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Event Detail Information
Event Detail Information
Ever since Darwin, paleoanthropoligists have assumed that our earliest hominid ancestors began walking on two legs when forests dwindled and they entered African savanna grasslands.
Carbon isotope ratios of fossil soils and teeth provide a tracer of the expansion of tropical savanna grasslands. Fossil soils collected across a 9 km W-E transect of the Aramis Member of the Sagantole Formation in the Middle Awash Valley of Ethiopia, dated 4.4 million years (Ma). Their carbon isotope ratios reflect floral habitats representing woodlands to wooded grassland. Carbon and oxygen isotope ratios increase from west to east, reflecting a gradient from woodlands, with Ardipithecus fossils, to grassy drier habitats lacking Ardipithecus. Carbon and oxygen isotopes of tooth enamel show that Ardipithecus had a diet similar to that of chimpanzees, and unlike that of savanna-dwelling hominids younger than 3.2 Ma. These data are consistent with diverse lines of evidence support the hypothesis that bipedalism may have evolved in woodlands rather than open grasslands.