The University Museum, The University of Tokyo, Tokyo, Japan.
Proc Biol Sci. 2012 Jul 7;279(1738):2561-70. doi: 10.1098/rspb.2012.0190. Epub 2012 Feb 22.
Forelimb posture has been a controversial aspect of reconstructing locomotor behaviour in extinct quadrupedal tetrapods. This is partly owing to the qualitative and subjective nature of typical methods, which focus on bony articulations that are often ambiguous and unvalidated postural indicators. Here we outline a new, quantitatively based forelimb posture index that is applicable to a majority of extant tetrapods. By determining the degree of elbow joint adduction/abduction mobility in several tetrapods, the carpal flexor muscles were determined to also play a role as elbow adductors. Such adduction may play a major role during the stance phase in sprawling postures. This role is different from those of upright/sagittal and sloth-like creeping postures, which, respectively, depend more on elbow extensors and flexors. Our measurements of elbow muscle moment arms in 318 extant tetrapod skeletons (Lissamphibia, Synapsida and Reptilia: 33 major clades and 263 genera) revealed that sprawling, sagittal and creeping tetrapods, respectively, emphasize elbow adductor, extensor and flexor muscles. Furthermore, scansorial and non-scansorial taxa, respectively, emphasize flexors and extensors. Thus, forelimb postures of extinct tetrapods can be qualitatively classified based on our quantitative index. Using this method, we find that Triceratops (Ceratopsidae), Anhanguera (Pterosauria) and desmostylian mammals are categorized as upright/sagittally locomoting taxa.
前肢姿势一直是重建已灭绝四足动物的运动行为的一个有争议的方面。这部分是由于典型方法的定性和主观性，这些方法主要集中在骨骼关节上，而这些关节往往是模糊的，并且没有经过验证的姿势指标。在这里，我们概述了一种新的、基于定量的前肢姿势指数，该指数适用于大多数现存的四足动物。通过确定几种四足动物肘关节内收/外展的程度，腕屈肌被确定也起到肘内收肌的作用。这种内收在伸展姿势的站立阶段可能起主要作用。这种作用与垂直/矢状面和树懒样蠕动姿势不同，后者分别更多地依赖于肘伸肌和屈肌。我们对 318 种现存四足动物骨骼（有尾两栖动物、合弓类动物和爬行动物：33 个主要分支和 263 个属）的肘肌力臂进行了测量，结果表明，分别为伸展、矢状面和蠕动的四足动物，分别强调肘内收肌、伸肌和屈肌。此外，分别为攀爬和非攀爬的分类群，分别强调屈肌和伸肌。因此，灭绝的四足动物的前肢姿势可以根据我们的定量指数进行定性分类。使用这种方法，我们发现三角龙（角龙科）、风神翼龙（翼龙目）和绝灭的哺乳动物被归类为垂直/矢状面运动的分类群。
