Seal, any of 32 web-footed aquatic mammals that live primarily in cold seas and have a body shape that is round in the middle and tapered at the ends to allow for swift and graceful swimming. Seals are classified into two families: earless or true seals (family Phocidae) and eared seals (family Otariidae), which includes sea lions and fur seals. Eared seals have longer flippers than earless seals, in addition to having external ears. Also, the fur of eared seals is more visible, particularly in sea lions.
Seals are carnivores that primarily eat fish, though some also eat squid, mollusks, and crustaceans. Unlike other seals, the Antarctic leopard seal (Hydrurga leptonyx) feeds primarily on penguins, seabirds, and other seabirds.
The Baikal seal (Phoca sibirica) of Lake Baikal in Siberia, Russia, is the smallest, measuring 1.1-1.4 meters (3.6-4.6 feet) in length and weighing 50-130 kg (110-290 pounds), though some female fur seals weigh less. The male elephant seal (genus Mirounga leonina) of coastal California (including Baja California, Mexico) and South America is the largest, reaching 6.5 metres (21 feet) in length and 3,700 kg in weight (8,150 pounds).
The upper parts of seals' limbs have evolved into flippers, but the long feet and digits have remained. Seals have a thick layer of fat (blubber) beneath their skin that acts as insulation, a food reserve, and contributes to buoyancy.