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Parallel evolution of vertebrate ears. Tympanic middle-ears capable of receiving air-borne sound evolved separately among the ancestors of mammals (blue), modern frogs (“Anura,” green), “reptiles” (yellow), and birds (“Archosaurs,” orange/red) in the Triassic ∼210–230 million years ago (indicated by black closed circles/oval). Note that no common ancestor with tympanic ears had existed.
