Possess hair which is made of keratin. The evolution of mammalian keratin is believed to be independent of reptilian keratin.
Hair provides insulation .
The majority of the heat energy is used to maintain their high body temperature. 4 chambered heart. Mammary glands are used to produce milk to nourish their young. Female glands are the only functional glands. The diaphragm is a muscle that separates the thoracic cavity from the abdominal cavity.