Reconstructing skull evolution of fossil crown birds

在大的时间尺度上，是什么过程塑造了脊椎动物的多样性？以前对这个问题的研究集中在许多不同的因素上，从生活史、生态学和生物地理到大范围的环境变化和灭绝，并可以使用许多不同的衡量标准来量化多样性。到目前为止，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，特别是分类单元计数或单变量指标，如身体大小。然而，基于这两种方法中的任何一种，都无法区分大象和鲸鱼，这两种体型相似的哺乳动物在理解和重建生物进化方面的大多数重要属性都不同。多变量形态数据需要更多的时间和精力来收集，但最终提供了关于进化和古生态变化的更完整的图景。此外，形态特征在古生态和古生物变化的研究和遗传和发育因素的研究之间架起了一座桥梁，遗传和发育因素本质上塑造了生物形态，而且还必须影响大规模的进化变化模式。因此，要完全理解潜在的进化模式和过程，需要一种方法来完全代表有机体的表现组，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分支的表观进化。近年来在数据收集和数据分析方面的巨大改进使进化速度的准确性和影响多样性的因素的识别发生了逐步变化，特别是通过量化生物体的复杂形态。在我的实验室里，我们使用来自表面和CT扫描的高密度3D表面形态测量学来重建生物形状从发育到深层的演变，将数据集从胚胎连接到化石。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支系，如鸟类，缺乏在3-D中保存完好的化石，这阻碍了它们被纳入这些分析。在这项研究中，这位学生将使用尖端的逆向变形技术，从国际收藏的早期冠状化石鸟类的MicroCT扫描中重建颅骨形态，对这些化石进行高密度3D形态测量分析，并将它们与Goswami教授实验室现有的400多种现存鸟类的数据结合起来，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。利用我们最近在鸟类中发现的七个颅骨模块的分析，S/他将检验几个假说，这些假说与现存和灭绝鸟类形态多样性的生态和发展驱动因素有关，分析了进化的节奏和模式，以及生态地貌学。仅重建早起的鸟类就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的了解，以及是什么推动了它们的巨大多样性。

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.