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 frolicked along Panama’s Caribbean shores, researchers report September 1 in PeerJ. Unearthed in 2011, a fossilized skull, jaw and other bones belong to a new dolphin species (Isthminia panamensis).

Researchers rescued the specimen from a coastal area battered by breaking waves. Sediments and other fossils in the same rock layers date the species to between 6.1 million and 5.8 million years ago. By scanning the specimen and printing a 3-D copy, the team found that I. panamensis had a snout and teeth optimized for ocean fishing. But in comparing the fossils with both extinct and living dolphins, the researchers determined that the animal’s closest relative is the modern Amazon river dolphin (Inia geoffrensis).

That kinship suggests that all river dolphins descended from marine species and evolved separately to live in freshwater ecosystems. 

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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