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How Does a Platypus's Fur Help Underwater?

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With a duck-like bill, webbed feet, a tail like a beaver and fur like an otter, the platypus may be the most evolutionarily unique animal on the planet. It's no wonder when the first dried specimens of the animal were presented to the British Museum in 1799, the curator thought he was the victim of a hoax. The creature's fur is one of many adaptations that help this mammal live a semi-aquatic life.

Two Coats Are Better Than One

Platypuses have two layers of fur that perform separate functions and work together to ensure the creatures stay warm and dry as they navigate streams and lakes in search of food. This fur is usually darker brown on their heads and backs, fading to lighter shades of gray and gold on their bellies. Their wooly undercoats are made up of very fine hair packed tightly together. With between 15,000 and 20,000 hairs per square inch of skin, this undercoat is even denser than those of other marine mammals like polar bears and otters. This undercoat is covered with a layer of long, flat-bladed guard hairs that seem to shine when wet.

Tiny Bubbles

When a platypus is swimming, he is followed by a trail of tiny bubbles. These aren't signs the animal can breathe underwater; rather, they are pockets of air released by the platypus's fur as he swims. On land, the two layers of fur work together to trap a layer of air next to the platypus's skin. The trapped air makes the platypus more buoyant when he enters the water. It also keeps his body dry -- important for an animal who spends hours foraging underwater for food he returns to the surface to eat.

Jump In, the Water's Fine

Platypuses are nocturnal and active year-round, which means they spend many winter nights swimming in frigid water. In winter months when water temperatures plummet to near-freezing, their double-layered fur helps keep these mammals warm. While they typically return to the surface after a minute or two when foraging for food, platypuses may remain submerged for more than 10 minutes when resting. Although they can't hold their breath this long, their dense fur ensures platypuses can maintain healthy body temperatures for as many as 12 hours while their bodies remain fully submerged.

A Blessing and a Curse

Their dense fur may help keep these semi-aquatic mammals warm and dry while swimming, but people also had an interest in platypus' waterproof pelts. Until the early 20th century, people hunted platypuses extensively for their fur. Since adults only grow to between 15 and 20 inches long, quite a few platypus pelts were required to make a garment -- as many as 40 pelts just to make a cape. Government conservation programs and protection under Australia's National Parks and Wildlife Act of 1974 have helped populations recover, and platypuses aren't considered endangered or threatened.