Isotopic evidence of C4 grasses in southwestern Europe during the Early Oligocene–Middle Miocene. 2010. M.A. Urban, et al. Geology, First published online November 12.
C4 plants compose only 3 percent of flowering plant species, yet account for about 25 percent global terrestrial productivity. About 60% of C4 species are grasses, and they dominate the world's grassland and savanna biomes, particularly those in warmer, lower latitude areas. Their ecological success results from the way these species concentrate and then fix carbon dioxide in order to power photosynthesis. link