what makes a mammal a mammal

A mammal is defined primarily by three unique characteristics: the presence of mammary glands which produce milk to feed their young, having hair or fur on their bodies at some stage of life, and having three middle ear bones that aid in hearing. Additionally, mammals are warm-blooded vertebrates with a backbone, typically give live birth (except for the egg-laying monotremes), have a four-chambered heart, possess differentiated types of teeth, and have a well-developed brain region called the neocortex. These features collectively distinguish mammals from other animals.