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16.12.2015 16:56 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.1 Carnivores - Seals and Odobenidae
Автор: valentint Категория: Забавление   
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Odobenidae
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1. Acrophoca 2. Allodesmus 3. Aivukus 4. Enaliarctos 5. Thalassoleon
Odobenidae
is a family of pinnipeds. The only living species is the walrus. In the past, however, the group was much more diverse, and includes more than ten fossil genera.
The walrus is a mammal in the order Carnivora. It is the sole surviving member of the family Odobenidae, one of three lineages in the suborder Pinnipedia along with true seals (Phocidae) and eared seals (Otariidae).While there has been some debate as to whether all three lineages are monophyletic, i.e. descended from a single ancestor, or diphyletic, recent genetic evidence suggests all three descended from a caniform ancestor most closely related to modern bears.Recent multigene analysis indicates the odobenids and otariids diverged from the phocids about 20–26 million years ago, while the odobenids and the otariids separated 15–20 million years ago.Odobenidae was once a highly diverse and widespread family, including at least twenty species in the subfamilies Imagotariinae, Dusignathinae and Odobeninae.The key distinguishing feature was the development of a squirt/suction feeding mechanism; tusks are a later feature specific to Odobeninae, of which the modern walrus is the last remaining (relict) species.



The largest Odobenids was Giant Walrus (Pontolis magnus) at 3000 - 5000 сm in length and 2000 - 4000 kg weight
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The giant walrus Pontolis was described in 1905 and dates from the late Miocene (7-9 million years ago). The length of its skull was 60 cm, and the size it was contemporary with elephant seals. In general, Pontolis is a third more than the largest modern walrus. These huge pinnipeds have more simple structure of the teeth, the more massive skull, rather large fangs and a more concave and elongated palate than the walrus of the middle Miocene.


Gomphotaria pugnax
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Gomphotaria pugnax (pugnacious wedge-seal) was a species of very large shellfish-eating dusignathinewalrus found along the coast of what is now California, during the late Miocene. It had four tusks, with one pair in the lower and upper jaws, and according to wear on the tusks, G. pugnax hammered shellfish open, rather than simply sucking them out of their shells as do modern walruses. In terms of the postcranial skeleton, Gomphotaria and other dusignathine walruses were built more like sea lions than modern walrus. Gomphotaria is a prime example of the extreme diversity that walruses once exhibited.



 

 







 




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Автор: valentint
Категория: Политика
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