Developmental plasticity and disparity in early dipnoan (lungfish) dentitions.

Although the lungfish (Dipnoi) belong within the Osteichthyes, their dentitions are radically different from other osteichthyans. Lungfish dentitions also show a uniquely high structural disparity during the early evolution of the group, partly owing to the independent variation of odontogenic and odontoclastic processes that are tightly and stereotypically coordinated in other osteichthyans. We present a phylogenetic analysis of early lungfishes incorporating a novel approach to coding these process characters in preference to the resultant adult dental morphology. The results only partially resolve the interrelationships of Devonian dipnoans, but show that the widely discussed hypothesis of separate tooth-plated, dentine-plated, and denticulated lineages is unlikely to be true. The dipnoan status of Diabolepis is corroborated. Lungfish dentitions seem to have undergone extensive and nonparsimonious evolution during the early history of the group, but much of the resulting disparity can be explained by a modest number of evolutionary steps in the underlying developmental processes, those for dental formation (odontogenic) and those for the remodeling of dentine tissue (odontoclastic). Later in lungfish evolution, this disparity was lost as the group settled to a pattern of dental development that is just as stereotypic as, but completely different from, that of other osteichthyans.