Mammals (from Latin mamma "breast") are a group of vertebrate animals constituting the class Mammalia (/məˈmeɪliə/), and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones.
<img src="https://upload.wikimedia.org/wikipedia/commons/a/a2/Mammal_Diversity_2011.png" width="500">
From [Wikipedia](https://en.wikipedia.org/wiki/Mammal) under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.