This is an accepted version of this page Pinnipeds (pronounced /ˈpɪnɪˌpɛdz/), commonly known as seals,[a] are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals.

Pinnipeds belong to the suborder Caniformia of the order Carnivora; their closest living relatives are musteloids (weasels, raccoons, skunks and red pandas), having diverged about 50 million years ago.

Besides hunting, pinnipeds also face threats from accidental trapping, marine pollution, climate change and conflicts with local people.

[6] In 1989, Annalisa Berta and colleagues proposed the unranked clade Pinnipedimorpha to contain the fossil genus Enaliarctos and modern seals as a sister group.

This animal is noticeable from its larger size (exceeded only by the elephant seals), nearly hairless skin, flattened snout and long upper canines, known as tusks.

[21] Both Puijila and Potamotherium fossils have been found in lake deposits, suggesting that seal ancestors were originally adapted for fresh water.

[20] Enaliarctos, a fossil species of late Oligocene/early Miocene (24–22 mya) California, closely resembled modern pinnipeds; it was adapted to an aquatic life with flippers and a flexible spine.

[13] One species, Enaliarctos emlongi, exhibited notable sexual dimorphism, suggesting that this physical characteristic may have been an important driver of pinniped evolution.

Males of sexually dimorphic species also tend to have secondary sex characteristics, such as larger or more prominent heads, necks, chests, crests, noses/proboscises and canine teeth as well as thicker fur and manes.

Seals are more agile and flexible,[39] and some otariids, such as the California sea lion, can make dorsal turns as the back of their heads can touch their hind flippers.

[42][43] Compared to terrestrial carnivorans, the fore-limb bones of otariids are reduced in length, giving them less resistance at the elbow joint as the flippers flap;[44] the hind-flippers maneuver them.

[59] The walrus can project its eyes out from its sockets in both a forward and upward direction due to its advanced extraocular muscles and absence of an orbital roof.

Compared to terrestrial mammals, the moustache-like whiskers or vibrissae of pinnipeds have ten times more nerve connections, allowing them to effectively detect vibrations in the water.

[70] Unlike terrestrial mammals, such as rodents, pinnipeds do not sweep their whiskers over an object when examining it, but can protract the hairs forward while holding them steady, maximizing their detection.

[74] During deep dives, any remaining air in their bodies is stored in the bronchioles and trachea, which prevents them from experiencing decompression sickness, oxygen toxicity and nitrogen narcosis.

In addition, seals can tolerate large amounts of lactic acid, which reduces skeletal muscle fatigue during intense physical activity.

[78] The circulatory system of pinnipeds is large and elaborate; retia mirabilia line the inside of the trunk and limbs, allowing for greater oxygen storage during diving.

[83] Like other marine mammals, seals sleep in water with half of their brain awake so that they can detect and escape from predators, as well as surface for air without fully waking.

In non-polar regions, they haul out on to rocky shores, sandy and pebble beaches, sandbanks, tidal flats or pools, and in sea caves.

[99] Complex serrations in the teeth of filter-feeding species, such as crabeater seals, allow water to leak out as they swallow their planktonic food.

[112] Male ringed, crabeater, spotted and hooded seals follow and defend nearby females and mate with them when they reach estrus.

[122] Younger or subdominant male pinnipeds may attempt to achieve reproductive success in other ways including sneakiness, harassment of females or even coordinated disruption of the colony.

Dominant male elephant seals display their status and power with "clap-threats" and loud drum-like calls[146] that may be modified by the proboscis.

These differences are likely important for territorial males becoming accustomed to their neighbors (dear enemy effect) and mothers and pups who need to remain in contact on crowded beaches.

[156] For sea lions used in entertainment, trainers toss a ball at the animal or simply place the object on its nose, so it will eventually understand the behavior desired.

[163] California sea lions are used in military applications by the U.S. Navy Marine Mammal Program, including detecting naval mines and enemy divers.

Weddell seal hunting is forbidden between September and February if the animal is older than a year, to ensure healthy population growth.

The seals were easy targets for organized sealers, fishermen, turtle hunters and buccaneers because they evolved with little pressure from terrestrial predators and were thus "genetically tame".

[181][182] In the Antarctic, the decreased duration and extent of the sea ice and nutrient availability could potentially reduce the survival of Weddell seal pups and may have important implications for population growth rates.

[189] In the 1980s and 1990s, South African politicians and fishermen demanded that brown fur seals be culled, believing that the animals competed with commercial fisheries.