When it comes to being mammal, dolphins fit the bill in all respects: they give birth to live young and nurse them, they're warm-blooded, they've got lungs and breathe air (they're also descendants of terrestrial mammals from the Cetartiodactyla clade, which also includes pigs, cows, hippos and camels, among others, and left life on land some 50 million years ago). If you've gotten to pet one at an aquarium, though, you've noticed that dolphins lack the one thing all... READ ON