The skull came from the Wando River, which today runs past Charleston, South Carolina to the ocean.

Thirty million years ago, it was all under the sea. Ancient dolphins and whales swam over what would become Charleston's cobblestone streets. For millions of years, megalodons also swam in this sea, leaving behind shark teeth bigger than your hand. And it was divers looking for megalodon teeth who initially found the fossilized skull, loose on the bottom of the Wando River.

The skull—unusually wide and unusually squat—made its way to a collector who gave it to the College of Charleston’s Mace Brown Museum of Natural History. By the time the paleontologist Robert Boessenecker came to it, he says “It was already known as something new and very strange.” It was definitely a cetacean, but like none they had ever seen before. Its snout was too short. Its body was likely only a few feet long. And it had no teeth, no tooth sockets even.

It’s hard to overstate just how weird cetaceans are as mammals. Modern whales, dolphins, and porpoises all descended from a wolf-sized creature that returned to the sea, losing its hind legs and most of its fur in the process. Their dental evolution is odd, too. Unlike most mammals, cetaceans do not chew. The ones with teeth grasp and tear like reptiles and then swallow the chunks whole. The ones with baleen filters feed on giant amounts of krill. And about 30 million years ago, there were apparently cetaceans like the one found in South Carolina, that had lost their teeth and ate by suction.

As Boessenecker and his colleagues measured the partial skull, they realized it is related to modern odontocetes, also known as toothed whales—a name that’s obviously a bit misleading. “It’s definitely a weird, weird toothed whale.” says John Gatesy, who studies cetaceans at the American Museum of Natural History and was not involved in the study. The team studying the South Carolina skull named it Inermorostrum xenops.