The Middle Awash Research Project has collected a large sample of fossil cercopithecids from the Aramis, Kuseralee, and Sagantole drainages in the Middle Awash paleoanthropological study area of Ethiopia. These sites have been securely dated to 4.4 Ma. The craniodental material from this assemblage supports the diagnoses of two distinct new genera and species, which are described here. Pliopapio alemui is a mid-sized papionin represented by a complete cranium, several partial jaw fragments, and many isolated teeth. Kuseracolobus aramisi is a medium-sized colobine represented by several maxillae, mandibles, and other cranial fragments, as well as by isolated teeth. Stratigraphically associated postcranial remains will be discussed in a separate report.

Pliopapio alemui is distinctive from other known African papionins in the combination of its cranial, mandibular, and dental morphology. It lacks the diagnostic facial features of Parapapio as well as the flattened muzzle dorsum, facial fossae, and maxillary ridges of Papio Moreover, it does not possess any of the derived dental and cranial specializations of Theropithecus. Kuseracolobus aramisi is larger than all modern African colobines, but smaller than all known Cercopithecoides, Paracolobus and Rhinocolobus It is distinctive from Cercopithecoides and the colobine from Leadu in its symphyseal, corporal, and gonial morphology, and from Libypithecus, Paracolobus and Rhinocolobus in its facial morphology.

This early Pliocene sample fills a temporal gap between the terminal Miocene and later Pliocene sites and documents the existence of two new cercopithecid taxa, increasing known diversity in the family.