Farrell Hannah N, Alemseged Zeresenay
The University of Chicago, Department of Organismal Biology and Anatomy, 1027 E 57th Street, Chicago, IL, 60637, USA.
The University of Chicago, Department of Organismal Biology and Anatomy, 1027 E 57th Street, Chicago, IL, 60637, USA.
J Hum Evol. 2025 Apr;201:103652. doi: 10.1016/j.jhevol.2025.103652. Epub 2025 Feb 24.
Reconstructions of the locomotor behavior of early hominins have been hindered by our incomplete understanding of the form-function relationship in the extant hominoid shoulder. Although extensive research has highlighted the role of the highly mobile shoulder in supporting the locomotor diversity and versatility observed in hominoids, the contribution of the clavicle and its morphological diversity to shoulder function remains significantly underexplored. In this study, we analyzed the cross-sectional geometry of the ape clavicle using a large ontogenetic sample to identify new osteological signals related to locomotor adaptation in the shoulder. We assessed the interspecific and intraspecific differences in cortical bone distribution, with ratios of cortical properties describing the relative eccentricity of the cross section (the ratio of the second moments of area about the maximum [I] and minimum [I] principal axes [I/I]), the orientation of the anatomical plane that eccentricity is occurring in (the ratio of the second moments of area relative to the craniocaudal [I] and dorsoventral [I] axes [I/I]), and the relative proportion of cortical bone in each section. Our analyses demonstrate that the hominoid clavicle holds strong signals of locomotor adaptation that can be identified both across taxa and through ontogeny. Gibbons and orangutans have a relatively uniform clavicular cortical geometry throughout life, with gibbon clavicles built to best withstand habitual, unidirectional bending forces and orangutan clavicles remodeled to resist unpredictable, multidirectional loading. Furthermore, we find a clear signal of increased clavicular bending in the same portion of the diaphysis through ontogeny in the cortical geometry of chimpanzees and gorillas, likely reflecting both the shifts toward terrestriality through ontogeny and bending rigidity needed for continued arboreality at a larger body mass. Ultimately, these results are promising for the identification of locomotor adaptation in the shoulder of early hominins, especially Australopithecus, and highlight the key structural role of the clavicle in ape locomotion.
由于我们对现存类人猿肩部形态与功能关系的理解不完整，早期人类运动行为的重建工作受到了阻碍。尽管大量研究强调了高度灵活的肩部在支持类人猿观察到的运动多样性和多功能性方面的作用，但锁骨及其形态多样性对肩部功能的贡献仍未得到充分探索。在本研究中，我们使用大量个体发育样本分析了猿类锁骨的横截面几何形状，以识别与肩部运动适应相关的新骨学信号。我们评估了皮质骨分布的种间和种内差异，用皮质特性比率描述横截面的相对偏心率（关于最大[I]和最小[I]主轴的面积二次矩之比[I/I]）、偏心率发生的解剖平面的方向（相对于头尾[I]和背腹[I]轴的面积二次矩之比[I/I]）以及每个截面中皮质骨的相对比例。我们的分析表明，类人猿锁骨具有强大的运动适应信号，这些信号既可以在不同分类群之间识别，也可以通过个体发育来识别。长臂猿和猩猩一生的锁骨皮质几何形状相对均匀，长臂猿的锁骨结构最能承受习惯性的单向弯曲力，而猩猩的锁骨经过重塑以抵抗不可预测的多向负荷。此外，我们在黑猩猩和大猩猩的皮质几何形状的骨干同一部分发现了通过个体发育锁骨弯曲增加的明显信号，这可能既反映了个体发育过程中向陆地生活的转变，也反映了在更大体重下继续树栖所需的弯曲刚度。最终，这些结果对于识别早期人类，尤其是南方古猿肩部的运动适应很有前景，并突出了锁骨在猿类运动中的关键结构作用。
