Teeth outside the jaw: Evolution and development of the toothed head clasper in chimaeras

What is it about?

The origin and evolution of teeth is a central theme in vertebrate biology, but most of what we know comes from teeth in the mouth. Far less attention has been given to teeth that arise in unusual places on the body. Chimaeras—also known as ghost sharks or ratfish—are deep-sea relatives of sharks and rays that provide an exceptional case. Male chimaeras grow a distinctive cartilaginous appendage on their heads, called the tenaculum, which is used during mating. This structure is covered in rows of tooth-like elements, yet their developmental origin and evolutionary history have remained largely unknown. Our findings show that the ratfish’s tenaculum teeth are not just skin structures but true teeth that grow from the same developmental pathways as those in the jaws. This discovery pushes the boundaries of what we thought was possible for tooth formation, showing that teeth can reappear in surprising places on the body. It reveals a hidden flexibility in how vertebrates build and evolve their skeletons, giving us a rare glimpse into evolutionary “tinkering” at work.

Featured Image

Why is it important?

We uncover how teeth can arise outside the mouth by studying the unusual head appendage of male ghost sharks. This is important because it shows that tooth-forming ability is not confined to the jaws but can be reactivated in new parts of the body. We find that the tenaculum produces true teeth through the same developmental pathway as oral teeth, and that this unique dentition retains replacement cycles that have been lost in the jaws of modern chimaeras. Together these findings reveal an unexpected flexibility in how vertebrates build and maintain teeth, offering new insight into the evolution of craniofacial diversity.

Perspectives