Swiderski Donald L
Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, 48109.
Evolution. 1993 Dec;47(6):1854-1873. doi: 10.1111/j.1558-5646.1993.tb01274.x.
The mammalian scapula, like many bones, is a single structural element that serves as an attachment site for several muscles. The goal of this study was to determine whether the scapula evolves as an integrated unit, or as a collection of distinct parts. Shape differences among the scapulae of tree squirrels, chipmunks, and ground squirrels were described using thin-plate spline analysis. This technique produces a geometric description of shape differences that can be decomposed into a series of components ranging in scale from features that span the entire form to features that are highly localized. Shape differences among tree squirrel scapulae were found only in large-scale features, indicating spatially integrated shape change. Chipmunks and ground squirrels differ from tree squirrels in several features, but shared differences reflecting divergence of their common ancestor were found only in the small-scale features. Divergence of ground squirrels from the common ancestor involved some large-scale changes but was dominated by small-scale changes. Divergence of chipmunks was dominated by large-scale changes. Thus, the scapula evolved as an integrated unit during some transitions but as a collection of distinct parts during others. These results suggest that evolutionary patterns of the postcranial skeleton may be as complex as the patterns that have been described for skulls and feeding mechanisms.
与许多骨骼一样，哺乳动物的肩胛骨是一个单一的结构元素，是几块肌肉的附着部位。本研究的目的是确定肩胛骨是作为一个整体单元进化，还是作为不同部分的集合进化。使用薄板样条分析描述了松鼠、花栗鼠和地松鼠肩胛骨之间的形状差异。该技术产生了形状差异的几何描述，可分解为一系列从跨越整个形态的特征到高度局部化的特征的不同尺度的组件。仅在大型特征中发现了松鼠肩胛骨之间的形状差异，表明存在空间整合的形状变化。花栗鼠和地松鼠在几个特征上与松鼠不同，但仅在小型特征中发现了反映其共同祖先分歧的共同差异。地松鼠与共同祖先的分歧涉及一些大型变化，但以小型变化为主。花栗鼠的分歧以大型变化为主。因此，肩胛骨在某些转变过程中作为一个整体单元进化，而在其他过程中作为不同部分的集合进化。这些结果表明，颅后骨骼的进化模式可能与已描述的头骨和进食机制的模式一样复杂。
