The microstructure of enamel, dentine and cementum in advanced Taeniodonta (Mammalia) with comments on their dietary adaptations

The cheek teeth of Ectoganus and Stylinodon, the most derived genera of Taeniodonta following recent phylogenies, show various morphological and microstructural characteristics that are unusual for herbivores of their size. Their continuously growing premolars and molars have blunt occlusal surfaces without shearing facets and enamel is restricted to the lingual and buccal sides of the teeth. The anterior and posterior walls of the teeth are covered with a thick layer of cementum to which the periodontal ligament is attached. The enamel band is relatively thin. The schmelzmuster is one-layered and features weakly developed Hunter-Schreger bands that are only recognizable in longitudinal section. In cross-section, the enamel prisms show a 'keyhole pattern' with an incomplete prism sheath. There is no interprismatic matrix. The microstructure of the dentine has the regular mammalian pattern and shows no special similarity to that of xenarthrans. Taeniodonts seem to have used their hypsodont cheek teeth almost exclusively for squeezing and some crushing of food and only to a minor degree for grinding. Weakly developed Hunter-Schreger bands indicate only light loading during mastication.