Mammals are a class of vertebrate animals scientifically known as the Mammalia. They are primarily characterized by the presence of mammary glands in the female which produce milk to feed their young, which (except in the case of the Monotremata which lay eggs), are born live. Mammals are warm-blooded and most are hairy.
The first fossils of mammals appeared 178 million years ago during the Jurassic.[1]- ↑ Pickrell, J. (2019, October 23). How the earliest mammals thrived alongside dinosaurs. Nature News. Retrieved March 10, 2022, from https://www.nature.com/articles/d41586-019-03170-7#:~:text=Mammals%20first%20appeared%20at%20least,out%2066%20million%20years%20ago.