Microstructural features of dipnoan tooth enamel.

Tooth plates of extant lungfishes were examined by contact microradiography, light microscopy and TEM, to elucidate the nature and origin of the hypermineralized surface layer. TEM indicated that the matrix of this layer consisted of organic filamentous material, and no collagen fibres were seen in the matrix. The matrix appeared to be secreted by oral epithelial cells of the inner fold surrounding the surface of the tooth plate, and deposited in the area between the cell membrane and basal lamina-like structure of these epithelial cells. Therefore, it is suggested that the hypermineralized surface layer of lungfish plates is enamel of ectodermal origin.