A walrus, a massive marine mammal of the Arctic, does not possess true legs, but rather highly specialized limbs called flippers. These appendages are an adaptation from the terrestrial limbs of their ancestors, designed primarily for life in the water. Unlike many other seals, the walrus uses these flippers to move on land in a manner resembling walking. The four flippers are multifunctional tools that enable the walrus to navigate the ice and the open ocean of its frigid habitat.
The Specialized Anatomy of Walrus Limbs
The limbs of the walrus are scientifically classified as flippers, having evolved from the forelimbs and hind limbs of land mammals. The foreflippers, also known as pectoral flippers, contain the same skeletal elements as a human hand and arm, but they are shortened and encased in thick, leathery skin. These foreflippers are relatively short and squared, featuring five digits of nearly equal length, each tipped with a small claw.
The hind flippers are triangular and more robust, holding five bony digits with noticeably larger claws on the three middle digits. The skin on the soles of all four flippers is thick and rough, providing traction on slippery ice floes and rocky haul-out sites. Unlike many other marine mammals, walrus flippers are mostly hairless, which helps reduce drag when the animal is swimming.
Locomotion on Land and Ice
The walrus’s ability to move on land in a manner resembling walking is possible due to the unique rotation of the hind flippers. Like sea lions, the walrus can rotate its hind flippers forward and under its pelvic girdle, bringing them beneath the body. This allows the walrus to move quadrupedally, supporting its enormous body weight on all four appendages.
This rotation, known as plantigrade locomotion, distinguishes the walrus from true seals. True seals have hip joints that prevent their hind flippers from moving forward, forcing them to “galumph” or shimmy on their bellies. When moving on a solid surface, the walrus positions its foreflippers at right angles to the body for support and propulsion. It uses a synchronized, alternating movement of the fore and hind flippers to push and pull itself across the ice and land.
The tusks also play a role in land locomotion, particularly when the walrus is hauling its massive body out of the water onto ice or rocky shores. The tusks are used as tools to hook into the ice, helping to pull the animal’s weight forward. Though they appear slow, walruses can move surprisingly quickly on land for short distances.
Aquatic Movement and Adaptation
While the flippers support the animal on land, their primary function is propulsion in the water. Walruses are primarily hind-flipper-driven swimmers, relying on the alternating strokes of their large, triangular rear flippers for thrust. This swimming method, where the posterior body undulates laterally, is similar to the technique used by true seals.
The foreflippers are not the main source of power for swimming but are used for fine-tuning movement and steering. While moving through the water, the walrus often holds its foreflippers close to its body, using them only to maintain stability and change direction. The flippers are also utilized during benthic foraging, where the walrus uses them to move slowly across the seafloor and create water currents to clear sediment away from prey.