Ecological traits of the franciscana dolphin (Pontoporia blainvillei) from the Late Pleistocene to the present days based on stable isotope analysis

Late Pleistocene fossils from southern Brazil provide a unique opportunity to study the diet and habitat use of the extant franciscana dolphin (Pontoporia blainvillei) prior to human influence. Here, we subject 19 fossil and 21 contemporary specimens to stable carbon and oxygen isotope analysis (after first ruling out diagenesis via Fourier transform infrared spectroscopy). The two groups differ in their isotopic composition (PERMANOVA, p <.01), with fossils yielding more disparate δ13C values and recent samples more disparate δ18O values. Their isotopic niches show an overlap of ~20%, with that of the fossils being slightly wider (SEAc = 2.25‰2 versus 1.84‰2). We attribute these differences to impoverished modern fish communities and temporal changes in freshwater influx.