Pinniped

Pinniped

Overview
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s comprising the families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Odobenidae
Odobenidae
Odobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...

 (the walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

), Otariidae (eared seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

s, including sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s and fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...

s), and Phocidae (earless seal
Earless seal
The true seals or earless seals are one of the three main groups of mammals within the seal superfamily, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae...

s).


Pinnipeds are typically sleek-bodied and barrel-shaped. Their bodies are well adapted to the aquatic habitat where they spend most of their lives. Their limbs consist of short, wide, flat flippers
Flipper (anatomy)
A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins , cetaceans A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins (also called...

.
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Encyclopedia
Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s comprising the families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Odobenidae
Odobenidae
Odobenidae is a family of Pinnipeds. The only living species is walrus.In the past, however, the group was much more diverse, and includes more than ten fossil genera.- Taxonomy :All genera, except Odobenus, are extinct.*Prototaria...

 (the walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

), Otariidae (eared seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

s, including sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s and fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...

s), and Phocidae (earless seal
Earless seal
The true seals or earless seals are one of the three main groups of mammals within the seal superfamily, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae...

s).

Overview



Pinnipeds are typically sleek-bodied and barrel-shaped. Their bodies are well adapted to the aquatic habitat where they spend most of their lives. Their limbs consist of short, wide, flat flippers
Flipper (anatomy)
A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins , cetaceans A flipper is a typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example penguins (also called...

. The smallest pinniped, the Baikal seal, weighs about 70 kg (155 lb) on average when full-grown and is 1.3 m (4 ft 3 in) long; the largest, the male southern elephant seal
Southern Elephant Seal
The Southern Elephant Seal is one of the two extant species of elephant seal. It is both the most massive pinniped and member of the order Carnivora living today...

, is over 4 metres (13.1 ft) long and weighs up to 4000 kilograms (8,818.5 lb).

Phocidae


Earless seal
Earless seal
The true seals or earless seals are one of the three main groups of mammals within the seal superfamily, Pinnipedia. All true seals are members of the family Phocidae . They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae...

s, also called true seals, or phocids, are the most diverse and widespread pinnipeds. They lack external ears, have more streamlined snouts, and are generally more aquatically adapted than otariids. They swim with efficient, undulating whole-body movements using their more-developed rear flippers. The swimming efficiency and an array of other physiological adaptations make them better built for deep and long diving and long distance migration. These mammals are, however, very clumsy on land, moving by wriggling their front flippers and abdominal muscles. The two back flippers form a tail-like structure which does not aid walking on land. True seals generally communicate by slapping the water and grunting rather than vocalising.

Otariidae



Eared seal
Eared Seal
The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

s, also called walking seals or otariids, include the animals commonly known as sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s and fur seal
Fur seal
Fur seals are any of nine species of pinnipeds in the Otariidae family. One species, the northern fur seal inhabits the North Pacific, while seven species in the Arctocephalus genus are found primarily in the Southern hemisphere...

s. These vocal, social animals are somewhat better adapted to terrestrial habitats, with rear flippers that can turn forward so they can move on all fours on land. Their fore flippers are larger than those of earless seals and are used as a primary source of maneuverability in the water. Eared seals have external ears, as their name suggests, and more dog-like snouts, further distinguishing them from 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) is unjustified in light of genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 evidence suggesting several fur seal species are more closely related to some sea lions than other fur seals. The iconic ball-balancing circus
Circus
A circus is commonly a travelling company of performers that may include clowns, acrobats, trained animals, trapeze acts, musicians, hoopers, tightrope walkers, jugglers, unicyclists and other stunt-oriented artists...

 seal is generally some species of sea lion, most commonly a California sea lion
California Sea Lion
The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...

.

Odobenidae



The walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

 is an exclusively Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

 species—the sole surviving member of the once diverse and widespread Odobenidae family. They are easily recognized by their long tusks and great bulk of up to 2000 kilograms (4,409.2 lb). 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
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

 in the water column, walrus generally prefer clam
Clam
The word "clam" can be applied to freshwater mussels, and other freshwater bivalves, as well as marine bivalves.In the United States, "clam" can be used in several different ways: one, as a general term covering all bivalve molluscs...

s and other invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s living on the ocean floor
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...

. The unique squirt and suck method of feeding on mollusks
Mollusca
The Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...

 first differentiated the original walrus ancestor from other pinniped lineages. There remains debate as to whether the walrus diverged from the eared seals before or after the true seals.

Flippers



Pinniped limbs, or flippers, are proportionally shorter than those of most other mammals. Because the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of water is much higher than that of air, pinniped flippers can also be proportionally much smaller than the wings of birds or bats, relative to total body size. The digits of each limb are bound together by a web of skin (fingers and toes), and have claws on either their front flippers (earless seals), or their back flippers (eared seals).

Skin/coat/molting



Fur seals have both blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

 and a specially adapted fur coat, including outer guard hairs that repel water and a layer of insulating underfur. For this reason they were particularly prized by sealers. Many species were nearly hunted to extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

.

For most pinniped species, molting is an annual process of replacing worn fur (and in some cases, skin) that temporarily grounds them. Molting can compromise thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...

, so some species, such as elephant seal
Elephant seal
Elephant seals are large, oceangoing seals in the genus Mirounga. There are two species: the northern elephant seal and the southern elephant seal . Both were hunted to the brink of extinction by the end of the 19th century, but numbers have since recovered...

s, fast and remain onshore for a month or more.

In many species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, pups are born with a natal coat of a different length, texture and/or color than adults. This coat is adapted for the terrestrial, preweaning period, either a thick pelage to keep them warm in arctic environments, or a thin layer of fur to keep them cool on summer sands. During their first molt (about 11 days after birth for harp seals), the pups replace this with an adult coat better suited to life at sea. Until this age, pups risk hypothermia
Hypothermia
Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

 and drowning if they spend too much time in the ocean.

Thermoregulation



Pinnipeds use several strategies to conserve body heat while foraging in cold waters. Most primarily rely on a thick layer of blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

 (fat) under their skin, which also provides buoyancy, hydrodynamic shape, and stores energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

. Some young seals have a thick fur
Fur
Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...

 coat as well as blubber
Blubber
Blubber is a thick layer of vascularized adipose tissue found under the skin of all cetaceans, pinnipeds and sirenians.-Description:Lipid-rich, collagen fiber–laced blubber comprises the hypodermis and covers the whole body, except for parts of the appendages, strongly attached to the musculature...

. Additionally, the pinniped circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

 is uniquely adapted to redirect blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 away from body surface areas to prevent heat loss.

Pinnipeds living in warmer climes, such as Galapagos or Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n sea lions, must keep cool when they haul out onto land to rest, breed, and nurse their pups. Strategies include resting in the shade or in tide pool
Tide pool
Tide pools are rocky pools by oceans that are filled with seawater. Many of these pools exist as separate entities only at low tide.Tide pools are habitats of uniquely adaptable animals that have engaged the special attention of naturalists and marine biologists, as well as philosophical...

s, or covering themselves in a thin layer of sand ("sand-flipping"). They can also shunt blood to the surface of their flippers for rapid cooling by waving or dipping in pools.


Pulmonary surfactant


Pinnipeds have unique lungs with airways highly reinforced with cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 and smooth muscle, and alveoli that completely collapse during deeper dives. While overemptying of the lungs in humans classifies as a lung disease and terrestrial mammals are in general unable to empty their lungs, pinnipeds are able to reinflate their lungs even after complete respiratory collapse. Thus, surfactant as an antiadhesive in the regular collapse and reopening of alveoli may be the primary function of the system in pinnipeds. The hydrostatic pressure pinnipeds experience during diving is hypothesized to have acted as an external selection force during evolution for adaptations in their pulmonary surfactant system to meet the challenges of extreme hydrostatic pressure and regularly collapsing lungs. It has been argued that a surfactant complex that functions as an antiadhesive needs to be fluid and highly spreadable. When the surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

 systems of different pinnipeds are analyzed and compared to terrestrial mammals, pinnipeds show different surfactant composition and secretion, probable adaptations for an efficient surfactant system to deal with the pressures of collapsing lungs.

Surfactant composition


When compared to terrestrial mammals (cattle, sheep, pigs, humans), California sea lions (Zalophus californianus), northern elephant seals (Mirounga angusturistris), ringed seal
Ringed Seal
The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the Arctic and sub-Arctic regions...

s (Phoca hispida), and harbor seal
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...

s (Phoca vitulina) have lower levels of anionic surfactant phospholipid
Phospholipid
Phospholipids are a class of lipids that are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from...

s [phosphatidyldlycerol (PG) and phosphatidylinositol (PI)]. Although the role of PG and PI are not clear, they appear to interact with hydrophobic surfactant proteins SP‐B and SP‐C to prevent the irreversible removal of the phospholipids from the surfactant film during alveolar compression and collapse for rapid reinsertion upon re-expansion. There is also a greater percentage of short fatty acid phosphatidylcholine, the primary phospholipid contributor to surfactant function, in pinnipeds than in terrestrial mammals. Since fluidity of the surfactant mixture is also dependent on fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 tail length where length leads to increased surfactant fluidity, the change in tail length may indicate a surfactant system adaptation in response to the selection for an effective antiadhesive surfactant in collapsed lungs of diving pinnipeds.

Surfactant secretion


There is also environmental pressure for a pulmonary surfactant system capable of controlled surfactant secretion even under long periods of hydrostatic
pressure. Alveolar epithelial type II cells, which secrete surfactant when stretched, appear to have decreased sensitivity to pressure in California sea lions compared to terrestrial mammals so that constant levels of surfactant are maintained under long periods of pressure. Furthermore, the gene for leptin
Leptin
Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones...

, a hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 that has a role in surfactant phospholipid synthesis, was found to have nonsynonymous substitutions that are under positive selection in phocids within otherwise highly conserved regions in mammals. The sites of substitution are predicted to be on the exposed sides of leptin, where the changes likely alter leptin function. The modified leptin can then affect surfactant production in phocids.

Other adaptations


Pinniped eyes are well adapted for seeing both above and below the water surface. The animal has a clear membrane
Biological membrane
A biological membrane or biomembrane is an enclosing or separatingmembrane that acts as a selective barrier, within or around a cell. It consists of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content...

 that covers and protects its eyes underwater. In addition, its nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...

s close and blood circulation stops to most of its organs when diving. Testicle
Testicle
The testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...

s and mammary gland
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...

s are located in slits under the skin to maintain the pinniped’s streamlined shape. They also have whiskers to help navigate, and sensors in their skull to absorb sounds underwater and transmit them to the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

.

Reproduction


Males of some species, including elephant seal
Elephant seal
Elephant seals are large, oceangoing seals in the genus Mirounga. There are two species: the northern elephant seal and the southern elephant seal . Both were hunted to the brink of extinction by the end of the 19th century, but numbers have since recovered...

s, South American sea lion
South American Sea Lion
The South American sea lion , also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria...

s, and northern fur seal
Northern Fur Seal
The Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...

s, aggressively defend groups of specific females, referred to as harems. Males of other species, including most sea lions and brown fur seals, defend territories on reproductive rookeries while females move freely between them. Occasionally, violent competition for females or territories is an integral part of male breeding strategy among most pinnipeds. Otariids, which are generally more land-adapted, form major aggregations in the summer months on beaches or rocky outcrops. Consequently, their reproductive behavior is easier to observe and relatively well-studied. Walruses and many phocids, on the other hand, form smaller aggregations, often in remote locations or on ice, and copulate in the water. Their reproductive behavior is less well known.

Females have a postpartum
Postnatal
Postnatal is the period beginning immediately after the birth of a child and extending for about six weeks. Another term would be postpartum period, as it refers to the mother...

 estrus
Estrous cycle
The estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...

 that allows them to mate soon after giving birth. Delayed embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 implantation (embryonic diapause
Embryonic diapause
Delayed Implantation or Embryonic Diapause is a reproductive strategy used by approximately 100 different mammals in seven or eight different orders. In embryonic diapause, the embryo does not immediately implant in the uterus, but is maintained in a state of dormancy. Little to no development...

) obviates the need to come ashore (haul out) to twice a year, once to give birth and again to mate. After giving birth, mothers suckle their young for a variable period. Phocid lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...

 varies from four to 50 days, whereas otarids lactate from four to 36 months. This reflects the fact that phocid feeding grounds tend to be far off shore, so lactation is associated with maternal fasting
Fasting
Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day , or several days. Other fasts may be only partially restrictive,...

. To compensate for the short lactation period, the fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...

 content of phocid milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 (45–60% fat) is higher than in any other marine mammal species. After lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...

, most females migrate to feeding grounds for intensive foraging to recoup energy reserves. Otariid feeding grounds are generally closer to shore and mothers take foraging trips. Otariid milk fat content is lower than that of phocids, owing to the protracted lactation period (typically 25–50%). Protracted nursing also leads to the formation of social bonds.

After the female returns from her first feeding trip, the most important task for her is to find her own pup out of the mass of other pups. Feeding a different mother's pup is a significant waste of energy, as milk production has a high parental cost. The seal overcomes this complication by voice recognition. The mother and pup must learn each other's voices in the first few days after the pup is born, before the dam goes on her next hunt. On returning, the mother seal calls out to her pup, causing the pup to call back. This enables the mother to find her own pup and not waste any energy feeding and taking care of the wrong pup, as this would only decrease her own fitness.

Diving


Pinnipeds can hold their breath for nearly two hours underwater by conserving oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. When the animal starts diving, its heart rate
Heart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....

 slows to about one-tenth of its normal rate. The arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 squeeze shut and the sense organ
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...

s and nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

 are the only organs to receive normal blood flow. They are able to resist more pain and fatigue caused by lactic acid
Lactic acid
Lactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...

 accumulation than other mammals. However, once they return to the surface, they need time to recover and normalize their body chemistry.

Sleep


Pinnipeds spend many months at a time at sea and so they must sleep in the water. Scientists have recorded them sleeping for minutes at a time while slowing drifting downward belly up.

Diet



Pinnipeds are carnivorous
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...

, eating fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, shellfish
Shellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...

, squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

, penguins, and other marine creatures. Most are generalist feeders, but some specialize. For example, Ross seal
Ross Seal
The Ross seal is a true seal with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during James Clark Ross' British Antarctic Expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic...

s and southern elephant seal
Southern Elephant Seal
The Southern Elephant Seal is one of the two extant species of elephant seal. It is both the most massive pinniped and member of the order Carnivora living today...

s mainly feed on squid. Crabeater seal
Crabeater Seal
The crabeater seal, Lobodon carcinophagus, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium to large-sized , relatively slender and pale-colored, found primarily on the free floating pack ice that extends seasonally out from the Antarctic coast, which...

s eat mostly krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...

, and ringed seal
Ringed Seal
The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the Arctic and sub-Arctic regions...

s almost exclusively consume crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s. The walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

 consumes its molluscan prey by sucking the soft parts from the shell.

Some seals eat warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

 prey, including other seals. The leopard seal
Leopard Seal
The leopard seal , also referred to as the sea leopard, is the second largest species of seal in the Antarctic...

, which is probably the most carnivorous and predatory pinniped, eats penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...

s as well as crabeater and Ross seals. The South American sea lion
South American Sea Lion
The South American sea lion , also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria...

 also eats penguins, flying seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...

s and young South American fur seal
South American Fur Seal
The South American Fur Seal is a species of fur seal that breeds on the coasts of Chile and Argentina. The total population is around 250,000....

s. Steller sea lions eat northern fur seal
Northern Fur Seal
The Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...

 pups, common seal
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...

 pups, and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s.

Predation


Almost all pinnipeds are potential prey for orcas and larger shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s. Arctic species are an important component of polar bear
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...

 diets.

Survival


As the Arctic ice pack diminishes due to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

, more species of pinnipeds are hauling out on the shores. Walrus and spotted seals on the coasts of the U.S., Canada and Russia, show increasing signs of an often-fatal, mystery disease of unknown etiology. Harp seals in Greenland may be similarly affected.

Taxonomy


Formerly classified as a separate biological suborder, Pinnipedia is now sometimes considered a subgroup within the suborder Caniformia
Caniformia
Caniformia, or Canoidea , is a suborder within the order Carnivora. They typically possess a long snout and non-retractile claws . The Pinnipedia evolved from caniform ancestors and are accordingly assigned to this group...

 of the order Carnivora
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...

.

Image:Pinniped-phylogeny.gif|803px
rect 684 1 800 11 Canidae
Canidae
Canidae is the biological family of carnivorous and omnivorous mammals that includes wolves, foxes, jackals, coyotes, and domestic dogs. A member of this family is called a canid . The Canidae family is divided into two tribes: Canini and Vulpini...


rect 684 12 800 22 Ursidae
Bear
Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...


rect 684 23 800 33 Odobenus rosmarus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...


rect 684 34 800 44 Callorhinus ursinus
Northern Fur Seal
The Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...


rect 684 45 800 55 Neophoca cinerea
Australian Sea Lion
The Australian Sea Lion , also known as the Australian Sea-lion or Australian Sealion, is a species of sea lion that breeds only on the south and west coasts of Australia...


rect 684 56 800 66 Otaria byronia
rect 684 67 800 77 Arctocephalus pusillus
rect 684 78 800 88 Phocarctos hookeri
New Zealand Sea Lion
The New Zealand Sea Lion also known as Hooker's Sea Lion or Whakahao in Māori is a species of sea lion that breeds around the coast of New Zealand's South Island and Stewart Island/Rakiura to some extent, and to a greater extent around the New Zealand Sub-Antarctic Islands, especially the Auckland...


rect 684 89 800 99 Arctocephalus forsteri
rect 230 191 300 202 Arctocephalus forsteri
rect 684 100 800 110 Arctocephalus australis
South American Fur Seal
The South American Fur Seal is a species of fur seal that breeds on the coasts of Chile and Argentina. The total population is around 250,000....


rect 230 203 300 213 Arctocephalus australis
South American Fur Seal
The South American Fur Seal is a species of fur seal that breeds on the coasts of Chile and Argentina. The total population is around 250,000....


rect 684 111 800 121 Arctocephalus galapagoensis
Galapagos Fur Seal
The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...


rect 230 214 300 224 Arctocephalus galapagoensis
Galapagos Fur Seal
The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...


rect 684 122 800 132 Arctocephalus gazella
Antarctic Fur Seal
The Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. As its name suggests, the Antarctic fur seal is distributed in Antarctic waters. Around 95% of the world population breeds at the Island of South Georgia...


rect 230 225 300 235 Arctocephalus gazella
Antarctic Fur Seal
The Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. As its name suggests, the Antarctic fur seal is distributed in Antarctic waters. Around 95% of the world population breeds at the Island of South Georgia...


rect 684 133 800 143 Arctocephalus tropicalis
Subantarctic Fur Seal
The subantarctic fur seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.- Description :The subantarctic fur seal is...


rect 230 236 300 246 Arctocephalus tropicalis
Subantarctic Fur Seal
The subantarctic fur seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.- Description :The subantarctic fur seal is...


rect 684 144 800 154 Arctocephalus philippii
Juan Fernandez Fur Seal
The Juan Fernández Fur Seal is a fur seal that breeds on the Juan Fernández Islands off the coast of Chile. It is the second smallest of the otariid seal . Discovered by navigator Juan Fernández in the sixteenth century, the seals became a target for sealers in the Maritime Fur Trade era...


rect 230 247 300 257 Arctocephalus philippii
Juan Fernandez Fur Seal
The Juan Fernández Fur Seal is a fur seal that breeds on the Juan Fernández Islands off the coast of Chile. It is the second smallest of the otariid seal . Discovered by navigator Juan Fernández in the sixteenth century, the seals became a target for sealers in the Maritime Fur Trade era...


rect 684 155 800 165 Arctocephalus townsendi
Guadalupe Fur Seal
The Guadalupe fur seal is one of six members of the fur seal genus Arctocephalus. Sealers reduced the population to just a few dozen by the late 19th century, but the species had recovered to 10,000 in number by the late 1990s...


rect 230 258 300 268 Arctocephalus townsendi
Guadalupe Fur Seal
The Guadalupe fur seal is one of six members of the fur seal genus Arctocephalus. Sealers reduced the population to just a few dozen by the late 19th century, but the species had recovered to 10,000 in number by the late 1990s...


rect 684 166 800 176 Eumetopias jubatus
rect 684 177 800 187 Zalophus californianus
California Sea Lion
The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...


rect 684 188 800 198 Erignathus barbatus
Bearded Seal
The bearded seal , also called the square flipper seal, is a medium-sized pinniped that is found in and near to the Arctic Ocean. It gets its generic name from two Greek words that refer to its heavy jaw...


rect 684 199 800 209 Cystophora cristata
Hooded Seal
The hooded seal is an arctic pinniped found only in the central and western North Atlantic ranging from Svalbard in the east to the Gulf of St...


rect 684 210 800 220 Pusa hispida
Ringed Seal
The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the Arctic and sub-Arctic regions...


rect 230 285 300 295 Pusa hispida
Ringed Seal
The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the Arctic and sub-Arctic regions...


rect 684 221 800 231 Pusa sibirica
rect 230 296 300 306 Pusa sibirica
rect 684 232 800 242 Halichoerus grypus
rect 230 307 300 317 Halichoerus grypus
rect 684 243 800 253 Pusa caspica
Caspian Seal
Caspian seals , one of the smallest members of the earless seal family, are unique in that they are found exclusively in the brackish Caspian Sea. They can be found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea...


rect 230 218 300 328 Pusa caspica
Caspian Seal
Caspian seals , one of the smallest members of the earless seal family, are unique in that they are found exclusively in the brackish Caspian Sea. They can be found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea...


rect 684 254 800 264 Phoca largha
Spotted Seal
The spotted seal , also known as the larga or largha seal, is a member of the family Phocidae, and is considered a "true seal". It inhabits ice floes and waters of the north Pacific Ocean and adjacent seas...


rect 230 269 300 339 Phoca largha
Spotted Seal
The spotted seal , also known as the larga or largha seal, is a member of the family Phocidae, and is considered a "true seal". It inhabits ice floes and waters of the north Pacific Ocean and adjacent seas...


rect 684 265 800 275 Phoca vitulina
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...


rect 230 280 300 350 Phoca vitulina
Harbor Seal
The harbor seal , also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere...


rect 684 276 800 286 Histriophoca fasciata
Ribbon Seal
The ribbon seal is a medium-sized pinniped from the true seal family . A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white...


rect 684 287 800 297 Pagophilus groenlandicus
Harp Seal
The harp seal or saddleback seal is a species of earless seal native to the northernmost Atlantic Ocean and adjacent parts of the Arctic Ocean. It now belongs to the monotypic genus Pagophilus. Its scientific name, Pagophilus groenlandicus, means "ice-lover from Greenland", and its synonym, Phoca...


rect 684 298 800 308 Lobodon carcinophagus
Crabeater Seal
The crabeater seal, Lobodon carcinophagus, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium to large-sized , relatively slender and pale-colored, found primarily on the free floating pack ice that extends seasonally out from the Antarctic coast, which...


rect 684 309 800 319 Ommatophoca rossii
Ross Seal
The Ross seal is a true seal with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during James Clark Ross' British Antarctic Expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic...


rect 684 320 800 330 Hydrurga leptonyx
Leopard Seal
The leopard seal , also referred to as the sea leopard, is the second largest species of seal in the Antarctic...


rect 684 331 800 341 Leptonychotes weddellii
Weddell Seal
The Weddell seal , is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound...


rect 684 342 800 352 Mirounga angustirostris
Northern Elephant Seal
The northern elephant seal is one of two species of elephant seal . It is a member of the family Phocidae . Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating...


rect 684 353 800 363 Mirounga leonina
Southern Elephant Seal
The Southern Elephant Seal is one of the two extant species of elephant seal. It is both the most massive pinniped and member of the order Carnivora living today...


rect 684 364 800 375 Monachus monachus
Mediterranean Monk Seal
The Mediterranean monk seal is a pinniped belonging to the Phocidae family. At some 450-510 remaining individuals, it is believed to be the world's second-rarest pinniped , and one of the most endangered mammals in the world.It is present in parts of the Mediterranean Sea and the eastern Atlantic...


rect 684 376 800 387 Monachus schauinslandi
Hawaiian Monk Seal
The Hawaiian monk seal, Monachus schauinslandi, is an endangered species of earless seal in the Phocidae family that is endemic to the Hawaiian Islands....


rect 684 388 800 398 Monachus tropicalis
Caribbean Monk Seal
The Caribbean monk seal or West Indian monk seal is an extinct species of seal. It is the only seal ever known to be native to the Caribbean Sea and the Gulf of Mexico. The last verified recorded sighting occurred in 1952 at Serranilla Bank...


desc none

Above: Phylogeny
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...

 determined from parsimony analysis
Maximum parsimony
Parsimony is a non-parametric statistical method commonly used in computational phylogenetics for estimating phylogenies. Under parsimony, the preferred phylogenetic tree is the tree that requires the least evolutionary change to explain some observed data....

 of 50 maximum likelihood
Maximum likelihood
In statistics, maximum-likelihood estimation is a method of estimating the parameters of a statistical model. When applied to a data set and given a statistical model, maximum-likelihood estimation provides estimates for the model's parameters....

 gene trees


  • Family Odobenidae
    Walrus
    The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

    • Walrus
      Walrus
      The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...

      , Odobenus rosmarus
    • Imagotaria downsi
      Imagotaria
      Imagotaria is an extinct monotypic genus of walrus with the sole species Imagotaria downsi. Fossils of Imagotaria are known from the early late Miocene of California .-Description:...

      (extinct)
  • Family Otariidae
    Eared Seal
    The eared seals or otariids are marine mammals in the family Otariidae, one of three groupings of Pinnipeds. They comprise 16 species in seven genera commonly known either as sea lions or fur seals, distinct from true seals and the Walrus...

    • Genus Arctocephalus
      • Antarctic Fur Seal
        Antarctic Fur Seal
        The Antarctic fur seal is one of eight seals in the genus Arctocephalus, and one of nine fur seals in the subfamily Arctocephalinae. As its name suggests, the Antarctic fur seal is distributed in Antarctic waters. Around 95% of the world population breeds at the Island of South Georgia...

        , A. gazella
      • Guadalupe Fur Seal
        Guadalupe Fur Seal
        The Guadalupe fur seal is one of six members of the fur seal genus Arctocephalus. Sealers reduced the population to just a few dozen by the late 19th century, but the species had recovered to 10,000 in number by the late 1990s...

        , A. townsendi
      • Juan Fernández Fur Seal
        Juan Fernandez Fur Seal
        The Juan Fernández Fur Seal is a fur seal that breeds on the Juan Fernández Islands off the coast of Chile. It is the second smallest of the otariid seal . Discovered by navigator Juan Fernández in the sixteenth century, the seals became a target for sealers in the Maritime Fur Trade era...

        , A. philippii
      • Galápagos Fur Seal
        Galapagos Fur Seal
        The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.- Description :...

        , A. galapagoensis
      • Brown Fur Seal, A. pusillus
        • South African Fur Seal, A. pusillus pusillus
        • Australian Fur Seal, A. pusillus doriferus
      • Australasian Fur Seal, A. forsteri
      • Subantarctic Fur Seal
        Subantarctic Fur Seal
        The subantarctic fur seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.- Description :The subantarctic fur seal is...

        , A. tropicalis
      • South American Fur Seal
        South American Fur Seal
        The South American Fur Seal is a species of fur seal that breeds on the coasts of Chile and Argentina. The total population is around 250,000....

        , A. australis
    • Genus Callorhinus
      • Northern Fur Seal
        Northern Fur Seal
        The Northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea and the Sea of Okhotsk. It is the largest member of the fur seal subfamily and the only species in the genus Callorhinus.-Physical description:Northern fur seals have extreme sexual dimorphism, with males...

        , C. ursinus
    • Genus Eumetopias
      • Steller Sea Lion, E. jubatus
    • Genus Neophoca
      • Australian Sea Lion
        Australian Sea Lion
        The Australian Sea Lion , also known as the Australian Sea-lion or Australian Sealion, is a species of sea lion that breeds only on the south and west coasts of Australia...

        , N. cinerea
    • Genus Otaria
      • South American Sea Lion
        South American Sea Lion
        The South American sea lion , also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria...

        , O. flavescens
    • Genus Phocarctos
      • New Zealand Sea Lion
        New Zealand Sea Lion
        The New Zealand Sea Lion also known as Hooker's Sea Lion or Whakahao in Māori is a species of sea lion that breeds around the coast of New Zealand's South Island and Stewart Island/Rakiura to some extent, and to a greater extent around the New Zealand Sub-Antarctic Islands, especially the Auckland...

        , P. hookeri
    • Genus Zalophus
      • California Sea Lion
        California Sea Lion
        The California sea lion is a coastal sea lion of western North America. Their numbers are abundant , and the population continues to expand about 5% annually. They are quite intelligent and can adapt to man-made environments...

        , Z. californianus
      • Japanese Sea Lion
        Japanese Sea Lion
        The Japanese Sea Lion is thought to have become extinct in the 1970s. Prior to 2003 it was considered to be a subspecies of California Sea Lion as Zalophus californianus japonicus. However, it was subsequently reclassified as a separate species. Some taxonomists still consider it as a subspecies...

        , Z. japonicusextinct
        Extinction
        In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

         (1950s)
      • Galápagos Sea Lion
        Galápagos Sea Lion
        The Galápagos sea lion , a species of sea lion, exclusively breeds on the Galápagos Islands and – in smaller numbers – on Isla de la Plata . Being fairly social, and one of the most numerous species in the Galápagos archipelago, they are often spotted sun-bathing on sandy shores or rock groups or...

        , Z. wollebaeki
  • Family Phocidae
    • Subfamily Monachinae
      • Tribe Monachini
        • Monachopsis (extinct)
        • Pristiphoca (extinct)
        • Properiptychus (extinct)
        • Messiphoca (extinct)
        • Mesotaria (extinct)
        • Callophoca (extinct)
        • Pliophoca (extinct)
        • Pontophoca (extinct)
        • Hawaiian Monk Seal
          Hawaiian Monk Seal
          The Hawaiian monk seal, Monachus schauinslandi, is an endangered species of earless seal in the Phocidae family that is endemic to the Hawaiian Islands....

          , Monachus schauinslandi
        • Mediterranean Monk Seal
          Mediterranean Monk Seal
          The Mediterranean monk seal is a pinniped belonging to the Phocidae family. At some 450-510 remaining individuals, it is believed to be the world's second-rarest pinniped , and one of the most endangered mammals in the world.It is present in parts of the Mediterranean Sea and the eastern Atlantic...

          , Monachus monachus
        • Caribbean Monk Seal
          Caribbean Monk Seal
          The Caribbean monk seal or West Indian monk seal is an extinct species of seal. It is the only seal ever known to be native to the Caribbean Sea and the Gulf of Mexico. The last verified recorded sighting occurred in 1952 at Serranilla Bank...

          , Monachus tropicalis (probably extinct around 1950)
      • Tribe Miroungini
        • Northern Elephant Seal
          Northern Elephant Seal
          The northern elephant seal is one of two species of elephant seal . It is a member of the family Phocidae . Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating...

          , Mirounga angustirostris
        • Southern Elephant Seal
          Southern Elephant Seal
          The Southern Elephant Seal is one of the two extant species of elephant seal. It is both the most massive pinniped and member of the order Carnivora living today...

          , Mirounga leonina
      • Tribe Lobodontini
        • Monotherium wymani (extinct)
        • Ross Seal
          Ross Seal
          The Ross seal is a true seal with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during James Clark Ross' British Antarctic Expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic...

          , Ommatophoca rossi
        • Crabeater Seal
          Crabeater Seal
          The crabeater seal, Lobodon carcinophagus, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium to large-sized , relatively slender and pale-colored, found primarily on the free floating pack ice that extends seasonally out from the Antarctic coast, which...

          , Lobodon carcinophagus
        • Leopard Seal
          Leopard Seal
          The leopard seal , also referred to as the sea leopard, is the second largest species of seal in the Antarctic...

          , Hydrurga leptonyx
        • Weddell Seal
          Weddell Seal
          The Weddell seal , is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound...

          , Leptonychotes weddellii
      • Swan-necked Seal
        Acrophoca
        Acrophoca longirostris is an extinct species of pinniped whose fossils have been discovered in Peru and Chile. It is thought to have been the ancestor of the modern leopard seal....

        , Acrophoca longirostris (extinct)
      • Piscophoca pacifica (extinct)
      • Homiphoca capensis (extinct)
    • Subfamily Phocinae
      • Kawas benegasorum (extinct)
      • Leptophoca lenis (extinct)
      • Preapusa (extinct)
      • Cryptophoca (extinct)
      • Bearded Seal
        Bearded Seal
        The bearded seal , also called the square flipper seal, is a medium-sized pinniped that is found in and near to the Arctic Ocean. It gets its generic name from two Greek words that refer to its heavy jaw...

        , Erignathus barbatus
      • Hooded Seal
        Hooded Seal
        The hooded seal is an arctic pinniped found only in the central and western North Atlantic ranging from Svalbard in the east to the Gulf of St...

        , Cystophora cristata
      • Tribe Phocini
        • Common Seal or Harbor Seal, Phoca vitulina
        • Spotted Seal
          Spotted Seal
          The spotted seal , also known as the larga or largha seal, is a member of the family Phocidae, and is considered a "true seal". It inhabits ice floes and waters of the north Pacific Ocean and adjacent seas...

           or Larga Seal, Phoca largha
        • Ringed Seal
          Ringed Seal
          The ringed seal , also known as the jar seal and as netsik or nattiq by the Inuit, is an earless seal inhabiting the Arctic and sub-Arctic regions...

          , Pusa hispida (formerly Phoca hispida)
        • Baikal Seal or Nerpa, Pusa sibirica (formerly Phoca sibirica)
        • Caspian Seal
          Caspian Seal
          Caspian seals , one of the smallest members of the earless seal family, are unique in that they are found exclusively in the brackish Caspian Sea. They can be found not only along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea...

          , Pusa caspica (formerly Phoca caspica)
        • Harp Seal
          Harp Seal
          The harp seal or saddleback seal is a species of earless seal native to the northernmost Atlantic Ocean and adjacent parts of the Arctic Ocean. It now belongs to the monotypic genus Pagophilus. Its scientific name, Pagophilus groenlandicus, means "ice-lover from Greenland", and its synonym, Phoca...

          , Pagophilus groenlandica (formerly Phoca groenlandicus)
        • Ribbon Seal
          Ribbon Seal
          The ribbon seal is a medium-sized pinniped from the true seal family . A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white...

          , Histriophoca fasciata (formerly Phoca fasciata)
        • Phocanella (extinct)
        • Platyphoca (extinct)
        • Gryphoca (extinct)
        • Gray Seal, Halichoerus grypus

Evolution


Recent molecular evidence suggests that pinnipeds evolved from a bearlike ancestor about 23 million years ago during the late
Chattian
The Chattian is, in the geologic timescale, the youngest of two ages or upper of two stages of the Oligocene epoch/series. It spans the time between and . The Chattian is preceded by the Rupelian and is followed by the Aquitanian .-Stratigraphic definition:The Chattian was introduced by Austrian...

 Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...

 or early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

 epochs, a transitional period between the warmer Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...

 and cooler Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...

 period.
The earliest fossil pinniped that has been found is Puijila darwini, of about 23 million years ago. Pujilla had heavy limbs, indicative of upright movement on land, and flattened phalanges, indicating they were probably webbed, but not yet flippers. The discovery of Pujilla in northern Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 strongly suggests pinnipeds originated in the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

. The reference to Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

 is in honor of his contention made in On the Origin of Species (1859) that
A strictly terrestrial animal, by occasionally hunting for food in shallow water, then in streams or lakes, might at last be converted in an animal so thoroughly aquatic as to brace the open ocean
The otter-like mustelid Potamotherium
Potamotherium
Potamotherium an extinct genus from the Miocene period, which has been assigned both to the mustelids and to the pinnipeds....

may actually represent an even earlier phase in the evolution of pinnipeds.

Another (more advanced) early pinniped is Enaliarctos
Enaliarctos
Enaliarctos is an extinct genus of pinniped.Prior to the discovery of Puijila, the five species in the genus Enaliarctos represented the oldest known pinniped fossils, having been recovered from late Oligocene and early Miocene strata of California and Oregon.It had a short tail and developed...

, 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
Otter
The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

 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 the latter hypothesis is more likely.

Orkney folklore


The folklore of Orkney includes tales of the selkie
Selkie
Selkies are mythological creatures that are found in Faroese, Icelandic, Irish, and Scottish folklore....

 folk ("selkie" being the Orcadian dialect
Orcadian dialect
Orcadian dialect is a dialect of Insular Scots, itself a dialect of the Scots language. It is derived from Lowland Scots with a degree of influence from the Norn language, which is an extinct North Germanic language. Orcadian is spoken in Orkney, north of mainland Scotland.The other Insular Scots...

 word for "seal"), a race of shape-shifting seals that can take human form. To do so they have to remove their seal skin, revealing what appears to be a human underneath. They would also venture onto land for encounters with human women, often unsatisfied ones.

See also



  • Ambulocetus
    Ambulocetus
    Ambulocetus was an early cetacean that could walk as well as swim. It lived during early Eocene some 50-49 million years ago. It is a transitional fossil that shows how whales evolved from land-living mammals. The Ambulocetus fossils were found in Pakistan by anthropologist Johannes Thewissen...

  • Cetacea
    Cetacea
    The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...

  • Nothosaur
    Nothosaur
    Nothosaurs were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail. The feet were paddle-like, and are known to have been webbed in life, to help...

  • Pinnipeds in popular culture
    Pinnipeds in popular culture
    Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine mammals. Seals, sea lions, and walruses are popular pinnipeds in the media. They are often portrayed balancing beach balls on their noses and clapping with their flippers...

  • Seal hunting
    Seal hunting
    Seal hunting, or sealing, is the personal or commercial hunting of seals. The hunt is currently practiced in five countries: Canada, where most of the world's seal hunting takes place, Namibia, the Danish region of Greenland, Norway and Russia...

  • Sirenia
    Sirenia
    Sirenia is an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. Four species are living, in two families and genera. These are the dugong and manatees...

  • Tagging of Pacific Predators
    Tagging of Pacific Predators
    Tagging of Pacific Predators began in 2000 as one of many projects formed by Census of Marine Life, an organization whose goal is to help understand and explain the diversity and abundances of the ocean in the past, present, and future...

  • Vocal learning
    Vocal learning
    Vocal learning is the ability of animals to modify vocal signals in form as a result of experience with those of other individuals. This can lead to signals that are either similar or dissimilar to the model...