River dolphins are one of the rarest and most endangered vertebrates in the planet, so there's no wonder that it took scientists a very long time before they discovered a new species of this marine mammal.

In a report published in the journal PLOS ONE, Jan. 22, a group of scientists reported the discovery of the Inia araguaiaensis, the fifth known river dolphin species in the world, and named it after Araguaia, one of the two major rivers in Brazil, where it was found. The discovery is the first of its kind after almost 100 years since the now extinct river dolphin, Lipotes vexillifer, was discovered in 1918.

The researchers took DNA from the river dolphins in the Araguaia and Tocantins rivers and found that they are different from other known species in Brazil. They also have 24 teeth per jaw as compared to the 25 to 29 found in the other river dolphins in the Amazon river.

Nonetheless, the researchers believe that the new species originated from the river dolphins in the main Amazon river basin but were separated more than two million years ago when the Araguaia-Tocantins basin was separated from the rest of the Amazon river system. The shifting landscape and the river dolphins' inability to swim fast have isolated them from other South American river species.

The Lipotes vexillifer, discovered at the end of World War I, became extinct because of human activity and experts believe the newly discovered species face the same extinction threats. The creatures' vulnerability is also exacerbated by the fact that only 1,000 of them are believed to be living in the Araguaia-Tocantins basin.

"Since the 1960s the Araguaia river basin has been experiencing significant anthropogenic pressure via agricultural and ranching activities, and the construction of hydroelectric dams," the authors wrote.

Study co-author Tomas Hrbek of the Federal University of Amazonas in Brazil said that man-made activities such as dam construction can wipe out the newly discovered breed of river dolphins. "Its future is pretty bleak," he said. "The Araguaia-Tocantins basin suffers huge human disturbance and there are probably less than 1000 I. araguaiaensis in existence."

The research team is urging the International Union for Conservation of Nature (IUCN) to categorize the species on the Red List as Vulnerable.

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