How do palaeontological data refine our understanding of adaptive radiation and the evolution of modern biodiversity?

剑鱼（公海的尖鼻捕食者），比目鱼（烹饪上熟悉的，奇怪的不对称的海底居民），鱼（用头上的吸盘在鲨鱼身上悬挂的真正的悬挂者）：很少有鱼类，或者实际上是脊椎动物，表现出如此惊人的不同的解剖结构或生活方式。基因研究表明，尽管这些鱼类存在分歧，但它们与其他几种鱼类有着密切的关系，在被称为Carangimorpha的生命树上形成了一个分支。像这样的情况，具有共同祖先的生物随着时间的推移而分支出不同的身体计划和生活方式，被称为适应性辐射。此前对这一主题的研究主要集中在化石记录较差的生活群体上，比如变色蜥蜴、慈鲷鱼和达尔文著名的雀类。然而，化石是确定进化事件时间的唯一直接手段，并提供了因灭绝而从生命之树上剪掉的解剖结构的独特证据；因此，它们对于理解现代生物多样性是如何形成的至关重要。我们将把这一特殊的鱼类群体作为实验室来研究，不仅要了解它们的专业化是如何产生的，而且还要探索化石在回答生物多样性和进化问题方面特别有用的方式。具体来说，我们会问：(1)什么步骤导致奇特的变形金刚身体“设计”；(2)这些变化发生在什么地质时代？(3)化石告诉我们这些变化发生的速度和方式是什么？化石是解决这些问题的关键。例如，最近的发现揭示了比目鱼是如何进化成双眼长在头部一侧的。这种过渡形式通常是罕见的，但大量完整的化石补充了现存龙形目的多样性。现代制备（化学处理或类似喷砂的方法）和成像（CT扫描）技术可以从围岩中提取化石。我们将发现一些特殊化石的细节，这些化石显示了现存的龙形目动物在进化的早期阶段的显著适应性，包括长嘴鱼的剑杆状鼻子和䲟鱼的吸盘。化石不能为自己说话，我们也不能简单地通过剥离岩层来追踪进化。我们必须发现化石与现存物种的关系。我们将把古生物学数据、解剖学数据和现代鱼类的DNA数据结合起来，把化石和活着的近亲放在一起，使我们能够重建导致专门的现代身体结构的转变。包括已灭绝物种和现存物种也很重要，因为化石会影响现存物种之间的关系，反之亦然。为了建立一个龙形兽进化的时间表，我们需要找出地球历史上它们家族树中的每一个分支是在什么时候分离出来的。石化是一个罕见的事件，所以即使是一个特定分支的最古老的化石也可能是相对较晚出现的。因此，我们需要将化石数据与一种被称为分子钟的间接方法结合起来。如果我们知道基因突变形成的速度，我们就可以估计出现存物种彼此分离的时间，并得出一个“时间树”：一个具有绝对时间尺度的家谱。有了这些组成部分，我们可以测试化石如何影响我们对适应性辐射和生物多样性进化的理解，以carangimorphs作为测试案例。我们的时间树允许我们应用统计工具来发现解剖特征随时间变化的速率。这可以用来观察在进化史的早期变化是快速的还是缓慢渐进的，以及在海洋和淡水环境中变化的速度是否不同。我们将在有化石和没有化石的情况下进行分析，这使我们能够决定那些只基于现代数据的分析是否会产生误导，以及其他生物学家是否因此应该努力将灭绝的物种包括在他们的研究中。

Swordfishes (needle-nosed predators of the high seas), flounders (gastronomically familiar and bizarrely asymmetrical bottom dwellers), remoras (literal hangers-on that hitch rides on sharks using a suction cup on their heads): few fishes, or indeed vertebrates, show more strikingly different anatomies or modes of life. Divergent as they are, genetic studies indicate that these fishes, as well as several others, are closely related, forming a bough in the tree of life called Carangimorpha. Cases like this, where organisms with shared ancestry branch out over time to assume divergent bodyplans and lifestyles, are known as adaptive radiations. Previous research on this topic has focused on living groups with poor fossil records, like anole lizards, cichlid fishes, and Darwin's famous finches. However, fossils are the only direct means of timing evolutionary events, and yield unique evidence of anatomies pruned from the tree of life by extinction; as such, they are critical in understanding how modern biodiversity came to be. We will study this exceptional group of fishes as a laboratory to not only understand how their specialisations arose, but also explore the ways in which fossils can be especially useful for answering questions of biodiversity and evolution. Specifically, we will ask: (1) what are the steps leading to peculiar carangimorph body 'designs'; (2) when in geological time did these changes occur?; and (3) what do fossils tell us about the speed and manner in which these changes took place?Fossils are critical in solving these problems. For instance, recent discoveries revealed how flatfishes evolved to have both eyes on one side of their head. Such transitional forms are typically rare, but the diversity of living carangimorphs is complemented by a trove of complete fossils. Modern preparation (chemical treatment or methods akin to sandblasting) and imaging (CT scan) techniques can extract fossils from surrounding rock. We will uncover details of exceptional fossils that show the early stages in the evolution of remarkable adaptations of living carangimorphs, including the rapier-like snout of billfishes and the suction disc of remoras.Fossils cannot speak for themselves and we cannot simply trace evolution by peeling back rock layers. We must discover the relationships of fossils to living species. We will combine palaeontological data with anatomy and DNA data from modern fishes to place fossils in a tree alongside living relatives, allowing us to reconstruct the transformations leading to specialized modern bodyplans. Including both extinct and living species is also important because fossils influence estimated relationships among living species and vice versa.To build a timeline for carangimorph evolution, we need to find out when in Earth's history each branch in its family tree split off. Fossilization is a rare event, and so even the oldest fossil of a particular branch might be a relatively late arrival. We therefore need to combine our fossil data with an indirect approach known as the molecular clock. If we know the rate at which genetic mutations build up, we can estimate how long ago living species split from each other and produce a 'time tree': a family tree with an absolute time scale. With these components in place, we can test how fossils impact our understanding of adaptive radiation and the evolution of biodiversity, using carangimorphs as a test case. Our time tree allows us to apply statistical tools for finding the rate at which anatomical features changed over time. This can be used to see whether change was rapid early in evolutionary history or whether it was slow and gradual, and whether rates varied between marine and freshwater environments. We will conduct our analyses with and without fossils, allowing us to decide whether those based only on modern data might be misleading, and if other biologists should therefore strive to include extinct species in their studies.