Dissertation Research: Origin of the modern avian locomotor system across a neglected evolutionary interval: insight from new methods and new fossils

尽管鸟类飞行在生物学上具有新颖性，但人们对鸟类最新的共同祖先是什么样子，以及该祖先是如何飞行的知之甚少。利用壮观的新化石材料、复杂的成像技术和严格的统计方法，这项研究将重建最有可能的现存鸟类共同祖先的解剖和功能属性，使我们更接近了解现代鸟类及其飞行能力是如何产生的。通过博物馆展品、媒体曝光和创新的在线活动，该项目具有强大的潜力，教育儿童和成年人关于进化生物学和古生物学。研究将从对全面的化石分类群样本进行异速生长分析开始。这项分析的初步结果(基于现有鸟类的13,000个数据点)表明，现有的会飞的鸟类和不会飞的鸟类之间存在基本的异速生长划分。这种划分基于肩关节尺寸和身体质量之间的关系，首次能够描绘出明确的飞行？然后呢？不会飞吗？用于形态的区域。这项新颖的生物力学测试？可以很容易地将动力飞行潜力的概念应用于中生代化石，初步结果表明，获得生物力学上有利的肩/体质量比，使动力飞行在鸟类进化史上的进化时间比传统假设要晚得多。这些结果为一种新的中生代茎鸟后颅骨的几何分析奠定了基础，这将阐明几何现代鸟类飞行装置的出现时间，并将有助于揭示这一深度整合的形态系统的进化动力学。下一步，这项研究将聚焦于鸟类的冠支，并将产生有史以来第一个成年现存鸟类的三维原位肌肉和羽毛重建，这将有助于对现存鸟类的最新祖先的飞行肌肉形态进行稳健的推断。这将为两种关键的化石茎鸟的飞行装置的运动范围模拟奠定基础，并通过来自不同现存分类群的数据进行验证。总之，这里概述的项目将严格地记录和机械地解释脊椎动物进化史上最重要的功能转变之一--获得现代的、动力的鸟类飞行能力。

Despite the biological novelty of avian flight, little is known about what the most recent common ancestor of birds looked like, nor about how that ancestor flew. Using spectacular new fossil material, sophisticated imaging techniques, and rigorous statistical methods, this research will reconstruct the most likely anatomical and functional attributes of the most recent common ancestor of living birds, bringing us closer to understanding how modern birds and their flying ability came to be. Through museum exhibits, media exposure, and innovative online activities, this project has strong potential to educate both children and adults about evolutionary biology and paleontology.The study will begin with allometric analysis of a comprehensive sampling of fossil taxa. Preliminary results from this analysis (based on 13,000 data points from extant birds) indicate a fundamental allometric division between extant flying and flightless birds. This division, based on the relationship between shoulder joint dimensions and body mass, enables, for the first time, the delineation of well-defined ?flying? and ?flightless? zones for morphology. This novel biomechanical ?test? of powered flying potential can easily be applied to Mesozoic fossils, and preliminary results indicate that the acquisition of a biomechanically favorable shoulder:body mass ratio, enabling powered flight, evolved considerably later in avian evolutionary history than is conventionally assumed. These results set the stage for a novel geometric analysis of Mesozoic stem bird postcrania, which will illustrate when the geometrically modern avian flight apparatus arose, and will shed light on the evolutionary dynamics of this deeply integrated morphological system. Next, the study will focus on the avian crown clade, and will generate the first ever three-dimensional in situ muscle and feather reconstructions of adult extant birds, which will facilitate the robust inference of flight muscle morphology for the most recent ancestor of extant birds. This will form the basis of range-of-motion simulations for the flight apparatus of two pivotal fossil stem birds, validated by data from diverse extant taxa. Together, the project outlined here will rigorously document and mechanically interpret one of the most important functional transitions in vertebrate evolutionary history?the acquisition of modern, powered flying ability in birds.