Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having ...

They're warm-blooded. They have lungs and breathe air. They're also descendants of terrestrial mammals from the Cetartiodactyla clade, which also includes pigs, cows, hippos, camels, and other ...