By STAN LEHMAN, Associated Press

SAO PAULO (AP) — Scientists have made the first discovery in 100 years of a new river dolphin species in the waters of the Araguaia river in Brazil's vast Amazon rainforest.

The discovery of the "Inia araguaiaensis" was officially announced earlier this week in a study posted online by the Plos One scientific journal.

The study's lead author, biologist Tomas Hrbek, of the Federal University of Amazonas in the city of Manaus, said the new species is the third ever found in the Amazon region.

"It was an unexpected discovery that shows just how incipient our knowledge is of the region's biodiversity," Hrbek said by telephone.

"River dolphins are among the rarest and most endangered of all vertebrates, so discovering a new species is something that is very rare and exciting."

He said "people always saw them in the river but no one ever took a close up look at them."

Hrbek added that scientists concluded the large dolphin was a new species by analyzing and comparing DNA samples of several types of dolphins from the Amazon and Araguaia river basins.

"The Araguaia dolphin is very similar to its Amazon river cousin although somewhat smaller and with fewer teeth," he said. He added that there were about 1,000 "Inia araguaiaensis" dolphins living in the 2,627 kilometer-long (1,630 miles) river.