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. Most are viviparous though some are oviparous. Teeth are imbedded in the jaw bone and come in a variety of forms. Well developed brain. Mammals developed from the therapsid ancestors during the Triassic period.