Enamel Structure in Two Triassic Mammals

Abstract

The dental enamel of the Upper Triassic mammals, Morganucodon and an unnamed Pantothere, were examined by polarization microscopy. These enamels, structureless in transmitted light, showed alternating light and dark bands when the enamel layer is parallel to either primary polarization axis. Study with a 1st order red plate demonstrated a non-prismatic or continuous structural arrangement produced by a mean preferential orientation of the hydroxyapatite c axes in the volume of enamel studied which regularly and continuously alternates between being perpendicular to the enamel surface and being inclined towards the cervical end of the crown. The phylogenetic appearance of mammalian tooth gross morphology was prior to and independent of the appearance of the prismatic enamel structure.