Lacruz Rodrigo S, Rozzi Fernando Ramirez, Bromage Timothy G
Institute for Human Evolution, School of GeoSciences, University of the Witwatersrand, Johannesburg, South Africa.
J Hum Evol. 2006 Dec;51(6):580-90. doi: 10.1016/j.jhevol.2006.05.007. Epub 2006 Aug 5.
Dental tissues provide important insights into aspects of hominid palaeobiology that are otherwise difficult to obtain from studies of the bony skeleton. Tooth enamel is formed by ameloblasts, which demonstrate daily secretory rhythms developing tissue-specific structures known as cross striations, and longer period markings called striae of Retzius. These enamel features were studied in the molars of two well known South African hominid species, Australopithecus africanus and Paranthropus robustus. Using newly developed portable confocal microscopy, we have obtained cross striation periodicities (number of cross striations between adjacent striae) for the largest sample of hominid teeth reported to date. These data indicate a mean periodicity of seven days in these small-bodied hominids. Important differences were observed in the inferred mechanisms of enamel development between these taxa. Ameloblasts maintain high rates of differentiation throughout cervical enamel development in P. robustus but not in A. africanus. In our sample, there were fewer lateral striae of Retzius in P. robustus than in A. africanus. In a molar of P. robustus, lateral enamel formed in a much shorter time than cuspal enamel, and the opposite was observed in two molars of A. africanus. In spite of the greater occlusal area and enamel thickness of the molars of both fossil species compared with modern humans, the total crown formation time of these three fossil molars was shorter than the corresponding tooth type in modern humans. Our results provide support for previous conclusions that molar crown formation time was short in Plio-Pleistocene hominids, and strongly suggest the presence of different mechanisms of amelogenesis, and thus tooth development, in these taxa.
牙齿组织为了解原始人类古生物学的各个方面提供了重要见解，而这些方面很难从骨骼研究中获得。牙釉质由成釉细胞形成，成釉细胞表现出每日分泌节律，形成称为横纹的组织特异性结构，以及称为芮氏线的较长周期标记。在两种著名的南非原始人类物种——南方古猿和粗壮傍人——的臼齿中研究了这些牙釉质特征。使用新开发的便携式共聚焦显微镜，我们获得了迄今为止报道的最大的原始人类牙齿样本的横纹周期（相邻芮氏线之间的横纹数量）。这些数据表明，这些体型较小的原始人类的平均周期为七天。在这些分类群之间，观察到牙釉质发育推断机制存在重要差异。在粗壮傍人的颈部牙釉质发育过程中，成釉细胞在整个过程中保持高分化率，但在南方古猿中则不然。在我们的样本中，粗壮傍人的芮氏线侧纹比南方古猿的少。在一颗粗壮傍人的臼齿中，侧面牙釉质的形成时间比牙尖牙釉质短得多，而在两颗南方古猿的臼齿中则观察到相反的情况。尽管与现代人类相比，这两种化石物种的臼齿咬合面积和牙釉质厚度更大，但这三颗化石臼齿的总牙冠形成时间比现代人类相应的牙齿类型短。我们的结果为先前的结论提供了支持，即上新世 - 更新世原始人类的臼齿牙冠形成时间较短，并强烈表明这些分类群中存在不同的釉质形成机制，从而牙齿发育机制。
