Intense debate surrounds the evolution of grasses using the C 4 (Hatch-Slack) photosynthesis pathway and the emergence of African grasslands, often assumed to be one and the same. Here, we bring new insights with the combination of plant leaf wax carbon isotopic com-position (δ 13 C wax) and pollen data from marine sediments of the Gulf of Aden (northeast Africa), which show that C 4 biomass increases were not necessarily associated with regional grassland expansion. We fi nd broadly opposing trends toward more enriched δ 13 C wax val-ues and decreased grass pollen proportions between 12 and 1.4 Ma. This apparently contradictory evidence can be reconciled if a greater proportion of the Late Miocene northeast African landscape were covered by C 3 grasses than previously thought, such that C 4 grasses and shrubs replaced a C 3 ecosystem including trees and productive grasslands. In addition, δ 13