It looked like a marine mystery creature. Even dead, washed up on some rocks by the shore, it appeared impressive, almost other-worldly: a whale’s hulking body, covered in sleek purple-black skin, paired with a dolphin-like slender snout.

Indeed, the animal that came ashore at a Plymouth, Mass., beach on Friday is so rarely seen that biologists still aren’t quite sure what it is. Officials at the New England Aquarium have tentatively identified it as a Sowerby’s beaked whale — a little-understood species that dwells in the deep waters of the North Atlantic and almost never comes to shore.

“They live in a world of their own,” aquarium spokesman Tony La­Casse told the Boston Herald. “… They’re very, very rare. It’s definitely one of those things you’re not quite sure what to make of it.”

The 17-foot, one ton carcass that was found on shore Friday belonged to a female whale. It’s been so long since a whale of this type has been seen in Massachusetts that “everybody was kind of scratching their heads,” Plymouth harbormaster Chad Hunter told the Boston Globe. Deep-sea whales like the Sowerby’s rarely come so close to shore — as LeCasse put it, the creature had “no business” in the shallow waters of Cape Cod Bay. And the fact that these creatures are so strange looking made for even more of a spectacle.

Though the body was reported around 10 a.m., it had been stranded on the rocky shore as the tide receded, so there was no way to remove move it until high tide returned about 7 hours later. The body was “fairly fresh” when it arrived at the aquarium, LaCasse said, and it’s not clear what killed the creature. Aquarium staff found no obvious signs that she had become entangled in fishing gear or been struck by a ship, and biologists at the Woods Hole Oceanographic Institute are working on a necropsy to figure out what exactly happened, according to CNN.

There are nearly two dozen species of beaked whale — a family named for their pointed, dolphin-like noses and known for their elusiveness. Though sightings of Sowerby’s whales have been recorded since the early 19th century, several of their cousins have only been identified in the past few decades.

Beaked whales are some of nature’s most extreme divers, the hardiest among them capable of plunging to nearly 10,000 feet below the surface in search of a meal. No other mammal has reached anywhere near those depths. Even the less deep-diving species regularly roam several thousand feet below the waves.

Studying these species is notoriously difficult, marine mammal biologist Randall Davis told National Geographic last year. Though they range throughout the deep, chilly waters below Greenland and between Canada to Northern Europe, they spend much of their time at depth and don’t tend to approach boats voluntarily, as dolphins do. Data on the animals is so sparse that the National Oceanographic Institute has no official estimate of their population size, and several species of beaked whale are known only by carcasses that, like the female found on Friday, were discovered stranded on a shore somewhere.

That’s why the marine biology community is quick to pay attention when a beaked whale body does show up, LaCasse said. These specimens can help scientists better understand the elusive species.

“It’s a glimpse into a habitat that’s not so far away, but it’s still a world away,” he said.