It happens more often than you’d think: Research scientists go digging around the dusty collections of your local natural history museum and find species hitherto unknown to science. Whatever sits on display when you visit – ancient human art, towering dinosaurs, slightly off-putting taxidermy – is just the tip of the iceberg. Countless specimens remain unseen – not just by museum patrons, but often by staff as well.

“There’s all this stuff that no one has ever had time to go through,” Alexandra Boersma, who studies fossil marine mammals at the Smithsonian, told The Washington Post. So to find new species, all you have to do is wander around the museum’s dustiest corridors. Along with her lab’s principal investigator Nicholas D. Pyenson, Boersma went hunting for interesting projects.

“Some of it has been sitting there for decades,” Boersma said. “No one has gotten around to describing it.”

On Tuesday, she and Pyenson introduced their latest find to the scientific community: A 25 million-year-old river dolphin they’ve dubbed Arktocara yakataga. The species, described for the first time in a study published in PeerJ, sat on the shelf for more than half a century and caught Boersma’s eye because of its “beautiful, cute little skull.”

But as luck would have it, Arktocara yakataga appears to be a close relative of Platanista, a dolphin that swims on its side and uses echolocation to navigate murky rivers without the ability to see. Arktocara yakataga is the oldest member of the Platanistoidea family ever found – it lived right at the time when whales were breaking into the ancestral groups that would evolve into modern whales – which helps prove that Platanista represents the remains of an ancient lineage.

Unfortunately, that ancient lineage is hanging on by a thread. Platanista is poorly understood and tragically endangered. Fishing nets, pollution and habitat disruption have left just a few thousand dolphins swimming in the rivers of Nepal, India, Bangladesh and Pakistan. The researchers hope that this evidence will help conservationists push for greater protection of the Platanista holdouts.

The other intriguing thing about Arktocara yakataga is that it was reportedly found up in Alaska, which would mean the dolphin dwelled in the ancient Arctic.

“It was striking and really kind of bizarre that this huge group of marine dolphins that were up in the Arctic and all over the world has dwindled to this one species that’s stuck in freshwater systems in Asia,” Boersma said, adding that the whales that live in the Arctic today – belugas and narwhals, for example – are known to have descended from whales that lived farther south during Arktocara yakataga’s time.

“It would be interesting to know what whales started out in the Arctic,” Boersma said. “It would give us a better sense of how whales first adapted to those new climates, and maybe give us a sense of how well they might adapt in the future, now that climate is changing so rapidly.”