UW scientists discover teeth growing on forehead of deep-sea fish

To say spotted ratfish are unusual is an understatement. Related to sharks, they abound in the inky, dark depths of the Puget Sound. Armed with a venomous fin, they swim gracefully  along the sea floor trailing a long, pointed tail half the length of their bodies, with green, glowing eyes hunting for mates or prey to crack open with their beak-like mouths. And if all that wasn’t weird enough, they are now the first animal documented to have teeth growing outside of the jaw, according to new research led by a team of scientists at the University of Washington. 

Scientists have known for some time that male spotted ratfish have a club-like, barbed structure between their foreheads they use during mating to grasp females and intimidate reproductive rivals. But they didn’t know if the sharp barbs that ring this structure were actually teeth or denticles, tiny, rough projections that cover sharks’ skin. So they caught hundreds of specimens to study them at various stages of development, from embryos to adulthood and used 3D X-ray imaging to solve this mystery. 

Karly Cohen is a post-doctoral researcher at Friday Harbor Labs at the University of Washington and lead author of the recently published paper documenting this research. She joins us to share her findings and how they might expand our understanding of the evolution of teeth, and their purpose, to not only feed but to mate.