In the vast ocean, mating can be a tricky affair for slippery, limbless fish. However, the ratfish has a clever strategy. The male ratfish possesses a distinct club-shaped organ on its forehead called a tenaculum, which it utilizes to grasp onto the female’s pectoral fin during mating.
Previously, scientists believed these organs were covered in hard, spiny scales similar to those found on sharks and rays. Recent research contradicts this assumption. According to marine biologist Karly Cohen from the University of Washington, the structures are actually teeth, akin to those found in human and animal mouths.
Published in the Proceedings of the National Academy of Sciences, the findings shed new light on deep-sea creatures, challenging the long-standing notion in evolutionary biology that teeth only develop in mouths. Cohen emphasized the significance of this discovery, showcasing the adaptability of vertebrates and animals in expressing fundamental traits like teeth in unique ways.
Ratfish, which can grow up to 60 centimeters in length, are denizens of the deep sea belonging to the chimaera group of cartilaginous fish, diverging from sharks approximately two million years ago. Often referred to as ghost sharks or spookfish due to their iridescent bodies and luminous green-glowing eyes, these creatures captivate observers with their beauty.
To investigate further, Cohen and her team studied spotted ratfish, a species abundant in Puget Sound off Washington state’s coast, conducting observations in the wild and analyzing 40 specimens using micro-CT scans. Within the tenaculum, they uncovered rows of shark-like teeth set in a band of tissue called the dental lamina, a discovery previously unseen outside of animal jaws. Genetic analysis of the tenaculum tissue revealed genes associated with vertebrate teeth formation.
Paleontologist Aaron LeBlanc from King’s College London, specializing in tooth evolution, expressed astonishment at the findings. Initially skeptical, he acknowledged the researchers’ thorough documentation, confirming that the teeth within the tenaculum developed similarly to conventional teeth.
Despite these revelations, mysteries remain surrounding the evolutionary purpose of the ratfish’s forehead teeth. The study examined fossil records of Helodus simplex, a prehistoric chimaera with a similar appendage, and identified juvenile males and females of the spotted ratfish possessing comparable structures, hinting at unresolved questions regarding their function and evolution.
Marine biologist Milton Love from the University of California’s Marine Science Institute in Santa Barbara remarked on the endearing nature of the ratfish’s behavior, noting parallels with mating habits observed in certain shark species. Such discoveries underscore the marvels of nature and the endless possibilities for exploration in understanding these fascinating marine creatures.
