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

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

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

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