Stable isotope and molecular data suggest that C 4 grasses first appeared globally in the Oligocene. In East Africa, stable isotope data from pedogenic carbonate and fossil tooth enamel suggest a first appearance between 15-10 Ma and subsequent expansion during the Plio-Pleistocene. The fossil enamel record has the potential to provide detailed information about the rates of dietary adaptation to this new resource among different herbivore lineages. We present carbon isotope data from 452 fossil teeth that record differential rates of diet change from C 3 to mixed C 3 /C 4 or C 4 diets among East African herbivore families at seven different time periods during the Late Miocene to the Pliocene (9.9-3.2 Ma). Significant amounts of C 4 grasses were present in equid diets beginning at 9.9 Ma and in rhinocerotid diets by 9.6 Ma, although there is no isotopic evidence for expansive C 4 grasslands in this part of the Late Miocene. Bovids and hippopotamids followed suit with individuals that had C 4 -dominated (>65%) diets by 7.4 Ma. Suids adopted C 4 -dominated diets between 6.5 and 4.2 Ma. Gomphotheriids and elephantids had mostly C 3 -dominated diets through 9.3 Ma, but became dedicated C 4 grazers by 6.5 Ma. Deinotheriids and giraffids maintained a predominantly C 3 diet throughout the record. The sequence of differential diet change among herbivore lineages provides ecological insight into a key period of hominid evolution and valuable information for future studies that focus on morphological changes associated with diet change.carbon isotopes | herbivore diet | bioapatite | paleodiet | mammal

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Extant African great apes and humans are thought to have diverged from each other in the Late Miocene. However, few hominoid fossils are known from Africa during this period. Here we describe a new genus of great ape (Nakalipithecus nakayamai gen. et sp. nov.) recently discovered from the early Late Miocene of Nakali, Kenya. The new genus resembles Ouranopithecus macedoniensis (9.6 -8.7 Ma, Greece) in size and some features but retains less specialized characters, such as less inflated cusps and better-developed cingula on cheek teeth, and it was recovered from a slightly older age (9.9 -9.8 Ma). Although the affinity of Ouranopithecus to the extant African apes and humans has often been inferred, the former is known only from southeastern Europe. The discovery of N. nakayamai in East Africa, therefore, provides new evidence on the origins of African great apes and humans. N. nakayamai could be close to the last common ancestor of the extant African apes and humans. In addition, the associated primate fauna from Nakali shows that hominoids and other noncercopithecoid catarrhines retained higher diversity into the early Late Miocene in East Africa than previously recognized.hominoid evolution

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