The histology of tooth formation in the Australian lungfish, Neoceratodus forsteri Krefft

The histology of developing toothplates of Neoceratodus forsteri from the time of first appearance of the tooth primordia to the adult condition has been investigated. The dentition develops by the formation of a shell of primary epithelial and mesenchymal matrices. Within the shell, secondary mesenchymal matrix and central material, both containing columns of tertiary matrix, are laid down. Primary epidielial matrix appears to contain collagen and is closely associated with the epithelium of the mouth. All other tooth tissues as well as the supporting bone develop in association with mesenchyme. Primary, secondary and tertiary mesenchymal matrices appear to contain collagen. Central dentine contains some fibres, possibly of reticulin or collagen, within a matrix of unknown composition. The tooth is attached to the underlying bone by a pedestal of bone and this grows with the tooth material. New tooth tissues are formed in the pulp cavity in layers below the older material, causing the toothplate to grow in every dimension as the animal grows. An evolutionary pathway is suggested for lungfish with a dentition of cusps arranged in radiating ridges.