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