The dentition ofDiabolepis speratusChang and Yu, with further consideration of its relationships and the primitive dipnoan dentition

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Abstract
The pterygoid plates and inner bones of the lower jaw of Diabolepis were further prepared and sections made of one dental plate to examine additional features of the dentition and to relate macrostructure to histology and growth. These observations confirm the position of Diabolepis within dipnoans. The growth pattern inferred from these observations is compatible with the general model for the growth of dipnoan tooth plates proposed by Smith (1988). New teeth are added from the anterolateral margin, the older posteromedial teeth are retained until worn flat, and the worn surface is repaired by new tissue forming as a blister superimposed on the old tissue. It is proposed that the dentition in Diabolepis is the most primitive for dipnoans. These primitive features include 1) paired dental plates consisting of radial rows of teeth that converge on the posteromedial corner, 2) radial tooth rows in which the teeth gradually increase in size from posteromedial to labial, 3) tooth patches of graded size teeth on the shortened premaxilla and dentary, and 4) a complete cover of denticles and teeth on the palate and the inner bones of the lower jaw. New observations support a previous suggestion that the entopterygoid and prearticular in dipnoans may incorporate the dermopalatine, ectopterygoid, and coronoids.