Supplementary Online Material Table S1: Trabecular data of the capitate and third metacarpal through ontogeny in chimpanzees and gorillas

Chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) both knuckle-walk in adulthood but have been argued to develop their locomotor strategies differently in terms of timing and in positioning of the manus. Using dentally-defined age groups of both Pan and Gorilla, this study presents an internal trabecular bone approach to better understand the morphological ontogeny of knuckle-walking in these taxa. Capitate and third metacarpal bones were microCT scanned at 23–40 micron resolution with scaled volumes of interest placed centrally within the head of the capitate and base of the third metacarpal. Trabecular measures associated with activity frequency were expected to decrease through ontogeny, while degree of anisotropy (DA) was expected to increase through ontogeny in Pan alone. Bone surface area to volume ratio (BS/BV) showed expected patterns related to activity level in both bones. DA did not show statistical support for predicted patterns, but this may be due to sample size, as observed changes through ontogeny reflect expected trends in the capitate. Analyses of principal trabecular orientation corroborated known behavioral differences related to variation of hand use in these taxa, but only Pan showed biomechanical patterning associated with suggested wrist posture. Assessment of allometry showed that trabecular bone of larger animals is characterized by fewer and more spaced out trabeculae, supporting a constant trabecular geometry model of changes associated with body size changes through ontogeny. In combination, these findings lend support to behavioral and biomechanical arguments that knuckle-walking has evolved independently in Pan and Gorilla.成年黑猩猩（Pan troglodytes）与大猩猩（Gorilla gorilla）在成年后均采用指关节行走（knuckle-walk）方式，但学界认为二者在该运动策略的发育时机与手部姿态调控模式上存在差异。本研究以基于牙齿界定的两个类群的年龄组为研究对象，采用骨小梁（trabecular bone）内部分析方法，以期更深入地理解这两类灵长类指关节行走行为的形态个体发育过程。研究人员对头状骨与第三掌骨进行了分辨率为23~40微米的显微CT（microCT）扫描，并在头状骨小头及第三掌骨基底部的中央区域设置了缩放后的感兴趣体积。研究预期，与活动频率相关的骨小梁参数会随个体发育进程逐渐降低；而仅在黑猩猩类群中，骨小梁各向异性程度（DA）会随发育逐步升高。骨表面积与体积之比（BS/BV）在两块骨骼中均呈现出与活动水平相符的预期变化模式。各向异性程度（DA）未表现出与预测模式一致的统计学支持，这一结果可能受限于样本量——但头状骨中观察到的发育变化趋势符合预期。骨小梁主取向分析验证了已知的两类群手部使用差异相关的行为学特征，但仅黑猩猩类群呈现出与推测腕部姿势相关的生物力学模式。异速生长（allometry）分析结果显示，体型更大的个体其骨小梁更为稀疏且间距更大，这支持了"随个体发育的体型变化伴随恒定骨小梁几何模型"的假说。综合来看，本研究结果为"指关节行走行为在黑猩猩与大猩猩类群中独立演化"的行为学与生物力学论点提供了支撑。