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.