''Pelagiarctos'' was a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

that lived during the Mid

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

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

Kern County Kern County is a county (United States), county located in the U.S. state of California. As of the 2020 United States census, 2020 census, the population was 909,235. Its county seat is Bakersfield, California, Bakersfield. Kern County compris ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. 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 jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

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, tear ...

have two

root In vascular plants, the roots are the plant organ, 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 bel ...

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

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

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

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 nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

, specifically borophagine dogs and

hyaenids Hyenas or hyaenas ( ; from Ancient Greek , ) are feliformia, feliform carnivoran mammals belonging to the Family (biology), family Hyaenidae (). With just four extant species (each in its own genus), it is the fifth-smallest family in the orde ...

. This, coupled with the robust dentary, indicates that ''Pelagiarctos'' probably had a large bite force. Though no postcranial 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 the 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'', '' Sphyrna'', '' Carcharocles''), turtles ('' Psephophorus''), seabirds ('' Osteodontornis'', '' Diomedea'', '' Puffinus''), Cetaceans ('' Prosqualodon'', '' Aulophyseter'', '' Parietobalaena'') and other pinnipeds ('' Allodesmus'', '' 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 inhabited ...

'' or '' Paleoparadoxia''. But in a 2014 study indicates that it was not an

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

References

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