The dolphin is clearly the odd one out here - it's the only marine animal in a lineup of terrestrial mammals! While pigs, rhinos, giraffes, hippos, deer, cows, camels, and goats all evolved to thrive on land, dolphins took the evolutionary road less traveled and went back to the ocean about 50 million years ago. Their ancestors were actually land-dwelling mammals who decided dry land was overrated and returned to the sea. Talk about commitment to the "work from home" lifestyle before it was cool! Taxonomically speaking, dolphins belong to the order Cetacea while the others are scattered across Artiodactyla, Perissodactyla, etc. Next-level biological trick question that would make Darwin chuckle.