The walrus, Odobenus rosmarus, is a distinctive Arctic marine mammal uniquely adapted to its icy environment. Its massive body, prominent tusks, and thick, wrinkled skin make it instantly recognizable among pinnipeds, which include seals and sea lions. These specialized physical features enable the walrus to navigate, forage, and survive in the harsh, frigid waters and ice floes of the Northern Hemisphere.
Overall Size, Weight, and Body Shape
The walrus possesses a massive, robust, and fusiform body shape, reflecting its adaptation for both aquatic life and resting on land or ice. It is one of the largest pinnipeds, exceeded in size only by the two species of elephant seals. The body is broad at the chest and neck, tapering toward the tail, giving it a bulky appearance when hauled out.
A significant difference in size exists between the sexes, known as sexual dimorphism, with males being notably larger than females. Adult Pacific males are the largest, typically weighing 800 to 1,700 kilograms and reaching 2.7 to 3.6 meters in length. Pacific females weigh less, averaging 400 to 1,250 kilograms. Atlantic walruses are generally smaller; males average around 900 kilograms and females closer to 560 kilograms.
Defining Features: Tusks and Vibrissae
The most prominent physical feature is the pair of tusks, which are elongated upper canine teeth composed primarily of dentine (ivory). Both male and female walruses possess tusks, but those of the males tend to be longer, straighter, and thicker, sometimes growing up to one meter. The tusks grow continuously throughout the animal’s life, serving as multi-purpose tools.
The tusks help the walrus haul its substantial body out of the water onto ice floes or rocky shores, acting as anchors or levers. They also establish social hierarchy and dominance among males, particularly during the breeding season. Walruses use their tusks to create and maintain breathing holes, or savssats, in sea ice up to 20 centimeters thick.
The snout is covered by a dense mat of stiff, sensitive whiskers, called vibrissae. A walrus can have between 400 and 700 individual vibrissae arranged in 13 to 15 rows. These whiskers are supplied with a rich network of nerves and blood vessels, making them highly tactile organs.
The primary function of the vibrissae is to locate prey on the dark, murky seabed. By dragging its snout along the ocean floor, the walrus uses these sensitive bristles to detect and differentiate benthic invertebrates, like clams. This sensory reliance compensates for the walrus’s relatively small eyes and poor underwater visibility.
Skin Texture, Coloration, and Thermoregulation
The walrus’s skin is extremely thick and wrinkled, particularly around the neck and shoulders of males, where it can reach 10 centimeters in thickness. Beneath the skin lies a layer of blubber, up to 15 centimeters thick, providing insulation in the frigid Arctic environment. The skin is sparsely covered with hair, giving the animal a nearly bald appearance.
The skin texture is often characterized by pronounced bumps or nodules, sometimes called bosses, which are more distinct on the shoulders and neck of older males. This nodular texture is considered a secondary sexual characteristic that develops with age and may offer protection during sparring.
Walrus coloration changes dramatically based on temperature, a process related to thermoregulation. When submerged in icy water or after a period of cold, blood vessels near the skin’s surface constrict to conserve heat, causing the walrus to appear pale brown or almost white. Conversely, when the animal hauls out and warms up, peripheral blood vessels dilate to release excess heat. This vasodilation floods the skin with blood, causing the walrus to take on a distinctive reddish or cinnamon-pink coloration.
Specialized Flippers for Movement
The walrus has four flippers: two fore-flippers (pectoral) and two hind-flippers (pelvic), adapted for both aquatic and terrestrial movement. The fore-flippers are relatively short and square-shaped, primarily used for steering and maneuvering while swimming. In the water, the walrus uses alternating strokes of its hind-flippers for propulsion, similar to true seals.
A distinguishing trait of the walrus, shared with sea lions but not true seals, is its ability to rotate its hind-flippers forward and underneath its body. This flexibility allows the animal to lift its torso and support its massive weight, enabling it to “walk” or lumber across land and ice on all four limbs. This adaptation gives the walrus a unique, though slow, terrestrial mobility that is essential for hauling out onto ice floes and rocks.