The Arctic's two-ton tooth walkers are more than just good-looking. By Mifi Purvis
Walruses have 18 teeth. Two of them, the canids, grow into the animal's trademark enamel tusks. These tusks break through in calves in their first year -- and grow for another 15 years or more.
An Inuit legend says the northern lights are a celestial game of football played by spirits using a walrus skull for a ball. Another story says the lights are walrus spirits playing ball with a human skull, a kind of revenge for all those earthly showdowns between man and beast. Looking at a herd of raucous walruses sunbathing on an ice floe, it seems plausible.
Good at ramming their way through ice, walruses have heads like cannon balls and tusks to die for. Also notable are their sensitive vibrissae, whiskers that the presumed-shortsighted beasts use to find their prey, the mollusks they devour by the ton on the murky seabeds 90 metres underwater.
Walk this way
Walruses have foreshortened limbs evolved from the legs of a terrestrial ancestor. To get around on land or sea ice uglit (places to haul out of the water and rest) they rotate these goofy flipper-feet under their formidable girth, galumphing along like tanks on tiptoe. Awkward? Certainly, but in the water, where they spend two-thirds of their time, they are ballerinas, with hind flippers powering them, and front flippers steering them with precision and grace.
Despite their watery alter egos, walruses rely on uglit for rest, as well as calving. With a mass comprising up to one-third insulating blubber, hauling their huge bodies out of the water is no trivial matter, and their flippers aren't much help. So walruses employ their tusks, up to 100 centimetres long, for the job. Their scientific family name, odobenus, means 'tooth walker' in Greek.
Cozy friends, loving mothers
Walruses are extremely social. They seem to love lying amongst and up against their fellows on uglit, hundreds or even thousands deep. Packed together, they protect their calves from marauding polar bears and share body heat. Ironically, the walruses will stampede towards water when startled, occasionally squashing a smaller member of the herd in their panic.
Walruses enjoy long lives, up to 40 years, so infrequent calving and excellent mothering skills are an adaptive advantage. Mothers fiercely defend calves, piggy back them in water and nurse them for more than two years.
Sizing each other up
Aside from hauling out, tusks are also used to establish social dominance. And for a walrus, size is everything, both in body girth and tusk length. Mature Atlantic bulls from Hudson Bay, Cumberland Sound and the High Arctic Islands average around 1000 kilograms; their Pacific cousins weigh even more. Tusks are flashy, and are mostly just for showing off and jousting for cows. Males have added flesh around their necks that helps compensate for the inevitable jab wounds, but fights rarely get too serious. Inflatable pharyngeal pouches, built-in life preservers that can keep both sexes afloat in the water, also serve to make the sonorous males sing louder during mating season.