A young gray seal. (Carsten Rehder/AFP/Getty Images)

You'd think a gray seal would be hard to misplace. After all, adults of this blubbery marine mammal species can range from five to 10 feet in length and weigh from 220 to 680 pounds, depending on their sex. But for over a century, zoologists misplaced the most scientifically significant gray seal of all time.

To be fair, the gray seal in question wasn't an entire animal — just a skull. But that skull is the piece of bone that was used to define what a gray seal is. You see, for every species — living or extinct — scientists have to designate a holotype. This is the specimen from which the initial description of the species is made. It doesn't have to be the most complete, perfect or exceptional representative. It just has to be first.

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In the case of the grey seal, however, the story is more complicated. Way back in 1791, before scientists were in the habit of carefully storing and caring for holotype specimens, the Danish missionary and naturalist Otto Fabricius presented a description of what he thought was a previously unknown seal from the coast of Denmark. He named the species Phoca grypus, or the hook-snouted seal.

Confusion quickly set in.

Other naturalists dumped Fabricius's name for the title Halichoerus grypus — the hook-snouted salt-pig — and no one was quite certain where the actual name-bearing specimen ended up. Errors in translation, misquotations and assumptions mangled the history of this creature for decades.

(NOAA's Historic Fisheries Collection)

For example, even though Fabricius stated that his special seal had come from the shores of Denmark, the fact that he named it in a book called "Detailed Description of the Seals of Greenland" led some skim-reading experts to believe that the original specimen had come from that icy island instead. With so much confusion, zoologists pretty much gave up on puzzling out the seal's true history. No one could say for sure where Fabricius's specimen came from or where it wound up.

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But now University of Copenhagen geneticist Morten Olsen and colleagues have solved the mystery. Fabricius's original gray seal had been hiding in the collections of the Natural History Museum of Denmark this whole time.

(Olsen et al. 2016, Wiley)

Through old labels, museum documents and anatomical comparisons, Olsen and his co-authors were able to determine that the yellowed skull marked M1525 is the same that Fabricius illustrated over two centuries ago. More than that, the researchers analyzed the genetic makeup of the skull to narrow down what population of gray seals it might have belonged to. The results placed Fabricius's seal in the Baltic Sea, just as the 18th-century naturalist had said.

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This is about more than tracking down a lost title-holder, however. Conservation hinges upon proper labeling. Species, subspecies and populations are all designated and tracked. In this case, Olsen and his co-authors said, the realization that Fabricius's seal came from the Baltic Sea places it in one subspecies — distinct from the Atlantic subspecies — while sinking a third possible subspecies that had been bobbing around. Names such as Halichoerus grypus grypus — the subspecies so nice they named it twice — might sound like technical jargon, but these titles hold great power as naturalists try to understand and save life on Earth. Without them, scientists have no idea how many distinct genetic populations we stand to lose as regional groups of animals disappear.

Brian Switek is a freelance science writer and the author of "My Beloved Brontosaurus." For more, read his Scientific American blog and follow him on Twitter or Instagram

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