The distribution and significance of enamel and enameloid in the dermal skeleton of osteolepiform rhipidistian fishes

Abstract

Teeth and other dermal skeletal elements from three osteolepid and two eusthenopterid rhipidistians were examined with the scanning electron microscope to establish whether the hypermineralized outer layer was enameloid or enamel. Using Smith's (1978) morphological criteria to infer the developmental history of enamel and enameloid, enamel was found in the teeth and dermal bones of the osteolepids, whereas enameloid was identified in scales. Hyneria and Eusthenopteron teeth also had enamel. As enamel has also been found in teeth of living lungfishes and extant Latimeria, the presence of enamel in tetrapod teeth represents a primitive character retained from a lobe-finned ancestor and is not useful for phylogenetic studies within the lobe-finned/tetrapod group. Shellis and Miles' (1974) hypothesis that the transition from enameloid to enamel occurred via a fairly simple regulatory change is discussed.