Freshwater fish δ18O indicates a Messinian change of the precipitation regime in Central Africa

Tracking terrestrial environmental change throughout the Neogene is a challenge, notably in areas such as Central Africa where the few available data consist of a few vertebrate fossil assemblages. Here we aim to quantify the evolution of the delta O-18 of the main water body between four Neogene wet episodes in the Chad basin, ranging from the Late Miocene to the early Pliocene. The delta O-18 of the open water body was inferred from oxygen isotope measurements of phosphate in the apatite of open water fish tooth enamel. The more open the fish habitat, the lower the delta O-18, as revealed by the teeth of the large tiger fish (Hydrocynus) sampled in the four available Chadian vertebrate fossiliferous areas, i.e., Toros-Menalla (anthracotherid unit), Kossom Bougoudi, Kolle, and Koro Toro, all located in the Djurab Desert (Chad) and dated at 7.04 +/- 0.18 Ma, 5.26 +/- 0.23 Ma, 3.96 +/- 0.48 Ma, and 3.58 +/- 0.27 Ma, respectively. The delta O-18 values increased by similar to 2% between the two sites having ages that bracket the Messinian time period, and there was a slight increase of similar to 0.6% difference between the three Pliocene sites. These results reflect unambiguously change in the water cycle in Central Africa during the late Neogene, interpreted as a constant drying trend between the four successive wet episodes registered in the Djurab and a shift during the Messinian.