Hard tissues in fish evolution: history and current issues
A short survey of the distribution of scale characters in osteichthyans is mapped onto recently published cladograms of gnathostomes. The recently confirmed relationship of polypterids with scanilepids places their early ontogenetic features as advanced features within palaeonisciform actinopterygians. The pore-canal system (which seems to hold nerves for sensing water pressure changes) of cosmoid scales appears as a singular feature of dipnoans and rhipidistians without connection to the rich vascular system in basal osteichthyans. Elasmoid scales appear many times independently within actinopterygians and sarcopterygians. Elasmodine is a homoplastic feature in osteichthyans, it is a new formation in neopterygian elasmoid scales, supposedly even here twice independently derived in teleosts and halecomorphs.