White-eyelid mangabeys (genus Cercocebus) live in groups of highly variable size. Because of their semi-terrestrial behaviour and preference for dense forest habitats, re-liable data on group size are scarce. During a 5-month study, we collected 17 group counts on a habituated group of agile mangabeys (C. agilis) at Bai Hokou in the Central African Republic. We found a stable group size of approximately 135 individuals. This permanent large grouping pattern is known to occur among several populations of white-eyelid mangabeys and is congruent with extreme group sizes reported in mandrills at Lopé in Gabon.

The molecular backbone view is also congruent with recent genetic analyses and assessments based on the fossil record, but awaits confirmation with additional data. This phylogeny suggests that Cercocebus and Cercocebus + Mandrillus arose in western equatorial Africa with subsequent dispersals westward, eastward, and possibly southward over the last > 3 million years. Am J Phys Anthropol 158:227-241, 2015. © 2015 Wiley Periodicals, Inc.