The origin of powered avian flight was a locomotor innovation that expanded the ecological potential of maniraptoran dinosaurs, leading to remarkable variation in modern birds (Neornithes). The avian sternum is the anchor for the major flight muscles and, despite varying widely in morphology, has not been extensively studied from evolutionary or functional perspectives. We quantify sternal variation across a broad phylogenetic scope of birds using 3D geometric morphometrics methods. Using this comprehensive dataset, we apply phylogenetically informed regression approaches to test hypotheses of sternum size allometry and the correlation of sternal shape with both size and locomotory capabilities, including flightlessness and the highly varying flight and swimming styles of Neornithes. We find evidence for isometry of sternal size relative to body mass and document significant allometry of sternal shape alongside important correlations with locomotory capability, reflecting the effects of both body shape and musculoskeletal variation. Among these, we show that a large sternum with a deep or cranially projected sternal keel is necessary for powered flight in modern birds, that deeper sternal keels are correlated with slower but stronger flight, robust caudal sternal borders are associated with faster flapping styles, and that narrower sterna are associated with running abilities. Correlations between shape and locomotion are significant but show weak explanatory power, indicating that although sternal shape is broadly associated with locomotory ecology, other unexplored factors are also important. These results display the ecological importance of the avian sternum for flight and locomotion by providing a novel understanding of sternum form and function in Neornithes. Our study lays the groundwork for estimating the locomotory abilities of paravian dinosaurs, the ancestors to Neornithes, by highlighting the importance of this critical element for avian flight, and will be useful for future work on the origin of flight along the dinosaur-bird lineage.

中文翻译：

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鸟类胸骨变异与运动方式的关系


鸟类动力飞行的起源是一种运动创新，它扩大了手盗龙恐龙的生态潜力，导致现代鸟类（新鸟类）的显着变异。鸟类胸骨是主要飞行肌肉的锚，尽管形态差异很大，但尚未从进化或功能角度进行广泛研究。我们使用 3D 几何形态测量方法量化鸟类广泛系统发育范围内的胸骨变异。使用这个综合数据集，我们应用系统发育回归方法来测试胸骨尺寸异速的假设以及胸骨形状与尺寸和运动能力的相关性，包括新鸟的不会飞行和高度变化的飞行和游泳风格。我们找到了胸骨尺寸相对于体重等距的证据，并记录了胸骨形状的显着异速生长以及与运动能力的重要相关性，反映了身体形状和肌肉骨骼变化的影响。其中，我们表明，具有较深或向颅骨突出的胸骨龙骨的大胸骨对于现代鸟类的动力飞行是必要的，较深的胸骨龙骨与较慢但较强的飞行相关，坚固的尾部胸骨边界与较快的扑动方式相关，并且较窄的胸骨与跑步能力有关。形状和运动之间的相关性很显着，但解释力较弱，这表明虽然胸骨形状与运动生态学广泛相关，但其他未探索的因素也很重要。这些结果通过提供对新鸟类胸骨形式和功能的新理解，显示了鸟类胸骨对于飞行和运动的生态重要性。 我们的研究通过强调这一关键因素对鸟类飞行的重要性，为估计近鸟恐龙（新鸟的祖先）的运动能力奠定了基础，并将有助于未来研究恐龙-鸟类谱系飞行的起源。