Everything about Pinniped totally explained
Pinnipeds ("fin-feet", lit. "winged feet") or
fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine
mammals comprising the families
Odobenidae (
walruses),
Otariidae (
eared seals, including
sea lions and
fur seals), and
Phocidae (
true seals). Formerly classified as a separate biological
suborder,
Pinnipedia is now sometimes considered a
superfamily within
Caniformia, a suborder in the
Carnivora order.
Evolution
Recent molecular evidence suggests that pinnipeds evolved from a bearlike ancestor about 23 million years ago during the
late Oligocene or early
Miocene epochs, a transitional period between the warmer
Paleogene and cooler
Neogene period.
The earliest fossil pinniped that had been found is
Enaliarctos, which lived 24 – 22 million years ago. It is believed to have been a good swimmer, but to have been able to move on land as well as in water, more like an otter than like modern pinnipeds. There has been longstanding debate as to whether walruses diverged from a common otariid-phocid ancestor, or whether the phocids diverged before a common otariid-odobenid ancestor. The most recent evidence suggest that the latter hypothesis is more likely.
Overview
Pinnipeds are typically sleek-bodied, barrel-shaped and can be rather large. Their bodies are well adapted to the aquatic habitat where they spend most of their lives. Their limbs have evolved into short, wide, flat
flippers whence the name (derived from the
Latin pinna = "feather", "wing" or "fin", and
ped = foot). The smallest pinniped, the
Galapagos fur seal, weighs about 30 kg (65
lb) when full-grown and is 1.2 m (4
ft) long; the largest, the male
southern elephant seal, is over 4 m (13 ft) long and weighs up to 2,200 kg (4,850 lb, more than 2
tons).
Otariidae
Eared seals, also called "walking seals" and "otariids", include the animals commonly known as
sea lions and
fur seals. These are vocal, social animals that are somewhat better adapted to terrestrial habitats with rear flippers that can turn forward such that they can move on all fours on land. Their foreflippers are larger than those of earless seals and are used as a primary source of maneuverablity in the water. Eared seals have
external ears, as their name suggests, and more dog-like snouts, further distinguishing them from the true seals. While sea lions are generally larger than fur seals and lack the dense underfur of the latter, the long-standing division into subfamilies (
Arctocephalinae and
Otariinae for fur seals and sea lions respectively) has been shown to be unjustified in light of recent genetic evidence suggesting that several fur seal species are more closely related to some sea lions than other fur seals. The iconic ball-balancing
circus seal is generally some species of sea lion, most commonly a
California sea lion.
Phocidae
Earless seals, also called “true seals" or "phocids" are the most diverse and widespread of the pinnipeds. They lack external ears and more streamlined snouts and are generally more aquatically adapted. They swim with efficient undulating whole body movements using their more developed rear flippers. The efficiency of their swimming and an array of other physiological adaptations make them better built for deep and long diving and long distance migrations. They are, however, very cumbersome on land, moving by wriggling their front flippers and abdominal muscles. True seals generally communicate by slapping the water and grunting, rather than vocalizing.
Odobenidae
The
walrus is an exclusively
Arctic species - the sole surviving member of the once diverse and widespread
Odobenidae family. They are easily recognized by their long tusks and great bulk (up to 2000 kg). While they share with otariids the ability to turn their rear flippers forward, their swimming is more reminiscent of that of true seals, relying more on sinuous whole body movements. They also lack external ears. Unlike eared seals and true seals, which feed primarily by hunting fish and squid in the water column, walrus generally prefer
benthic invertebrates, in particular
clams. It is the development of the unique squirt and suck method of feeding on molluscs that differentiated the original walrus ancestor from the other pinniped lineages. There remains debate as to whether the walrus diverged from the eared seals before or after the true seals.
Adaptations
Flippers
Pinnipeds have shorter limbs than most other mammals. As noted above, their limbs have evolved into flippers with true seals having more developed hind flippers and eared seals having more developed fore flippers. The walrus is intermediate between the two. A pinniped’s fingers and toes are bound together by a web of skin. They also have claws that are found either on the front flippers (earless seals) or back flippers (eared seals). Because water has a much higher
density than air, their flippers can be much smaller proportionately in relation to their size than the wings of a bird or bat. Additionally pinnipeds are essentially
weightless in the water, allowing them to come to a standstill, and perform
aquabatic feats in water that would be impossible for atmospheric flying creatures..
Oxygen conservation
Pinnipeds can conserve oxygen for long period of time underwater. When the animal starts diving its heart rate slows to about one-tenth of the normal rate. The arteries squeeze shut and the sense organs and nervous system are the only organs to continue to receive a normal flow of blood. Pinnipeds are able to resist more pain and fatigue caused by lactic acid accumulation than other mammals. However, once they return to the water surface, they need time to recover and bring their body chemistry back to normal.
Warmth
To keep warm in cold waters, pinnipeds have a layer of blubber under their skin (which also provides buoyancy). The thickness depends on the species. Their blubber can also provide food for the animal. Newborn pinnipeds have no blubber.
Some pinnipeds can also can get warm from their fur. The white coat of the infant
harp seal, may trap the energy of sunlight as heat near the skin. As noted above, fur seal have underfur.
Molting
Like other mammals, pinnipeds have to shed their fur once in a while. Eared seals shed more slowly than earless seals. Most earless seals spend time in the water while molting.
Other adaptations
A pinniped’s eyes are well adapted for seeing both above and below the water. When diving the animal has a clear membrane that covers and protects its eyes. In addition, its nostrils close automatically. Testicles and mammary glands are located in slits under the skin to keep the pinniped’s streamlined shape. They also have
whiskers to help navigate and sensors in their skull to absorb sounds underwater and trasmit them to the
cochlea.
Feeding
All pinnipeds are
carnivorous, eating
fish,
shellfish,
squid, and other marine creatures. Most are generalist feeders, but some are specialists. For example;
Ross Seals and
Southern elephant seals mainly feed on squid.
Crabeater seals eat mostly krill, and Ringed seals feed almost exclusively on
crustaceans. Additionally, the
Walrus consumes molluscan prey items by sucking the soft parts from the shell.
Some seals will even eat warm-blooded prey including other seals. The
leopard seal, which is probably the most carnivorous and predatory of all the pinnipeds, will eat
penguins as well as Crabeater and Ross Seals. The
South American sea lion also eats penguin as well as flying seabirds and young
South American fur seals.
Steller sea lions have been recorded eating
Northern fur seal pups,
Common seal pups and birds.
Almost all pinnipeds are potential prey for
orcas and larger
sharks. Arctic species are an important component of
polar bear diet.
Reproduction
Pinnipeds often come ashore or haul out on ice to breed, often travelling long distances from their feeding grounds to suitable
mating grounds with a high level of
reproductive synchrony. Almost all pinnipeds are
polygynous, for example males breed with up to several dozen females in a season. Males of many species, (for example
elephant seals,
South American sea lions and
Northern fur seals) aggressively defend groups of specific females, referred to as
harems. Males of other species (for example most sea lions and
Cape fur seals) defend territories on reproductive rookeries while females move freely between them. Some form of competition, either for females or territories, some of which can be violent, is an integral part of the male breeding strategy among most pinnipeds. Otariids, which are generally more land-adapted, tend to form major aggregations in the summer months on beaches or rocky outcrops. Consequently, their reproductive behavior is easier to observe and well studied. Walruses and many phocids, on the other hand, tend to form smaller aggregations, often in remote locations or on ice, and copulate in the water. Their reproductive behavior is therefore generally less well known.
Females have a
postpartum oestrus allowing them to mate soon after giving birth. Subsequent implantation of the
embryo is delayed (
embryonic diapause) thus removing the need to come ashore (haul-out) twice, once to give birth and again later to mate. After giving birth, mothers suckle their young for a variable length of time. Amongst the phocids, lactation varies from 4 to 50 days, whereas the otarids may lactate from 4 to 36 months. This reflects the fact that phocid feeding grounds tend to be a long way off-shore, so lactation is associated with maternal
fasting. To compensate for the short lactation period, the
fat content of phocid
milk is higher than in any other species of marine mammal (45 – 60% fat). After
lactation most female phocids make extensive migratory movements to feeding grounds for intensive foraging to recoup depleted energy reserves. On the other hand, otarid feeding grounds are generally closer to shore and females go on foraging trips to maintain lactation. Fat content of otarid milk is lower than that of the phocids, owing to the protracted lactatory period (typically 25 – 50%). Protracted nursing also leads to the formation of social bonds.
Taxonomy
- Family Odobenidae
- Family Otariidae
- Genus Arctocephalus
- Genus Callorhinus
- Genus Eumetopias
- Genus Neophoca
- Genus Otaria
- Genus Phocarctos
- Genus Zalophus
- Family Phocidae
- Subfamily Monachinae
- Subfamily Phocinae
In culture
Seals, sea lions, and walruses are popular animals in the media. They are often portrayed balancing beach balls on their noses and clapping with their flippers.
Notable fictional seals include:
Lou Seal: mascot for the San Francisco Giants
Kotick: the main character in Rudyard Kipling's short story The White Seal, later made into a cartoon by Chuck Jones
Salty a seal that appears in the Disney cartoons Pluto's Playmate and Mickey and the Seal and later in Mickey's Mouseworks and House of Mouse
The title character of Andre
Slappy the sea lion from Slappy and the Stinkers
Whiskers from Manta and Moray
Esmeralda the sea lion from the Disney version of 20,000 Leagues Under the Sea
The San-X company characters Mamegoma
The main characters of
Sparky, an escaped seal in the episode "Love and Sandy" from the 1964 television series Flipper
The title character of the two-part television show Sammy, the Way-Out Seal from 1962
An unnamed robotic seal in Sonic the Hedgehog 2 (8-bit), who serves as the boss of the Aqua Lake Zone.
A Pokémon creature Seel
Because of the creature's name being coincidentally spelled the same as the unrelated word "seal" for a stamp, the confusion of one with the other is an occasional comic gag, as in "Christmas seal", or the live seal produced by Harpo Marx in Horse Feathers when Groucho Marx tries to find the legal seal for a contract document.
Notable fictional walruses include:
Chumley, the walrus sidekick to Tennessee Tuxedo (the Penguin) (External Link
)
At least three professional sports teams in the San Francisco, California, area have been known as the "Seals".
Further Information
Get more info on 'Pinniped'.
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