Inia araguaiaensis: New Species of River Dolphin Found in Brazil

Scientists from Brazil and the United Kingdom have described a new species of true river dolphin from the Araguaia River basin, the first such discovery in nearly 100 years.

Inia araguaiaensis. Image credit: © Nicole Dutra.

Inia araguaiaensis. Image credit: © Nicole Dutra.

True river dolphins are only distantly related to marine dolphins and found only in freshwater environments of Asia and South America. These dolphins are some of the rarest and most endangered of all vertebrates.

True river dolphins have very long snouts and small eyes. They have poor eyesight because vision is almost useless in the muddy waters where they live.

Until now, only five species were known: the Amazon river dolphin (Inia geoffrensis), the Bolivian river dolphin (Inia boliviensis), the South Asian river dolphin (Platanista gangetica), the La Plata dolphin (Pontoporia blainvillei) and the Baiji. However, the latter was last sighted in 2001 and now considered extinct.

In a paper published in the open-access journal PLoS ONE, biologists from the Federal University of Amazonas and the National Research Institute of the Amazon, both in Brazil, and the University of Dundee describe the first new species of true river dolphin since 1918, when the Baiji was discovered.

The new river dolphin, named Inia araguaiaensis, was distinguished from other members of the genus on the basis of DNA data as well as differences in skull morphology.

According to the scientists, samples were collected either from carcasses, or from live animals using minimally invasive sampling procedures. In total, they sampled 45 Bolivian river dolphins from the Bolivian sub-basin, 44 Amazon river dolphins from the Amazon-Solimões basin and 32 Inia dolphins from the Araguaia River.

Inia araguaiaensis. Image credit: © Nicole Dutra.

Inia araguaiaensis. Image credit: © Nicole Dutra.

The team found strong evidence that Inia dolphins from the Araguaia River represent a biological group distinct from Amazon and Bolivian river dolphins.

The findings also show that Inia araguaiaensis diverged from its Amazonian sister taxon during the early Pleistocene, around 2.1 million years ago.

Lead author Dr Tomas Hrbek from the Federal University of Amazonas and his colleagues said in the paper that the new species occurs in the central region of Brazil, in the Araguaia River basin.

“We recorded it in the lower and middle Araguaia River from Barra do Garças to the Santa Isabel rapids, and in several tributaries such as Vermelho, Peixe, Crixás-Açú and Água Limpa Rivers, and dos Tigres and Rico Lakes, all in the state of Goiás, and Lake Montaria in the state of Mato Grosso.”

“The species is likely present in the Tocantins River, and potentially in the whole Araguaia-Tocantins River Basin.”

The scientific name of Inia araguaiaensis refers to the geographic area where it is currently known to occur.

“We propose the common names Boto-do-Araguaia and Araguaian boto for this species. Boto is the common regional and international name of species of Inia, and Araguaia refers to the geographic distribution of this species,” the scientists said.


Hrbek T et al. 2014. A New Species of River Dolphin from Brazil or: How Little Do We Know Our Biodiversity. PLoS ONE 9 (1): e83623; doi: 10.1371/journal.pone.0083623