Wiseman Ashleigh L A, Demuth Oliver E, Pomeroy Emma, De Groote Isabelle
McDonald Institute for Archaeological Research, University of Cambridge, Cambridge CB2 1TN.
Research Centre in Evolutionary Anthropology and Paleoecology, Liverpool John Moores University, Liverpool, Merseyside L3 5UX.
Integr Org Biol. 2022 Jul 28;4(1):obac031. doi: 10.1093/iob/obac031. eCollection 2022.
The postcranial skeleton of (AL 288-1) exhibits clear adaptations for bipedality, although there is some debate as to the efficiency and frequency of such upright movement. Some researchers argue that AL 288-1 walked with an erect limb like modern humans do, whilst others advocate for a "bent-hip bent-knee" (BHBK) gait, although in recent years the general consensus favors erect bipedalism. To date, no quantitative method has addressed the articulation of the AL 288-1 hip joint, nor its range of motion (ROM) with consideration for joint spacing, used as a proxy for the thickness of the articular cartilage present within the joint spacing which can affect how a joint moves. Here, we employed ROM mapping methods to estimate the joint spacing of AL 288-1's hip joint in comparison to a modern human and chimpanzee. Nine simulations assessed different joint spacing and tested the range of joint congruency (i.e., ranging from a closely packed socket to loosely packed). We further evaluated the sphericity of the femoral head and whether three rotational degrees of freedom (DOFs) sufficiently captures the full ROM or if translational DOFs must be included. With both setups, we found that the AL 288-1 hip was unlikely to be highly congruent (as it is in modern humans) because this would severely restrict hip rotational movement and would severely limit the capability for both bipedality and even arboreal locomotion. Rather, the hip was more cartilaginous than it is in the modern humans, permitting the hip to rotate into positions necessitated by both terrestrial and arboreal movements. Rotational-only simulations found that AL 288-1 was unable to extend the hip like modern humans, forcing the specimen to employ a BHBK style of walking, thus contradicting 40+ years of previous research into the locomotory capabilities of AL 288-1. Therefore, we advocate that differences in the sphericity of the AL 288-1 femoral head with that of a modern human necessitates all six DOFs to be included in which AL 288-1 could osteologically extend the hip to facilitate a human-like gait.
阿法南方古猿（AL 288-1）的颅后骨骼展现出了对双足行走的明显适应性，尽管对于这种直立行走的效率和频率存在一些争议。一些研究人员认为，AL 288-1像现代人类一样以直立的肢体行走，而另一些人则主张“弯臀屈膝”（BHBK）步态，不过近年来普遍的共识倾向于直立双足行走。迄今为止，尚无定量方法研究AL 288-1髋关节的关节连接情况，也没有在考虑关节间隙的情况下研究其运动范围（ROM），关节间隙可作为关节间隙内存在的关节软骨厚度的替代指标，而关节软骨厚度会影响关节的运动方式。在此，我们采用ROM映射方法来估计AL 288-1髋关节的关节间隙，并与现代人类和黑猩猩进行比较。九个模拟评估了不同的关节间隙，并测试了关节一致性的范围（即从紧密贴合的髋臼到宽松贴合的范围）。我们进一步评估了股骨头的球形度，以及三个旋转自由度（DOF）是否足以捕捉整个ROM，或者是否必须纳入平移自由度。在两种设置下，我们发现AL 288-1的髋关节不太可能像现代人类那样高度一致，因为这会严重限制髋关节的旋转运动，并且会严重限制双足行走甚至树栖运动的能力。相反，该髋关节的软骨比现代人类的更多，这使得髋关节能够旋转到陆地和树栖运动所需的位置。仅旋转模拟发现，AL 288-1无法像现代人类那样伸展髋关节，迫使该标本采用BHBK行走方式，从而与过去40多年来对AL 288-1运动能力的研究相矛盾。因此，我们主张，AL 288-1股骨头与现代人类股骨头在球形度上的差异使得必须纳入所有六个自由度，在这六个自由度下，AL 288-1在骨骼学上可以伸展髋关节以促进类人步态。
