A close-up at the paleoecology of the most western gelada relatives: Insights from dental microwear texture analysis

Exploring the paleoecology of extinct species of the genus Theropithecus, which was widespread and diversified in Africa during the Pliocene and the Pleistocene, is crucial to have a full picture of the evolutionary history of this taxon. It also gives insights into the fundamental ecological range of the genus, now restricted to the Ethiopian highlands in a reduced set of habitats. This study aims to investigate the diet of Theropithecus atlanticus (n = 8) from the Plio-Pleistocene site of Ahl al Oughlam (Morocco) through dental microwear texture analysis. We used a recently developed software program, 'trident,' that quantifies the heterogeneity of texture parameters through subsampled wear surfaces to improve dietary discriminations. We considered a comparative dataset of extant primates (n = 104) with different diets, including the leaf-eater Colobus guereza, the grass-eater Theropithecus gelada, and the generalists Papio hamadryas and Chlorocebus aethiops. In addition, we compared with specimens of theropiths (n = 80) from the eastern African Shungura Formation (Lower Omo Valley, Ethiopia) that are nearly contemporaneous to T. atlanticus. Our results indicate that T. atlanticus was mostly feeding on grasses, as do its extant relatives. Some similarities with opportunistic species suggest it might have consumed a substantial amount of challenging foods. This dental microwear texture is in line with open, arid, and harsh environments and the presence and abundance of C3 grasses at Ahl al Oughlam detected by enamel stable isotope analysis on various mammals including theropiths. This contrasts with the environment described on nearly contemporaneous specimens from the Lower Omo Valley where grasses were abundant but composed of C4 ones.