Teeth between the eyes: Extra-oral dentition in chimaeras as evidence for biological codes

The recent discovery of functional dentition on the cranial tenaculum of male Hydrolagus colliei (spotted ratfish), published in a 2025 issue of the Proceedings of the National Academy of Sciences, provides a compelling empirical example for the theory of biological codes. Described as a reversal of the long-standing assumption that teeth are exclusively oral structures, this case demonstrates how codified developmental programs can be reused in novel anatomical and functional contexts.

This paper explores how the appearance of extra-oral teeth illustrates the triadic structure of code, mediator, and artifact as proposed by Code Biology. Drawing on Barbieri's framework and recent research bridging biological, neural, and symbolic systems, the study argues that biological meaning arises through arbitrary yet functional correspondences, activated and modulated by developmentally regulated mediators, leading to adaptive morphological innovations.

The framework presented is not merely metaphorical; it is empirically grounded, conceptually robust, and testable — offering a powerful explanation not only for evolutionary novelty but also for how structured meaning arises in living, cognitive, and cultural systems. By tracing how biological codes give rise to artifacts of both functional and formal relevance, this case contributes to a broader theoretical model that connects morphogenesis, neural semiosis, and archetypal patterns within a unified semiotic view of life.