It’s fascinating to think that teeth can develop outside of mouths. A recent study reveals that the spotted ratfish, often called “ghost sharks,” grows teeth in a surprising place: on a structure called the tenaculum, located on its forehead.
Adult male spotted ratfish use this unique appendage to grip their mates during reproduction. Researcher Karly Cohen from the University of Washington describes this finding as revolutionary. She notes it challenges the long-held belief that teeth are only found in mouths. “This is the first clear example of teeth developing outside the jaw,” she explains.
The study, published in the Proceedings of the National Academy of Sciences, shows that these forehead teeth form from the same tissue that creates oral teeth. This suggests that, early in evolution, tooth-forming cells might have migrated away from the mouth.
What is a Spotted Ratfish?
Spotted ratfish belong to an ancient group called chimaeras, which diverged from sharks millions of years ago. These fish typically reach about two feet in length and have long, slender tails. Only adult males develop the tenaculum, a white, barbed structure that catches the attention of a mate. Cohen likens it to a tool for underwater mating, saying, “Sharks don’t have arms, but they still need to connect with a mate.”
To investigate the tenaculum’s origins, researchers caught hundreds of ratfish near San Juan Island in Puget Sound. They employed advanced techniques like micro-CT scans to analyze the structure’s development. Interestingly, both male and female ratfish begin to grow a tenaculum early on, but it only fully develops in males.
Cohen expressed the thrill of discovering dental tissue in an unexpected place. “When we first saw the dental lamina, we were amazed. It’s usually found only in the mouth,” she shared.
The Bigger Picture
Experts like Michael Coates, a professor at the University of Chicago, emphasize the importance of this discovery. He points out that it highlights how these fish creatively repurposed a pre-existing process for forming teeth, making it essential for reproduction. “This shows the diversity of dental structures throughout history,” adds Gareth Fraser from the University of Florida.
This discovery prompts a broader question about tooth development in vertebrates. What other surprising structures might have teeth? Cohen is optimistic: “The more we study vertebrates, the more we may find teeth in unusual locations.”
In a time when scientists are increasingly looking back at evolutionary history, this research sheds light on how creatures adapt in surprising ways. Understanding the unique biology of the spotted ratfish can give us deeper insights into developmental processes and evolutionary strategies.
To read more about this intriguing study, visit the Proceedings of the National Academy of Sciences.
