Elephant seals
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Group of Northern Elephant Seals |
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| Mirounga | ||||||||||||
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The elephant seals ( Mirounga ) are the largest seals in the world. They are named after the trunk-like enlarged nose of the adult males. They belong to the dog seals , although they are more similar to the ear seals in behavior and in some characteristics .
There are two very similar types:
- Northern elephant seal , Mirounga angustirostris ( Gill 1866 ), west coast of North America
- Southern elephant seal , Mirounga leonina ( Linnaeus 1758 ), Subantarctic
features
general characteristics
The size differences between males and females are considerable. A bull can be 6½ meters long and weigh 3500 kilograms, a cow only 3½ meters and 900 kilograms. The elephant seals differ from other seal species mainly in their size, pronounced sexual dimorphism and the development of the nose, which in adult males forms a conspicuous trunk . After constant growth, the trunk reaches its full size around the age of eight and then hangs with the nostrils down over the mouth. During the mating season, this trunk can be enlarged again considerably by increasing the blood and air supply and is used to reinforce the bulls' calls.
The northern elephant seal differs from the southern elephant seal mainly in its somewhat smaller size and the somewhat less extreme development of the sex differences; the trunk of the male of the northern species is, however, proportionally larger (up to 30 cm) than that of the southern elephant seal.
Features of the skull
| 2 | · | 1 | · | 3 | · | 0-4 | = 30 |
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In both sexes, the teeth are primarily designed to grab and hold the prey, which is then swallowed whole. The animals each have two incisors in the upper jaw , followed by a strong canine tooth (caninus), followed by a total of 3 to 7 very small and simple teeth (postcaninae), which are made up of three premolar teeth and a variable number of molars (Molares) together. There is only one incisor in the branch of the lower jaw. The animals have a total of 30 teeth, but the postcaninae are almost inoperable and support the large canine teeth when holding the prey. The canines are enlarged and sharp in both sexes, but in the males they are much stronger than in the females. The strong canine teeth are also used by the males in rival fights during the mating season.
Way of life
During the mating season, the otherwise rather solitary elephant seals gather in large colonies. One bull has ten to twenty cows. The cops fight violently for ownership of a harem. Younger and weaker bulls are pushed to the edge of the colony, where they find less favorable conditions. But they are constantly in waiting and try again and again to mate, which leads to fights over and over again for weeks. Under the protection of a dominant bull, the so-called beach master , the cows throw their offspring that were conceived the previous year. They care for the young for a few weeks before they mate with the bulls again.
If a bull wants to mate with a cow, he puts a front flipper over her and bites her neck. After that, copulation begins. When the cow struggles, the bull will roll on her and make her unable to move with his weight.
The constant fights as well as the brutal copulations lead to young animals being crushed by old males. As a result, a not inconsiderable number of calves die every year in an elephant seal colony.
Elephant seals become sexually mature when they are three to four years old. However, bulls are not strong enough to guard a harem until they are eight or nine years old, so mating at an earlier point in time is unlikely. Because of the exhaustion caused by the fighting, the life expectancy of a male elephant seal at 14 years is significantly lower than that of a female at around 18 years.
The food of the elephant seals is fish and octopus . Typical diving depths for elephant seals are between 200 and 600 meters, depending on the time of day. However, significantly greater depths can also be reached; a southern elephant seal was registered at a depth of 2388 meters as part of the Census of Marine Life . Reaching such depths is made possible for them by the fact that, due to their body (similar to whales ), they have an enormous volume of blood that can absorb and store a lot of oxygen . In addition, like whales, organs (e.g. liver and kidneys ) are shut down during dives to reduce oxygen consumption.
The natural enemies of the elephant seals are the great white shark and the orca , which can be dangerous especially near the surface of the water.
Fossil History and Evolution
There are two theories about the origin of the two species of elephant seals, according to which either the northern species is regarded as a descendant of the southern or the southern species is regarded as a descendant of the northern one. According to an older theory, the northern elephant seals originated from a group of southern elephant seals that migrated to the North Pacific during the Pleistocene and became separated from the original population after the warming of the equatorial regions. Alternatively, it is believed that the origin of the elephant seals lies in the more northern tropical areas of the Pacific and from there a group split off and migrated south, where the southern elephant seal emerged. The latter is seen as more likely and it is assumed that the family group around the elephant seals and the fossil genus Callophoca originated in the Miocene in the area of today's Caribbean and the ancestors of the elephant seals through the as yet open gap between North and South America arrived in the Pacific in the early Pliocene . As a result of the cooling of the equatorial areas in the Pleistocene, the populations of the later northern and southern elephant seals separated and were genetically isolated accordingly. The oldest fossil record of the northern elephant seal is from the late Pleistocene, found in southern California. Fossil finds of the southern kind are known from South Africa and the north of Chile .
Systematics
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Phylogenetic system of dog seals according to Higdon et al. 2007
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The generic name Macrorhinus , which was given by Georges Cuvier , is often found for elephant seals . However, this is identical to the name of a genus of beetles, so that the younger name Mirounga from John Edward Gray became valid. The name Mirounga is derived from "miouroung", the name for southern elephant seals in a language of the Australian Aborigines .
The affiliation of the elephant seals to the dog seals is undisputed, but their position within the dog seals has been debated repeatedly. In 1983, for example, King put forward the theory, which is still often cited today, that the elephant seals are most closely related to the monk seals and that both were particularly original representatives of the dog seals . On the other hand, Bininda-Emonds and Russell could not find any evidence of such a close relationship in 1996, but confirmed the basic position of the elephant seals in the dog seal system. Based on molecular biological results from the year 2007, the elephant seals are currently a sister group of the Lobodontini combined species group from Ross Seal ( Ommatophoca rossii ), Crabeater ( Lobodon carcinophaga ), leopard seals ( Hydrurga leptonyx ) and Weddell ( Leptonychotes weddellii considered) , The monk seals are seen as a sister group of both taxa, elephant seals and lobodontini.
Within the genus, two species are distinguished: the northern elephant seal ( Mirounga angustirostris ) and the southern elephant seal ( Mirounga leonina ).
supporting documents
- ↑ a b c d Brent S. Stewart, Harriet S. Huber: Mirounga angustirostris . In: Mammalian Species . tape 449 , 1993, pp. 1–10 ( full text ( memento of March 18, 2014 in the Internet Archive ) (PDF file; 1.27 MB)).
- ↑ Brent S. Stewart: "Northern Elephant Seal - Miounga angustirostris." In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; Pp. 170-171, ISBN 978-84-96553-93-4 .
- ↑ M. Biuw, L. Boehme, C. Guinet, M. Hindell, D. Costa, J.-B. Charrassin, F. Roquet, F. Bailleul, M. Meredith, S. Thorpe, Y. Tremblay, B. McDonald, Y.-H. Park, SR Rintoul, N. Bindoff, M. Goebel, D. Crocker, P. Lovell, J. Nicholson, F. Monks, MA Fedak: Variations in behavior and condition of a Southern Ocean top predator in relation to in situ oceanographic conditions . In: Proceedings of the National Academy of Sciences . tape 104 , no. 34 , August 2007, p. 13705-13710 , doi : 10.1073 / pnas.0701121104 .
- ↑ Census of Marine Life 2009 - From the Edge of Darkness to the Black Abyss: Marine Scientists Census 17,500+ Species and Counting (PDF; 3.1 MB)
- ↑ JL Davies: The Pinnipedia: An Essay in Zoogeography. Geographical Review 48 (4), October 1958; Pp. 474-493, doi : 10.2307 / 211670 .
- Jump up ↑ Ana M. Valenzuela-Toro, Carolina S. Gutstein, Mario E. Suárez, Rodrigo Otero & Nicholas D. Pyenson: Elephant seal (Mirounga sp.) From the Pleistocene of the Antofagasta Region, northern Chile. Journal of Vertebrate Paleontology 35 (3), April 2015; e918883, doi : 10.1080 / 02724634.2014.918883 .
- ↑ a b Jeff W Higdon, Olaf RP Bininda-Emonds, Robin MD Beck, Steven H. Ferguson: Phylogeny and divergence of the pinnipeds (Carnivora: Mammalia) assessed using a multigene dataset. BMC Evolutionary Biology 7, 2007, doi : 10.1186 / 1471-2148-7-216 .
- ↑ Olaf RP Bininda-Emonds, AP Russell: A morphological perspective on the phylogenetic relationships of the extant phocid seals (Mammalia: Carnivora: Phocidae) . In: Bonner Zoologische Monographien 1996, Vol. 41, ISBN 3925382445 .
literature
- Ronald M. Nowak: Walker's Mammals of the World . Johns Hopkins University Press, 1999, ISBN 0-8018-5789-9 .
- Olaf RP Bininda-Emonds & AP Russell: A morphological perspective on the phylogenetic relationships of the extant phocid seals (Mammalia: Carnivora: Phocidae) . In: Bonner Zoologische Monographien 1996, Vol. 41, ISBN 3925382445 .
- Judith E. King : Seals of the World . Cornell University Press, 1983, ISBN 0-8014-1568-3 .
