1. Mammals are endothermic amniotes that possess mammary glands and hair (fur)‏ Mammary glands – produce milk (females only)‏ for offspring Hair – made out of the protein keratin ; helps maintain endothermy There are three groups of mammals

2. While most mammals give birth to young, the monotremes are egg-laying mammals

3. Marsupials – pouched mammals that give birth to undeveloped embryos that then develop inside a pouch

4. Placental mammals – embryo develops inside the mother’s uterus where an organ called the placenta provides the embryo with nutrients and oxygen and removes waste products