''Pelagiarctos'' was a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial no ...

walrus The walrus (''Odobenus rosmarus'') is a large 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 the fam ...

that lived during the Mid

Miocene The Miocene ( ) is the first 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 means "less recent ...

, approx. 13-15 mya. Its remains have been found in the Sharktooth Hill

Bonebed A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätte ...

, in Kern County,

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the mo ...

. It was originally described as an Otariidae, though it is now usually considered to be a basal Odobenidae.

Anatomy

To date, the only material of ''Pelagiarctos'' that has been found includes a handful of partial

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

s. The mandibles themselves are approximately the same size as those of the contemporaneous pinniped '' Allodesmus kernensis'', but differ in that the cheek

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

have two

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

s (instead of one, as in ''Allodesmus'') and that the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

itself is much thicker. They are also highly vascularized and covered in unusually large mental foramina, indicating that ''Pelagiarctos'' may have had somewhat fleshy lips. The cheek teeth resemble those of several

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 ...

carnivores A carnivore , or meat-eater ( Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and ot ...

, specifically borophagine dogs and hyaenids. This, coupled with the robust dentary, indicates that ''Pelagiarctos'' probably had a large bite force. Though no

postcranial Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated ...

remains have yet been found, the size of the dentary suggests an overall length of approx. 2.5–3 meters.

Environment

The remains of ''Pelagiarctos'' have so far only been discovered in the Sharktooth Hill Bonebed, located in Kern County, California. The bonebed is approximately 15.97 - 13.65 million years old, and is interpreted to have been laid down in a coastal environment off the shore of the Miocene

North Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

. The sediments that have yielded ''Pelagiarctos'' have also yielded numerous other species of ocean-going vertebrates, including sharks (''

Isurus ''Isurus'' is a genus of mackerel sharks in the family Lamnidae, commonly known as the mako sharks. Description The two living species are the common shortfin mako shark (''I. oxyrinchus'') and the rare longfin mako shark (''I. paucus''). Th ...

'', '' Sphyrna'', '' Carcharocles''), turtles ('' Psephophorus''), seabirds ('' Osteodontornis'', '' Diomedea'', '' Puffinus''), Cetaceans ('' Prosqualodon'', '' Aulophyseter'', '' Parietobalaena'') and other pinnipeds (''

Allodesmus ''Allodesmus'' is an extinct genus of pinniped from the middle to late Miocene of California and Japan that belongs to the extinct pinniped family Desmatophocidae. Description and biology ''Allodesmus'' measured about long and weighed . ''A ...

'', '' Neotherium'').

Paleobiology

Because of its large size, adaptations geared toward crunching bones, and rarity in the fossil record, ''Pelagiarctos'' is formerly interpreted as being a predator of other large marine vertebrates. If so, it would make ''Pelagiarctos'' unique among pinnipeds, as most other species are adapted to much smaller prey such as fish or squid. ''Pelagiarctos'' most likely preyed upon the pinniped ''Allodesmus'' (which was very common in its environment), but it could also have preyed upon other marine mammals such as ''

Metaxytherium ''Metaxytherium'' is an extinct genus of dugong that lived from the Oligocene until the end of the Pliocene. Fossil remains have been found in Africa, Europe, North America and South America. Generally marine seagrass specialists, they inhab ...

'' or ''

Paleoparadoxia ''Paleoparadoxia'' ("ancient paradox") is a genus of large, herbivorous aquatic mammals that inhabited the northern Pacific coastal region during the Miocene epoch (). It ranged from the waters of Japan ( Tsuyama and Yanagawa), to Alaska in the ...

''. But in a 2014 study indicates that it was not an apex predator.

References

* {{Taxonbar, from=Q7161149 Miocene pinnipeds Prehistoric carnivoran genera Prehistoric pinnipeds of North America Odobenids Fossil taxa described in 1988