Retention of the flight-adapted avian finger-joint complex in the Ostrich helps identify when wings began evolving in dinosaurs

The functional anatomies of avian finger joints have never been compared with those of the basal avian <i>Archaeopteryx lithographica</i> or maniraptoran theropod dinosaurs. These startling oversights are due to unfamiliarity of the joints outside of highly specialised studies of bird-wing biomechanics. Here fleshed to skeletonised repeated-measures analyses of finger-joint ranges of motion (ROMs) in a basal palaeognath, the Ostrich <i>Struthio camelus</i>, were utilised as a model to begin filling in these knowledge gaps. Results verified that all of the flight-adapted, avian-specific finger joints are retained in the flightless, yet large and well-differentiated fingers of the Ostrich. Moreover, Ostrich finger joints still possess flight-restricted ROMs within the semi-pronated plane of the manus. The osteological markers of these highly conserved flight-adapted characters in Ostrich show that prior descriptions have unknowingly demonstrated that the main avian finger-joint complex began evolving at the base of Pennaraptora (Oviraptorosauria + Paraves). This detailed functional analysis provides non-embryological support for the hypothesis that maniraptoran theropods shared digital homologies with birds, and supports recent pronation studies indicating that pennaraptoran theropods had evolved avian distal wing joints stiffened for aerial locomotion.

迄今为止，尚未有研究将鸟类指关节的功能解剖结构与基干鸟类始祖鸟（Archaeopteryx lithographica）以及手盗龙类兽脚类恐龙的指关节功能解剖结构进行对比。这类显著的研究疏漏，源于学界仅在鸟类翼生物力学的高度专业化研究中涉及此类关节，除此之外对其了解甚少。本研究以基干古颚类动物鸵鸟（Struthio camelus）为模型，开展了经软组织到骨骼化的指关节活动范围（ROM，Range of Motion）重复测量分析，旨在填补这一知识空白。研究结果证实，尽管鸵鸟不会飞行，但其指骨虽体型庞大且分化程度高，却保留了所有适应飞行的鸟类特异性指关节。此外，鸵鸟指关节在前肢半旋前平面内仍具备飞行限制性活动范围。对鸵鸟体内这些高度保守的适应飞行特征的骨骼学标记分析显示，此前的相关研究已在无意中证实：鸟类主要指关节复合体的演化起始于羽龙类（Pennaraptora）的基部，即窃蛋龙亚目（Oviraptorosauria）与近鸟类（Paraves）的分支起点。本项详细的功能解剖分析，为“手盗龙类兽脚类恐龙与鸟类具有指骨同源性”这一假说提供了非胚胎学证据支持，并佐证了近期的旋前研究结论——羽龙类兽脚类恐龙已演化出用于空中运动的硬化鸟类远端翼关节。