#inioidea

Amazon river dolphin (Inia geoffrensis)

Amazon river dolphin (Inia geoffrensis geoffrensis)

Amazon river dolphin (Inia geoffrensis geoffrensis)

Artistic reconstruction of Isthminia panamensis, a new fossil dolphin from Panama, feeding on a flatfish.

NEW FOSSIL  RIVER DOLPHIN SPECIES FOUND IN PANAMA

In contrast to dominant mode of ecological transition in the evolution of marine mammals, different lineages of toothed whales have repeatedly invaded freshwater ecosystems during the Cenozoic (65 mya). The so-called ‘river dolphins’ are now recognized as independent lineages that converged on similar morphological specializations. Nowadays, there are only four species of river dolphins (platanistoids) living in freshwater or coastal ecosystems. All of them are endangered, including the Chinese river dolphin, probably already gone

Now, in the Caribbean coast of Panama, near the town of Piña, researchers have found a 5.8–6.1 million years old fossil from a new extinct species of river dolphin, called Isthminia panamensis. According to scientists at the Smithsonian Institution, the finding sheds light on the evolution of living species of freshwater dolphins.

“Isthminia is actually the closest relative of the living Amazon river dolphin,” said study co-author Aaron O’Dea, staff scientist at the Smithsonian Tropical Research Institute in Panama. “While whales and dolphins long ago evolved from terrestrial ancestors to fully marine mammals, river dolphins represent a reverse movement by returning inland to freshwater ecosystems. As such, fossil specimens may tell stories not just of the evolution these aquatic animals, but also of the changing geographies and ecosystems of the past.”

Isthm- reflects the type specimen’s provenance from the Isthmus of Panama and the crucial role that the formation of this isthmus played in Earth history and evolution of the biota of the Americas.

 Isthminia panamensis’s skull by Nicholas D. Pyenson / NMNH Imaging / Smithsonian Institution and illustration by Julia Molnar / Smithsonian Institution

Reference: Pyenson et a. 2015.  Isthminia panamensis, a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of ‘river dolphins’ in the Americas. PeerJ