Stable isotope ecology of fossil hippopotamids from the Lake Turkana Basin of East Africa

The diet of African hippopotamids can be documented through δ ¹³C analyses of enamel and other tissues. Analysis of a 10-million-year sequence of hippopotamids in and near the Lake Turkana Basin of northern Kenya shows that hippos have included a substantial fraction of C₃ vegetation in their diets since the late Miocene when C₄ vegetation first appears in hippo diet as a measurable fraction. The C₄ component of vegetation becomes dominant (>50%) by Upper Burgi time ( c . 2 million years ago) but does not reach 100% for all individuals. It is therefore not unexpected that the δ ¹³C values of modern hippopotamids show a higher fraction of dietary C₃ biomass than has been estimated from traditional observations. Analysis of δ ¹⁸O of hippos from different stratigraphic levels shows no systematic trend over time; the average value for fossil hippos over the last 10 million years is similar to that of modern hippos from the Omo River system.