Department of Earth Sciences, Natural History Museum, London, UK.
Department of Cell and Developmental Biology, University College London, London, UK.
Sci Rep. 2020 Nov 4;10(1):19053. doi: 10.1038/s41598-020-76032-2.
Third permanent molars (M3s) are the last tooth to form but have not been used to estimate age at dental maturation in early fossil hominins because direct histological evidence for the timing of their growth has been lacking. We investigated an isolated maxillary M3 (SK 835) from the 1.5 to 1.8-million-year-old (Mya) site of Swartkrans, South Africa, attributed to Paranthropus robustus. Tissue proportions of this specimen were assessed using 3D X-ray micro-tomography. Thin ground sections were used to image daily growth increments in enamel and dentine. Transmitted light microscopy and synchrotron X-ray fluorescence imaging revealed fluctuations in Ca concentration that coincide with daily growth increments. We used regional daily secretion rates and Sr marker-lines to reconstruct tooth growth along the enamel/dentine and then cementum/dentine boundaries. Cumulative growth curves for increasing enamel thickness and tooth height and age-of-attainment estimates for fractional stages of tooth formation differed from those in modern humans. These now provide additional means for assessing late maturation in early hominins. M3 formation took ≥ 7 years in SK 835 and completion of the roots would have occurred between 11 and 14 years of age. Estimated age at dental maturation in this fossil hominin compares well with what is known for living great apes.
第三磨牙（M3）是最后形成的牙齿，但由于缺乏其生长时间的直接组织学证据，因此尚未用于估计早期化石人类的牙成熟年龄。我们研究了来自南非斯瓦特克朗斯 150 万至 180 万年前（Mya）遗址的孤立上颌 M3（SK 835），该标本归因于粗壮傍人。使用 3D X 射线微断层扫描评估了该标本的组织比例。薄的地面切片用于对牙釉质和牙本质中的每日生长增量进行成像。透射光显微镜和同步加速器 X 射线荧光成像揭示了钙浓度的波动与每日生长增量相吻合。我们使用区域每日分泌率和 Sr 标记线来重建牙釉质/牙本质和牙骨质/牙本质边界处的牙齿生长。随着牙釉质厚度和牙高度的增加，累积生长曲线以及牙齿形成的分数阶段的获得年龄估计值与现代人不同。这些现在为评估早期人类的晚期成熟提供了额外的手段。SK 835 中 M3 的形成需要≥7 年，并且根的完成将发生在 11 至 14 岁之间。这个化石人类的牙成熟估计年龄与已知的现生大猿的牙成熟估计年龄相当。
