Washington, August 21 : Scientists have announced that the newly discovered Bolivian river dolphin is a separate species from the Amazon River dolphin, based on DNA tests.
According to a report in National Geographic News, the announcement was made at a recent conservation workshop in Santa Cruz de la Sierra in Bolivia.
Thousands of years ago, a powerful drought dried up Brazil's Madeira River, causing a "radical separation" as dolphin populations were caught on different sides of the newly created rapids, according to researcher Manuel Ruiz-Garcia.
The Madeira split into today's Beni and Mamore rivers of northeastern Bolivia.
"When they separated, (the dolphins) were never again able to return and reproduce," said Ruiz-Garcia, who heads the Molecular Genetics Lab at Javeriana University in Bogota, Colombia.
"Thus isolated, the Bolivian river dolphin, Inia boliviensis, eventually developed," he added.
Ruiz-Garcia took DNA samples from 40 river dolphins from Bolivia and 56 from Colombia by extracting tissue from their tail muscles.
A limited comparison of the DNA revealed significant genetic differences between the two river-dolphin populations.
This led Ruiz-Garcia to initially estimate that the species separated five to six million years ago.
But after comparing 32 more genes from DNA in another 40 Bolivian dolphins and about 60 Colombian and Peruvian dolphins, he concluded that the separation happened much sooner-about 100,000 to 500,000 years ago.
"Bolivian dolphins are totally different molecularly from other dolphins," said Ruiz-Garcia said. "After being split up, they accumulated mutations and formed a new species," he added.
Bolivian river dolphins-especially females-also look different from their Amazon relatives.
In contrast to Amazon river dolphins, which are considered "pink," the members of this new species are a pale gray. They also have more teeth, smaller heads, and smaller bodies.
Ruiz-Garcia also considers the Bolivian species to be chubbier and rounder.
The Bolivian river dolphin population may include as many as 25,000 individuals, making the mammal "very abundant," said Ruiz-Garcia.
And unlike the havoc wrought on its relatives by fishers on Brazilian rivers, Bolivia's newfound dolphin can roam safely through pristine freshwater channels.