Earliest known crown-group salamanders

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Abstract
Salamanders are a model system for studying the rates and patterns of the evolution of new anatomical structures1,2,3,4. Recent discoveries of abundant Late Jurassic and Early Cretaceous salamanders are helping to address these issues5,6,7,8. Here we report the discovery of well-preserved Middle Jurassic salamanders from China, which constitutes the earliest known record of crown-group urodeles (living salamanders and their closest relatives). The new specimens are from the volcanic deposits of the Jiulongshan Formation (Bathonian)9,10,11,12,13, Inner Mongolia, China, and represent basal members of the Cryptobranchidae, a family that includes the endangered Asian giant salamander (Andrias) and the North American hellbender (Cryptobranchus). These fossils document a Mesozoic record of the Cryptobranchidae, predating the previous record of the group by some 100 million years14,15,16,17. This discovery provides evidence to support the hypothesis that the divergence of the Cryptobranchidae from the Hynobiidae had taken place in Asia before the Middle Jurassic period.