Earless seals, also known as true seals or phocids, are carnivorous mammals belonging to the family Phocidae. They are distinguished by their streamlined bodies, two pairs of flippers, retractable nipples, and internal testicles. Compared to the eared seals of the family Otariidae, earless seals lack the external ear flaps. They also possess retractable nipples and internal testicles, traits absent in their eared counterparts.
These seals inhabit polar, temperate, and tropical waters worldwide, occupying diverse environments such as ice sheets, floes, open waters, and coastlines. The Baikal seal is the only species that lives exclusively in freshwater.
Currently, there are 18 living species of earless seals, classified into two monophyletic subfamilies (Monachinae and Phocinae).
They are generally large and bulky, with the largest species, the southern elephant seal (which is also the largest living member of the order Carnivora), measuring about 19 ft (5.8 m) in length and weighing around 8,800 lb (4,000 kg).
One of the smallest, the Caspian seal, is around 50 in (126 cm) long and weighs approximately 190 lb (86 kg). Even smaller is the ringed seal, which measures 3.8 ft (1.17 m) and 99 lb (45 kg).
The males are generally larger than the females.
These mammals have sleek, hydrodynamic bodies with short, clawed front flippers and longer, paddle-like hind flippers. Unlike eared seals of the Otariidae family, they lack external ear flaps, which is why they are called earless seals. Additionally, they have retractable nipples, internal testicles, and an internal penile sheath, features that further enhance their streamlined form.
Beneath their skin is a smooth, vascularized layer of fat or blubber, which insulates the body. Their coloration ranges from dark gray and black to shades of brown, tan, or even silvery white.
These seals have small noses equipped with hairy whiskers that enhance their ability to detect prey in their aquatic environment.
Recent molecular studies suggest that the family Phocidae includes 2 monophyletic subfamilies: Monachinae and Phocinae. While Monachinae currently contains 5 tribes and 9 genera, Phocinae comprises a single tribe with 5 genera.
In total, there are 18 extant species of earless seals.
Earless seals are sometimes called crawling seals to distinguish them from members of the family Otariidae.
One of the oldest earless seal fossils, Noriphoca gaudini, dates back to the Chattian–Aquitanian boundary, the transition period between the Late Oligocene and Early Miocene epochs (around 23 million years ago). Other fossils that have been discovered belong to the Middle Miocene Epoch (around 15 million years ago).
It was initially believed that earless seals evolved separately from eared seals and walruses, descending from otter-like creatures such as Potamotherium, which lived in European freshwater lakes. However, recent evidence reveals that all these pinnipeds have originated from a single ancestor, the Enaliarctos, which is most closely related to bears and mustelids.
Previously, scientists thought that monk seals and elephant seals entered the Pacific through gaps between North and South America, while Antarctic seals may have traveled along Africa’s west coast. However, recent studies suggest that all three groups actually evolved in the Southern Hemisphere and later spread to their current locations.
Earless seals inhabit oceans across both hemispheres. While most species thrive in polar, subpolar, and temperate regions, only the Hawaiian monk seal occupies tropical waters.
These seals adapt to diverse habitats, including ice sheets, open waters, coastlines, and estuaries. The Baikal seal, found in Lake Baikal, Siberia, is the only species that exclusively inhabits freshwater environments.
They are carnivorous, typically consuming fish, cephalopods (like squid and octopus), crustaceans (like krill and crabs), and mollusks (such as clams and mussels). Depending on the age and season, leopard seals, besides consuming marine invertebrates, also feed on penguins and other pinnipeds, including crabeater seals and Antarctic fur seals.
Unlike eared seals with high speed and maneuverability, earless seals have an efficient movement pattern that helps them travel long distances to attain resources. They typically swim by twisting their bodies sideways and moving their hind flippers. The front flippers help steer the body forward. Females of some species, like the Northern elephant seal, have been found to migrate up to 10,000 km across the Pacific Ocean during a single foraging trip.
On land, however, they move awkwardly, relying on their front flippers and abdominal muscles since they cannot turn their hind flippers downward.
Most earless seals are opportunistic feeders, employing a range of feeding strategies depending on their prey. These include grip-and-tear feeding, filter feeding, suction feeding, and pierce feeding. For instance, leopard seals use suction feeding to consume small fish, filter-feeding to capture krill, and grip-and-tear feeding to hunt penguins.
Unlike eared seals that bark, earless seals emit low-frequency grunts (typically less than 1 kHz) to communicate with their conspecifics. In some North Atlantic colonies, male grey seals have been observed slapping their fore-flippers underwater during the breeding season.
On average, these seals live between 25 and 30 years.
Although these seals spend most of their time at sea, they usually return to land (on pack ice and floes) to breed and give birth. However, some, like harbor seals and northern elephant seals, prefer mating in the water.
Pregnant females spend extended hours foraging at sea, accumulating fat reserves to sustain them during reproduction. The females undergo a gestation period of around 9 months in harbor seals to 11 months in elephant seals, after which they typically give birth to a single pup. Weddell seals have been found to give birth to twins, though such cases are rare.
The newborns are nourished with fat-rich milk, which supports rapid growth and energy storage.
Since the feeding grounds of the mothers are usually miles away from the breeding site, they fast during lactation. The lactating phase lasts for 5 to 7 weeks in monk seals and 3 to 5 days in the hooded seal, after which the mother leaves for the sea, and the pups are weaned.
In the post-weaning phase (ranging from weeks to months, depending on the species), the pups eat no food, drink no water, and live off the fat gathered from their mother’s milk. During this time, they develop their muscles, neural pathways, and oxygen stores. Eventually, when these pups become fully developed, they venture into the waters.
These seals face predation from both aquatic and terrestrial predators. In water, they are hunted by killer whales, sharks, and even other earless seals, such as leopard seals. On land, particularly in the Arctic region, they are vulnerable to polar bears, Arctic foxes, and wolves, whereas in temperate regions, they are occasionally preyed upon by coyotes and red foxes.
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