Scientists have discovered a new genus and species of river dolphin that has long been extinct. They have named it Isthminia panamensis in recognition of where it was found and believe it is the closest relative of the Amazon River dolphin (boto). Scientists made their discovery in ancient marine rocks of Panama, Central America. These incredible fossils shed new light on the evolution of today’s freshwater river dolphin species.
Researchers believe that river dolphins’ ancestors were marine dolphins which invaded fresh water river systems as is the case for other fresh water species such as turtles, manatees and sting rays. But until now, the fossil record of river dolphins in this basin has not revealed much about their marine ancestry. This fossil find now gives us a clear boundary in geologic time for understanding when marine dolphins invaded Amazonia.
Isthminia panamensis is the closest relative of the living Amazon River dolphin. It is a marine dolphin with a typical river dolphin body plan – that includes broad, paddle-like flippers, flexible necks and heads with particularly long, narrow snouts—all evolved to navigate and hunt in silty rivers and the flooded forest.
Scientists estimate that the ancient dolphins were about 2.84m (9.4 feet) long, which is a little larger than the average boto which lives in the Amazon and Orinoco River Basins of South America.
All living river dolphin species are particularly vulnerable to threats from human activities as they share their fresh water homes and live side by side with human communities. Botos are illegally hunted for fish bait in the Amazon which is threatening their future survival.
Illustration: Life reconstruction of Isthminia panamensis, feeding on a flatfish, which would have been abundant in the neritic zone of the late Miocene equatorial seas of Panama. Art by Julia Molnar.
Photo of river dolphins: Fernando Trujillo/Fundacion Omacha
Full scientific paper: Pyenson ND, Vélez-Juarbe J, Gutstein CS, Little H, Vigil D, O’Dea 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 3:e1227 https://dx.doi.org/10.7717/peerj.1227