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| Sea Lion Skull |
They are also large, noisy mammals that gather on beaches, docks and navigation buoys to bark at one another as though someone has violated a complicated parking agreement.
They belong to the family Otariidae, the group known as the eared seals. This family includes both sea lions and fur seals, which means that a fur seal is a sea lion’s closest living relative.
Their next-nearest pinniped cousins are walruses and the “true,” or earless, seals. All belong to the carnivoran group Pinnipedia, a name meaning “fin-footed.”
They are not closely related to actual lions, despite the whiskers, impressive males and tendency to occupy prime waterfront property while roaring at the neighbours.
You can usually distinguish a sea lion from a true seal by looking for three things: visible external ear flaps, long front flippers and an ability to rotate the hind flippers beneath the body.
That rotating hip-and-flipper arrangement allows a sea lion to rise up and walk remarkably well on land.
True seals cannot bring their hind flippers beneath them and must wriggle or bounce along on their bellies. Both approaches are effective, but only one looks as though the animal has temporarily misplaced its legs.
SEA LIONS IN THE FOSSIL RECORD
The deeper history of sea lions begins with the evolution of pinnipeds, whose oldest definitive fossils date from roughly 30.6 to 23 million years ago, during the Oligocene. These early fin-footed carnivores were not modern sea lions, seals or walruses but members of an evolutionary experiment that was gradually transforming land-dwelling hunters into marine specialists.
One famous transitional pinniped is Puijila darwini, an otter-like animal that lived in the Canadian Arctic about 24 million years ago. Puijila had a long tail, muscular limbs and webbed feet rather than full flippers.
It swam through freshwater lakes using its legs, offering us a glimpse of what an early stage in the move from land to sea may have looked like. Picture a large aquatic mustelid testing the water and unknowingly beginning an evolutionary journey that would eventually produce a thousand-kilogram animal shouting from a rock.
The oldest known members of the sea lion and fur seal family are species of Eotaria, discovered in marine rocks of southern California. Eotaria crypta, known from part of a lower jaw with preserved teeth, lived approximately 17.1 to 15 million years ago during the middle Miocene.
These early otariids were much smaller than today’s great bull sea lions and retained some primitive features in their teeth. Their fossils help bridge the anatomical gap between earlier pinnipeds and the more specialized eared seals that followed.
By the late Miocene, otariids such as Pithanotaria and Thalassoleon were swimming in the North Pacific. Fossils of these animals have been recovered from California, Mexico and Japan. Pithanotaria was relatively small, while species of Thalassoleon were larger and more robust.
Together, they document an early radiation of eared seals along the productive coastlines of the North Pacific.
The fossil record suggests that this region was the evolutionary cradle of the family. Sea lions and fur seals remained northern animals for much of their early history before some lineages crossed the equator. Fossil and evolutionary evidence indicates that otariids expanded into the Southern Hemisphere roughly six to seven million years ago, perhaps helped by periods of cooler water and increased marine productivity along the eastern Pacific.
Once across, they diversified around South America and eventually reached the coasts and islands of Australia, New Zealand and the Southern Ocean.
Recognizable members of the living sea lion genera appear much later, mainly during the Pliocene and Pleistocene. An early fossil identified as the modern Steller sea lion, Eumetopias jubatus, comes from Early Pleistocene deposits in Japan.
The fossil record of modern sea lions is frustratingly incomplete, however. Marine mammals often die offshore, where their skeletons may be scattered, scavenged, dissolved or buried somewhere inconvenient beneath several million years of ocean sediment. Palaeontology does not always deliver a complete skeleton with a name tag attached.
WHO ARE THEIR CLOSEST RELATIVES?
Sea lions’ nearest living relatives are the fur seals, with which they share the family Otariidae. The familiar division between “sea lion” and “fur seal” is useful but does not form two perfectly separate evolutionary branches. Genetic research shows that some animals called fur seals are more closely related to particular sea lions than they are to other fur seals. Evolution, as usual, has looked at our tidy filing system and scattered the folders across the floor.
Fur seals generally have dense underfur, more pointed faces and somewhat smaller bodies. Sea lions tend to be larger, with shorter, coarser coats and broad snouts. Both have visible ears and can rotate their hind limbs forward.
Beyond the otariid family, sea lions are related to walruses and true seals. Their more distant living relatives on land lie among the musteloid carnivorans, the broader assemblage that includes weasels, otters, badgers, skunks, raccoons and red pandas. So, if you have ever thought that a sea lion resembles an otter that joined a gym, developed a booming voice and acquired beachfront real estate, you are not entirely without evolutionary support.
WHERE SEA LIONS LIVE TODAY
- Living sea lions occur almost entirely around the Pacific Ocean and in the Southern Hemisphere. The six living species are:
- Steller sea lion — Eumetopias jubatus: Found around the North Pacific, from Japan and Russia through Alaska and south along the western coast of North America.
- California sea lion — Zalophus californianus: Inhabits the Pacific coast of North America, particularly California and Mexico, with animals sometimes travelling much farther north.
- Galápagos sea lion — Zalophus wollebaeki: Lives primarily around the Galápagos Islands.
- South American sea lion — Otaria byronia: Occurs along both the Atlantic and Pacific coasts of South America, from Peru and Brazil southward around Tierra del Fuego.
- Australian sea lion — Neophoca cinerea: Restricted to the southern and western coasts of Australia.
- New Zealand sea lion — Phocarctos hookeri: Found around New Zealand and its subantarctic islands.
A seventh modern species, the Japanese sea lion, Zalophus japonicus, once lived around Japan and neighbouring waters but disappeared during the twentieth century after intense hunting and other human pressures.
Curiously, there are no native sea lions in the North Atlantic. If you encounter a large pinniped lounging on the Canadian Atlantic coast, you are probably looking at a true seal rather than a sea lion.
On the Pacific coast of British Columbia that I call home, however, Steller and California sea lions are familiar residents and visitors. Steller sea lions are the giants of the family: adult males can exceed 1,000 kilograms, making them roughly the mass of a small car, although considerably more opinionated.
BUILT FOR WATER—AND QUITE CAPABLE ON LAND
Sea lions swim mainly by sweeping their long front flippers through the water like wings. Their flexible bodies and powerful shoulders allow them to pursue fish, squid and other marine prey with impressive agility. They can dive for several minutes, slow their heart rate and direct oxygen toward vital organs while underwater.
Their whiskers, properly called vibrissae, are extraordinarily sensitive. They can detect tiny movements and pressure changes left behind by swimming prey, allowing a sea lion to follow a fish’s underwater trail even when visibility is poor. To us, a fish has vanished. To a sea lion, it has left the aquatic equivalent of a glowing arrow marked LUNCH WENT THIS WAY.
Sea lions are also highly intelligent. They can learn complex behaviours, recognize patterns and retain information for long periods. Studies have shown that they can understand relationships between symbols and apply learned rules to new situations.
Their trainability explains their long history in aquariums and marine research programs, although it is worth remembering that “trainable” does not mean “domesticated.” A wild sea lion is still a powerful predator with large teeth and firm opinions about personal space.
They are intensely social, gathering at breeding colonies called rookeries and resting sites called haul-outs. Adult males may establish territories and compete loudly for access to females.
The resulting colony is a dense mixture of barks, growls, grunts, pups calling for their mothers and enormous males arguing over several metres of beach. Imagine a family reunion, a crowded campground and a municipal council meeting occurring simultaneously, but everyone is wearing the same brown coat.
Sea lions are elegant swimmers, successful marine hunters and living representatives of an evolutionary lineage stretching back into the Miocene. Their fossils preserve the story of carnivorous mammals moving into the sea, transforming limbs into flippers and spreading from the North Pacific into southern oceans.
They are, in short, magnificent products of evolution: fast in the water, surprisingly mobile on land, equipped with sensitive whiskers—and absolutely convinced that the entire coastline needs to hear what they have to say.
