Intra-tooth isotopic profiles of canines from extant Hippopotamus amphibius and late Pliocene hippopotamids (Shungura Formation, Ethiopia): Insights into the seasonality of diet and climate

We investigated the potential use of intra-tooth variations of stable carbon and oxygen isotopes in hippopotamid canines to retrieve signals of seasonality in continental contexts. A high-resolution serial isotope analysis of enamel was performed on both lower and upper canines of one extant common hippopotamus from the Sarh region (Chad). We discussed three methodological points: canine growth rates, optimal sampling resolution, and record of seasonality within hippopotamid canine enamel. In this 21-year old specimen, growth rates of 39.1 mm/year and 31 mm/year were established for the lateral part of lower and upper canines respectively. Our results suggest that the optimal sampling resolution to capture the seasonality is ca. 1-3 mm. Seasonal changes were observed in both delta C-13 and delta O-18 values, indicating an important C-3 component in the diet during the rainy seasons (up to 50%) and a diet dominated by C-4 grasses during the dry seasons (around 70%). Next, we performed a similar test on two fossils from the Shungura Formation (south-western Ethiopia). Seasonal variations in delta C-13 of the diet were also observed in the fossil specimens and the palaeoenvironmental implications are discussed. Preliminary conclusions from the delta O-18 and delta C-13 sequences seem consistent with a rise of seasonality during the Pliocene, synchronous with the global aridification and opening of the environments. (c) 2012 Elsevier B.V. All rights reserved.