Data from: Theropod forelimb design and evolution

We examined the relationship between forelimb design and function across the 230-million-year history of theropod evolution. Forelimb disparity was assessed by plotting the relative contributions of the three main limb elements on a ternary diagram. Theropods were divided into five functional groups: predatory, reduced, flying, wing-propelled diving, and flighdess. Forelimbs which maintained their primitive function, predation, are similarly proportioned, but non-avian theropods with highly reduced forelimbs have relatively longer humeri. Despite the dramatically different forces imparted by the evolution of flight, forelimb proportions of basal birds are only slighdy different from those of their non-avian relatives. An increase in disparity accompanied the subsequent radiation of birds. Each transition to flightlessness has been accompanied by an increase in relative humeral length, which results from relatively short distal limb elements. We introduce theoretical predictions based on five biomechanical and developmental factors that may have influenced the evolution of theropod limb proportions.本研究探讨了兽脚类（theropod）恐龙2.3亿年演化历史中前肢构型与功能之间的关联。研究通过将前肢三大主要骨骼元素的相对贡献率绘制于三元图（ternary diagram）中，对前肢形态分异度进行了评估。研究将兽脚类恐龙划分为五大功能类群：掠食型、退化型、飞行型、翼驱动潜水型以及无飞行能力型。保留原始掠食功能的前肢具有相似的骨骼比例，但前肢高度退化的非鸟类兽脚类恐龙，其肱骨（humerus，复数形式为humeri）相对长度更长。尽管飞行演化带来了截然不同的受力变化，但基干鸟类的前肢骨骼比例仅与它们的非鸟类近亲存在细微差异。伴随鸟类后续的辐射演化，前肢形态分异度有所提升。每一次向无飞行能力的演化转变，均伴随着肱骨相对长度的增加，这一变化源于远端肢体骨骼的相对缩短。本研究基于五个可能影响兽脚类前肢骨骼比例演化的生物力学与发育学因素，提出了相应的理论预测。