Ma'anar ƙamus na kalmar "mammaliyan" yana da alaƙa da ko halayen dabbobi masu shayarwa, waɗanda dabbobin kashin baya masu ɗumi-ɗumi masu gashi ko gashi, suna samar da madara don ciyar da 'ya'yansu, kuma yawanci suna haifuwar zuriya. Dabbobi masu shayarwa suna cikin ajin Mammalia, wanda ya haɗa da dabbobi kamar mutane, karnuka, kuliyoyi, saniya, dawakai, da whales. Halayen da ke da alaƙa da dabbobi masu shayarwa sun haɗa da samun zuciya mai ɗaki huɗu, haɗaɗɗiyar kwakwalwa, da diaphragm don numfashi.