On a remote island in Disko Bay, Greenland, a scientist in 1990 was collecting specimens of narwhals, the whales with unicorn-like tusks. He noticed an unusual skull on a hunter’s roof.

The teeth were bizarre: The top ones pointed forward. A couple spiraled out. They looked like a mix of narwhal and beluga, but with too many for a narwhal, too few for a beluga.

The hunter told the scientist that the skull had belonged to a strange animal he’d killed in the late 1980s. He had also killed two other similarly strange whales the same day. All had beluga-like flippers, narwhal-like tails and solid gray skin, he said.

Mads Peter Heide-Jørgensen, the narwhal scientist, convinced the hunter to donate it to the Natural History Museum of Denmark for analysis. But at the time, he could only conclude it was a possible hybrid or deformed beluga.