Metaceratodus baibianorum from the La Colonia Formation: tooth plate anomalies and the possible presence of tertiary dentine

Abstract

The dentition of Mesozoic dipnoans is formed by tooth plates that are not replaced throughout their lives. These can suffer different types of lesions that may be permanent or disappear with wear through action of the jaws. Here, we describe pathologies on the tooth plates of Metaceratodus baibianorum from the Late Cretaceous (Maastrichtian) La Colonia Formation of Patagonia in Argentina. Of the total number of analysed tooth plates (N ¼ 127), 27.5% show signs of different pathologies including caries, abscesses, hyperplasia, fractures, alterations in growth, and erosion. No tooth plates with parasitic invasions, attrition or osteopenia were observed. Some examples of occlusal caries show pulpal overgrowths on the pulp surface. CT scanning demonstrates that these are similar to tertiary dentine in their coincidence with lesions, higher density relative to the surrounding dentine, and fewer pulp canals resulting in fewer dentinal tubules. Such features may indicate that dipnoans are, or at least were, able to generate some form of reparative or reactionary dentine.