Microstructure and chemical composition of fossil mammalian teeth.

Sectioned Cretaceous mammalian teeth were studied by light microscopy and SEM equipment with an electron microprobe. Structures resembling odontoblast processes were found. Their S/Fe ratio was similar to that of rat odontoblast processes, but the amounts of these elements were far higher than in processes of recent teeth. It was concluded that they consisted of pyrite, but their reaction with mercurochrome indicated presence of proteins with SH groups. Fluorescence microscopy indicated traces of collagen in the dentin. In the fossil enamel and dentin the Ca/P ratio was similar to that of recent teeth. Two samples of fossil teeth were analyzed for Pb, Cd, Zn, and Cu content by atomic absorption spectrophotometry. The levels of the latter two elements were normal, whereas that of Cd and especially that of Pb were higher than in laboratory rats. The probability that original protein fractions exist and that the different elements were those of the living animals is discussed.