Abstract

delta(13)C values in paleosols and fossil teeth have been used to document the expansion of C-4 plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C-4 vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the delta(13)C values of soil carbonate rise above a threshold of -8 parts per thousand, suggesting the presence of C-4 plants, starting at 7.3-6.7 Ma. delta(13)C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C-4 plants in the diets of large herbivores. These results show that the late Miocene expansion of C-4 plants was global, but occurred at different rates in each region. While it is has been suggested that declining pCO(2) levels during the late Neogene caused C-4 plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The delta(18)O soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4 parts per thousand in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.