Reconstructing skull evolution of fossil crown birds

什么过程在大时间尺度上形成脊椎动物的多样性？以前的方法集中在许多不同的因素上，从生活史、生态学、生物地理学到大规模的环境变化和灭绝，并且可以使用许多不同的指标来量化多样性。迄今为止，大多数关于脊椎动物多样性进化的研究都集中在相对简单的指标上，特别是分类群计数或单变量指标，如体型。然而，基于这两种方法中的任何一种方法都无法区分大象和鲸鱼，这两种大小相似的哺乳动物在理解和重建生物进化的大多数结果属性上都是不同的。多元形态数据需要更多的时间和精力来收集，但最终提供了一个更完整的进化和古生态变化的画面。此外，形态特征在古生态和古生物学变化研究与遗传和发育因素研究之间提供了一座桥梁，这些因素本质上塑造了生物形态，也必须影响大规模的进化变化模式。因此，要完全理解进化的模式和过程，就需要一种能够完全代表生物体的现象组的方法，即它们可观察到的特征的总和。幸运的是，成像和形态测量数据分析的最新进展现在允许研究大型进化枝的现象进化。近年来，数据收集和数据分析方面的巨大进步，特别是通过对生物体复杂形态的量化，使进化速度的准确性和形成多样性的因素的识别发生了巨大变化。在我的实验室里，我们使用高密度的3D表面形态测量学和CT扫描来重建生物形状的进化，通过发育和跨越时间，连接从胚胎到化石的数据集。许多研究表明，化石数据显著提高了进化重建的准确性；然而，一些高度多样化的现代进化枝，如鸟类，缺乏保存完好的3d化石，这阻碍了它们被纳入这些分析。在这项研究中，该学生将使用尖端的反向变形技术，通过微型ct扫描重建国际收藏的早期冠状鸟类化石的颅骨形态，对这些化石进行高密度3D形态测量分析，并将其与Goswami教授实验室现有的400多只现存鸟类的数据相结合，重建鸟类的早期进化，并确定形成这种高度成功的辐射的生态和环境因素。利用我们最近的分析，确定了鸟类的7个颅模块，他/她将测试与现存和已灭绝鸟类形态多样性的生态和发育驱动因素有关的几个假设，分析进化的速度和模式，以及生态形态学。对早期鸟类的重建本身将对更广泛的社区具有巨大的价值，但该项目最终将提供对鸟类进化的更准确理解，以及是什么推动了它们的巨大多样化。

What processes shape vertebrate diversity over large time scales? Previous approaches to this question have focused on many different factors, from life history, ecology, and biogeography to large-scale environmental change and extinction, and can use many different metrics to quantify diversity. To date, the majority of studies on the evolution of vertebrate diversity have focused on relatively simple metrics, specifically taxon counts or univariate measures, such as body size. However, an approach based on either of those measures would be unable to distinguish between an elephant and a whale, similarly-sized mammals that otherwise differ in most attributes of consequence for understanding and reconstructing organismal evolution. Multivariate morphological data requires more extensive time and effort to collect but ultimately provides a more complete picture of evolutionary and palaeoecological change. Moreover, morphological traits provide a bridge between studies of palaeoecological and palaeobiological change and studies of the genetic and developmental factors that intrinsically shape organismal morphology, and must also influence large-scale patterns of evolutionary change. Thus, a complete understanding of the patterns and processes underlying evolution requires an approach that can fully represent an organism's phenome, the sum total of their observable traits. Fortunately, recent advances in imaging and morphometric data analysis now allow for study of phenomic evolution across large clades. Huge improvements in data collection and data analysis in recent years have produced a step change in accuracy of evolutionary rates and identification of factors shaping diversity, in particular through quantifying the complex morphology of organisms. In my lab, we use high-density 3D surface morphometrics from surface and CT scans to reconstruct the evolution of organismal shape through development and across deep time, bridging datasets from embryos to fossils. Many studies have demonstrated that fossil data significantly improve the accuracy of evolutionary reconstructions; however, several hyperdiverse modern clades, such as birds, lack fossils that are well-preserved in 3-D, hindering their inclusion in these analyses. In this study, the student will use cutting-edge retrodeformation techniques to reconstruct the cranial morphology from micro-CT scans of early crown fossil birds housed in international collections, conduct high-density 3D morphometric analyses of those fossils, and combine them with existing data from Prof. Goswami's lab for over 400 extant birds to reconstruct the early evolution of birds and identify the ecological and environmental factors that shaped this highly successful radiation. Using our recent analyses identifying seven cranial modules in birds, s/he will test several hypotheses relating to ecological and developmental drivers of morphological diversity in living and extinct birds, analysing tempo and mode of evolution, and ecomorphology. The reconstructions of early birds alone will be of immense value to the broader community, but the project will ultimately provide a much more accurate understanding of the evolution of birds and what drove their immense diversification.