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

ABSTRACT

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.

ACKNOWLEDGMENTS

We are deeply indebted to P. D. Gingerich for his valuable comments on an earlier draft of the manuscript. He and G. Gunnell (both UM, Ann Arbor), K. D. Rose (Johns Hopkins University School of Medicine, Baltimore), A. K. Gishlick (YPM, New Haven), and M. K. Brett-Surman (USMN) kindly supplied us with the valuable taeniodontid material to be studied. We thank T. Kaiser and E. Schulz (Biocenter Grindel and Zoological Museum, University of Hamburg) for help with microtexture analysis. We appreciate the helpful comments of R. Asher as the responsible editor of JVP and those of the reviewers M. T. Silcox and an anonymous one.

This research was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) for WvK and DK. It is publication no. 18 of the DFG Research Unit 771 ‘Function and performance enhancement in the mammalian dentition—phylogenetic and ontogenetic impact on the masticatory apparatus’ at the University of Bonn, Germany.