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Overview

Brief Summary

Seals are the acrobats of the sea, but they are very clumsy on land. A seal easily races through the water at 35 kilometers per hour, while it is lucky to cover 2 kilometers per hour on land. With its cute, round eyes, seals see very well under water. However, they would need eyeglasses to see sharply above water. Seals are completely adapted to life under water. Nevertheless, you can spot them regularly on the surface. They like to lie in the sun while resting on a sandbar or beach.
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Ecology

Associations

Known predators

Phocidae is prey of:
Cetacea
Ursus maritimus
Aves
Chondrichthyes
Homo sapiens

Based on studies in:
Southern Ocean (Marine, Tropical)
South Africa, Southwest coast (Marine)
Norway: Spitsbergen (Coastal)
USA, Northeastern US contintental shelf (Coastal)

This list may not be complete but is based on published studies.
  • B. C. Patten and J. T. Finn, Systems approach to continental shelf ecosystems. In: Theoretical Systems Ecology, E. Halfon, Ed. (Academic Press, New York, 1979) pp. 183-212 from p. 202.
  • V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
  • Link J (2002) Does food web theory work for marine ecosystems? Mar Ecol Prog Ser 230:1–9
  • Yodzis P (2000) Diffuse effects in food webs. Ecology 81:261–266
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Known prey organisms

  • B. C. Patten and J. T. Finn, Systems approach to continental shelf ecosystems. In: Theoretical Systems Ecology, E. Halfon, Ed. (Academic Press, New York, 1979) pp. 183-212 from p. 202.
  • V. S. Summerhayes and C. S. Elton, Contributions to the ecology of Spitsbergen and Bear Island, J. Ecol. 11:214-286, from p. 232 (1923).
  • Link J (2002) Does food web theory work for marine ecosystems? Mar Ecol Prog Ser 230:1–9
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
  • Yodzis P (2000) Diffuse effects in food webs. Ecology 81:261–266
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Guard hairs form waterproof barrier: seals
 

The guard hairs of seals form a waterproof barrier due, in part, to their flattened shape.

       
  "Guard hairs may be flattened in shape; this adaptation is most marked among aquatic mammals such as seals, so it is evidently a waterproofing device." (Foy and Oxford Scientific Films 1982:83)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Functional adaptation

Fur and feathers get grip on ice: seals and penguins
 

Fur and feathers of seals and penguins help them get a grip to climb ice floes and snow thanks to their stiffness.

     
  "For the seals of the icy seas and the penguins of the antarctic shore this gliding and braking mechanism is vital. When they leave the water to climb an ice floe, they get a grip with their stiff fur or feathers. They can scale 60° inclines in this manner. When they rush back into the water, they simply slide down on their stomachs. Numerous other animals that live in the snow have bristles on their running or creeping surfaces, for the same mechanical reasons." (Tributsch 1984:73)
  Learn more about this functional adaptation.
  • Tributsch, H. 1984. How life learned to live. Cambridge, MA: The MIT Press. 218 p.
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Functional adaptation

Fur decreases water turbulence: seals
 

The fur of seals may help them swim efficiently by maintaining laminar flow.

     
  "the short wiry hair or feather coats of such good swimmers as seals and penguins seem to be a great advantage for the maintenance of laminar flows. This is borne out by technical experiments with fine wire on surfaces in a flow field (M. D. Kramer, 1938), as well as by indirect clues. The splendid fur of the seal, for instance, provides no protection against getting wet; it gets soaked through in the water. And, when exposed to the air, wet fur presents a considerable risk of a chill. We must assume that wet fur represents an advantage for swimming. And, like the seal's coat of hair, the feathers of birds may have a favorable effect on the boundary layer." (Tributsch 1984:49)
  Learn more about this functional adaptation.
  • Tributsch, H. 1984. How life learned to live. Cambridge, MA: The MIT Press. 218 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:158Public Records:124
Specimens with Sequences:130Public Species:21
Specimens with Barcodes:125Public BINs:18
Species:23         
Species With Barcodes:21         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Phocidae

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Wikipedia

Hadrokirus

Hadrokirus martini is an extinct species of true seal (Phocidae) that lived on the coast of Peru about 6 million years ago. It was found in the Pisco Formation, together with other marine animals such as crustaceans, sharks, coastal birds, whales and aquatic sloths. The main particularity of this seal dwells in its teeth: they are extremely robust, hence the name (hadros, stout in Greek; kiru, tooth in Quechua). It is assumed that Hadrokirus martini was durophagous, its diet probably comprised crustaceans, small bivalves and other shelled animals, as it is seen for instance in the living sea otter. The extant seals the most closely related to Hadrokirus martini are the Lobodontini (seals from Antarctica).

References[edit]

  • Amson, E.; de Muizon, C. (2013). "A new durophagous phocid (Mammalia: Carnivora) from the late Neogene of Peru and considerations on monachine seals phylogeny". Journal of Systematic Palaeontology. doi:10.1080/14772019.2013.799610. 
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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 (pron.: /ˈfsəd/). 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 are mostly confined to polar, subpolar, and temperate climates, with the exception of the more tropical monk seals.

Contents

Anatomy

Adult phocids vary from 1.17 meters (3.8 ft) in length and 45 kilograms (99 lb) in weight, in the ringed seal, to 4.9 meters (16 ft) and 2,400 kilograms (5,300 lb) in the southern elephant seal.[2]

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 penis 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.

Limbs

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 body 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.

Phocids have fewer teeth than land-based members of the Carnivora, although they retain powerful canines. Some species lack molars altogether. The dental formula is: Upper: 2-3.1.4.0-2, lower: 1-2.1.4.0-2

Physiology

Respiration and circulation

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.[2]

Life history

Swimming

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.[2]

Communication

True seals do not communicate by "barking" like otariids. Instead, they communicate by slapping the water and grunting.

Reproduction

Photo of seven adult and juvenile seals packed closely on beach
Phocids in Argentina

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. The common seal displays a reproductive strategy similar to that 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, 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 whale's strategy. They fast 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 single 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 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. 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.

Taxonomy

In the 1980s, phylogenetic analysis of the phocids has led to a few 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, Halichoerus, and Phoca) is also monophyletic. More recently, five species have been split off from Phoca, forming three additional genera. However, the family Monachinae (the lobodonts plus Monachus and Mirounga) is probably paraphyletic.[1]

Fossil Pliophoca skull

Superfamily Pinnipedia

Evolution

The earliest fossil phocids date from the mid-Miocene, 15 million years ago in the north Atlantic. Until recently, many researchers believed phocids evolved separately from otariids and odobenids 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 closed only in the Pliocene. The various Antarctic species may have either used the same route, or traveled down the west coast of Africa.[4]

References

  1. ^ a b Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=14001028.
  2. ^ a b c McLaren, Ian (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 270–275. ISBN 0-87196-871-1.
  3. ^ Peter Saundry. 2010. True Seals. Encyclopedia of Earth. topic ed. C.Michael Hogan, ed. in chief C.Cleveland, National Center for Science and the Environment, Washington DC
  4. ^ Savage, RJG, & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 94–95. ISBN 0-8160-1194-X.
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