The largest freshwater odontocete: A South Asian river dolphin relative from the proto-Amazonia.

Several dolphin lineages have independently invaded freshwater systems. Among these, the evolution of the South Asian river dolphin and its relatives (Platanistidae) remains virtually unknown as fossils are scarce. Here, we describe gen. et sp. nov., a dolphin from the Miocene proto-Amazonia of Peru, recovered in phylogenies as the closest relative of . Morphological characters such as an elongated rostrum and large supraorbital crests, along with ecological interpretations, indicate that this odontocete was fully adapted to fresh waters. constitutes the largest freshwater odontocete known, with an estimated body length of 3 meters, highlighting the ample resource availability and biotic diversity in the region, during the Early to Middle Miocene. The finding of in proto-Amazonian layers attests that platanistids ventured into freshwater ecosystems not only in South Asia but also in South America, before the modern Amazon River dolphin, during a crucial moment for the Amazonian evolution.