A new study in journal Peer J announces the discovery of a previously unknown river dolphin species that, oddly enough, populated Earth's ancient seas.

The species lived about 6 million years ago

A new study in journal Peer J announces the discovery of a previously unknown river dolphin species that, oddly enough, populated Earth's ancient seas. 

The species, named Isthminia panamensis, was documented based on fossilized remains recovered from a site on the Caribbean coast, close to the town of Piña in Panama.

Having analyzed the fossils, researchers at the Smithsonian’s National Museum of Natural History determined that they date back to around 5.8 to 6.1 million years.

This means the newly discovered species lived sometime towards the end of the Miocene epoch, in turn spanning since about 23 to 5 million years ago.

The creature is an ancestor of modern river dolphins

The site that led to the discovery of this previously undocumented river dolphin species produced a Isthminia panamensis skull, a lower jaw complete with an almost intact set of conical teeth, a shoulder blade and two fairly small flipper blades.

Judging by the size of these remains, paleontologists estimate that the ancient aquatic creature, an ancestor of modern river dolphins, could grow to measure 9 feet (2.7 meters) from head to tail.

The animal had a flexible neck and its head ended with a long and narrow snout, as shown in the illustration below. As for its flippers, evidence indicates they were broad and shaped like paddles.

Why are they calling Isthminia panamensis a river dolphin? 

As mentioned, fossilized remains belonging to this ancient species were pulled from marine rocks on the coast of Panama. Besides, the creature's skull and jaws suggest that it preferred marine environments, just like most modern dolphins.

Why is it then that researchers are calling this long-lost species a river dolphin? Surely they should know better than defy common sense with such swiftness.

Well, the thing about Isthminia panamensis is that, although fossil evidence hints that it populated ancient seas, its anatomy indicates that it is more closely related to the Amazon river dolphin than to proper marine species of the kind.

“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,” study lead author Nicholas D. Pyenson said in a statement.

“Isthminia is actually the closest relative of the living Amazon river dolphin,” added specialist Aaron O’Dea at the Smithsonian Tropical Research Institute in Panama.

Since moder river dolphins evolved from species that eons ago left our planet's seas and oceans and headed into freshwater ecosystems, specialists hope the discovery of Isthminia panamensis will help better our understanding of ancient biodiversity.

 An artistic reconstruction of Isthminia panamensis