Mammal: Blue whale

The blue whale is the largest animal on earth, and perhaps the largest ever to have existed, usually ranging between 70 and 90 feet in length (though there are records of some that have exceeded the 100-foot mark). These whales have been found in every ocean across the globe, often traveling in pairs; areas off the California coast hold the densest population. Unsurprisingly, being that big requires many calories: Blue whales can eat between 2 and 4 tons of krill (a shrimp-like crustacean) a day.