Scientists have discovered the fossilized remains of a new species of ancient river dolphin, which lived around 5.8 million years ago, in Panama. The discovery could help scientists throw some light on the evolutionary history of these freshwater mammals.

A half a skull, a lower jaw with nearly complete set of conical teeth, a right shoulder blade and two small bones from a flipper have been unearthed by the scientists. In the study, researchers mentioned that the fossils are probable between 5.8 million and 6.1 million years old which means they belong to the late Miocene epoch.

The study suggested that the ancient river dolphin, known as Isthminia panamensis, was over 9 feet long.

The researchers added that the ancient mammal has been found on the Caribbean coast of Panama, at the same place where other marine animal fossils were discovered, suggesting that Isthminia panamensis was also a saltwater species. They mentioned that Isthminia panamensis is the only fossil of a river dolphin known from the Caribbean.

In a statement, study's lead author Nicholas Pyenson said, "We discovered this new fossil in marine rocks, and many of the features of its skull and jaws point to it having been a marine inhabitant, like modern oceanic dolphins".

The researchers said that although Isthminia panamensis dwelled in the salty waters of the Caribbean Sea, it is actually more closely linked to modern-day freshwater river dolphins. Study co-author Aaron O'Dea mentioned that in fact, Isthminia is the closest relative of the living Amazon River dolphin.