''Proneotherium'' is an extinct genus of

pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant families Odobenidae (whose only living member is the walru ...

that lived approximately 20.43 to 15.97 mya during the

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was prece ...

in what is now

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

, U.S. It belonged to the family

Odobenidae Odobenidae is a family of pinnipeds. The only living species is the walrus (''Odobenus rosmarus''). In the past, however, the group was much more diverse, and includes more than a dozen fossil genera. Taxonomy All genera, except ''Walrus, Odob ...

, the only extant species of which is the

walrus The walrus (''Odobenus rosmarus'') is a large pinniped, flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living species in ...

Discovery

Four specimens of ''Proneotherium'' were discovered in the

Astoria Formation The Astoria Formation is a geologic formation in Oregon. It preserves fossils dating back to the Neogene period. See also *List of fossiliferous stratigraphic units in Oregon *Paleontology in Oregon The location of the state of Oregon Paleon ...

of Lincoln County, Oregon, U.S. These specimens included cranial and postcranial remains and are all believed to be adult male animals.

Description

''Proneotherium'' were more similar in appearance to modern

fur seal Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family '' Otariidae''. They are much more closely related to sea lions than true seals, and share with them external ears (pinnae), relatively lon ...

s and

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

s than walruses. They lacked the long tusks of walruses, and were more slender and smaller than their modern relatives.

Autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

of ''Proneotherium'' fossils include a continuous, horizontal crest connecting the mastoid and paroccipital processes of the skull. The teeth are also less secodont in function and appearance than more basal species. This likely represents the slow shift from a

piscivorous A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

diet to the

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

-based diet of modern walruses. The

hindlimb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hindl ...

s of ''Proneotherium'' also show the beginnings of evolutionary shifts from a

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

lifestyle to a more aquatic one.

Taxonomy

''Proneotherium'' represents some of the most basal members of Odobenidae. The sister group is the closely related ''

Prototaria ''Prototaria'' is an extinct genus of pinniped that lived approximately 15.97 to 13.65 mya during the Middle Miocene in what is now Japan. It belonged to the family Odobenidae, the only extant species of which is the walrus. Members of the genu ...

.''

References

{{Taxonbar, from=Q64623706 Odobenids Prehistoric carnivoran genera