Structure and composition of tooth enamel in quaternary soricines (Mammalia)

One of the main characteristics of the soricines (Eulipotyphla, Mammalia) is the red pigmentation of the outer part of the enamel in the cusps of the teeth. This gives the group its popular name: the red-toothed shrews. Several studies of extant species show that they have a complex enamel structure with three different parts and that the pigmentation is related to the presence of Fe oxides or hydroxides in the outer enamel. We have prepared transverse sections of the incisors of fossil shrews. These belong to the Early Pleistocene shrew Dolinasorex glyphodon and to an indeterminate species of Sorex. FESEM and EDS analyses of the sections show that Fe percentages reach their highest values in the outer part of the intermediate layer of the enamel and in the internal part of the outermost layer. The variations in Fe content are related to the change in direction of the enamel prisms in the intermediate parts of the enamel, instead of being at the surface as previous studies suggested. The location of the Fe seems to be related to the strength of the tooth.