Evolutionary Studies Institute, University of the Witwatersrand, Wits, South Africa; Department of Geology and Palaeontology, Georgian National Museum, Tbilisi, Georgia.
School of Statistics and Actuarial Science, University of the Witwatersrand, Wits, South Africa.
PLoS One. 2015 Jan 30;10(1):e0117905. doi: 10.1371/journal.pone.0117905. eCollection 2015.
Diaphyseal morphology of long bones, in part, reflects in vivo loads experienced during the lifetime of an individual. The first metatarsal, as a cornerstone structure of the foot, presumably expresses diaphyseal morphology that reflects loading history of the foot during stance phase of gait. Human feet differ substantially from those of other apes in terms of loading histories when comparing the path of the center of pressure during stance phase, which reflects different weight transfer mechanisms. Here we use a novel approach for quantifying continuous thickness and cross-sectional geometric properties of long bones in order to test explicit hypotheses about loading histories and diaphyseal structure of adult chimpanzee, gorilla, and human first metatarsals. For each hallucal metatarsal, 17 cross sections were extracted at regularly-spaced intervals (2.5% length) between 25% and 65% length. Cortical thickness in cross sections was measured in one degree radially-arranged increments, while second moments of area were measured about neutral axes also in one degree radially-arranged increments. Standardized thicknesses and second moments of area were visualized using false color maps, while penalized discriminant analyses were used to evaluate quantitative species differences. Humans systematically exhibit the thinnest diaphyseal cortices, yet the greatest diaphyseal rigidities, particularly in dorsoplantar regions. Shifts in orientation of maximum second moments of area along the diaphysis also distinguish human hallucal metatarsals from those of chimpanzees and gorillas. Diaphyseal structure reflects different loading regimes, often in predictable ways, with human versus non-human differences probably resulting both from the use of arboreal substrates by non-human apes and by differing spatial relationships between hallux position and orientation of the substrate reaction resultant during stance. The novel morphological approach employed in this study offers the potential for transformative insights into form-function relationships in additional long bones, including those of extinct organisms (e.g., fossils).
长骨的骨干形态在一定程度上反映了个体一生中所经历的体内负荷。第一跖骨作为足的基石结构，推测其骨干形态反映了足在步态站立相期间的负重历史。人类的脚在负重历史方面与其他猿类有很大的不同，比较站立相期间的压力中心轨迹，这反映了不同的重量转移机制。在这里，我们使用一种新的方法来量化长骨的连续厚度和横截面几何特性，以便检验关于成年黑猩猩、大猩猩和人类第一跖骨的负重历史和骨干结构的明确假设。对于每个跖骨，在 25%到 65%长度之间，以 2.5%长度为间隔提取 17 个横截面。在一个半径方向上以 1 度的增量测量横截面中的皮质厚度，而关于中性轴的二次力矩面积也以 1 度的半径方向上的增量测量。使用假彩色图可视化标准化的厚度和二次力矩面积，同时使用惩罚判别分析评估定量的物种差异。人类系统地表现出最薄的骨干皮质，但最大的骨干刚性，特别是在背跖区域。最大二次力矩面积在骨干上的取向的变化也将人类的跖骨与黑猩猩和大猩猩的跖骨区分开来。骨干结构反映了不同的负荷机制，通常以可预测的方式，人类与非人类的差异可能既来自于非人类猿类对树木基质的使用，也来自于大脚趾位置与站立相期间基质反作用力方向之间的空间关系的不同。本研究中采用的新形态学方法有可能为其他长骨（包括已灭绝生物的化石）的形态-功能关系提供变革性的见解。
