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Walruses are famous for their teeth specifically, the enormous tusks that project from their upper jaws. Both sexes have these tusks. In fact, tusks tend to be longer on female Walruses. And what purpose do these massive teeth serve? Well, contrary to popular belief, Walruses don't use their tusks for raking up clams and other food from the ocean bottom. Tusks establish social status, help the Walruses haul themselves onto ice floes, and offer some degree of protection.

Another mammal with unusual teeth is the Sea Otter. It's not their size, though, that distinguishes a Sea Otter's teeth but their color: purple. The color, it seems, is derived from Purple Sea Urchins, a favorite Sea Otter food. Even before they can munch and crunch sea urchins for themselves, baby Sea Otters get purple-stained teeth, presumably from their mother's milk. Of course, Sea Otters in areas that lack Purple Sea Urchins have white teeth.

The mammals with the most teeth are oceanic dolphins. A single such dolphin can have up to 260 teeth, all cone-shaped and spread evenly between the jaws. Whales that eat fish and squid also have a great number of teeth, usually in both the upper and lower jaws. Sperm Whales, Pygmy Sperm Whale, and Risso's Dolphin, though, have teeth only in the lower jaw. And the ten species of baleen whales, the largest mammals on Earth, have no teeth at all. Instead, these whales strain their food by means of long baleen plates.

The land-based North American mammals with the fewest teeth are the many species of rodents with sixteen: two pairs of front teeth (or incisors) for cutting and twelve molars for grinding. A rodent skull of any size is instantly recognizable because of the conspicuous gap between the incisors and molars.

The Lynx and Bobcat both come equipped with twenty-eight teeth, including twelve incisors and four powerful canines. The Alaska Brown Bear, the world's largest land carnivore, has the same number of incisors and canines as these cats but forty-two teeth overall. It does a lot more chewing than the cats and needs more molars. The Virginia Opossum is land record holder for most teeth, with a mouthful of fifty.

The most bizarre mammalian teeth are those of the Narwhal, the Unicorn Whale of Arctic seas. Male Narwhals have only two teeth, both set in the upper jaw. It's the left tooth that makes the animal famous. Imbedded a foot deep in the jaw, the tooth spirals away from the head in a counterclockwise direction, growing up to 9 feet in length.

Unlike the Walrus, a Narwhal actually uses its tusk to dig up food as well as intimidate rivals. Some scientists have even theorized that the Narwhal tusk can funnel and direct a stream of high-frequency call notes from one male toward others in a kind of sonic battle, with ultrasonic sounds the main weapons.