Mammal Traits: Hair and Mammary Glands
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State
Mammals are defined by hair or fur at some life stage and by mammary glands producing milk to nourish offspring.
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A nursing mammal's young feed on milk from mammary glands, a trait no non-mammal vertebrate lineage shares.
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Hair coverage varies widely among adult mammals, including species with little visible hair, but the trait appears at some stage in every mammal.