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In the late 1800s, famed explorer Robert Edwin Peary — the man credited with leading the first expedition to reach the North Pole — returned from his Arctic excursion with a unique souvenir: the long, sword-like tusk of a narwhal.

The narwhal’s spiral tusk, which is actually an enlarged tooth that protrudes from the whale’s head, eventually made its way to a museum in Philadelphia. But more than 40 years ago, the tusk disappeared from the institution’s collections.

The tusk was not heard of again until FBI special agent Randolph Deaton came across a peculiar clue last year.

Deaton, who works in the FBI’s New Orleans division and is a member of the bureau’s Art Crime Team, was investigating an unrelated case when he found a deposition in a civil suit that referenced the missing tusk.

“This person mentioned the museum he worked for, and that someone associated with the institution had stolen a narwhal tusk that was part of the museum’s collection,” Deaton said, refusing to divulge the name of the museum where it was taken from in order to not compromise the investigation. He also added that the artifact’s disappearance had not been reported to law enforcement when it happened.

Now, Deaton is hoping that by spreading the word to the public, and especially within museum associations, he’ll be able to locate the missing tusk. Part of his motivation is to keep the tusk off the black market, where smugglers traffic ivory, fossils and other priceless artifacts.

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Narwhals are among the most beloved of sea creatures, earning the charismatic nickname “unicorn of the sea” because of their distinctive head adornment. Throughout history, narwhals have been closely linked to the supernatural, with centuries-old European beliefs that these mysterious Arctic creatures are mystical animals and their ivory tusks hold magical healing properties.

After Peary returned from the Arctic expedition with the tusk, Deaton said, the explorer gifted the artifact to Rear Admiral George Wallace Melville, a naval engineer and fellow Arctic explorer. Melville eventually donated the tusk to the Philadelphia museum, where it went missing sometime before 1980.

Deaton said the narwhal tusk may have been sold in or around 1981 in a private estate auction, and it’s not known if the tusk is currently in a museum or a private collection.

There is no photo of the tusk available, but Deaton said it has a metal plate that will help him confirm the identity of the object.

“The inscription on the metal plate is so unique, it’s almost like a serial number,” he said.

Deaton said he’s not sure if the missing tusk will ever be found, but he hopes it is because of the artifact’s historical value.

Last year, a deadly knife attack on London Bridge was stopped when a fearless chef wielded a narwhal tusk — allegedly the closest weapon he could find as he rushed to the scene of the crime — to overpower the assailant. The bizarre episode added further intrigue to the narwhal’s fabled reputation.

Deaton said he was driven to open a case into the missing narwhal tusk because of its unique provenance and because of its ties to the heyday of Arctic exploration.

“It ticks all the boxes of Americana,” he said. “It’s more than worthy of the FBI’s effort to try to locate it.”

If you have information about this case, Deaton can be reached at the FBI’s New Orleans division at 504-816-3000.