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Earless seal

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Earless seal
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{{Automatic taxobox
pages = | id = 14001028}}| image = Seehund.jpg| image_caption = Harbor seal, Phoca vitulinaearliest=Chattianpresent}}Early Miocene – Holocene, possible late Oligocene recordLEONARD DEWAELE >AUTHOR2=OLIVIER LAMBERT YEAR=2018 MONOTHERIUM (CARNIVORA, PHOCIDAE) >JOURNAL=ROYAL SOCIETY OPEN SCIENCE ISSUE=5 DOI=10.1098/RSOS.171669 PMC=5990722, | taxon = PhocidaeJohn Edward Gray>Gray, 1821| subdivision_ranks = Genera| subdivision = }}(File:Harbor seal with skeleton GS.jpg|thumb|Skeletal anatomy of a harbor seal. 1. Skull. 2. Spine. 3. Tail. 4. Hindlimb. 5. Forelimb. 6. Shoulder. 7. Pelvis. 8. Rib cage.)The seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae {{IPAc-en|ˈ|f|oʊ|s|ᵻ|d|iː}}. They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Taxonomy

Phylogeny

In the 1980s, phylogenetic analysis of the phocids led to new conclusions about the interrelatedness of the various genera. The four genera Hydrurga, Leptonychotes, Lobodon, and Ommatophoca form a monophyletic group, the tribe Lobodontini. Likewise, the Phocinae subfamily (Erignathus, Cystophora, and Phocini) is also monophyletic. More recently, five species have been split off from Phoca, forming three additional genera. However, the subfamily Monachinae (the lobodonts Mirounga) is probably paraphyletic.{{MSW3 Wozencraft | pages = | id = 14001028}}(File:Cranio Pliophoca etrusca, Orciano.JPG|thumb|Fossil Pliophoca skull) Superfamily Pinnipedia †Monachopsis †Pristiphoca †Properiptychus †Messiphoca †Callophoca †Pliophoca †Pontophoca Mediterranean monk seal, Monachus monachus Hawaiian monk seal, Neomonachus schauinslandi †Caribbean monk seal, Neomonachus tropicalis (probably extinct around 1952)
      • Tribe Miroungini
Northern elephant seal, Mirounga angustirostris Southern elephant seal, Mirounga leonina †Piscophoca pacifica †Hadrokirus martini †Homiphoca capensis Ross seal, Ommatophoca rossi Crabeater seal, Lobodon carcinophagus Leopard seal, Hydrurga leptonyx Weddell seal, Leptonychotes weddellii †Acrophoca longirostris Genus Phoca* Harbor seal or common seal, Phoca vitulina* Spotted seal, Phoca largha Genus Pusa* Ringed seal, Pusa hispida (formerly Phoca hispida)* Baikal seal, Pusa sibirica (formerly Phoca sibirica)* Caspian seal, Pusa caspica (formerly Phoca caspica) Genus Pagophilus* Harp seal, Pagophilus groenlandicus (formerly Phoca groenlandica) Genus Histriophoca* Ribbon seal, Histriophoca fasciata (formerly Phoca fasciata) †Phocanella †Platyphoca †Gryphoca Genus Halichoerus* Grey seal, Halichoerus grypus{hide}cladogram|align=right|title=|clade={{clade|style=font-size:75%;line-height:50%;width:330px;|label1=Phocidae
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1={{clade
|1=ringed seal
|2=Baikal seal
{edih}
|2=Caspian seal
}}
|2={{clade
|1=spotted seal
|2=harbor seal
}}
}}
|2=grey seal
}}
|2={{clade
|1=ribbon seal
|2=harp seal
}}
}}
|2=hooded seal
}}
|2=bearded seal
}}
|2={{clade
|1={{clade
|1={{clade
|1=Weddell seal
|2=leopard seal
}}
|2=crabeater seal
}}
|2=Ross seal
}}
}}
|2={{clade
|1=southern elephant seal
|2=northern elephant seal
}}
}}
|2={{clade
|1=Mediterranean monk seal
|2=Hawaiian monk seal
}}
}}
}}
Cladogram showing relationships among the extant earless seals, combining several phylogenetic analyses.BERTA, A. TITLE=PINNIPED TAXONOMY: REVIEW OF CURRENTLY RECOGNIZED SPECIES AND SUBSPECIES, AND EVIDENCE USED FOR THEIR DESCRIPTION YEAR=2012 ISSUE=3 DOI=10.1111/J.1365-2907.2011.00193.X, }}

Evolution

missing image!
- Piscophoca pacifica.JPG -
Piscophoca pacifica fossil
The earliest known fossil earless seal is Noriphoca gaudini from the late Oligocene or earliest Miocene (Aquitanian) of Italy. Other early fossil phocids date from the mid-Miocene, 15 million years ago in the north Atlantic. Until recently, many researchers believed that phocids evolved separately from otariids and odobenids; and that they evolved from otter-like animals, such as Potamotherium, which inhabited European freshwater lakes. Recent evidence strongly suggests a monophyletic origin for all pinnipeds from a single ancestor, possibly Enaliarctos, most closely related to the bears.Monk seals and elephant seals are believed to have first entered the Pacific through the open straits between North and South America, which only closed in the Pliocene. The various Antarctic species may have either used the same route, or traveled down the west coast of Africa.BOOK, Savage, RJG, Long, MR, yes, 1986, Mammal Evolution: an illustrated guide, Facts on File, New York, 94–95, 978-0-8160-1194-0,

Biology

External anatomy

{{unreferenced section|date=May 2013}}File:Phoca vitulina 02 MWNH 1464.JPG|thumb|left|Harbor sealHarbor sealAdult phocids vary from {{convert|1.17|m|ft|abbr=on}} in length and {{convert|45|kg|lb|abbr=on}} in weight in the ringed seal to {{convert|4.9|m|ft|abbr=on}} and {{convert|2400|kg|lb|abbr=on}} in land-based members of the Carnivora, although they retain powerful canines. Some species lack molars altogether. The dental formula is:{{DentalFormula|upper=2–3.1.4.0–2|lower=1–2.1.4.0–2}}While otariids are known for speed and maneuverability, phocids are known for efficient, economical movement. This allows most phocids to forage far from land to exploit prey resources, while otariids are tied to rich upwelling zones close to breeding sites. Phocids swim by sideways movements of their bodies, using their hind flippers to fullest effect.BOOK, Macdonald, D., McLaren, Ian, 1984, The Encyclopedia of Mammals, Facts on File, New York, 270–275, 978-0-87196-871-5, registration,weblink Their fore flippers are used primarily for steering, while their hind flippers are bound to the pelvis in such a way that they cannot bring them under their bodies to walk on them. They are more streamlined than fur seals and sea lions, so can swim more effectively over long distances. 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.(File:Seal kidney-- FMVZ USP-08.jpg|thumb|Seal kidney)Phocid respiratory and circulatory systems are adapted to allow diving to considerable depths, and they can spend a long time underwater between breaths. Air is forced from the lungs during a dive and into the upper respiratory passages, where gases cannot easily be absorbed into the bloodstream. This helps protect the seal from the bends. The middle ear is also lined with blood sinuses that inflate during diving, helping to maintain a constant pressure.Phocids are more specialized for aquatic life than otariids. They lack external ears and have sleek, streamlined bodies. Retractable nipples, internal testicles, and an internal penile sheath provide further streamlining. A smooth layer of blubber lies underneath the skin. Phocids are able to divert blood flow to this layer to help control their temperatures.

Communication

{{unreferenced section|date=July 2017}}Unlike otariids, true seals do not communicate by 'barking'. Instead, they communicate by slapping the water and grunting.

Reproduction

{{unreferenced section|date=May 2013}}(File:Earless seal (Puerto Madryn, Argentina).jpg|thumb|left|Southern elephant seals in Argentina|alt=Photo of seven adult and juvenile southern elephant seals packed closely on beach)Phocids spend most of their time at sea, although they return to land or pack ice to breed and give birth. Pregnant females spend long periods foraging at sea, building up fat reserves, and then return to the breeding site to use their stored energy to nurse pups. However, the common seal displays a reproductive strategy similar to that used by 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, she must fast while lactating. This combination of fasting with lactation requires the mother to provide large amounts of energy to her pup at a time when she is not eating (and often, not drinking). Mothers must supply their own metabolic needs while nursing. This is a miniature version of the humpback whales' strategy, which involves fasting during their months-long migration from arctic feeding areas to tropical breeding/nursing areas and back.Phocids produce thick, fat-rich milk that allows them to provide their pups with large amounts of energy in a short period. This allows the mother to return to the sea in time to replenish her reserves. Lactation ranges from five to seven weeks in the monk seal to just three to five days in the hooded seal. The mother ends nursing by leaving her pup at the breeding site to search for food (pups continue to nurse if given the opportunity). "Milk stealers" that suckle from unrelated, sleeping females are not uncommon; this often results in the death of the mother's pup, since a female can only feed one pup.

Growth and maturation

The pup's diet is so high in calories, it builds up a fat store. Before the pup is ready to forage, the mother abandons it, and the pup consumes its own fat for weeks or even months while it matures. Seals, like all marine mammals, need time to develop the oxygen stores, swimming muscles, and neural pathways necessary for effective diving and foraging. Seal pups typically eat no food and drink no water during the period, although some polar species eat snow. The postweaning fast ranges from two weeks in the hooded seal to 9–12 weeks in the northern elephant seal.JOURNAL, The energetics of lactation in the Northern elephant seal, Mirounga angustirostris, Journal of Zoology, 1986-03-01, 1469-7998, 21–33, 209, 1, 10.1111/j.1469-7998.1986.tb03563.x, D. P., Costa, B. J. Le, Boeuf, A. C., Huntley, C. L., Ortiz, The physiological and behavioral 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.

See also

{{Clear}}

References

{{Reflist}}

External links

{{Wikispecies|Phocidae}}{{Commons and category|Phocidae|Phocidae}}{{Carnivora|C1.}}{{Taxonbar|from=Q25587}}


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