The evolution of manus shape in sauropod dinosaurs: Implications for functional morphology, forelimb orientation, and phylogeny
The evolution of manus shape in sauropod dinosaurs: Implications for functional morphology, forelimb orientation, and phylogeny
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DOI：
10.1671/a1108
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发表时间：
2003-09-12
影响因子：
1.4
通讯作者：
Bonnan, MF
中科院分区：
文献类型：
--
作者：
Bonnan, MF
蜥脚类动物有一个独特的指形和半管状的手，其形状被用作连接大多数蜥脚类动物的突触形态。掌骨的垂直方向和半管状排列表明蜥脚类动物的手改善了前肢的机械能力，以支持巨大的重量。然而，进化机制负责修改相对平坦的掌骨的基础saurischians到一个semitubular安排仍然没有调查。此外，足迹证据显示，蜥脚类动物的手内旋比其他蜥坐骨类动物更发达。然而，由于蜥脚类动物的桡骨和尺骨并不完全交叉，因此很难将螳螂脚印的方向与前肢骨骼学联系起来。重新研究北美新蜥脚类动物的骨骼学和解剖学表明，蜥脚类动物独特的手形与恢复四足姿势和手旋前的必要性暂时相关。新蜥脚类动物前肢和石膏的发音和操作，以及比例模型的迷惑龙路易，表明，作为蜥脚类动物前肢恢复负重的作用，桡骨的前外侧位置转移到承担更内部（前内侧）的方向，与尺骨近端和远端。桡骨的内移可能随后使手内旋，同时改变了趾弓的形状，将平坦的桡骨手转变为指行性半管状结构。这里提出的形态学证据表明，半管状的手是一种外适应，最终作为一个重量分布结构，这种独特的形态可能已经存在于基底蜥脚类动物。
Sauropods have a unique digitigrade and semi-tubular manus whose shape has been used as a synapomorphy that unites most sauropod taxa. The vertical orientation and semi-tubular arrangement of the metacarpals suggest the sauropod manus improved the mechanical ability of the forelimb to support great weight. However, the evolutionary mechanism responsible for modifying the relatively flat metacarpus of basal saurischians into a semitubular arrangement has remained uninvestigated. Furthermore, trackway evidence shows that manus pronation was more developed in sauropods than other saurischians. However, because the radius and ulna do not cross completely in sauropods, reconciling mantis print orientation with forelimb osteology has been difficult. Restudy of North American neosauropod appendicular osteology and anatomy suggests that the unique manus shape of sauropods is linked temporally with reversion to a quadrupedal posture and the necessity of manus pronation. Articulation and manipulation of neosauropod forelimbs and casts, as well as a scale model of Apatosaurus louisae, suggest that, as the sauropod forelimb resumed a weight-bearing role, the primitively anterolateral position of the radius shifted to assume a more internal (anteromedial) orientation in relation to the ulna proximally and distally. The internal shift of the radius may have subsequently pronated the manus while simultaneously altering the shape of the digital arch, transforming a flat dinosaurian manus into a digitigrade, semi-tubular structure. Morphological evidence presented here suggests a semitubular manus was an exaptation that ultimately functioned as a weight-distributing structure, and that this unique morphology may have been present in basal sauropods.