Evolution of modern amphibians

了解现代两栖动物(青蛙、火蜥蜴和无肢毛虫)的进化史，有助于我们深入了解对我们生态系统重要组成部分的生存和多样性至关重要的因素。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比较棘手的问题之一。每一个生物群体的高度专业化的头骨与两栖化石的解剖结构有很大的不同，化石记录中的巨大缺口意味着缺乏保留中间解剖结构的化石，这使得关系的重建变得复杂。由于运动行为和小型化，共同祖先的证据还被相似之处所叠加。我的实验室最近的研究在青蛙和火蜥蜴与一种特殊的两栖动物化石之间建立了密切的联系，这使得我的研究能够集中在两个后续问题上：导致青蛙和火蜥蜴的这种进化变化的机制，以及盲肠起源的性质。申请的探索补助金将支持从许多不同的方法对这些问题进行研究。将继续利用微型CT成像记录现代和化石两栖动物的脑壳解剖结构，其中保存了独立于功能汇聚的共同祖先的证据。我们将使用同步加速器扫描来研究普通火蜥蜴头骨形状的变化，然后将其与直接发育或无法变性的火蜥蜴进行比较，以了解与不同生活史相关的更多机制。将对一组穴居化石两栖动物进行详细研究，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限度。通过这些研究揭示的新数据将被纳入一项大规模的进化关系研究，首次在两栖动物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.