Selby Michael S, Lovejoy C Owen
Department of Biomedical Sciences, Georgia Campus - Philadelphia College of Osteopathic Medicine, Suwanee, Georgia, 30024-2937.
Department of Anthropology, School of Biomedical Sciences, Kent State University, Kent, Ohio, 44242-0001.
Am J Phys Anthropol. 2017 Apr;162(4):682-700. doi: 10.1002/ajpa.23158. Epub 2017 Jan 27.
The higher primate scapula has been subject to many explanations of the putative "adaptive value" of its individual traits. However, the shift from the bone's position in above branch quadrupeds to its more posterolateral position in recent hominoids obviously required fundamental changes to its general form. We hypothesize that most features argued to be individually adaptive are more likely secondary consequences of changes in its fundamental bauplan, a view more consistent with modern developmental biology.
We tested this hypothesis with scapular metrics and angles from a broad anthropoid sample.
Our results support our hypothesis. Contrary to earlier predictions, vertebral border length differs little relative to body size in anthropoids, inferior angle position primarily reflects mediolateral scapular breadth, and supraspinous and infraspinous fossa sizes largely reflect scapular spine orientation. Suspensory taxa have cranially oriented glenoids, whereas slow clamberers and humans do not. Australopithecus most closely resembles the latter.
Most scapular features can be explained by only two primary changes: (1) reduction in mediolateral breadth and (2) change in the glenoid position relative to the vertebral border with increased reliance on suspension, which led to a more cranially angled scapular spine. Virtually all other scapular traits appear to be byproducts of these two changes. Based on fossil morphology, hominids were derived from a last common ancestor primarily adapted for clambering and not for suspension. Scapular form in early hominids such as Australopithecus is therefore primitive and largely reflects the genus's general clambering heritage.
高等灵长类动物的肩胛骨其各个特征的假定“适应价值”已经有多种解释。然而，从该骨骼在树上四足动物中的位置转变到其在现代类人猿中更靠后外侧的位置，显然需要其总体形态发生根本性变化。我们假设，大多数被认为具有个体适应性的特征更可能是其基本结构变化的次要结果，这一观点与现代发育生物学更为一致。
我们用来自广泛类人猿样本的肩胛骨测量指标和角度来检验这一假设。
我们的结果支持了我们的假设。与早期预测相反，类人猿中椎骨边缘长度相对于身体大小的差异很小，下角位置主要反映肩胛骨的内外侧宽度，冈上窝和冈下窝的大小很大程度上反映肩胛冈的方向。树栖类群的关节盂朝向头部，而缓慢攀爬者和人类则不然。南方古猿与后者最为相似。
大多数肩胛骨特征仅可由两个主要变化来解释：（1）内外侧宽度的减小；（2）随着对树栖依赖的增加，关节盂相对于椎骨边缘位置的变化，这导致肩胛冈的角度更偏向头部。几乎所有其他肩胛骨特征似乎都是这两个变化的副产品。基于化石形态，原始人类源自一个主要适应攀爬而非树栖的最后共同祖先。因此，早期原始人类如南方古猿的肩胛骨形态是原始的，并且在很大程度上反映了该属的一般攀爬特征。
