Napoli James G, Fabbri Matteo, Ruebenstahl Alexander A, O'Connor Jingmai K, Bhullar Bhart-Anjan S, Norell Mark A
Department of Anatomical Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY, USA.
Paleontology, North Carolina Museum of Natural Sciences, Raleigh, NC, USA.
Nature. 2025 Jul 9. doi: 10.1038/s41586-025-09232-3.
The carpus (wrist) of birds has a complex evolutionary history, long known to involve carpal reduction and recently shown to include topological replacement of one carpal (the ulnare) by another (the pisiform). The pisiform plays a crucial role in stabilization of the distal wingtip during flight, and facilitates kinematic integration that 'automates' wing motion. The apparent absence of a pisiform in all but the earliest theropod dinosaurs led to the proposal that it was lost early in theropod evolution and regained only in birds as a key step in the origin of flight. Here, we describe the forelimb skeletons of two newly prepared theropod dinosaur specimens from the Gobi Desert of Mongolia, each of which preserves a pisiform, establishing its presence in Oviraptorosauria and Troodontidae in addition to birds. Reinterpretation of published material in light of these specimens shows a pisiform in a wide range of theropod species, including Microraptor, Ambopteryx and Anchiornis. Our results indicate that the pisiform replaced the ulnare by origin of the clade Pennaraptora, phylogenetically coincident with the hypothesized origin(s) of flight in birds and their closest relatives. Taken together, our results indicate that replacement of the ulnare by the pisiform was a terminal step in assembly of the dinosaurian flight apparatus that occurred close to the origins of flight in theropod dinosaurs, rather than a novelty restricted to birds.
鸟类的腕骨有着复杂的进化史，长期以来人们已知其涉及腕骨简化，最近又发现其中包括一块腕骨（尺腕骨）被另一块（豌豆骨）进行拓扑替换。豌豆骨在飞行过程中对稳定翅尖起着关键作用，并促进了使翅膀运动 “自动化” 的运动整合。除了最早的兽脚亚目恐龙外，在所有其他恐龙中豌豆骨明显缺失，这导致有人提出它在兽脚亚目恐龙进化早期就已丢失，直到鸟类出现时才重新获得，这是飞行起源的关键一步。在此，我们描述了两件新修复的来自蒙古戈壁沙漠的兽脚亚目恐龙标本的前肢骨骼，每件标本都保留了一块豌豆骨，这证明除了鸟类外，窃蛋龙科和伤齿龙科中也存在豌豆骨。根据这些标本重新解读已发表的材料后发现，包括小盗龙、近鸟龙和安氏原羽鸟在内的多种兽脚亚目恐龙都有豌豆骨。我们的研究结果表明，在近鸟类演化支出现时，豌豆骨取代了尺腕骨，这在系统发育上与鸟类及其近亲飞行的假设起源相一致。综合来看，我们的研究结果表明，豌豆骨取代尺腕骨是恐龙飞行器官组装的最后一步，发生在兽脚亚目恐龙飞行起源的时期，而不是仅限于鸟类的新特征。
