Cercopithecid Monkeys From the Pleistocene Markaytoli Site at Ledi-Geraru, Afar Region, Ethiopia.

OBJECTIVES: Cercopithecid monkeys are ubiquitous across much of sub-Saharan Africa today, where they contribute much to the ecological and taxonomic diversity seen in modern African primate communities. Plio-Pleistocene assemblages from eastern Africa also preserve a rich cercopithecid fossil record, albeit one dominated by papionins and by larger-bodied colobine taxa; smaller-bodied colobines and guenons remain relatively rare in this period. Here we report on a fossil monkey assemblage from the Markaytoli collection area within the Ledi-Geraru Research Project permit region.

MATERIALS AND METHODS: From 2012 to 2020, approximately 750 fossil specimens were recovered from the Markaytoli, including nearly 100 assigned to the family Cercopithecidae. These are compared to modern African cercopithecids and to fossil evidence from other Pleistocene sites in eastern Africa, especially the Afar Region.

RESULTS: The cercopithecid fauna from Markaytoli is dominated by specimens we attribute here to Colobus sp. and Chlorocebus sp., with limited evidence for a large papionin. The Colobus and Chlorocebus material is comparable to that from other Middle Pleistocene sites (e.g., Asbole, Andalee) but shows some potential differences compared with Late Pleistocene samples (e.g., Halibee) and modern representatives.

DISCUSSION: These fossils add to a growing record of fossil colobines and guenons from the Pleistocene of the Afar Region. Similarities with other Middle Pleistocene monkey samples support initial biochronological analyses from non-primate taxa for the site. More work is needed to clarify the meaning of potential morphological differences between a growing ~Middle Pleistocene sample and Late Pleistocene or modern Chlorocebus and Colobus in the Awash Valley Region.