哺乳动物(mammal)
哺乳纲的成员，温血脊椎动物，四肢（有些水生物种除外），与脊索动物门其他各纲的区别在於雌性分泌乳汁的腺体，在发育的一些阶段有毛发存在。其他特徵还包括：下巴直接铰接在头骨上，藉着中耳的骨头听声音，肌肉的横膈分开胸腔与腹腔，以及无核的成熟红血球细胞。哺乳动物小如鼩鼱，大至蓝鲸。单孔目（鸭嘴兽和针鼹）产卵，其他所有的哺乳动物都是直接产下幼雏。有袋目的新生幼子在子宫外面完成发育，有时候是在类似袋囊的构造之中。胎盘哺乳动物（参阅placenta）出生时是较为高等的发育阶段。最早的哺乳动物可追溯至三叠纪晚期（在2亿600万年前结束）；最接近的祖先是兽孔目爬行动物。7000万年来，哺乳动物已经成为地球生态系的优势动物，主要有两个原因：哺乳动物幼子向长辈学习的能力（依靠母亲养育的结果）使其具有强大的行为适应性；温血的身体可适应各种气候与环境。亦请参阅carnivore、cetacean、herbivore、insectivore、omnivore、primate、rodent。
English version：
mammal
Any member of a class (Mammalia) of warm-blooded vertebrates having four limbs (except for some aquatic species) and distinguished from other chordate classes by the female's milk-secreting glands and the presence of hair at some stage of development. Other unique characteristics include a jaw hinged directly to the skull, hearing through bones in the middle ear, a muscular diaphragm separating the pectoral and abdominal cavities, and nonnucleated mature red blood cells. Mammals range in size from the tiny shrew to the enormous blue whale. Monotremes (platypus and echidna) lay eggs; all other mammals bear live young. Marsupial newborns complete their development outside the womb, sometimes in a pouchlike structure. Placental mammals (see placenta) are born at a relatively advanced stage of development. The earliest mammals date from the late Triassic period (ended 206 million years ago); their immediate ancestors were the reptilian therapsids. For 70 million years mammals have been the dominant animals in terrestrial ecosystems, a consequence of two principal factors: the great behavioral adaptability provided by the ability of mammalian young to learn from their elders (a consequence of their dependence on their mothers for nourishment), and the physical adaptability to a wide range of climates and conditions provided by their warm-bloodedness. See also carnivore, cetacean, herbivore, insectivore, omnivore, primate, rodent.