Unaffiliated, 43125, Parma, Italy.
European Synchrotron Radiation Facility, 38043, Grenoble, France.
Sci Rep. 2021 Jul 19;11(1):14722. doi: 10.1038/s41598-021-94285-3.
The furcula is a distinctive element of the pectoral skeleton in birds, which strengthens the shoulder region to withstand the rigor of flight. Although its origin among theropod dinosaurs is now well-supported, the homology of the furcula relative to the elements of the tetrapod pectoral girdle (i.e., interclavicle vs clavicles) remains controversial. Here, we report the identification of the furcula in the birdlike theropod Halszkaraptor escuilliei. The bone is unique among furculae in non-avian dinosaurs in bearing a visceral articular facet in the hypocleideal end firmly joined to and overlapped by the sternal plates, a topographical pattern that supports the primary homology of the furcula with the interclavicle. The transformation of the interclavicle into the furcula in early theropods is correlated to the loss of the clavicles, and reinforced the interconnection between the contralateral scapulocoracoids, while relaxing the bridge between the scapulocoracoids with the sternum. The function of the forelimbs in theropod ancestors shifted from being a component of the locomotory quadrupedal module to an independent module specialized to grasping. The later evolution of novel locomotory modules among maniraptoran theropods, involving the forelimbs, drove the re-acquisition of a tighter connection between the scapulocoracoids and the interclavicle with the sternal complex.
叉骨是鸟类胸带骨骼中的一个独特元素，它增强了肩部区域的强度，以承受飞行的严苛要求。虽然它在兽脚亚目恐龙中的起源现在已经得到很好的支持，但叉骨相对于四足动物胸带骨骼元素（即锁骨与间锁骨）的同源性仍然存在争议。在这里，我们报告了在似鸟恐龙 Halszkaraptor escuilliei 中识别出叉骨。在非鸟兽脚类恐龙中，该骨骼在其末端的肋软骨关节面上具有独特的特征，该关节面与胸骨板牢固结合并重叠，这种拓扑结构支持了叉骨与间锁骨的主要同源性。早期兽脚类恐龙中，间锁骨向叉骨的转化与锁骨的丧失有关，并加强了对侧肩带与胸骨之间的连接，同时放松了肩带与胸骨之间的连接。在兽脚类恐龙祖先中，前肢的功能从作为四足运动模块的组成部分转变为专门用于抓握的独立模块。手盗龙类兽脚类恐龙中新型运动模块的后期进化，涉及前肢，推动了肩带与胸骨之间更紧密的连接的重新建立，其中包括间锁骨与胸骨的连接。
