Evolution of modern amphibians

了解当今世界范围内数量急剧减少的现代两栖动物（青蛙、蝾螈和无肢无脊椎动物）的进化史，有助于我们深入了解生态系统重要组成部分的生存和多样化的重要因素。数百年来，现代两栖动物的进化起源一直是脊椎动物动物学中较为棘手的问题之一。每个生活群体的高度专门化的头骨与化石两栖动物的解剖结构有很大的不同，化石记录的巨大空白意味着化石保存了中间解剖结构的缺失，使关系的重建变得复杂。由于运动行为和体型的相似性，共同祖先的证据也被重叠。我的实验室最近的研究已经确定了青蛙和蝾螈与一种特殊的两栖动物化石之间的密切联系，这使我的研究能够集中在两个后续问题上：这种进化变化导致青蛙和蝾螈的机制，以及蛭形动物起源的本质。申请的发现基金将支持从许多不同的方法对这些问题进行研究。工作将继续记录脑壳的解剖结构，它保留了现代和化石两栖动物共同祖先独立于功能趋同的证据，使用微ct成像。我们将使用同步加速器扫描来研究一般蝾螈颅骨形状的变化，然后将其与直接发育或未变形的蝾螈进行比较，以了解更多与不同生活史相关的机制。一组穴居两栖动物化石将被详细研究，以了解头部优先运动如何影响形态，更好地理解共同祖先的证据被功能覆盖的极限。通过这些研究揭示的新数据将被纳入对进化关系的大规模研究，首次在两栖动物的研究中结合形态和分子数据。

Understanding the evolutionary history of modern amphibians (frogs, salamanders, and the limbless caecilians), which are currently undergoing drastic worldwide declines in numbers, provides insight into factors important to the survival and diversification of an important part of our ecosystem. The evolutionary origin of modern amphibians has been one of the more vexing problems in vertebrate zoology for hundreds of years. The highly specialized skulls of each of the living groups differ greatly with the anatomy of fossil amphibians, and large gaps in the fossil record mean fossils preserving intermediary anatomy are absent, complicating the reconstruction of relationships. Evidence for common ancestry is additionally overprinted by similarities due to locomotor behavior and miniaturization. Recent research in my laboratory has established a close link between frogs and salamanders and one particular group of fossil amphibians, which enables my research to focus on two subsequent questions: the mechanisms of this evolutionary change leading to frogs and salamanders, and the nature of caecilian origins. The requested Discovery Grant will support research into these problems from a number of different approaches. Work will continue to document the anatomy of the braincase, which preserves evidence of common ancestry independent of functional convergence, of modern and fossil amphibians using micro-CT imaging. We will use synchrotron scanning to study the change in shape of the skull of a generalized salamander and then compare this with salamanders that directly develop or fail to metamorphose to learn more about the mechanisms associated with different life histories. A group of burrowing fossil amphibians will be studied in detail to understand how head first locomotion can affect morphology, to better understand the limits to which the evidence for common ancestry is overwritten by function. New data revealed through these studies will be incorporated into a large-scale study of evolutionary relationships, combining morphological and molecular data for the first time in a study of amphibians.