Late Pliocene Bovidae from Ledi-Geraru (Lower Awash Valley, Ethiopia) and their implications for Afar paleoecology

ABSTRACT

Fossil bovids are described from the late Pliocene site of Ledi-Geraru, mainly from the Gurumaha and Lee Adoyta sedimentary packages (2.8–2.6 Ma). Finds include taxa already known from the slightly older Hadar Formation, such as the buffalo Ugandax coryndonae, the bongo-like Tragelaphus rastafari-nakuae lineage, an alcelaphin resembling Parmularius pachyceras, and a large impala. Differences from Hadar include the abundance of Kobus sigmoidalis, the absence of K. oricornus, and the presence of Tragelaphus gaudryi and probably also Menelikia lyrocera. The fossil bovids from Ledi-Geraru are mainly comparable to those known from contemporaneous assemblages in the Turkana Basin. Menelikia and T. gaudryi are characteristic of the Turkana Basin, and these are probably their first records from the Afar. A new species of Beatragus is also named. A well-preserved skull and skeleton of a fossil wildebeest from the Ogoyta sediments (<2.4 Ma) bears a mosaic of advanced and conserved traits that illuminate the evolution of the Connochaetes clade prior to the divergence of its two extant species. Taxonomic abundance, as well as functional analyses of postcranial elements, indicates that the ancient landscape at Ledi-Geraru was primarily made up of open habitats such as seasonal grasslands, with minor components of woodlands and wetlands. This contrasts with most localities from the Hadar Formation, which record more covered habitats. Comparisons with older Afar faunas indicate that environmental changes to drier and more open habitats were part of a long-term trend that goes back to at least 4 Ma, if not earlier.

ACKNOWLEDGMENTS

We thank the Ethiopian Authority for Research and Conservation of Cultural Heritage especially Y. Desta, D. Abebaw, G. Senishaw, T. Getachew, T. Assefa, and Y. Assefa. We also thank the Afar representative, M. Ahamedin, and the Ledi-Geraru field crew. The Ledi-Geraru project is funded by NSF (BCS-1157351 and BCS-1322017) and was also made possible through the support of a grant from the John Templeton Foundation to the Institute of Human Origins at Arizona State University. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of the John Templeton Foundation. F.B. acknowledges support from the AMNH Gerstner Scholars program, the AMNH Department of Mammalogy, and the German Research Foundation (DFG, grant BI 1879/1-1), and MoGES. J.R. acknowledges the National Science Foundation for a Graduate Research Fellowship. We also thank E. DiMaggio for preparing Figure 1, A. Barr for providing extant astragalus data and an updated classification function, C. Janis for measurements of extant bovid teeth, A. Gentry for discussion and for hypsodonty data for some fossil bovids, F. Witzmann for assistance, and the editor, T. Faith, D. Geraads, and an anonymous reviewer for their constructive reviews.