For the first time in almost 100 years, scientists have identified a new species of river dolphin. The Araguaian river dolphin (Inia araguaiaensis) lives in Brazil's Araguaia-Tocantins river basin. There are only a handful of species of river dolphin, so the discovery of a new species is an exciting development. Sadly, all of the river dolphin species in the world, including this one, are at risk of extinction because of habitat destruction, damming, overfishing and sonar pollution.

Amazon river dolphins. Photo by Stephanie Triltsch, Creative Commons License. The Araguaian river dolphin is most closely related to the Amazon river dolphin (Inia geoffrensis) and the Bolivian river dolphin (Inia boliviensis), which some consider a subspecies of the Amazon river dolphin. Researchers at the Federal University of Amazonas (UFAM) and the National Research Institute of the Amazon (INPA) in Manaus, Brazil, and the Centre for Remote Environments at the University of Dundee in the UK studied the morphological characteristics, the nuclear DNA and the mitochondrial DNA of the Araguaian dolphin. They compared them with those of the Amazon and Bolivian river dolphins. Their studies led them to conclude that the Araguaian river dolphin is, indeed, a separate species.

The scientists estimate that the newly identified species diverged from the Amazon and Bolivian river dolphins about 2.08 million years ago. Around that time, the Amazon and Araguaia-Tocantins river basins separated. Other living river dolphin species are the La Plata dolphin (Pontoporia blainvillei), and the Ganges and Indus river dolphin, also known as the South Asian river dolphin (Platanista gangetica). The Chinese, or Yangtze river dolphin (Lipotes vexillifer), is thought to have been extinct since the beginning of the 21st century. Ironically, the Chinese river dolphin was the last river dolphin, before the discovery of the Araguaian river dolphin, to be indentified—in 1918.

The La Plata dolphin is the only saltwater dolphin; the other species all live in fresh water. River dolphins are adapted to life in rivers and estuaries. Unlike dolphins that live in oceans, river dolphins can turn their heads to maneuver in shallow waters and through the roots of trees. They have long, thin snouts compared to the snouts of oceanic dolphins. River dolphins use their snouts to pick up prey, consisting of crustaceans and fish, on muddy river bottoms or in between tree roots. The Ganges and Indus river dolphin swims on its side, possibly to catch prey in the mud.

As they move through water that isn't very clear, river dolphins don't have very good vision. The Ganges and Indus river dolphin doesn't even have eyes. To make up for their bad or nonexistent eyesight, river dolphins are much better at echolocation than oceanic dolphins.

A vulnerable species

Although scientists have just become aware of its existence as a separate species, the Araguaian river dolphin may not be around for long. Since the 1960s, agricultural development, ranching and the construction of hydroelectric dams in the Araguaia-Tocantins basin have threatened river dolphins and other animals that are part of the Araguaia River ecosystem. The researchers who identified the new species have suggested that it be labeled "vulnerable" by the International Union for Conservation of Nature (IUCN). Read the full research study in PLOS ONE: A New Species of River Dolphin from Brazil or: How Little Do We Know Our Biodiversity.