A team of University of Washington scientists has discovered that spotted ratfish are the first known animal to grow teeth outside of the jaw.
The research, published Sept. 4 in Proceedings of the National Academy of Sciences (PNAS), overturns earlier assumptions that the male spotted ratfish’s club-like, barbed structure between its eyes was used to grasp females or fend off rivals during mating.
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The sharp barbs circling this structure were revealed instead to be teeth — or denticles, the same rough projections that cover sharks’ skin.
“The process of tooth development and emergence is highly conserved across gnathostomes (jawed vertebrates), but the chimaeras present the first example of a dental lamina outside of the jaw and offer expanded insights into the possibilities of gnathostome dental diversity,” the authors wrote in the study.
Lead author Karly Cohen, a post-doctoral researcher at UW’s Friday Harbor Laboratories, and her team examined hundreds of ratfish specimens, from embryos to adults. Using 3D X-ray imaging, they found that the forehead appendage grows from the same dental lamina that produces oral teeth — making it, in effect, a “forehead tooth organ.”
The spotted ratfish, Hydrolagus colliei, is a cartilaginous fish related to sharks and rays, found in deep waters off the Pacific Coast. This finding provides a rare glimpse into evolutionary pathways of vertebrate teeth and raises new questions about the diversity of dental development across species.