.