Characteristics of MammalsMammals display a remarkable array of adaptations that enable them to inhabit a wide range of habitats. Some of their characteristics are shared by no other groups of animals: hair, mammary glands, three specialized middle-ear bones. HairHair is a defining characteristic of mammals: no other organisms possess true hair and all mammals have hair covering at least part of their body at some time during their life. Hair grows from skin cells known as follicles. The hair shaft is made of a protein called keratin. Hair serves numerous functions.Mammary GlandsMammary glands, like hair, are a uniquely mammalian trait. Though present in both males and females, mammary glands only fully develop in females. Mammary glands consist of ducts and glandular tissues that secrete milk through nipples. Young mammals obtain milk from their mother by feeding from her nipples. The milk provides the young with much needed protein, sugars, fat, vitamins, and salts.Three Middle Ear BonesThese ear bones (the malleus, incus, and stapes) transform sound vibrations into neural impulses.DiaphramFour-Chambered HeartLarge Cerebral Cortex
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