Seals and walruses, both marine mammals, are often confused due to their aquatic lifestyles and similar appearances. While they share a common lineage and adaptations for life in the ocean, they also exhibit clear distinctions. This article explores their shared ancestry, highlights their differences, and examines their common characteristics.
Their Common Ancestry
Seals and walruses belong to the taxonomic order Carnivora, specifically within the suborder Caniformia, which includes dog-like carnivorans. Their evolutionary journey began approximately 50 million years ago, diverging from a common land-dwelling carnivore ancestor. Their closest living relatives are musteloids like weasels, raccoons, and skunks.
These fin-footed, semi-aquatic mammals are grouped under the parvorder Pinnipedia, meaning “fin-footed.” Pinnipedia encompasses three distinct families: Phocidae (true or earless seals); Otariidae (eared seals, including sea lions and fur seals); and Odobenidae, represented by the sole living member, the walrus. Their inclusion within Pinnipedia confirms their shared evolutionary history. Molecular evidence supports Pinnipedia as a monophyletic group, meaning they all descended from a single ancestor.
How They Differ
Walruses are recognizable by their prominent tusks, which are elongated upper canine teeth present in both sexes. These tusks can grow up to 100 centimeters (39 inches) in males and are primarily used for social dominance, hauling out onto ice, and foraging on the seabed. Walruses also possess thick, wrinkled skin and stiff facial bristles, called vibrissae, around their snout. In contrast, seals lack tusks and generally have a smoother appearance.
Locomotion on land differs between these groups. Eared seals (Otariidae) and walruses can rotate their hind flippers forward, enabling them to “walk” on all fours. True seals (Phocidae) cannot rotate their hind flippers; instead, they move on land by undulating their bodies in a caterpillar-like motion, often described as “galumphing.” In water, eared seals primarily use their front flippers for propulsion, while true seals and walruses mainly use their hind flippers, sweeping them side to side for thrust.
Their diets and preferred habitats also differ. Walruses are specialized bottom feeders, primarily consuming mollusks like clams, which they suction from the seabed. They are commonly found in colder Arctic regions, often around ice. Seals have more varied diets, typically feeding on fish, crustaceans, and cephalopods, and inhabit a wider range of marine environments, from polar to temperate waters.
What They Have in Common
Despite their differences, seals and walruses share many adaptations for their semi-aquatic existence. All possess streamlined, spindle-shaped bodies, which reduce drag and allow for efficient movement through water. A thick layer of blubber beneath their skin provides insulation against cold water and serves as an energy reserve, especially during fasting periods. Their limbs are modified into powerful flippers for propulsion and maneuvering in marine environments.
Pinnipeds exhibit shared physiological adaptations for diving, including the ability to hold their breath for extended periods (apnea) and a slowed heart rate (bradycardia), which conserves oxygen. They also have specialized circulatory systems that redistribute blood flow to prioritize organs like the brain, heart, and lungs during dives. Their lungs are designed to collapse under pressure, preventing decompression sickness at depth.
Reproduction in all pinnipeds occurs on land or ice. Females typically give birth to a single pup, and many species gather in large colonies for breeding and resting. Seals and walruses also share developed sensory abilities. Their vision and hearing are adapted for both aquatic and terrestrial environments. They possess sensitive whiskers, or vibrissae, on their snouts, which are used for detecting prey and navigating in murky waters by sensing subtle water movements.