The

true seal True most commonly refers to truth, the state of being in congruence with fact or reality. True may also refer to: Places * True, West Virginia, an unincorporated community in the United States * True, Wisconsin, a town in the United States * ...

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

Lobodontini, collectively known as the Antarctic seals or lobodontin seals, consist of four species of seals in four genera: the

crabeater seal The crabeater seal (''Lobodon carcinophaga''), also known as the krill-eater seal, is a true seal with a circumpolar distribution around the coast of Antarctica. They are the only member of the genus ''Lobodon''. They are medium- to large-sized ( ...

(''Lobodon carcinophaga''), the

leopard seal The leopard seal (''Hydrurga leptonyx''), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). It is a top order predator, feeding on a wide range of prey including cep ...

(''Hydrurga leptonyx''), the

Weddell seal The Weddell seal (''Leptonychotes weddellii'') is a relatively large and abundant Earless seal, true seal with a Subantarctic, circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expediti ...

(''Leptonychotes weddelli''), and the

Ross seal The Ross seal (''Ommatophoca rossii'') is a true seal (family Phocidae) with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus ''Ommatophoca''. First described during the Ross expedition in 1841, it is ...

(''Ommatophoca rossii''). All lobodontine seals have circumpolar distributions surrounding

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

. They include both the world's most abundant seal (the crabeater seal) and the only predominantly mammal-eating seal (the leopard seal). While the Weddell seal prefers the shore-fast ice, the other species live primarily on and around the off-shore

pack ice Pack or packs may refer to: Music * Packs (band), a Canadian indie rock band * ''Packs'' (album), by Your Old Droog * ''Packs'', a Berner album Places * Pack, Styria, defunct Austrian municipality * Pack, Missouri, United States (US) * ...

. Thus, though they are collectively the most abundant group of seals in the world, the combination of remote range and inaccessible habitat make them among the least well studied of the world's seals.

Adaptations

The Lobondontini are thought to have diverged from the elephant seals (''Mirounga'') during the late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

in the Southern Ocean. The leopard and crabeater seals possess lobes and cusps on their teeth useful for straining smaller prey items out of the water (the name "Lobodontini", meaning "lobe-toothed"). Nonetheless, they have diversified into specialized prey

ecological niches In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for e ...

, thereby illustrating the radiating

sympatric speciation Sympatric speciation is the evolution of a new species from a surviving Common descent, ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, ''sympatric'' and ''sympatry'' are ter ...

associated with colonization of a novel environment with multiple available niches. Thus, the crabeater seal, with the most specialized sieve-like dental features, is the only seal that feeds predominantly on

Antarctic krill Antarctic krill (''Euphausia superba'') is a species of krill found in the Antarctica, Antarctic waters of the Southern Ocean. It is a small, swimming crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000� ...

, while the leopard seal is the only seal which actively preys on other seals and

penguins Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

, while still retaining the ability to filter-feed on krill.

Abundance

The lobodontin seals in aggregate are among the most successful of all marine mammal groups, collectively accounting for at least 50% of all seals on Earth and about 80% of the global

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

of pinnipeds. The extremely high abundance of crabeater seals in particular, with possibly over 30,000,000 individuals, is a testament to the high productivity of the Southern Ocean, especially with respect to krill.Erickson, A. W., Siniff, D. B., Cline, D. R. and Hofman, R. J. (1971). Distributional ecology of Antarctic seals. In: G. Deacon (ed.), Symposium on Antarctic Ice and Water Masses, pp. 55-76. Sci. Comm. Antarct Res., Cambridge, UK. High numbers of seals may also be the indirect result of the wide-scale extermination of large

baleen whales Baleen whales (), also known as whalebone whales, are marine mammals of the order (biology), parvorder Mysticeti in the infraorder Cetacea (whales, dolphins and porpoises), which use baleen plates (or "whalebone") in their mouths to sieve plankt ...

in the Antarctic due to commercial whaling in the 19th and 20th centuries, and the subsequent increase in krill densities. Genetic evidence suggests that Weddell and crabeater seal populations may have increased in size during the Pleistocene. None of the four species are currently thought to be declining in numbers.

Genera

References

{{Taxonbar, from=Q13644959 True seals Lobodontins Mammal tribes Taxa named by John Edward Gray