Hidden in plain sight

Brazilian researchers describe a new dolphin from the Araguaia River, in the Amazon forest. The animal is the fifth species of a river dolphin discovered in all the world and is already endangered.

A group of pinkish skin river dolphins, two meters long and 440 pounds each is difficult not to be seeing. Even if this animal lives in a region of Brazil where people claim that just looking at them in the eye may cause a lifetime of bad luck. So, how could a distinguished animal like this passed unnoticed until now?

The truth is that everyone knew they existed, but people believed the river dolphin of the Araguaia River were from the same species as the one that lives at the Amazon river, the so called ‘pink boto’, boto-cor-de-rosa in Portuguese (Inia geoffrensis).

The misunderstanding was only resolved when Brazilian researchers from the Federal University of Amazonas and the National Institute of Amazonian Research decided to study the group of dolphins from the Araguaia River and compared them to the dolphins from the Amazon river.

By analyzing DNA samples from more than 120 dolphins of both rivers, the team concluded the Araguaia river creature was indeed a whole new species, despite their physical resemblance.

“The result was, in a way, surprising”, says Tomas Hrbek the lead author of the study published this week in the journal Plos One. “The new species was not discovered in a desert place. They live in an inhabited location, people see them all the time; the thing is nobody really looked.”

There were two known species of river dolphin in Brazil until now: the pink dolphin (I. geoffrensis) and the Bolivian dolphin (I.boliviensis). They are very similar except for little differences in body size and in the shape of their heads. When it comes to the new dolphin, the researches says he is just like the pink dolphin.

“The pink dolphin has only some teeth differences when compared to the araguaian dolphin”, says Hrbek.  “It is impossible to differentiate them just by looking. No one goes around opening dolphin’s mouths in the river to check it.”

Distant related
Hrbek believes that the araguain dolphin species was separated from the pink dolphin species more than two million years ago when the Amazon river and the Araguaian river — that used to be part of only one basin — became disconnected.

Scientists believe that the araguain dolphin diverged from the pink dolphin (above) 2 million years ago.
Scientists believe that the araguain dolphin diverged from the pink dolphin (above) two million years ago.

“Today the Araguaia river basin is almost completely disconnected from the Amazon river basin and the contact points between the two basins are full of rapids that isolate the dolphins”, explain the researcher. “After centuries of isolation, it is probable that the two groups of dolphins had evolved independently.”

The araguaian dolphin is the first river dolphin discovered in the last century. And it is already in danger.

Scientist estimate that there are about 1,200 of these animals living in the Araguaia river. All of them suffering the impact of human development. “Since the 60’s the river dolphins of this area are endangered because of the industries, the agriculture, the illegal fishing and the construction of dams”, says Hrbek. The scientist believes that as a result of these threats, the new species should be categorized as ‘vulnerable’ on the Red List.

“This study shows us the importance of preservation”, says Hrbek. “We think that we know our biodiversity, but maybe there are lot of other species out there to be known.”



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