Hundreds of Colobus (Cercopithecidae: Primates) fossils from the later Pleistocene of Ethiopia's Middle Awash study area

Abstract

Objectives: The aim of this study is to introduce and systematically assess a new assemblage of colobine fossils (n = 360) recovered from Late Pleistocene (ca. 100,000- years ago) sediments in the Middle Awash research area, Afar Rift, Ethiopia. Materials and Methods: We describe the colobine fossils relative to extant colobine taxa and Middle Pleistocene fossil samples from “Andalee” and Asbole, Ethiopia using linear dental, cranial, and postcranial metrics, as well as qualitative features. We also document the ontogenetic and sex profiles of this sample. Results: Based on morphological affinities to extant and fossil Colobus, we refer these 360 individuals to Colobus cf. guereza. The majority of the individuals (76%) fall into young- and middle-adult age categories. Females are slightly better represented than males, although the majority of individuals (84%) could not be assigned to sex. Discussion: Details of the last half million years of Colobus morphological evolution have remained obscured by a sparse fossil record. The newly recovered, prepared, and curated fossils described herein add significantly to the record of this group. Several morphologies seen in these new fossils fall between the Asbole Colobus sample and extant Colobus guereza, suggesting an ancestral-descendant phyletic relationship among the three time-successive samples. The populational variation documented among these samples indicates that the distinctive pattern of sexual dimorphism observed in C. guereza had evolved by 100 ka.