CARBON ISOTOPE DATA FROM EAST AFRICAN FOSSIL TEETH OF LATE MIOCENE TO PLIOCENE HERBIVORES RECORD DIFFERENTIAL TRANSITION FROM C3 TO C4 RESOURCES

Stable carbon isotope analysis of enamel from ~470 fossil teeth provide a detailed record of the dietary transition from C3 to C4 resources in a majority of herbivore families from the Late Miocene to the Pliocene in East Africa. Data from two fossil sites in the Suguta Depression and one site in the Turkana Basin record differential rates of diet change in bovids, deinotheres, equids, giraffids, gomphotheres, hippos, rhinos, and suids over a ~6.7 million year interval. K/Ar, ⁴⁰Ar/³⁹Ar, and paleomagnetic data from the three sites constrain the age ranges of fossil-bearing sediments from 9.9 to 9.8 Ma at Nakali, from 9.6 to 9.3 Ma at the Samburu Hills, and from 7.4 to 3.2 Ma at Lothagam.

All data from 9.9 to 9.8 Ma, with the exception of a subset of equids, indicate C3 diets for all families. By the 9.6 to 9.3 Ma interval, there are no longer any equids with a pure C3 diet. Bovids, gomphotheres, hippos, rhinos, and suids have also incorporated C4 resources into their diets, but still have individuals with pure C3 diets. During the 7.4 to 3.2 Ma interval, equids and gomphotheres become dedicated C4 grazers, but bovids, hippos, rhinos, and to a lesser extent, suids, maintain a diverse feeding strategy spanning nearly pure C3 to pure C4 diet. Deinotheres and giraffids maintain a C3 diet throughout the entire record. The dramatic increase in the range of δ¹³C values in enamel throughout the record indicates a diversification of diet that coincides with the appearance of new species in herbivore families.