It was a skull fossil with a broken snout, long forgotten until paleontologists from the Smithsonian's National Museum of Natural History took notice and realized what an incredible find it was.

Discovered in 1951 by geologist Donald J. Miller in Southeastern Alaska, the fossil belonged to what is now known as the extinct species of river dolphins called Arktocara yakataga. According to Nicholas Pyenson and Alexandra Boersma, the paleontologists who studied the fossil, the dolphin thrived 25 million years ago, swimming in subarctic marine waters.

Pyenson and Boersma reported their findings in the journal PeerJ and identified A. yakataga as a relative of the Platanista, a river dolphin in Southeast Asia, after comparing the fossil to those of other dolphins, both extinct and living. A. yakataga and Platanista are both part of a large and diverse group of dolphins called Platanistoidea.

Using nearby rocks as a guide, the researchers estimated the A. yakataga fossil came from the late Oligocene epoch, right around the time that ancient whales started to diversify into two groups: the toothed (odontocetes) and baleen (mysticetes) whales.

"It's the beginning of the lineages that lead toward the whales that we see today," said Boersma.

Platanista's relatives left fossils in marine deposits around the globe but the A. yakataga was the northernmost to be found so far. The species got its name from where the fossil was found: Arktocara for "the face of the north" in Latin and yakataga for what the indigenous Tlingit people called the region it was discovered in.

Considering the Platanista is a freshwater dolphin in Southeast Asia, for it to have a relative all the way up in Alaska living 25 million years ago has the researchers stumped. What they want to know is what exactly a group as diverse and as widespread as the Platanistoidea had to go through to end up as a single species in Southeast Asia, and the A. yakataga fossil is one piece of the puzzle that may be able to make sense of the events that occurred.

The Platanista interests researchers beyond Pyenson and Boersma because it is an unusual creature. Found in Pakistan, Bangladesh, India and Nepal, the river dolphin cannot see and swims on its side, using echolocation to find its way. Unfortunately, the Platanista is down to a few thousands today, no thanks to human activities that disrupt the river dolphin's habitat. Its endangered status also makes it more difficult for researchers to study the species.

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