Earless seal
| Earless seals[2] | |
|---|---|
| |
| Harbor seal,Phoca vitulina | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Clade: | Pinnipedia |
| Superfamily: | Phocoidea |
| Family: | Phocidae Gray,1821 |
| Type genus | |
| Phoca Linnaeus,1758
| |
| Subfamilies | |
Theearless seals,phocids,ortrue sealsare one of the three main groups ofmammalswithin the seal lineage,Pinnipedia.All true seals are members of the familyPhocidae(/ˈfoʊsɪdiː/). They are sometimes calledcrawling sealsto distinguish them from thefur sealsandsea lionsof the familyOtariidae.Seals live in theoceansof both hemispheres and, with the exception of the moretropicalmonk seals,are mostly confined topolar,subpolar, andtemperateclimates. TheBaikal sealis the only species of exclusivelyfreshwater seal.
Taxonomy and evolution
[edit]Evolution
[edit]
The earliest known fossil earless seal isNoriphocagaudinifrom the lateOligoceneor earliestMiocene(Aquitanian) ofItaly.[1]Other early fossil phocids date from the mid-Miocene, 15 million years ago in the north Atlantic.[1][3]Until recently, many researchers believed that phocids evolved separately fromotariidsandodobenids;and that they evolved fromotter-like animals, such asPotamotherium,which inhabited European freshwater lakes. Recent evidence strongly suggests a monophyletic origin for all pinnipeds from a single ancestor, possiblyEnaliarctos,most closely related to themustelidsandbears.[4]
Monk sealsandelephant sealswere previously believed to have first entered the Pacific through the open straits between North and South America,[5]with the Antarctic true seals either using the same route or travelled down the west coast of Africa.[6]It is now thought that themonk seals,elephant seals,andAntarctic sealsall evolved in the southern hemisphere, and likely dispersed to their current distributions from more southern latitudes.[7]
Taxonomy
[edit]
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| Cladogramshowing relationships among the phocids, combining several phylogenetic analyses.[8] |
In the 1980s and 1990s, morphologicalphylogeneticanalysis of the phocids led to new conclusions about the interrelatedness of the various genera. More recent molecular phylogenetic analyses have confirmed themonophylyof the two phocid subfamilies (Phocinaeand Monachinae).[9][10][11][5]The Monachinae (known as the "southern" seals), is composed of three tribes; the Lobodontini, Miroungini, and Monachini. The fourAntarcticgeneraHydrurga,Leptonychotes,Lobodon,andOmmatophocaare part of thetribeLobodontini.Tribe Miroungini is composed of theelephant seals.TheMonk seals(MonachusandNeomonachus) are all part of the tribe Monachini.[12]Likewise, subfamily Phocinae (the "northern" seals) also includes three tribes; Erignathini (Erignathus),Cystophorini (Cystophora),andPhocini(all other phocines). More recently, five species have been split off fromPhoca,forming three additional genera.[13]
Alternatively the three monachine tribes have been evaluated to familiar status, which elephant seals and the Antarctic seals are more closely related to the phocines.[14]
Extant genera
[edit]| Subfamily | Tribe | Image | Genus | species |
|---|---|---|---|---|
| SubfamilyMonachinae | TribeMonachini |  |
MonachusFleming, 1822 |
|
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NeomonachusSlater & Helgen, 2014 |
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| Tribe Miroungini |  |
MiroungaGray, 1827 |
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| TribeLobodontini |  |
OmmatophocaGray, 1844 |
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 |
LobodonGray, 1844 |
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 |
HydrurgaGistel, 1848 |
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 |
LeptonychotesGill, 1872 |
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| SubfamilyPhocinae | Tribe Cystophorini |  |
CystophoraNilsson, 1820 |
|
| Tribe Erignathini |  |
ErignathusGill, 1866 |
| |
| Tribe Phocini |  |
PhocaLinnaeus, 1758 |
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PusaScopoli, 1771 |
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PagophilusGray, 1844 |
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HistriophocaGill, 1873 |
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HalichoerusNilsson, 1820 |
|
Biology
[edit]External anatomy
[edit]
Adult phocids vary from 1.17 m (3.8 ft) in length and 45 kg (99 lb) in weight in theringed sealto 5.8 m (19 ft) and 4,000 kg (8,800 lb) in thesouthern elephant seal,which is the largest member of the orderCarnivora.Phocids have fewer teeth than land-based members of theCarnivora,although they retain powerfulcanines.Some species lackmolarsaltogether. Thedental formulais: 2–3.1.4.0–21–2.1.4.0–2
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 richupwellingzones close to breeding sites. Phocids swim by sideways movements of their bodies, using their hind flippers to fullest effect.[15]Their fore flippers are used primarily for steering, while their hind flippers are bound to thepelvisin 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 they 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 abdominalmuscles.
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 thelungsduring a dive and into the upper respiratory passages, where gases cannot easily be absorbed into the bloodstream. This helps protect the seal fromthe bends.Themiddle earis also lined with blood sinuses that inflate during diving, helping to maintain a constant pressure.[15]
Phocids are more specialized foraquaticlife than otariids. They lack external ears and have sleek, streamlined bodies. Retractablenipples,internaltesticles,[16]and an internalpenile sheathprovide further streamlining. A smooth layer ofblubberlies underneath the skin. Phocids are able to divertbloodflow to this layer to help control their temperatures.[17]
Communication
[edit]Unlike otariids, true seals do not communicate by 'barking'. Instead, they communicate by slapping the water and grunting.
Reproduction
[edit]
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 byotariids,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 mustfastwhilelactating.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 thehumpback 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 themonk sealto just three to five days in thehooded 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
[edit]The pup's diet is so high incaloriesthat 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.[19]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.
Feeding strategy
[edit]Phocids make use of at least four different feeding strategies: suction feeding, grip and tear feeding, filter feeding, and pierce feeding. Each of these feeding strategies is aided by a specialized skull, mandible, and tooth morphology. However, despite morphological specialization, most phocids are opportunistic and employ multiple strategies to capture and eat prey. For example, the leopard seal,Hydrurga leptonyx,uses grip and tear feeding to prey on penguins, suction feeding to consume small fish, and filter feeding to catch krill.[20]
See also
[edit]
References
[edit]- ^abcLeonard Dewaele; Olivier Lambert; Stephen Louwye (2018)."A critical revision of the fossil record, stratigraphy and diversity of the Neogene seal genusMonotherium(Carnivora, Phocidae) ".Royal Society Open Science.5(5): 171669.Bibcode:2018RSOS....571669D.doi:10.1098/rsos.171669.PMC5990722.PMID29892365.
- ^Wozencraft, W. C.(2005)."Order Carnivora".InWilson, D. E.;Reeder, D. M. (eds.).Mammal Species of the World: A Taxonomic and Geographic Reference(3rd ed.). Johns Hopkins University Press.ISBN978-0-8018-8221-0.OCLC62265494.
- ^Dewaele, Leonard; Lambert, Olivier; Louwye, Stephen (2017-02-21)."OnProphocaandLeptophoca(Pinnipedia, Phocidae) from the Miocene of the North Atlantic realm: redescription, phylogenetic affinities and paleobiogeographic implications ".PeerJ.5:e3024.doi:10.7717/peerj.3024.PMC5322758.PMID28243538.
- ^Paterson, Ryan S.; Rybczynski, Natalia; Kohno, Naoki; Maddin, Hillary C. (2020)."A Total Evidence Phylogenetic Analysis of Pinniped Phylogeny and the Possibility of Parallel Evolution Within a Monophyletic Framework".Frontiers in Ecology and Evolution.7.doi:10.3389/fevo.2019.00457.
- ^abFulton, Tara L.; Strobeck, Curtis (2010). "Multiple fossil calibrations, nuclear loci and mitochondrial genomes provide new insight into biogeography and divergence timing for true seals (Phocidae, Pinnipedia)".Journal of Biogeography.37(5): 814–829.Bibcode:2010JBiog..37..814F.doi:10.1111/j.1365-2699.2010.02271.x.S2CID59436229.
- ^Savage, RJG & Long, MR (1986).Mammal Evolution: an illustrated guide.New York: Facts on File. pp.94–95.ISBN978-0-8160-1194-0.
- ^Rule, James P.; Adams, Justin W.; Marx, Felix G.; Evans, Alistair R.; Tennyson, Alan J. D.; Scofield, R. Paul; Fitzgerald, Erich M. G. (2020-11-11)."First monk seal from the Southern Hemisphere rewrites the evolutionary history of true seals".Proceedings of the Royal Society B: Biological Sciences.287(1938): 20202318.doi:10.1098/rspb.2020.2318.PMC7735288.PMID33171079.
- ^Berta, Annalisa; Churchill, Morgan; Boessenecker, Robert W. (2018-05-30)."The Origin and Evolutionary Biology of Pinnipeds: Seals, Sea Lions, and Walruses".Annual Review of Earth and Planetary Sciences.46(1). Annual Reviews: 203–228.Bibcode:2018AREPS..46..203B.doi:10.1146/annurev-earth-082517-010009.ISSN0084-6597.S2CID135439365.
- ^Árnason, Úlfur; Bodin, Kristina; Gullberg, Anette; Ledje, Christina; Suzette, Mouchaty (1995). "A molecular view of pinniped relationships with particular emphasis on the true seals".Journal of Molecular Evolution.40(1): 78–85.Bibcode:1995JMolE..40...78A.doi:10.1007/BF00166598.PMID7714914.S2CID7537924.
- ^Arnason, Ulfur; Gullberg, Anette; Janke, Axel; Kullberg, Morgan; Lehman, Niles; Petrov, Evgeny A.; Väinölä, Risto (2006-11-01). "Pinniped phylogeny and a new hypothesis for their origin and dispersal".Molecular Phylogenetics and Evolution.41(2): 345–354.doi:10.1016/j.ympev.2006.05.022.PMID16815048.
- ^Fulton, Tara Lynn; Strobeck, Curtis (2010)."Multiple markers and multiple individuals refine true seal phylogeny and bring molecules and morphology back in line".Proceedings of the Royal Society B: Biological Sciences.277(1684): 1065–1070.doi:10.1098/rspb.2009.1783.PMC2842760.PMID19939841.
- ^Scheel, Dirk-Martin; Slater, Graham J.; Kolokotronis, Sergios-Orestis; Potter, Charles W.; Rotstein, David S.; Tsangaras, Kyriakos; Greenwood, Alex D.; Helgen, Kristofer M. (2014)."Biogeography and taxonomy of extinct and endangered monk seals illuminated by ancient DNA and skull morphology".ZooKeys(409): 1–33.Bibcode:2014ZooK..409....1S.doi:10.3897/zookeys.409.6244.PMC4042687.PMID24899841.
- ^Berta, Annalisa; Churchill, Morgan (2012). "Pinniped taxonomy: review of currently recognized species and subspecies, and evidence used for their description".Mammal Review.42(3): 207–234.doi:10.1111/j.1365-2907.2011.00193.x.
- ^Bonner, N. (1994).Seals and Sea Lions of the World.United Kingdom: Blandford. pp. 1–224.ISBN9780816057177.
- ^abMcLaren, Ian (1984). Macdonald, D. (ed.).The Encyclopedia of Mammals.New York: Facts on File. pp.270–275.ISBN978-0-87196-871-5.
- ^Perrin, William F.; Würsig, Bernd; Thewissen, J.G.M. (2009).Encyclopedia of Marine Mammals.Academic Press.ISBN978-0-08-091993-5.
- ^Favilla, Arina B.; Costa, Daniel P. (2020-09-11)."Thermoregulatory Strategies of Diving Air-Breathing Marine Vertebrates: A Review".Frontiers in Ecology and Evolution.8:555509.doi:10.3389/fevo.2020.555509.ISSN2296-701X.
- ^"Saimaa Ringed Seal".Retrieved22 December2018.
- ^Costa, D. P.; Boeuf, B. J. Le; Huntley, A. C.; Ortiz, C. L. (1986). "The energetics of lactation in the Northern elephant seal,Mirounga angustirostris".Journal of Zoology.209(1): 21–33.doi:10.1111/j.1469-7998.1986.tb03563.x.
- ^Kienle, Sarah S.; Berta, Annalisa (2016)."The better to eat you with: the comparative feeding morphology of phocid seals (Pinnipedia, Phocidae)".Journal of Anatomy.228(3): 396–413.doi:10.1111/joa.12410.PMC5341551.PMID26646351.
External links
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