Walruses are large, distinctive marine animals that capture public interest. These Arctic inhabitants, known for their prominent tusks and whiskered snouts, navigate icy waters and haul out on land or ice. Understanding their place in the animal kingdom clarifies their unique adaptations and behaviors.
The Walrus’s Mammalian Status
Walruses are indeed mammals. They belong to the class Mammalia, placing them in the same broad category as humans, dogs, and whales.
More specifically, the walrus (Odobenus rosmarus) is a large pinniped marine mammal. Pinnipeds are a diverse group of semi-aquatic marine mammals including seals, sea lions, and walruses. Walruses are part of the order Carnivora, which also encompasses terrestrial carnivores like bears and cats. They are the sole surviving member of the family Odobenidae.
Defining Mammals
Mammals share several fundamental characteristics that distinguish them from other animal classes. A defining trait is the presence of mammary glands, which produce milk to nourish their offspring. This milk provides essential nutrients and antibodies for the young’s early development.
Mammals are also endothermic, commonly known as warm-blooded, meaning they maintain a stable internal body temperature regardless of external conditions. They also have hair or fur at some point in their life cycle. This hair often provides insulation, aiding in temperature regulation.
Most mammals are viviparous, meaning they give birth to live young, with the developing offspring growing inside the mother’s uterus. These traits ensure parental care and developmental support.
Walrus Traits and Mammalian Classification
Walruses exhibit all defining characteristics of mammals, confirming their classification. Like other mammals, walruses are warm-blooded, maintaining a core body temperature of approximately 36.6°C (97.9°F) even in frigid Arctic waters. They achieve this through a thick layer of blubber, up to 10 cm (4 inches) thick, acting as insulation. They also regulate heat through a specialized blood circulation system, constricting blood vessels in colder conditions to reduce heat loss and dilating them when warm to release excess heat.
Walruses possess hair, though it is sparse across much of their bodies, being densest on juveniles and becoming less so with age. Their most prominent hair structures are the stiff, quill-like whiskers, or vibrissae, on their snouts. These vibrissae, numbering between 400 to 700 in 13 to 15 rows, are highly sensitive organs with rich nerve and blood supplies, which they use to detect prey on the seafloor.
Walruses also give birth to live young, typically a single calf after a gestation period of 15 to 16 months, which often includes a period of delayed implantation. Calves are born weighing between 45 to 75 kg (99-165 lb) and are approximately 95 to 123 cm (3-4 ft) long. Female walruses nurse their calves with milk, which is rich in fat and protein, for an extended period, often two years or more. This maternal care solidifies their mammalian status.