Otters

Armpit Pockets and Hammer Rocks

Sea otters wear a winter coat so thick that water never actually touches their skin. They have the densest fur on Earth, with up to one million hairs per square inch. That is more hair on a space the size of a postage stamp than you have on your entire head! Because they do not have blubber (thick layers of fat) like whales to keep them warm, this waterproof coat is their ultimate survival gear. Even cooler: otters have loose folds of skin under their arms that act like built-in pockets. They use these pockets to store food and their favorite rocks, which they use like hammers to smash open clams and crabs.

High-Speed Eaters

To keep their internal heaters running, otters have a super-fast metabolism (the process of turning food into energy). A sea otter has to eat about 25 percent of its body weight every single day. If you weighed 80 pounds, that would be like eating 80 quarter-pound school cafeteria hamburgers every single day just to stay warm. They hunt by diving down to the seafloor, grabbing shellfish, and popping back up to float on their backs while using their chest as a dinner table.

River Sliders vs. Ocean Drifters

There are 13 different species of otters, and they split their time between fresh water and the ocean. River otters are the gymnasts of muddy banks. They build slides on slippery clay slopes or snowbanks, zooming belly-first into the water at speeds up to 18 miles per hour. Sea otters, on the other hand, are the ultimate ocean chillers. To keep from drifting away into the deep ocean while they sleep, they wrap themselves in giant kelp (large sea plants) or hold hands with other otters to form giant, floating family groups called rafts.