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

剑鱼，公海中的针鼻捕食者；比目鱼，美食上熟悉的，奇怪的不对称的底栖生物；雷莫鱼，字面上的挂件，通过鲨鱼头上的吸盘搭在鲨鱼身上；很少有鱼或脊椎动物表现出更惊人的不同的解剖结构或生活模式。尽管它们是不同的，但遗传研究表明，这些鱼，以及其他几种同样具有奇怪特征的鱼，都是密切相关的，在生命树上形成了一个被称为Carangimoga的树枝。在这种情况下，具有共同祖先的生物体会随着时间的推移而分枝，承担不同的身体计划和生活方式，这种情况被称为适应性辐射。之前关于这一主题的研究主要集中在化石记录不佳的生物群体，如变色蜥蜴或慈唇鱼。然而，化石是对进化事件计时的唯一直接手段，并提供了因灭绝而从生命树上修剪下来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组装的至关重要。我们的项目试图将这一特殊的鱼类群体作为实验室，不仅了解它们的专门化是如何产生的，而且还探索化石如何能够特别有用地回答这些问题。具体地说，我们会问：(1)是什么步骤导致了奇特的Carangimorph形体‘设计’的起源；(2)这些变化发生在地质时代的什么时候？(3)关于这些变化发生的速度和方式，化石告诉了我们什么？化石是回答这些问题的关键。例如，最近的发现揭示了比目鱼是如何进化到双眼位于头部一侧的。发现这种过渡形式通常是罕见的，但壮观的活着的角形动物的阵列得到了一大批完整的化石的补充。可以使用现代准备(包括化学处理或类似喷沙的方法)和成像(CT扫描)技术从围岩中提取化石。我们将揭示特殊化石的细节，这些化石记录了现存角叉鱼适应进化的早期阶段，包括比目鱼的剑状鼻子和长臂鱼的吸盘。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之间的关系。我们将把古生物数据与现代鱼类的解剖学和DNA数据结合起来，将化石放在树上和活着的亲戚一起，使我们能够重建导致专门的现代人体计划的变化序列。包括化石和活物种也很重要，因为化石可以影响活物种之间的估计关系，反之亦然。为了建立脊椎动物进化中重大事件的时间表，我们需要找出地球历史上家谱中的每一个分支何时分裂出来。化石是一种罕见的事件，因此，即使是特定分支中最古老的化石也可能是相对较晚的到来。因此，我们需要将我们的化石数据与一种称为分子钟的间接方法结合起来。如果我们知道基因突变积累的速度，我们就可以估计活着的物种在多长时间前彼此分裂，并产生一棵“时间树”：一棵具有绝对时间尺度的家谱。有了所有这些组成部分，我们就可以解决有关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的重要问题。我们的时间树允许我们应用统计工具来确定解剖特征随时间变化的速率。这可以用来观察进化历史早期的变化是迅速的，还是缓慢而渐进的，以及进化的速度是否在海洋和淡水环境中有所不同。关键的是，我们将在有化石和没有化石的情况下进行分析，使我们能够决定仅基于现代数据的研究是否可能具有误导性。

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 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 with equally curious traits, are all 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 or cichlid fishes. 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 was assembled. Our project seeks to use 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 these questions. Specifically, we will ask: (1) what are the steps leading to the origin of 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 answering these questions. For instance, recent discoveries revealed how flatfishes evolved to have both eyes on one side of their head. Finding such transitional forms is typically rare, but the spectacular array of living carangimorphs is complemented by a trove of complete fossils. Modern preparation (involving chemical treatment or methods akin to sandblasting) and imaging (CT scanning) techniques can be used to extract fossils from surrounding rock. We will uncover details of exceptional fossils that document the early stages in the evolution of 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 reconstruct the sequence of changes leading to specialized modern bodyplans. Including both fossils and living species is also important because fossils can influence estimated relationships among living species and vice versa. To build a timeline for major events in 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 all of these components in place, we can address important questions about how fossils impact our understanding of adaptive radiation and the evolution of biodiversity. Our time tree allows us to apply statistical tools for determining 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 of evolution varied between marine and freshwater environments. Critically, we will conduct our analyses with and without fossils, allowing us to decide whether studies based only on modern data might be misleading.