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Earless seal

2007 Schools Wikipedia Selection. Related subjects: Mammals

    How to read a taxoboxEarless Seals
   Grey seal
   Grey seal
         Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Mammalia
   Order:    Carnivora
   Suborder: Pinnipedia
   Family:   Phocidae
             Gray, 1821

                                   Genera

   Monachus (Monk Seals)
   Mirounga (Elephant Seal)
   Lobodon (Crabeater Seals)
   Leptonychotes
   Hydrurga (Leopard Seals)
   Ommatophoca
   Erignathus (Bearded Seals)
   Phoca
   Halichoerus (Grey Seals)
   Cystophora (Hooded Seals)

   The true seals or earless seals are one of the three main groups of
   mammals within the seal suborder, 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 family
   Otariidae.

   Phocids are the more highly specialized for aquatic life of the two
   groups and, unlike otariids, lack external ears and cannot bring their
   hind flippers under their body to walk on them.

   They are more streamlined than fur seals and sea lions, and can
   therefore swim more effectively over long distances than those can.
   However, because they cannot turn their hind flippers downward, they
   are very clumsy on land, having to wriggle with their front flippers
   and abdominal muscles; this method of locomotion is called galumphing.

   Additionally, true seals do not communicate by "barking" like the fur
   seals and sea lions of family Otariidae. They communicate by slapping
   the water and grunting.

Feeding and reproduction

   Earless Seal in Argentina
   Earless Seal in Argentina

   While otariids are built for speed and maneuverability in the water,
   phocids are built for efficient, economical movement. This allows most
   phocids to make long foraging trips to exploit prey resources that are
   far from land, whereas otariids are tied to rich upwelling zones close
   to their breeding sites. The phocid reproductive cycle is characterized
   by temporal and spatial separation between feeding and maternal
   investment; in other words, a pregnant female spends a long period of
   time foraging at sea, building up her fat reserves, and then returns to
   the breeding site and uses her stored energy reserves to provide milk
   for her pup. It should be noted that the common seal ( harbour seal in
   the U.S.), Phoca vitulina, does not separate foraging and maternal
   investment; instead, it displays a reproductive strategy similar to
   those of otariids, in which the mother makes short foraging trips
   between nursing bouts.

   Because a phocid mother's feeding grounds are often hundreds of
   kilometers from the breeding site, this means that she must fast while
   she is lactating. This combination of fasting with lactation is one of
   the most unusual and extraordinary behaviors displayed by the Phocidae,
   because it requires the mother seal to provide large amounts of energy
   to her pup at a time when she herself is taking in no food (and often,
   no water) to replenish her stores. Because they must continue to burn
   fat reserves to supply their own metabolic needs while they are feeding
   their pups, phocid seals have developed an extremely thick, fat-rich
   milk that allows them to provide their pups with a large amount of
   energy in as small a period of time as possible. This allows the mother
   seal to maximize the efficiency of her energy transfer to the pup and
   then quickly return to sea to replenish her reserves. The length of
   lactation in phocids ranges from 28 days in the Northern Elephant Seal
   to just 3–5 days in the Hooded Seal. The nursing period is ended by the
   mother, who departs to sea and leaves her pup at the breeding site.
   Pups will continue to nurse if given the opportunity, and "milk
   stealers" that suckle from unrelated, sleeping females are not
   uncommon; this often results in the death of the pup whose mother the
   milk was stolen from, as any single female can only produce enough milk
   to provision one pup.

   Because the pup receives the milk energy from its mother so quickly,
   its development is typically not complete enough for it to begin
   foraging on its own as soon as the nursing period is complete. Seals,
   like all marine mammals, need time to develop the oxygen stores,
   swimming muscles and neural pathways necessary for effective diving and
   foraging. Because of this, most phocids undergo a postweaning fast, in
   which they remain on or near the breeding site and live off of the fat
   stores they acquired from their mothers until they are ready to begin
   foraging on their own. These pups typically eat no food and drink no
   water during the fast, although some polar species have been observed
   to eat snow. The postweaning fast ranges from 2 weeks in the Hooded
   Seal to 9-12 weeks in the Northern Elephant Seal. The physiological and
   behavioural adaptations that allow phocid pups to endure these
   remarkable fasts, which are among the longest for any mammal, remain an
   area of active study and research.

Classification

   SUBORDER PINNIPEDIA
     * Family Otariidae: fur seals and sea lions
     * Family Odobenidae: Walrus
     * Family Phocidae
          + Subfamily Monachinae
               o Tribe Monachini
                    # Monachopsis (extinct)
                    # Pristiphoca (extinct)
                    # Properiptychus (extinct)
                    # Messiphoca (extinct)
                    # Mesotaria (extinct)
                    # Callophoca (extinct)
                    # Pliophoca (extinct)
                    # Pontophoca (extinct)
                    # Hawaiian Monk Seal, Monachus schauinslandi
                    # Mediterranean Monk Seal, Monachus monachus
                    # Caribbean Monk Seal, Monachus tropicalis (probably
                      extinct around 1950)
               o Tribe Miroungini
                    # Northern Elephant Seal, Mirounga angustirostris
                    # Southern Elephant Seal, Mirounga leonina
               o Tribe Lobodontini
                    # Monotherium wymani (extinct)
                    # Ross Seal, Ommatophoca rossi
                    # Crabeater Seal, Lobodon carcinophagus
                    # Leopard Seal, Hydrurga leptonyx
                    # Weddell Seal, Leptonychotes weddellii
               o Swan-necked Seal, Acrophoca longirostris (extinct)
               o Piscophoca pacifica (extinct)
               o Homiphoca capensis (extinct)
          + Subfamily Phocinae
               o Kawas benegasorum (extinct)
               o Leptophoca lenis (extinct)
               o Preapusa (extinct)
               o Cryptophoca (extinct)
               o Bearded Seal, Erignathus barbatus
               o Hooded Seal, Cystophora cristata
               o Tribe Phocini
                    # Common Seal or Harbour Seal, Phoca vitulina
                    # Spotted Seal or Larga Seal, Phoca largha
                    # Ringed Seal, Phoca hispida
                    # Nerpa or Baikal Seal, Phoca sibirica
                    # Caspian Seal, Phoca caspica
                    # Harp Seal, Phoca groenlandica (or Pagophilus
                      groenlandicus)
                    # Ribbon Seal, Phoca fasciata
                    # Phocanella (extinct)
                    # Platyphoca (extinct)
                    # Gryphoca (extinct)
                    # Grey Seal, Halichoerus grypus

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