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Seals are pinnipeds, a group of animals with three separate families—phocidae (eared seals), otaridae (non-eared seals), and odobenidae (walruses)—that are the only mammals that feed in the water and breed on land. Where do they come from? Evidence suggests that pinnipeds evolved from a bear-like land animal that hunted in the water for food.
- 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
- They have been around for a long time. Fossil records indicate that the ancestors of modern seals first entered the ocean on the west coast, about 28–30 million years ago.
- There are three different major types of pinnipeds. “Phocid seals” are also called “true seals” and include several species such as harbor seals and gray seals.
- They have whiskers they use like cats do. Seals and sea lions have many well-developed whiskers, much like cats. Like cats, they have a very acute sense of touch.
- They can go for long periods of time without eating. A seal’s body stores enough fat in the blubber layer to allow the animal to go for extended periods of time without eating.
Sep 25, 2020 · The earless or true seal, also known as the common seal, are themselves part of the Phocidae family, and there are around 33 species of seals, and all are thought to have evolved from land-based, bear or otter-like, ancestors! Where do seals live? Common seals can be found around the coastal water of both the Atlantic and Pacific Oceans.
Feb 9, 2023 · There are over 30 various species of seals and sea lions living in the world’s oceans, all of which swim a great deal faster than the average human. Although they appear clumsy and awkward on land, in the water, the seal uses its torpedo-shaped body and fin-like feet to perform amazing feats of agility and predation.
At sea, these seals move their rear flippers back and forth like a fish's tail to propel themselves through the water. Phocids include the harbor seal and Hawaiian monk seal. Otariids, also known as eared seals, include sea lions and fur seals such as the Steller sea lion and the northern fur seal. Unlike true seals, they have external ear flaps.
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True seals (phocids) probably evolved from otter-like ancestors around the shores of the North Atlantic 15-20 million years ago and are the latest of the sea mammals to have evolved, with the exception of the sea otter. There is some debate as to whether they evolved from the same stock as otariids (sea lions and fur seals) and the walrus.
