Gantt D G, Rafter J A
Department of Biology, Georgia Southern University, Statesboro 30460, USA.
Connect Tissue Res. 1998;39(1-3):195-206; discussion 221-5. doi: 10.3109/03008209809023927.
The purpose of this investigation is to evaluate enamel thickness in extant and extinct hominoids. The material used in this study spans the evolutionary history of this group, from 20 million years ago to the present. The objectives of this investigation are to test three hypotheses: (1) the Loading Hypothesis: loading areas of the crown have thicker enamel than non-loading areas; (2) the Phyletic Hypothesis: differences in enamel thickness provide a basis for determining evolutionary relationships; and (3) the Functional Hypothesis: differences among hominoids result from adaptations to differing dietary and ecological habitats, that is from folivory to frugivory to hard object feeding and from tropical to forest to savanna habitats. Thin sections were prepared and polished to approximately 100 microm in thickness. Each section was then enlarged and digitally captured to the computer. Image processing and analysis software, SigmaImage (was used to measure the sections. Subsequent statistical analysis was conducted with SigmaStat and SPSS statistical software programs. The data provides statistical support for all hypotheses. In particular, the data support the proposal that "thick" enamel is the ancestral condition for the great apes and human clade. Therefore, Pongo would have retained its enamel thickness from the common ancestor of the great apes and Gorilla and Pan would have secondarily reduced enamel thickness to "thin." The common ancestor of the hominids, the australopithecines, would have "thick" enamel. The "hyper-thick" enamel of the australopithecines would be a derived character for this clade due to increased crushing and grinding and adaptation to savanna habitat. Homo would have secondarily reduced enamel thickness to "thick." Evolutionary biology of enamel differs markedly in hominids from that found in other hominoids and primates. Increased enamel thickness involved both increases in absolute thickness of enamel and crown size in response to increase masticatory loading.
本研究的目的是评估现存和已灭绝的类人猿的牙釉质厚度。本研究使用的材料涵盖了该类群从2000万年前至今的进化历史。本研究的目标是检验三个假设：（1）负荷假设：牙冠的负荷区域比非负荷区域具有更厚的牙釉质；（2）系统发育假设：牙釉质厚度的差异为确定进化关系提供了基础；（3）功能假设：类人猿之间的差异源于对不同饮食和生态栖息地的适应，即从食叶到食果再到硬食，以及从热带到森林再到稀树草原栖息地。制备薄片并抛光至约100微米厚。然后将每个切片放大并数码采集到计算机中。使用图像处理和分析软件SigmaImage测量切片。随后使用SigmaStat和SPSS统计软件程序进行统计分析。数据为所有假设提供了统计支持。特别是，数据支持了“厚”牙釉质是大猩猩和人类进化支系的原始状态这一观点。因此，猩猩会保留其从大猩猩的共同祖先那里继承的牙釉质厚度，而黑猩猩和倭黑猩猩会次生地将牙釉质厚度降低到“薄”。人族的共同祖先南方古猿会有“厚”牙釉质。南方古猿的“超厚”牙釉质将是该进化支系的一个衍生特征，这是由于咀嚼和研磨增加以及对稀树草原栖息地的适应。人类会次生地将牙釉质厚度降低到“厚”。人族的牙釉质进化生物学与其他类人猿和灵长类动物明显不同。牙釉质厚度的增加既包括牙釉质绝对厚度的增加，也包括牙冠大小的增加，以应对咀嚼负荷的增加。
