Smithsonian researchers have discovered a new species of ancient river dolphin. According to the researchers, the extinct species, which navigated the planet's deltas about six million years ago, has provided information on early evolution of river dolphins.

Earth has only four living species of river dolphins today, but the remains identified by the researchers suggested that there were many river dolphin species several million years ago. The new species and genus, discovered in Panama by Smithsonian researchers, has been classified as 'Isthminia panamensis'.

The discovered remains consist of a part of skull, lower jaw with teeth, a pair of bones and the dolphin's right shoulder blade. The researchers compared the remains with living river dolphins and some fossils, and found that full specimen was more than 9 feet long.

Nicholas D. Pyenson, curator of fossil marine mammals at the Smithsonian's National Museum of Natural History and member of the team that found the new species, said the new fossil was discovered in marine rocks. Skull and jaws' features suggested that it was a marine inhabitant, Pyenson added.

Pyenson said, "Many other iconic freshwater species in the Amazon, such as manatees, turtles and stingrays have marine ancestors, but until now, the fossil record of river dolphins in this basin has not revealed much about their marine ancestry".

According to the researchers, they found fossils of some other animals found near the specimen of the dolphin which meant that the ancient river dolphin species lived and hunted near the coast.