The plicidentine as an adaptation to the predation in living Osteichthyes? A review

Plicidentine is characterized by more or less regular folds of dentin which extend into the pulp cavity of the teeth. In certain cases, these simple folds can give rise to secondary folds which invade the entire pulp cavity as in many fossil sarcopterygian fishes, many fossil tetrapods (Labirinthodonts), the extant Varanidae, and lepisosteid actinopterygians. Recent studies have shown that several species of teleosts, belonging in particular to osteoglossiforms, characiforms, and lophiiforms (inter alia) also have teeth with plicidentine but limited to simple folds which do not invade the pulp cavity. This plicidentine, called simplexodont plicidentine (Meunier et al., 2013), is also found in coelacanths. When the simplexodont plicidentine is well developed, it can be recognized by its thin parallel ridges on the outer surface of the tooth base. Most often these teleosts are fish-eating species with caniniform teeth and fangs. If we take into account the wide distribution of plicidentine in the two lineages of Osteichthyes (sarcopterygians and actinopterygians), one can hypothesize that plicidentine presents a phylogenetic signal, with the simplexodont condition being the primitive state. Plicidentine originally had a functional significance, strengthening the attachment of teeth to jaw bones and other dentigerous bones, particularly in predators ichthyophagous species; its posterior evolution within the two lineages of sarcopterygians was very different.