title: The Omo Mursi Formation: a window into the East African Pliocene.
abstract: Dating to more than four million years ago (Ma), the Mursi Formation is among the oldest of the Plio-Pleistocene Omo Group deposits in the lower Omo Valley of southwestern Ethiopia. The sedimentary sequence is exposed along a strip ∼35 km by 4 km, but it has received relatively little attention due to the difficult access to this area. Although expeditions to the lower Omo Valley between 1968 and 1973 focused primarily on the Usno and Shungura Formations, survey of the Mursi Formation produced a faunal collection of about 250 specimens deriving exclusively from the Yellow Sands area at the southern extent of the exposures. In 2009, we reinitiated an investigation of the formation by focusing on the most northern exposures, and a new fossil site, Cholo, was identified. Cholo is depositionally similar to the lowermost exposures at the Yellow Sands, although no stratigraphic correlation between the two localities has yet been made. The fossiliferous sediments at Cholo are capped by a prominent vitric tuff that is compositionally distinct from any other known tephra preserved in East African rift basins, including the only known vitric tuff at the Yellow Sands. The faunal assemblage of the Yellow Sands area presents interesting characteristics: the fossils generally show little weathering and include a large proportion of suids (44% of the mammalian fauna) and a small proportion of bovids (14%) compared with other Pliocene African sites. The sample is also unusual in the high frequency of deinotheres (7%). Taxon-specific stable carbon isotopic composition of the Mursi mammals tends to show generally higher proportions of C3 diets compared with other Pliocene sites in East Africa and Chad. This and the particular faunal proportions suggest that the environments represented by the Mursi Formation were more closed than those of other Pliocene sites.
authors.affiliation: Département d'anthropologie, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, QC, H3C 3J7, Canada. Electronic address: m.drapeau@umontreal.ca.
authors.forename: Michelle S M
authors.initials: MS
authors.lastname: Drapeau
authors.affiliation: Department of Anthropology and Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 2110 G St., NW, Washington, DC 20052, USA; Interdisciplinary Center for Archaeology and Evolution of Human Behavior, Universidade do Algarve, 8005-139, Faro, Portugal. Electronic address: bobe@gwu.edu.
authors.forename: René
authors.initials: R
authors.lastname: Bobe
authors.affiliation: School of Geosciences, University of South Florida, 4202 E. Fowler Avenue, SCA 528, Tampa, FL 33620-8100, USA. Electronic address: wynnj@usf.edu.
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Wynn
authors.affiliation: Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, PO Box 874101, Tempe, AZ 85287-4101, USA. Electronic address: campisano@asu.edu.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Campisano
authors.affiliation: Department of Anthropology and Center for the Advanced Study of Hominid Paleobiology, The George Washington University, 2110 G St., NW, Washington, DC 20052, USA.
authors.forename: Laurence
authors.initials: L
authors.lastname: Dumouchel
authors.affiliation: Sorbonne Universités - CR2P - MNHN, CNRS, UPMC-Paris6, CP 38, Muséum National d'Histoire Naturelle, 57 rue Cuvier, 75231 Paris Cedex 05, France; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany. Electronic address: geraads@mnhn.fr.
authors.forename: Denis
authors.initials: D
authors.lastname: Geraads
mesh_terms: D000351:Africa, Eastern; D000818:Animals; D005075:Biological Evolution; D002247:Carbon Isotopes / Q000032:analysis; D005580:Fossils; D049690:History, Ancient; D010163:Paleontology; D014070:Tooth / Q000033:anatomy & histology; D014714:Vertebrates / Q000033:anatomy & histology / Q000502:physiology
chemical_list: D002247:Carbon Isotopes
keywords: Cholo; Omo Group; Paleoenvironment; Stable isotopes; Suidae; Yellow Sands