River Dolphin Fossils From Panama May Show How They Became Freshwater Species

A new ancient genus and species of river dolphins that could help us to gain an insight into their evolution has been provided by scientists, according to hngn.

In Panama, there were small fossil fragments that showed the existence of the ancient dolphin, called Isthminia panamensis, according to the Smithsonian.

The fossil is thought to go back to as far as 6.1 million years. It has "half a skull; a lower jaw with an almost full set of teeth; and bones from the shoulder and flipper."

Research shows that the animal measured nine feet in length.

About four species of dolphins---and all endangered---exist today. They are different from marine species due to their "broad, paddle-like flippers, flexible necks and heads with particularly long, narrow snouts," which helps them to live peacefully in freshwater environments.

All these discoveries show that freshwater dolphins were once more "widespread" than they are today. Researchers are trying to discover when then shifted from seas to 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."

Interestingly, more ancient marine fossils have been discovered at the Panama site, which suggest that a salt water environment existed here before the Panama Isthmus closed, according to hngn.

"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 of these aquatic animals, but also of the changing geographies and ecosystems of the past."

The study was published in a recent edition of the journal PeerJ.