Mammals exhibit extraordinary diversity, from the diminutive bumblebee bat, which weighs no more than a penny, to the largest animal to have ever lived, the blue whale. All members of this warm-blooded vertebrate group nurse their young on milk produced by the female’s mammary glands, and, with a few notable exceptions, most also give birth to live young and have bodies insulated by hair. Of the world’s c. 5,500 mammal species, almost one in four are threatened with extinction.

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