Why are bottlenose dolphins mammals?

Scientific Classification for Bottle Nosed Dolphin

keep* Kingdom: Animalia

pond* Phylum: Chordata

clean* Class: Mammalia

or* Order: Cetacea

froggy* Family: Delphinidae

gets* Genus: Tursiops

sick* Species: T. Truncatus

*just an easy way to remember it, hope it helps! :p