Scientists have unearthed several fossils of ancient dolphins that thrived in freshwater instead of saltwater, and they believe the find can provide more information the evolution of the cetacean mammal. The researchers published their study in this week's issue of PeerJ, a scientific journal.

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The ancient dolphin, called Isthminia panamensis, and was found in the coast of Panama. Scientists believe that the creatures existed around six million years ago in what was once a river at that time.

The animal's skeleton, however, is incomplete. The scientists found only an incomplete skull, half a jaw, on shoulder blade and some flipper bone fragments. Based on the ancients remains, it is believed that the freshwater dolphin's length is almost three meters.

Although the Isthminia was discovered in saltwater and probably lived in the sea, it is actually a near relative of the modern day Amazon river dolphin, according to Aaron O'Dea, one of the scientists who co-wrote the published study. Just like its freshwater relatives, the Isthminia sports a limber neck as well as a long snout filled with teeth and flippers that resembles a paddle. Such characteristics helped freshwater dolphins thrive in their river environment.

Researchers theorize that the Isthminia made its way toward the river the moment the rising sea water overflowed to the river banks. Nick Pyenson, a paleontologist working for the Smithsonian said that uncovering the evolution of the freshwater dolphins will help scientists better understand the species. The evolution of the river dolphins has been a mystery to scientists until now.

The study said that dolphins are one of the animals that once lived in land and then moved to lived in the sea. Interstingly, the freshwater dolphins return to the rivers after staying in salt waters for a very long period of time. O'Dea believes that something happened during that time which made these particular dolphins change their habitat and environment.

It is believed that there are only three species of rivers dolphins currently alive today. A fourth one, known to be living in the Yangtze river, is believed to be extinct. The other surviving species are also in danger of being wiped out.

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