Palaeogeography, Palaeoclimatology, Paiaeoecology, 36 (1981): 69--73 69 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands DIETS OF PLIOCENE MAMMALS FROM OMO, ETHIOPIA, DEDUCED FROM CARBON ISOTOPIC RATIOS IN TOOTH APATITE JONATHON E. ERICSON, CHARLES H. SULLIVAN and N. T. BOAZ Center for Archaeological Research and Development, Peabody Museum of Archaeology and Ethnology, Harvard University, Cambridge, Mass. 02138 (U.S.A.) Laboratory for Isotope Geochemistry, Department of Geosciences and Department of Anthropology, University of Arizona, Tucson, Ariz. 85721 (U.S.A.) Department of Anthropology, New York University, New York, N.Y. 10003 (U.S.A.) (Received April 23, 1981) ABSTRACT Ericson, J. E., Sullivan, C. H. and Boaz, N. T., 1981. Diets of Pliocene mammals from Omo, Ethiopia, deduced from carbon isotopic ratios in tooth apatite. Palaeogeogr., Palaeoclimatol., Palaeoecol., 36: 69--73. Carbon isotopic ratios in tooth apatite of Pliocene fossil mammals from Omo, Eth'iopia, dated at 2.0 m.y. ago reported here are consistent with dietary predictions based on modern herbivores of the African savannah. The results indicate the applicability of the technique in reconstructing dietary patterns of fossil animals including hominids. INTRODUCTION Stable isotope ratios of carbon, 13C/1~C, in body tissue can be used to deduce intake of various types of plants by animals (Minson et al., 1975; Fry, 1978; Fry et al., 1978a, b; DeNiro and Epstein, 1978a, b; Tieszen et al., 1979; Tieszen and Imbamba, 1979, Teeri and Schoeller, 1979). Plants utiliz- ing a Hatch--Slack (Hatch and Slack, 1966; Hatch et al., 1967) or C-4 photo- synthetic pathway fix atmospheric carbon dioxide more efficiently, and con- sequently discriminate less against the heavier carbon isotopes, than plants employing solely the Calvin or C-3 pathway. This difference in isotope fractionation between the two pathways is reflected in the 13C/1ZC ratios of plant tissues (Lerman and Troughton, 1975). The carbon isotope composition of animal tissues is directly related to the 13C/12C ratios of the primary photosynthesizing plants in the foodchain (DeNiro and Epstein, 1978a, b). An assessment of the relative dietary intake of C-3 and C-4 plants can be determined by ~3C/12C measurements. 0031-0182/81/0000--0000/$02.75 © 1981 Elsevier Scientific Publishing Company