This study aims at improving dietary discrimination among primates through a new analytic approach of dental microwear texture analysis integrating a surface sampling on facets of both phase I and II of mastication. The surface sampling is applied on these two types of molar facets on 104 specimens belonging to four extant cercopithecids, and on 207 Plio-Pleistocene specimens representing four taxa from the Shungura Formation, Ethiopia. The extant species, including Colobus guereza, Theropithecus gelada, Papio hamadryas, Chlorocebus aethiops, compose a model covering a wide range of feeding ecology from leaf-eating through grass-eating habits to opportunistic habits. A principal component analysis built with a selection of the most discriminant variables and extant species as a model displays that the two facets contribute equally to the dispersion of individuals and to the between-species differences. Also, most contributing variables along the components are not central values of texture parameters (mean and median of the parameters measured on subsurfaces or a single value for the whole surface) but rather statistics of their dispersion (percentiles) and distribution (kurtosis, skewness). Once the fossil specimens are inserted into the extant species model, the two large-bodied colobines, Paracolobus and Rhinocolobus, are found to differ from the extant Colobus guereza, one of the most leaf-eating colobines. This highlights ecological diversity among early African colobines. Besides, the analysis tracks between-genus as well as temporal differences between the extinct species of papionins, attesting of a low ecological overlapping between Theropithecus and non-theropith papionins, notably after 2.4 Ma. No significant difference was found between T. brumpti, T. oswaldi, Theropithecus sp. supporting similar feeding habits with the present-day gelada, at least from 2.9 Ma onwards.