Lobodontini
Encyclopedia
The Lobodontini tribe
of true seals (Phocidae), collectively known as the lobodontine seals, consist of four species of seals in four genera: the crabeater seal
(Lobodon carcinophaga), the leopard seal
(Hydrurga leptonyx), the Weddell seal
(Leptonychotes weddelli) and the Ross seal
(Ommatophoca rossii). All lobodontine seals have circumpolar distributions surrounding Antarctica. 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. 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.
The Lobondontini are thought to have diverged from the elephant seals (Mirounga) in the late Miocene
or early Pliocene
after moving southward from the Atlantic to the Southern Ocean
. All species share teeth adaptations including lobes and cusps useful for straining smaller prey items out of the water column (whence the name "Lobodontini", meaning "lobe toothed"). Nonetheless, they have diversified into specialized prey ecological niches, thereby illustrating the radiating sympatric speciation
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 in the world that feeds predominantly on Antarctic krill
, while the leopard seal is the only seal which actively preys on other seals and penguins, while still retaining the ability to filter-feed on krill.
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. High numbers of seals may also be the indirect result of the wide-scale extermination of large baleen whales in the Antarctic due to commercial whaling in the 19th and 20th centuries, and the subsequent increase in krill densities. None of the four species are currently thought to be declining in numbers.
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
of true seals (Phocidae), collectively known as the lobodontine seals, consist of four species of seals in four genera: the crabeater seal
Crabeater Seal
The crabeater seal, Lobodon carcinophagus, is a true seal with a circumpolar distribution around the coast of Antarctica. They are medium to large-sized , relatively slender and pale-colored, found primarily on the free floating pack ice that extends seasonally out from the Antarctic coast, which...
(Lobodon carcinophaga), the leopard seal
Leopard Seal
The leopard seal , also referred to as the sea leopard, is the second largest species of seal in the Antarctic...
(Hydrurga leptonyx), the Weddell seal
Weddell Seal
The Weddell seal , is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound...
(Leptonychotes weddelli) and the Ross seal
Ross Seal
The Ross seal is a true seal with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during James Clark Ross' British Antarctic Expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic...
(Ommatophoca rossii). All lobodontine seals have circumpolar distributions surrounding Antarctica. 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
Fast ice
Fast ice is sea ice that has frozen along coasts along the shoals, or to the sea floor over shallow parts of the continental shelf, and extends out from land into sea. In Antarctica, fast ice may also extend between grounded icebergs...
, the other species live primarily on and around the off-shore pack ice. 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
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
or early Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
after moving southward from the Atlantic to the Southern Ocean
Southern Ocean
The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...
. All species share teeth adaptations including lobes and cusps useful for straining smaller prey items out of the water column (whence the name "Lobodontini", meaning "lobe toothed"). Nonetheless, they have diversified into specialized prey ecological niches, thereby illustrating the radiating sympatric speciation
Sympatric speciation
Sympatric speciation is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms whose ranges overlap or are even identical, so that...
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 in the world that feeds predominantly on Antarctic krill
Antarctic krill
Antarctic krill, Euphausia superba, is a species of krill found in the Antarctic waters of the Southern Ocean. It is a shrimp-like crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre...
, while the leopard seal is the only seal which actively preys on other seals and penguins, while still retaining the ability to filter-feed on krill.
Abundance
The lobodontine 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 biomassBiomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
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. High numbers of seals may also be the indirect result of the wide-scale extermination of large baleen whales in the Antarctic due to commercial whaling in the 19th and 20th centuries, and the subsequent increase in krill densities. None of the four species are currently thought to be declining in numbers.