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Fossil Fragments Are New Extinct Species of River Dolphin


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Smithsonian scientists and colleagues have discovered a new genus and species of river dolphin that has long been extinct. They made the discovery after carefully examining fossil fragments from Panama. The fossil fragments also shed new light on the evolution of today’s freshwater river dolphin species. The team’s research was published Sept. 1 in the scientific journal Peer J.

The fossil, which dates from 5.8–6.1 million years ago, was found on the Caribbean coast near the town of Piña, Panama. It consists of half a skull, lower jaw with an almost entire set of conical teeth, right shoulder blade and two small bones from the dolphin’s flipper. In comparison with other river dolphins—both fossil and living—the shape and size of these parts suggests that the full specimen may have been more than 9 feet long.


The skull and jaws of “Isthminia panamensis,” a new fossil dolphin from Panama. The specimen is housed at the Smithsonian’s National Museum of Natural History, but a painted 3D print can be viewed at the BioMuseo in Panama City, Panama. A 3D model can also be downloaded and printed from the Smithsonian X 3D website at http://3d.si.edu/browser(Credit: Donald E. Hurlbert; NMNH Imaging, Smithsonian Institution)

Today there are only four species of river dolphins―all living in freshwater or coastal ecosystems and all endangered, including the Yangtze river dolphin, which is likely now extinct. Each of the modern river dolphin species show a common solution to the problem of adapting away from marine to freshwater habitats by converging upon a body plan that includes broad, paddle-like flippers, flexible necks and heads with particularly long, narrow snouts—all the better to navigate and hunt in winding, silty rivers.

But fossil evidence suggests that river dolphins’ ancestors were widespread around the globe. I. panamensis was clearly one of them, and its fossil remains have helped the team understand something less clear: When in their evolutionary tract did river dolphins transition from the saltwater of the ocean to the freshwater of rivers?

“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,” said the study’s lead author Nicholas D. Pyenson, curator of fossil marine mammals at the Smithsonian’s National Museum of Natural History. “Many other iconic freshwater species in the Amazon, such as manatees, turtles and stingrays have marine ancestors, but until now, the fossil record of river dolphins in this basin has not revealed much about their marine ancestry. Isthminia now gives us a clear boundary in geologic time for understanding when this lineage invaded Amazonia.”

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