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Initial Diversification of Living Amphibians Predated the Breakup of Pangaea

1. Departamento de Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales, Consejo Superior de Investigaciones Científicas, José Gutiérrez Abascal, 2, E‐28006 Madrid, Spain;2. Institute for Biodiversity and Ecosystem Dynamics, Zoological Museum, University of Amsterdam, Mauritskade 61, 1092 AD Amsterdam, The Netherlands;3. Lehrstuhl für Zoologie und Evolutionsbiologie, Department of Biology, University of Konstanz, 78457 Konstanz, Germany

The origin and divergence of the three living orders of amphibians (Anura, Caudata, Gymnophiona) and their main lineages are one of the most hotly debated topics in vertebrate evolution. Here, we present a robust molecular phylogeny based on the nuclear RAG1 gene as well as results from a variety of alternative independent molecular clock calibrations. Our analyses suggest that the origin and early divergence of the three living amphibian orders dates back to the Palaeozoic or early Mesozoic, before the breakup of Pangaea, and soon after the divergence from lobe‐finned fishes. The resulting new biogeographic scenario, age estimate, and the inferred rapid divergence of the three lissamphibian orders may account for the lack of fossils that represent plausible ancestors or immediate sister taxa of all three orders and the heretofore paradoxical distribution of some amphibian fossil taxa. Furthermore, the ancient and rapid radiation of the three lissamphibian orders likely explains why branch lengths connecting their early nodes are particularly short, thus rendering phylogenetic inference of implicated relationships especially difficult.