Male Ghost Sharks Develop Forehead Teeth for Mating, Study Finds

Research has unveiled that male ghost sharks, a unique group of deep-sea fish related to sharks and rays, possess a surprising adaptation for reproduction: a specialized structure called a tenaculum, which features sharp, retractable teeth. This discovery, published in the *Proceedings of the National Academy of Sciences*, suggests that these teeth, which protrude from the forehead, play a crucial role in mating.

The study, led by a team from the University of Florida, includes contributions from scientists at the University of Washington and the University of Chicago. They investigated both fossils and living specimens to understand the evolutionary significance of this peculiar anatomical feature. The tenaculum is the only source of distinct teeth in male ghost sharks, functioning similarly to how sharks use their mouths to grasp females during mating.

Gareth Fraser, a professor of biology at the University of Florida and the senior author of the study, emphasized the implications of this finding, stating, “If these strange chimaeras are sticking teeth on the front of their head, it makes you think about the dynamism of tooth development more generally.” The research team found that the tenaculum likely evolved from a pre-existing structure that originally served a different purpose.

The investigation included analysis of a 315-million-year-old fossil, which demonstrated that the tenaculum was once attached to the upper jaw and bore teeth remarkably similar to those found in the mouth of modern sharks. Additionally, contemporary ghost sharks collected from Puget Sound showed a similar tooth development pattern on their heads, indicating a lineage that has preserved this unique trait.

Genetic testing revealed that the tenaculum teeth express the same tooth-specific genes as oral teeth, providing further evidence of their evolutionary origins. Fraser noted, “What we found is that the teeth on this strange appendage look very much like rows of shark teeth. The ability to make teeth transferred onto that appendage, likely from the mouth.”

The collaborative effort among experts, including Karly Cohen from the University of Washington and Michael Coates from the University of Chicago, shed light on the central question of whether the tenaculum teeth are true teeth related to oral teeth or more akin to the tooth-like scales found on sharks. Using CT scans of both fossils and living chimaeras, the team gained unprecedented insights into the development of these teeth.

The genetic evidence was particularly compelling, confirming that the tenaculum teeth are distinct from the skin denticles found on sharks, which do not share the same genetic markers. Cohen, the first author of the paper, remarked, “The tenaculum is a developmental relic, not a bizarre one-off, and the first clear example of a toothed structure outside the jaw.”

This research highlights the remarkable adaptability of evolutionary processes, illustrating how structures can be repurposed for new functions. Fraser concluded, “There are still plenty of surprises down in the ocean depths that we have yet to uncover.” The study not only enhances our understanding of ghost sharks but also opens doors to further exploration of evolutionary biology and developmental processes in marine life.

For more detailed findings, refer to the study by Cohen et al. in the *Proceedings of the National Academy of Sciences* (2025).