A histological and histochemical study of developing teeth in Polypterus (Pisces, Actinopterygii)

The tooth cap matrix contained proteins of ectodermal and mesodermal origin which extended the data already available on teleost teeth and showed that a combined origin for the tooth cap should be regarded as a primitive feature of actinopterygian fish. Furthermore, the dual nature of the Polypterus tooth cap matrix suggested that evolution of tetrapod enamel did not occur within the actinopterygians. The collar tissue was an unmodified dentine, in contrast to its enameloid nature in many other actinopterygian teeth. The presence of a range of developmental states from unmodified dentine to hypermineralized enameloid within Polypterus teeth themselves and also in other parts of the dermal skeleton, as well as the combined origin of the tooth cap, demonstrates that the enamel/enameloid/dentine system forms a continuum of tissues that have diverged from one another by changes in the relative timing of developmental events and matrix production.