Data from: Ventilatory mechanics from maniraptoran theropods to extant birds

Shared behavioural, morphological and physiological characteristics are indicative of the evolution of extant birds from non-avian maniraptoran dinosaurs. One such shared character is the presence of uncinate processes; respiratory structures in extant birds. Recent research has suggested a respiratory role for these processes found in oviraptorid and dromaeosaurid dinosaurs. By measuring the geometry of fossil rib cage morphology we demonstrate that the mechanical advantage, conferred by uncinate processes, for movements of the ribs in the oviraptorid theropod dinosaur, Citipati osmolskae, basal avialan species Zhongjianornis yangi, Confuciusornis sanctus, and the more derived ornithurine Yixianornis grabaui, is of the same magnitude as found in extant birds. These skeletal characteristics provide further evidence of a flow-through respiratory system in non-avian theropod dinosaurs and basal avialans, and indicate that uncinate processes are a key adaptation facilitating the ventilation of a lung air sac system that diverged earlier than extant birds.现生鸟类由非鸟类手盗龙类恐龙演化而来的历程，可通过二者共有的行为、形态及生理特征加以佐证。其中一类共有特征为肋钩突（uncinate processes）——现生鸟类的呼吸结构。近期研究指出，窃蛋龙类与驰龙科恐龙体内的这类结构具备呼吸相关功能。本研究通过量化化石胸廓形态的几何特征，证实窃蛋龙类兽脚类恐龙嗜鸟龙（Citipati osmolskae）、基干鸟翼类物种杨氏建昌鸟（Zhongjianornis yangi）、孔子鸟（Confuciusornis sanctus），以及更进步的今鸟型类葛氏义县鸟（Yixianornis grabaui）中，肋钩突赋予肋骨运动的机械优势，其强度与现生鸟类的水平相当。这些骨骼特征进一步为非鸟类兽脚类恐龙与基干鸟翼类拥有单流通呼吸系统（flow-through respiratory system）提供了证据，并表明肋钩突是一项关键适应性特征，助力肺气囊系统的通气——该系统的分化时间早于现生鸟类。