Like many good mysteries, this one started with a corpse, but the body in question was 24 feet (7.3 meters) long.

The remains floated ashore in June of 2014, in the Pribilof Islands community of St. George, a tiny oasis of rock and grass in the middle of Alaska's Bering Sea. A young biology teacher spotted the carcass half-buried in sand on a desolate windswept beach. He alerted a former fur seal researcher who presumed, at first, that she knew what they'd found: a Baird's beaked whale, a large, gray, deep-diving creature that occasionally washes in dead with the tide.

But a closer examination later showed that the flesh was too dark, the dorsal fin too big and floppy. The animal was too short to be an adult, but its teeth were worn and yellowed with age.

View Images This whale washed up dead on Alaska's St. George Island in June 2014. Scientists say it is a newly discovered species of beaked whale. Photograph by Karin Holser

It turns out, according to new research published Tuesday, that this was not a Baird's beaked whale at all, but an entirely new species—a smaller, odd-shaped black cetacean that Japanese fishermen have long called karasu, or raven.

"We don't know how many there are, where they're typically found, anything," says Phillip Morin, a molecular geneticist at the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center. "But we're going to start looking."

It’s rare to uncover a new species of whale. Advances in DNA research have helped scientists identify five new cetaceans in the past 15 years but two were dolphins and most were simple category splits between fairly similar species. This animal, in the genus Berardius, looks far different than its nearest relative and inhabits an area of the North Pacific where marine mammal research has been conducted for decades.

"It's a really big deal," says study co-author Paul Wade of NOAA's National Marine Mammal Laboratory. "If you think about it, on land, discovery of new species of large mammals is exceptionally rare. It just doesn't happen very often. It's quite remarkable."

Skeletons, Beaks, and Bone Powder

Morin and his team examined the St. George carcass, took bone powder from old museum specimens, and reviewed DNA tests of whales from the Sea of Okhotsk. They studied skulls and beaks and analyzed records from whaling fleets in Japan. They even tracked down a skeleton hanging from the ceiling in a high school gymnasium in the Aleutian Islands.

The scientists conclude in their study published in Marine Mammal Science that this type of whale, which has not yet been named, is nearly as far removed genetically from the Northern Hemisphere's Baird's beaked whales as it is from its closest known relative, Arnoux's beaked whales, which swim in the Antarctic Ocean. The differences, in fact, are so dramatic that the animal has to be something else, they say.

"It's just so exciting to think that in 2016 we're still discovering things in our world—even mammals that are more than 20 feet long," Morin says.

View Images This skull of a newly discovered species of whale shows its blowhole vestibule and its nasal and frontal bones. Photograph by L. Michelle Ridgway

He is not alone in his enthusiasm. Robert Pitman serves on a taxonomy committee for the Society for Marine Mammalogy, which publishes an annual list of all recognized marine mammal species. He is not among the 16 co-authors on Morin's paper. But at a time when the diversity of marine mammals is shrinking—the Yangtze River dolphin is now functionally extinct and Mexico’s vaquita porpoise is dangerously close—Pitman calls the discovery "heartening."

"It boggles my mind to think that a large, very different-looking whale has gone unnoticed by the scientific community for so long," Pitman says. "It sends a clear message about how little we know about what is in the ocean around us."

The discovery also raises new questions about how well humans are understanding the threats posed by marine activities, from energy exploration to sonar use, given that so few people even knew such a creature existed.

An Unrecognizable, Baffling Creature

Of the 88 recognized living cetacean species, including orcas and humpbacks, bottlenose dolphins and Dall's porpoises, 22 are beaked whales. The largest of those, Baird's beaked whales, also called giant bottlenose whales, can reach 35 to 40 feet (10.7 to 12 meters) and weigh more than 24,000 pounds (10,900 kilograms). They travel in large groups, may dive 3,000 feet (914 meters), and can be underwater for an hour. While beaked whales are still hunted in Japan, little about them is known. In part that’s because they spend so much time feeding and exploring vast, deep canyons far from shore.

When Christian Hagenlocher on St. George, a 35-square-mile (91-square-kilometer) island inhabited by 100 people, frequented by hundreds of thousands of seals, and visited by 2.5 million birds, pointed out the dead whale in Zapadni Bay to former seal researcher Karin Holser, she thought it was a Baird's beaked whale. But later, as tides and currents revealed more of the animal, Holser realized she didn't recognize it at all. She consulted a colleague's cetacean identification book and sent pictures to other experts in Alaska.

View Images This skull provided scientists evidence that the whale was smaller and had different bone structure than other beaked whales. Photograph by L. Michelle Ridgway

"This dorsal fin was larger, further aft, and had more curvature than that of a Baird's beaked whale," says independent ecologist Michelle Ridgway, who arrived on the island days later. "The jaw structure and the shape of the melon were not quite right, either.” And this whale, while clearly an adult, was just two-thirds the size of full-grown Baird’s beaked whales.

Holser and other island residents measured the whale. Ridgway collected tissue, arranging to ship the slightly fetid samples through intermediaries to Morin's lab in Southern California.

Morin was intrigued.

So Mysterious It's 'Almost Folklore'

Just nine months earlier, he'd spied new research by Japanese scientists attempting to describe differences between Baird's beaked whales and a rare black form that whalers had whispered about since the 1940s. Groups of these smaller whales were sometime spotted in Japan’s Nemuro Strait, but only between April and June. There was no record of scientists ever seeing one alive.

"They're almost folklore," Morin says.

The Japanese scientists had speculated in fall of 2013 that this may be an unknown species of beaked whale. But they were forced to draw conclusions from DNA taken from just three of the creatures that had stranded off Hokkaido. They concluded more evidence was needed.

Even before receiving the samples from St. George, Morin had been trying to hunt down more specimens.

He went through NOAA's tissue collection, pulling all 50 or so that had previously been identified as a Baird's beaked whale. Using DNA testing he found that two were actually a closer genetic match to the small black whales tested by Japanese scientists in 2013. One of those was from a whale that washed ashore in 2004 and now hangs in a school gym in Dutch Harbor. Scientists there had long assumed it was a younger Baird's beaked whale.

Morin also took the suggestion of one of the Japanese scientists, who had identified a skeleton from 1948 with an unusual shaped head at the Smithsonian Institution. And he tracked down another skeleton from the Los Angeles County Museum of Natural History with body measurements that suggested they were the small black form. Morin took bone powder from both, and tested their DNA. They, too, were a match for karasu.

Along with the whale from St. George, Morin now had found five new specimens that were similar to the three found in Japan.

To describe a new species, however, "you build up lines of evidence, but that's very hard with an animal we've never seen alive," Morin says. But body measurements between Baird's beaked whales and the smaller black creature proved vastly different, as did their DNA.

Baird's beaked whales range throughout the North Pacific from Russia and Japan to Mexico. Genetic variation among Baird’s beaked whales was tiny. But for the five new black specimens Morin tested, all initially from the Bering Sea or the Aleutians, the sequences differed from the Baird's beaked whales significantly.

"The genetic variation within the forms was little, while the divergence between them was much larger," Morin says. "That's our strongest argument."

The whale still needs to be formally described and named, and Morin's findings would have to be accepted by outside experts who track cetacean taxonomy. But Pitman and others say the case is strong that it’s a new species.

"We're doing increasing damage to our environment, and we can't even begin to conserve the biodiversity we know is out there," Morin says. "Yet there's so much more about our world we don't even understand."