The long-term accumulation of biodiversity has been punctuated by remarkable evolutionary transitions that allowed organisms to exploit new ecological opportunities. Mesozoic flying reptiles (the pterosaurs), which dominated the skies for more than 150 million years, were the product of one such transition. The ancestors of pterosaurs were small and probably bipedal early archosaurs 1 , which were certainly well-adapted to terrestrial locomotion. Pterosaurs diverged from dinosaur ancestors in the Early Triassic epoch (around 245 million years ago); however, the first fossils of pterosaurs are dated to 25 million years later, in the Late Triassic epoch. Therefore, in the absence of proto-pterosaur fossils, it is difficult to study how flight first evolved in this group. Here we describe the evolutionary dynamics of the adaptation of pterosaurs to a new method of locomotion. The earliest known pterosaurs took flight and subsequently appear to have become capable and efficient flyers. However, it seems clear that transitioning between forms of locomotion 2 , 3 —from terrestrial to volant—challenged early pterosaurs by imposing a high energetic burden, thus requiring flight to provide some offsetting fitness benefits. Using phylogenetic statistical methods and biophysical models combined with information from the fossil record, we detect an evolutionary signal of natural selection that acted to increase flight efficiency over millions of years. Our results show that there was still considerable room for improvement in terms of efficiency after the appearance of flight. However, in the Azhdarchoidea 4 , a clade that exhibits gigantism, we test the hypothesis that there was a decreased reliance on flight 5 – 7 and find evidence for reduced selection on flight efficiency in this clade. Our approach offers a blueprint to objectively study functional and energetic changes through geological time at a more nuanced level than has previously been possible. Phylogenetic statistical analyses, biophysical models and information from the fossil record show that an evolutionary signal of natural selection acted to increase the flight efficiency of pterosaurs over millions of years.

中文翻译：

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1.5亿年翼龙飞行效率持续提升

生物多样性的长期积累被显着的进化转变所打断，这些转变使生物体能够利用新的生态机会。统治天空超过 1.5 亿年的中生代飞行爬行动物（翼龙）就是这样一种过渡的产物。翼龙的祖先很小，很可能是双足的早期主龙 1 ，它们当然很好地适应了陆地运动。翼龙在早三叠世时期（大约 2.45 亿年前）与恐龙祖先分离；然而，翼龙的第一批化石可以追溯到 2500 万年后的三叠纪晚期。因此，在没有原翼龙化石的情况下，很难研究飞行最初是如何在这个群体中进化而来的。在这里，我们描述了翼龙适应新运动方法的进化动力学。已知最早的翼龙飞行，随后似乎已经成为有能力和高效的飞行者。然而，似乎很明显，在运动 2 、 3 形式之间的转换——从陆地到飞跃——通过强加高能量负担挑战了早期翼龙，因此需要飞行来提供一些抵消的健康益处。使用系统发育统计方法和生物物理模型，结合化石记录的信息，我们检测到自然选择的进化信号，该信号在数百万年中起到了提高飞行效率的作用。我们的结果表明，飞行出现后，在效率方面仍有相当大的提升空间。然而，在 Azhdarchoidea 4 中，一个表现出巨大的进化枝，我们测试了对飞行 5-7 依赖减少的假设，并找到了在这个进化枝中减少对飞行效率的选择的证据。我们的方法提供了一个蓝图，可以在比以前更细致的水平上客观地研究地质时期的功能和能量变化。来自化石记录的系统发育统计分析、生物物理模型和信息表明，自然选择的进化信号在数百万年间提高了翼龙的飞行效率。我们的方法提供了一个蓝图，可以在比以前更细致的水平上客观地研究地质时期的功能和能量变化。来自化石记录的系统发育统计分析、生物物理模型和信息表明，自然选择的进化信号在数百万年间提高了翼龙的飞行效率。我们的方法提供了一个蓝图，可以在比以前更细致的水平上客观地研究地质时期的功能和能量变化。来自化石记录的系统发育统计分析、生物物理模型和信息表明，自然选择的进化信号在数百万年间提高了翼龙的飞行效率。