|MadSci Network: Development|
Good question. No, gills do not appear at any stage of mammalian development. Some amphibians do go through a stage of gill-breathing, however. We have an evolutionary remnant related to our having gill-breathing ancestors, however, as jaws developed long ago from bony gill support. This happened long ago in certain fish. Lungs also first developed in fish, but the are derived from the swim bladder, not from the gills.
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