Overview

• The PNAS study combined micro-CT scans, tissue histology and gene-expression assays to confirm the tenaculum bears true teeth rather than dermal denticles.
• Adult males use seven to eight rows of hooked, retractable teeth on the tenaculum to grip a female’s pectoral fin during mating.
• Developmental scans show both sexes begin forming a tenaculum, but only males complete a mineralized, toothed structure while females retain a small non-mineralizing remnant.
• Tooth-like elements on the pelvic claspers lacked tooth gene signatures, indicating those spikes are denticles and not true teeth.
• Comparisons with fossils, including Helodus simplex, suggest an evolutionary co-option of tooth-development programs and open questions about how widespread extraoral teeth may be.