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Classification and common traits:
mammals: mammary glands, hair/fur
reptile: hard covering
birds: hollow bones, can fly
fish: in water, cold blooded
amphibian: closely resembles reptiles

Classification and trait only the animals of the classification can have
mammals: gives birth to live young and cares for young
reptiles: vertebrates which have scaly covering
birds: feathers
fish: cold - blooded, have gills
amphibian: should have had gills even for part of their life, has permeable covering