On Aug. 10, 1741, explorer Georg Wilhelm Steller reported spotting “a very unusual and new animal” in the waters off southern Alaska. It was about 5 feet long, he said, with the head of a dog and the tail of a shark, and was covered with gray hair. It had long whiskers, large eyes, and erect ears. When it rose out the water to observe his ship, Steller saw that it had no flippers.

For two hours Steller and the animal watched each other. It passed some 30 times under the ship, he said, apparently in order to view it from both sides. At one point it juggled a bit of kelp in its mouth, occasionally biting off and swallowing pieces. An assistant finally shot at it twice with a musket, missing both times, and the animal disappeared.

In 250 years, no one has ever seen another “sea ape.” The consensus among biologists is that Steller saw a young northern fur seal, but he had observed these creatures on the same voyage and presumably would have recognized one. So what was it?