Warm blooded.
2) Possess hair which is made of keratin. The evolution of mammalian keratin is believed to be independent of reptilian keratin. Hair provides insulation .
3) Endothermic. The majority of the heat energy is used to maintain their high body temperature.
4) Four chambered heart.
5) Mammary glands are used to produce milk to nourish their young. Female glands are the only functional glands.
6) Thediaphragm is a muscle that separates the thoracic cavity from the abdominal cavity.
7) Seven cervical vertebrae (neck bones) are present in most mammals.
8) Most are viviparous though some are oviparous. An extended gestation period uterine development is common in most placental mammals.
9) Teeth are imbedded in the jaw bone and come in a variety of forms.
10) Well developed brain.