A new species of river dolphin has been found, the first of its kind for a century.
of the Federal University of Amazonas in Manaus, Brazil, and colleagues took DNA from river dolphins in the Araguaia and Tocantins rivers. He found they differed from all other species in Brazil. They also only have 24 teeth per jaw, rather than the 25 to 29 found in the Amazon鈥檚 other river dolphins. He calls the species Inia araguaiaensis.
The team鈥檚 analysis of I. araguaiaensis鈥榮 genes suggest that the species formed 2.08 million years ago, when the Araguaia-Tocantins basin was cut off from the rest of the Amazon river system by huge rapids and waterfalls. River dolphins are slow swimmers that rarely leap, so the shifting landscape isolated the dolphins from their fellows.
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Hrbek thinks the formation of rapids has been crucial to river dolphin evolution. The Madeira river鈥檚 Inia boliviensis arose 2.87 million years ago when the Teot么nio rapids formed, while the Casiquiare rapids in the Orinoco river gave rise to the subspecies Inia geoffrensis humboldtiana.
Dammed
However, a different obstacle poses a threat to I. araguaiaensis. Hrbek says dam construction on the Araguaia and Tocantins rivers may wipe it out. 鈥淚ts future is pretty bleak,鈥� he says. 鈥淭he Araguaia-Tocantins basin suffers huge human disturbance and there are probably less than 1000 I. araguaiaensis in existence.鈥� That means it could soon follow in the footsteps of China鈥檚 iconic baiji, which was declared extinct in 2007.
鈥淚t鈥檚 exciting evidence for a previously unrecognised species within the ancient lineage of Amazon river dolphins,鈥� says of Oregon State University in Newport. 鈥淵et it鈥檚 already rare, and its habitat is now fragmented by dams.鈥�
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