The fossil of a dolphin found on the Caribbean coast near the town of Piña, Panama, has revealed a new genus and species of river dolphin that has long been extinct, Nature World Report reports.

The study was published today in the scientific journal Peerj.

Smithsonian scientists and colleagues who have named it Isthminia panamensis discovered the fossil, which dates from 5.8-6.1 million years ago. The species name, panamensis, recognizes "the Republic of Panama, its people, and the many generations of scientists who have studied its geological and biological histories." The genus, Isthminia, recognizes the Panama Isthmus and the fossil 's living relative, the Amazon river dolphin, Inia geoffrensis.

"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," said the study's lead author Nicholas D. Pyenson, curator of fossil marine mammals at the Smithsonian's National Museum of Natural History.

"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. Isthminia now gives us a clear boundary in geologic time for understanding when this lineage invaded Amazonia."

The specimen will also reveal important information on the evolution of today's freshwater river dolphin species.

The dolphin fossil consists of half skull, lower jaw with an almost entire set of conical teeth, right shoulder blade and two small bones from the dolphin's flipper. The shape and size of these parts suggests that the dolphin must have been more than 9 feet long.