Overview

• Researchers report that male chimaeras (spotted ratfish) grow real rows of teeth on a forehead appendage known as the tenaculum, outside the mouth.
• Genetic tests show the appendage activates tooth‑specific genes and is built on a dental lamina, distinguishing the teeth from dermal denticles.
• CT scans of modern specimens and a 315‑million‑year‑old fossil reveal a long evolutionary history for the toothed tenaculum attached near the upper jaw.
• The structure occurs only in males and is likely used to grasp females during mating, with adults producing seven or eight rows of retractable, hooked teeth.
• The multidisciplinary study from the University of Florida, University of Washington and University of Chicago was published Sept. 4 in Proceedings of the National Academy of Sciences, with authors calling it the first clear vertebrate example of teeth forming outside the jaw.