First new river dolphin species found since World War I

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Lisa Winter

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259 First new river dolphin species found since World War I
Nicole Dutra

Researchers have discovered a new species of river dolphin for the first time in since 1918 in Brazil. Unfortunately, it might be lost as quickly as it was discovered due to habitat destruction. The discovery was made by a group of researchers led by Tomas Hrbek of the Federal University of Amazonas and was published in PLOS One.

The newly discovered dolphin has been named Inia araguaiaensis, or the Araguarian Boto. Hrbek and his team made the discovery in Brazil’s Araguaia River basin. This area is pretty well populated and the dolphins are seen quite frequently, but until genetic sequencing and skull comparisons were completed, they were assumed to be members of I. geoffrensis. However, since I. araguaiaensis is physically isolated, Hrbek and his team suspected that it was a novel species and began to investigate. He notes: “It is an area where people see them all the time, they are a large mammal, the thing is nobody really looked.”


Analysis of the mitochondrial genomes revealed that I. araguaiaensis diverged from I. geoffrensis about 2.08 million years ago, around the same time that the Araguaia River shifted to empty into the Atlantic Ocean instead of the Amazon River. There are some morphological differences between the two species as well. I. araguaiaensis has a smaller skull than its sister taxon, which leaves them with 24 teeth in each jaw, whereas other species can have about 25-29.

The discovery of I. araguaiaensis brings the total number of living river dolphin species up to five. The Yangtze river dolphin was officially declared extinct in 2006. Three of the remaining species face imminent danger of extinction, as they are on the IUCN’s Red List.

Some experts, however, are debating that I. araguaiaensis is indeed a new species, and not a subspecies of I. geoffrensis. Hrbek understands their skepticism, but maintains that there is no indication within the mitochondrial genomes that the two species have a shared lineage. 

It is estimated that there are only around 1,000 individuals in this species in the Araguaia River basin. The dolphins’ population trends will have to be closely monitored in order to determine their conservation status and if they require legal protection. Habitat destruction is the biggest problem the cetaceans face, as a hydroelectric dam has been choking off their food supply for the last 50 years. They have also been known to steal from fishermen’s nets, which can result in the dolphin getting shot if they are caught.


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