Evolution of modern amphibians

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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.