New dolphin fossil makes a splash

river dolphin fossil skull and jaw

The skull and jaws of Isthminia panamensis, a new fossil dolphin from Panama, provides clues to the evolution of river dolphins in the Americas.  

Nicholas D. Pyenson/NMNH Imaging/Smithsonian Institution

Six million years ago, a relative of modern river dolphins once frolicked along Panama’s Caribbean shores, researchers report September 1 in PeerJ. Unearthed in 2011, the fossilized skull, teeth and jaw bones belong to a novel dolphin species (Isthminia panamensis). 

Researchers originally rescued the fragile specimen from a coastal area battered by breaking waves. Sediments and other fossils found in the same rock layers put the species between 6.1 million and 5.8 million years old. By scanning and 3-D printing a copy of the specimen, the team found that I. panamensis had a snout optimized for ocean fishing and a small body like that of modern ocean dolphins. Still, its closest relation appears to be the modern Amazonian river dolphin.

River dolphins likely descended from marine species and evolved separately to live in freshwater ecosystems. With little fossil evidence to back that theory up, this species could represent a missing link of sorts, the researchers posit. 

A team of Smithsonian scientists collected fossils of Isthminia panamensis from the rocky shores of Panama’s Caribbean coast in 2011. Jorge Velez-Juarbe / Smithsonian Institution
An artist’s vision of Isthminia panamensis hunting flatfish six million years ago. Julia Molnar / Smithsonian Institution

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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