Tooth development in East African Paranthropus

Abstract A rapid differentiation rate in enamel with a "hyper-thick" enamel was suggested to represent a synapomorphic condition in Paranthropus species. To check this hypothesis we have analysed the enamel microstructure of molar teeth from Shungura Formation (Omo, Ethiopia) attributed, by teeth macrostructure, to P. aethiopicus and P. boisei. The number, course and angles of the enamel-dentine junction of striae of Retzius and the relative importance of cuspal and cervical stages were analysed with a stereomicroscope. We assumed the striae of Retzius are growth markers with a 7-day periodicity. Thus, the features analysed indicate the time of crown formation, the number of ameloblasts active at any one time, the differentiation rate and the relative importance of the number of ameloblasts active at any one time in relation to the overall number of ameloblasts implicated in the total crown formation respectively. Enamel thickness was also measured. Although overlap was found between some characteristics, it was possible to define dissimilar pathways in tooth development. Paranthropus aethiopicus, with a faster differentiation rate and a greater number of ameloblasts active at any given time, have a shorter time of crown formation than P. boisei. At first it seems that hyper-thick enamel is not present and that ameloblasts operate as a whole. In P. boisei the ameloblasts work as successive groups. Thus, if the selection to form teeth quickly and the synapomorphic features in Paranthropus' species, as suggested, are retained, P. aethiopicus would be more specialized than P. boisei.