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The earless seals, phocids, or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae (/ ˈ f oʊ s ɪ d iː /). They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae.
- Overview
- Seal diversity
seal, any of 32 species of web-footed aquatic mammals that live chiefly in cold seas and whose body shape, round at the middle and tapered at the ends, is adapted to swift and graceful swimming. There are two types of seals: the earless, or true, seals (family Phocidae); and the eared seals (family Otariidae), which comprise the sea lions and fur seals. In addition to the presence of external ears, eared seals have longer flippers than do earless seals. Also, the fur of eared seals is more apparent, especially in sea lions.
Seals are carnivores, eating mainly fish, though some also consume squid, other mollusks, and crustaceans. Unlike other seals, the leopard seal (Hydrurga leptonyx) of the Antarctic feeds largely on penguins, seabirds, and other seals, in addition to fish and krill. The main predators of seals are killer whales, polar bears, leopard seals, large sharks, and human beings.
The Baikal seal (Phoca sibirica) of Lake Baikal in Siberia, Russia, is the smallest at 1.1–1.4 metres (3.6–4.6 feet) long and 50–130 kg (110–290 pounds), but some female fur seals weigh less. The largest is the male elephant seal (genus Mirounga leonina) of coastal California (including Baja California, Mexico) and South America, which can reach a length of 6.5 metres (21 feet) and a weight of 3,700 kg (8,150 pounds). The upper portions of seals’ limbs are within the body, but the long feet and digits remain, having evolved into flippers. Seals possess a thick layer of fat (blubber) below the skin, which provides insulation, acts as a food reserve, and contributes to buoyancy.
True seals of the genus Phoca are the most abundant in the Northern Hemisphere. They are fairly small, with little difference in size between the sexes. Ringed seals (P. hispida) have blotches over their entire bodies, harp seals (P. groenlandica) have a large blotch of black on otherwise mostly silver-gray fur, harbour seals (P. vitulina) have a marbled coat, and ribbon seals (P. fasciata) have dark fur with ribbons of paler fur around the neck, front limbs, and posterior part of their body.
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Though especially abundant in polar seas, seals are found throughout the world, with some species favouring the open ocean and others inhabiting coastal waters or spending time on islands, shores, or ice floes. The coastal species are generally sedentary, but the oceangoing species make extended, regular migrations. All are excellent swimmers and divers—especially the Weddell seal (Leptonychotes weddellii) of the Antarctic. Various species are able to reach depths of 150–250 metres or more and can remain underwater for 20–30 minutes, with the Weddell seal diving for up to 73 minutes and up to 600 metres. Seals cannot swim as fast as dolphins or whales but are more agile in the water. When swimming, a true seal uses its forelimbs to maneuver in the water, propelling its body forward with side-to-side strokes of its hind limbs. Because the hind flippers cannot be moved forward, these seals propel themselves on land by wriggling on their bellies or pulling themselves forward with their front limbs. Eared seals, on the other hand, rely mainly on a rowing motion of their front flippers for propulsion. Because they are able to turn their hind flippers forward, they can use all four limbs when moving on land.
All seals must come ashore once a year to breed. Nearly all are gregarious, at least when breeding, with some assembling in enormous herds on beaches or floating ice. Most form pairs during the breeding season, but in some species, such as fur seals, the gray seal (Halichoerus grypus), and elephant seals, males (bulls) take possession of harems of cows and drive rival bulls away from their territory. Gestation periods average about 11 months, including a delayed implantation of the fertilized egg in many species. Cows are again impregnated soon after giving birth. Pups are born on the open ice or in a snow lair on the ice. The mother remains out of the water and does not feed while nursing the pups. The young gain weight rapidly, for the cow’s milk is up to about 50 percent fat.
- The Editors of Encyclopaedia Britannica
Seal - Classification, True (Earless) Seals & Eared Seals: Seals include 32 species belonging to 17 genera in two families, Phocidae (true, or earless, seals) and Otariidae (eared seals). They are classified as pinnipeds (suborder Pinnipedia).
- The Editors of Encyclopaedia Britannica
Earless seal, also known as true or crawling seal, is a commonly used name to refer to several species of seals in the family Phocidae, including the harbor seal, grey seal, and ringed seal. Unlike eared seals, they lack external ears. Instead, they have small openings on the sides of their heads.
An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known either as sea lions or fur seals , distinct from true seals (phocids) and the walrus ( odobenids ).
Seals, which are any pinnipeds other than walruses, are placed into two groups: earless seals, comprising the taxonomic family Phocidae (phocids), and eared seals ((or "walking seals"), comprising the family Otariidae. Walruses generally are considered a separate family of pinnipeds, the Obobenidae, although sometimes they are included with the ...
Despite the name, earless seals have ears—they’re just hidden beneath the surface of their skin. Pinnipeds can be found on every continent on Earth, though most species occur in...
