Largest freshwater dolphin ever

The largest species of freshwater dolphin ever was Pebanista yacuruna, a recently discovered prehistoric species estimated from its giant-sized fossil skull to have measured 3–3.5 m (9 ft 10 in–11 ft 5 in) in total length, and dating from the Miocene epoch. The skull was discovered in 2018 along the shore of the Napo River in the Peruvian Amazon, during an expedition to a 16.5-million-year-old fossiliferous outcrop in the Pebas Formation of north-east Peru and the findings were first discussed in Science Advances on 20 March 2024.

By comparison, the largest living species of freshwater dolphin, the Amazonian pink river dolphin or boto (Inia geoffrensis), measures up to 2.5 m (8 ft 2 in) in adult males.

Modern-day freshwater dolphins constitute six recognized species – one in southern Asia's Ganges and Indus Rivers, one in China's Yangtze River, and four in South America (though the Yangtze species, the baiji, may well be extinct as no confirmed sightings of this very distinctive creamy-white species have been recorded during the past two decades).

Interestingly, Peru's prehistoric P. yacuruna turns out to be more closely related to the river dolphin of southern Asia (genus Platanista) than to those of South America's Amazon region (genus Inia).

Formally described and named in 2024, its taxonomic species name, yacuruna, is derived from the Yacuruna, which are mythical aquatic entities believed by the indigenous Quechua people to live deep in the Napo River.