Scientists Discover Teeth Growing on Fish Head in Germany
Researchers at the University of Washington have identified teeth growing on the head of the spotted ratfish (Hydrolagus colliei), a cartilaginous fish related to sharks. This finding, published in the journal Proceedings of the National Academy of Sciences, sheds light on the origins and development of teeth in vertebrates.
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The Spotted Ratfish and the Tenaculum
The spotted ratfish, a common inhabitant of the northeastern Pacific Ocean including Puget Sound, belongs to the chimaera group, which diverged from sharks millions of years ago. Adult males of this species develop a unique appendage on their forehead called a tenaculum. This structure, which resembles a small nub when at rest, can be raised to reveal a hooked, barbed organ covered in teeth.
The tenaculum serves a purpose for male ratfish. They use it for display, raising it to ward off rivals. During mating, the males use the tenaculum to grip females by the pectoral fin, ensuring a secure connection during underwater reproduction. This grasping mechanism is particularly crucial for cartilaginous fish, like sharks and ratfish, which lack limbs for mating.
Challenging the Oral-Centric View of Tooth Evolution
For years, the prevailing understanding in evolutionary biology has been that teeth are strictly oral structures. This assumption stemmed from the fact that teeth, regardless of their size, shape, or sharpness, typically share the same genetic roots, similar physical makeup, and are almost always located in the jaw. The discovery of teeth on the tenaculum of the spotted ratfish contradicts this established view.
Karly Cohen, a postdoctoral researcher at the University of Washington’s Friday Harbor Labs, emphasized the significance of this finding, stating that the tenaculum represents “the first clear example of a toothed structure outside the jaw.” This discovery prompts a reevaluation of the factors that drive tooth development and the potential for teeth to evolve in unexpected locations.
Genetic Origins and Evolutionary Implications
To determine the nature of the teeth on the tenaculum, the researchers conducted micro-CT scans and tissue samples from hundreds of fish, comparing modern ratfish to ancestral fossils. These analyses revealed that the teeth on the tenaculum share the same genetic origins as oral teeth. This finding suggests that the cells responsible for tooth formation may have migrated to the forehead during development.
The research team considered two possibilities: that the “teeth” were simply modified denticles (tooth-like scales found on the skin of sharks) or that they were genuine teeth. The genetic evidence supports the latter, indicating that the tenaculum teeth are not just modified skin structures but true teeth that have evolved in an unusual location. The absence of denticles on most of the ratfish’s body further supports the idea that the tenaculum teeth may represent evolutionary remnants of these structures.
Future Research and Broader Implications
This discovery opens up new avenues for research into the evolution of teeth and other vertebrate structures. Scientists are now exploring how widespread such features might be in other species and what these structures reveal about the history of vertebrate dentition. Understanding the genetic and developmental mechanisms that allow teeth to form in non-oral locations could provide insights into the plasticity of vertebrate development and the potential for evolutionary innovation.
The spotted ratfish, once considered a relatively unremarkable species, has now become a model for understanding the complexities of tooth evolution. Its unique tenaculum and the teeth that adorn it offer a glimpse into the diverse ways in which life has adapted and evolved over millions of years.
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before making health decisions.
Sources: Information based on credible sources and industry analysis.
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