During a recent expedition in Panama, scientists have discovered the fossilized remains of an ancient river dolphin species that lived a minimum of 5.8 million years back. This discovery might shed light on these freshwater mammals’ evolutionary history. Scientists believe that they possibly have their origin in the ocean.

The remains spotted by the researchers included the animal’s lower jaw that carried almost an entire set of conical teeth, half of its skull, a couple of tiny bones, and the animal’s right shoulder blade.

After examining the fossils, researchers came to the conclusion that they are around 5.8 million to 6.1 million years old. This means, these ancient dolphins used to live during the late Miocene era. Additionally, the scientists are saying that the animal is more than 2.7 meters or 9 feet long.

The newly identified ancient river dolphin species was spotted in Panama’s Caribbean coast and has been named Isthminia panamensis based on its place of discovery. It’s the same site where fossils of several other marine animals have been discovered in the past. According to the researchers, this indicates that I. panamensis was actually a saltwater species. They also pointed out that I. panamensis is the only known river dolphin species native to the Caribbean.

Nicholas Pyenson, the study’s lead author, said that this new dolphin species was discovered in marine rocks. He added that the jaws and skull of the dolphin had many features which indicate that it might actually be a marine animal like the modern oceanic dolphins. Pyenson works for the Washington, D.C.-based National Museum of Natural History, an organization administered by the Smithsonian Institution, as a curator.

However, the researchers admitted that in spite of living in the Caribbean Sea, this newly discovered dolphin species had a closer association with the modern-day river dolphins.

Must Read: Newly identified species of ancient river dolphin originally lived in the ocean

What’s more, according to Aaron O’Dea, a coauthor of the study, I. Panamensis is the closest relative of a living dolphin species, the Amazon River Dolphins. O’Dea represents the Panama-based Smithsonian Tropical Research Institute as a staff scientist.

The entire study was published in the journal PeerJ on September 1.

Right now, the world is home to just four river dolphin species (one out of them i.e. the Yangtze River Dolphins are most likely almost extinct). Each of these species resides either in coastal ecosystems or in freshwater.