This ‘ghost shark’ has teeth on its forehead
Until now, scientists thought vertebrate teeth occurred exclusively in the mouth
Between the eyes of this spotted ratfish lies a retractable tooth-tipped structure used during mating.
K.E. Cohen et al/PNAS 2025
Some male “ghost sharks” have a bizarre way of giving love bites: They use teeth that sprout from their foreheads.
These otherworldly animals, also known as spotted ratfish, can grab onto mates using teeth that project from a finger of flesh between their eyes. It’s an area where most scientists wouldn’t expect to find dental structures, says Karly Cohen, a biologist at the University of Washington Friday Harbor Laboratories.
Unlike the teeth of other animals, which protrude from the jaw, ratfish teeth curve like cat claws from this odd forehead structure, called a tenaculum, Cohen’s team reports September 4 in the Proceedings of the National Academy of Sciences. “It’s pretty phenomenal to find true teeth outside of the mouth,” Cohen says. Her team’s discovery, in fact, is the first such example. Until now, scientists thought vertebrates’ teeth were exclusively oral.
Spotted ratfish (Hydrolagus colliei) have long intrigued researchers. The animals, classified as chimaeriformes, drift through the water on large, winglike fins, giving them a ghostly presence, Cohen says. Unlike their shark relatives, they lack regular rows of serrated teeth. They’re also slick and shimmery, without the rough sandpaper-like skin typical of sharks. Even weirder is the spike-tipped structure protruding from their forehead.
Scientists thought the spikes were an evolutionary remnant from an earlier ancestor — sandpaper skin gone strange. But Cohen’s work suggests that the spikes are actually teeth. “It’s kind of a crazy notion,” she says. 3-D imaging of ratfish, both young and old, indicate that the spikes develop from tissue called the dental lamina, like true teeth typically do, and the spike tissue shows activity of tooth-related genes.
Fossil evidence suggests that there’s precedent for such oddly located teeth: An ancient ratfish relative had similar toothlike forehead structures, the team reports.
It’s possible that ratfish teeth escaped identification for so long because these deep-sea dwellers can be hard to find. But they do rise from the depths — of up to about 1,000 meters — to breed in the shallow waters of Puget Sound in Washington, giving scientists an opportunity to study the eerie animals.
Cohen thinks there may be even more animals with teeth in unusual places. After all, the ocean is vast. If scientists are open to the idea of teeth outside the mouth, she says, “the more we look, the more we will find them.”
