With its long neck and small eyes, the ocean-going Isthminia panamensis is most closely related to Amazon river dolphins. (Julia Molnar/Smithsonian) With its long neck and small eyes, the ocean-going Isthminia panamensis is most closely related to the Amazon river dolphin. (Julia Molnar/Smithsonian)

On the coast of Panama in 2011, Smithsonian paleobiologist Nick Pyenson raced against the incoming tide to remove a fossil embedded in the rocky shore. As Pyenson and his team dug a trench around the fossil, Pyenson guessed that they were uncovering bones from an ancient marine mammal known as the shark-toothed dolphin. He was wrong.

“Once we got it back to D.C., and I got a close look at it, I could tell it was like nothing I’d ever seen before,” Pyenson says.

No one had, it turns out. The fossil represents a newly discovered genus and species, according to a study published today in the scientific journal PeerJ. Dubbed Isthminia panamensis, the marine mammal poses a bit of a mystery. Its elongated snout and small eyes are similar to that of the Amazon river dolphin, but this dolphin clearly lived in the open ocean.

“We think it lived in the channel that connected the Atlantic and Pacific oceans before the isthmus of Panama formed,” Pyenson says.

The finding suggests that ancient dolphins living off the coast of South America made their way inland as ocean levels rose around 6 million years ago, Pyenson says. If we enter another period of rising oceans, this line of research may help scientists predict what will happen next.

“My hope is that by reviewing deep evolutionary evidence about river dolphins, we can guess what their, and maybe our, future will be,” Pyenson says.

Watch as a team of scientists, led by Nicholas Pyenson, race against the tide to excavate a fossil in Panama. (Sadie Dingfelder/The Washington Post)