THE MID-PALAEOZOIC BIOTIC CRISIS: SETTING THE TRAJECTORY OF TETRAPOD EVOLUTION

该项目将揭示地球生命进化的一个关键阶段。四肢脊椎动物（四足动物）的出现是一个塑造地球未来进化的事件，包括人类的出现。这个过程开始于大约3.6亿年前的晚古生代，石炭纪早期。在接下来的2000万年里，有肢脊椎动物从泥盆纪的水生和鱼类祖先进化成完全的陆地形式，辐射到占据不同栖息地和生态位的各种身体形式。我们知道这一点，因为我们有足够的化石记录，最早的四肢脊椎动物来自泥盆纪晚期，与陆地形式相比，生活在石炭纪早期，大约3.4亿年前。同样清楚的是，泥盆纪末期发生了一次大规模灭绝事件，之后陆地和淡水栖息地的生命不得不重新建立。不幸的是，从泥盆纪时代结束的2000万年的形成过程中，四足动物化石及其同时代的节肢动物几乎没有代表。因此，我们对四足动物如何进化出适应陆地生活的能力、它们进化的环境以及这些事件的时间或顺序知之甚少。由于缺乏化石信息，这些早期四足动物之间的进化关系以及它们与现代形式的关系也不清楚和有争议。整个化石间隙被称为“罗默的差距”后，美国古生物学家谁第一次认识到这一点。现在，在世界上第一次，几个化石地点代表这一时期已被发现在苏格兰东南部。他们已经提供了丰富的四足动物，鱼类，无脊椎动物和植物的新化石，我们的团队是第一个有机会研究这些材料以及这一重大事件发生的环境，沉积和气候背景的团队。我们有几个主要目标。现有的化石材料将构成这项研究的基线，但该项目将通过进一步挖掘迄今为止发现的最丰富的遗址并对其进行详细的考古风格分析来加强这一点。我们将从其他最近认可的地点收集信息，并探索具有相关潜力的其他地点。将使用一系列现代技术来描述和分析化石材料，以回答与动植物进化有关的许多问题。不仅如此，利用地层学、沉积学、孢粉学、地球化学和同位素数据，我们将确定保存化石的沉积条件、生物生存和死亡的环境以及它们死亡的确切时间。我们将钻一个钻孔，在发现这些化石的整个地质构造中取芯。利用这个钻孔，我们将利用沉积记录提供的信号整合来自化石地点的数据，以建立一个详细的时间线，显示化石发现的层位，每次出现的年龄及其顺序关系。我们将把我们的数据与来自新斯科舍省的同期沉积物的数据进行比较和关联，新斯科舍省是唯一一个信息丰富到有意义的地方。我们的数据将使我们能够推断环境的变化和动物和植物在沉积过程中的进化轨迹，涵盖了泥盆纪末大灭绝后的2000万年。与晚泥盆世的类似数据进行比较，将使我们能够绘制大灭绝前后的变化，推断其原因和后果，并获得详细的记录，确切地了解环境变化与动物群和植物群变化之间的关系。

This project will shed light on a key stage in the evolution of life on Earth. The advent onto land of limbed vertebrates (tetrapods) was an event that shaped the future evolution of the planet, including the appearance of humans. The process began about 360 million years ago, during the late Palaeozoic, in the early part of the Carboniferous Period. Within the 20 million years that followed, limbed vertebrates evolved from their essentially aquatic and fish-like Devonian predecessors into fully terrestrial forms, radiating into a wide range of body forms that occupied diverse habitats and ecological niches. We know this because we have an adequate fossil record of the earliest limbed vertebrates from the Late Devonian, contrasting with the terrestrial forms that lived significantly later in the Early Carboniferous, about 340 million years ago. It is also clear that a mass extinction event occurred at the end of the Devonian, following which life on land and in fresh water habitats had to be re-established. Unfortunately, the formative 20 million years from the end of Devonian times has remained almost unrepresented for fossil tetrapods and their arthropod contemporaries. Thus, we know little about how tetrapods evolved adaptations for life on land, the environments in which they did so, and the timing or sequence of these events. The evolutionary relationships among these early tetrapods and how they relate to modern forms are also unclear and controversial as a result of this lack of fossil information. The entire fossil hiatus has been called 'Romer's Gap' after the American palaeontologist who first recognized it. Now, for the first time anywhere in the world, several fossil localities representing this period have been discovered in south-eastern Scotland. They have already provided a wealth of new fossils of tetrapods, fish, invertebrates and plants, and our team is the first to have the opportunity to study this material and the environmental, depositional, and climatic context in which this momentous episode took place. We have a number of major aims. The existing fossil material will form a baseline for this study, but the project will augment this by further excavating the richest of the sites so far found and subjecting it to a detailed archaeological-style analysis. We will collect from other recently recognized sites and explore for further sites with relevant potential. The fossil material will be described and analysed using a range of modern techniques to answer many questions related to the evolution of the animals and plants. Not only that, using stratigraphical, sedimentological, palynological, geochemical and isotopic data, we will establish the conditions of deposition that preserved the fossils, the environments in which the organisms lived and died, and the precise times at which they did so. We will drill a borehole that will core through the entire geological formation in which these fossils have been found. Using this, we will integrate data from our fossil sites using the signals provided by the sedimentary record to build a detailed time line showing in which horizons the fossils were found, the age of each occurrence and their sequential relationship. We will compare and correlate our data with that from contemporaneous deposits in Nova Scotia, the only other locality with information sufficiently rich to be meaningful. Our data will allow us to infer changes to the environment and the evolutionary trajectories of the animals and plants during the deposition of this formation, covering the 20 million years following the end-Devonian mass extinction. Comparison with similar data for the Late Devonian will allow us to chart the changes around the time of the mass extinction, to infer its causes and consequences, and obtain a detailed record of exactly how changes to the environment correlated with changes to the fauna and flora.