This specimen of Cercopithecoides williamsi is a partial skull with its upper dentition that includes the left upper Incisors, canine, through to the third molar. It was found in Area 131 on the Karari ridge in 1977. This maxilla was also preserved with its mandible and much of the skeleton.
The Genus Cercopithecoides is well known from South African deposits and are less common in the Turkana Basin. However here, three species have been recognised: C. williamsi ,a larger species C. kimeui, and a third smaller species in the lower parts of the geological section. Cercopithecoides was fully adapted to terrestrial locomotion.
