''Pelagiarctos'' was a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 ...

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 recen ...

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

Sharktooth Hill The Temblor Formation is a geologic formation in California. It preserves fossils dating back from the Late Oligocene to the Middle Miocene of the Neogene period. It is notable for the famous Sharktooth Hill deposit (otherwise known as Ernst Quar ...

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 Kern County is a county located in the U.S. state of California. As of the 2020 census, the population was 909,235. Its county seat is Bakersfield. Kern County comprises the Bakersfield, California, Metropolitan statistical area. The county sp ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

. It was originally described as an

Otariid An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera (another species became extinct in the 1950s) and are commonly known eithe ...

ae, though it is now usually considered to be a basal

Odobenid 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 ''Odobenus'', ...

ae.

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 tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

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 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 Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature by processes of sprouting and splitting ...

and covered in unusually large

mental foramina The mental foramen is one of two foramina (openings) located on the anterior surface of the mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels. Structure The ...

, 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 other sof ...

, specifically

borophagine The extinct Borophaginae form one of three subfamilies found within the canid family. The other two canid subfamilies are the extinct Hesperocyoninae and extant Caninae. Borophaginae, called "bone-crushing dogs", were endemic to North America dur ...

dogs and

hyaenids Hyenas, or hyaenas (from Ancient Greek , ), are feliform carnivoran mammals of the family Hyaenidae . With only four extant species (each in its own genus), it is the fifth-smallest family in the Carnivora and one of the smallest in the cla ...

. This, coupled with the robust dentary, indicates that ''Pelagiarctos'' probably had a large

bite force Bite force quotient (BFQ) is a numerical value commonly used to represent the bite force of an animal, while also taking factors like the animal's size into account. The BFQ is calculated as the regression of the quotient of an animal's bite f ...

. 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 sk ...

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 continen ...

. 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''). They ...

'', ''

Sphyrna ''Sphyrna'' (from the Greek word σφῦρα, "hammer") is a genus of hammerhead sharks with a cosmopolitan distribution in the world's oceans. Members of ''Sphyrna'' have a tendency to inhabit coastal waters along the intertidal zone rather th ...

'', ''

Carcharocles ''Otodus'' is an extinct genus of mackerel shark which lived from the Paleocene to the Pliocene epoch. The name ''Otodus'' comes from Ancient Greek (, meaning "ear") and (, meaning "tooth") – thus, "ear-shaped tooth". Anatomy This shark is k ...

''), turtles (''

Psephophorus ''Psephophorus'' is an extinct genus of sea turtle that lived from the Oligocene to the Pliocene. Its remains have been found in Europe, Africa, North America, and New Zealand. It was first named by Hermann von Meyer in 1847, and contains seve ...

''), seabirds (''

Osteodontornis ''Osteodontornis'' is an extinct seabird genus. It contains a single named species, ''Osteodontornis orri'' (Orr's bony-toothed bird, in literal translation of its scientific name), which was described quite exactly one century after the first sp ...

'', '' Diomedea'', ''

Puffinus ''Puffinus'' is a genus of seabirds in the order Procellariiformes that contains about 20 small to medium-sized shearwaters. Two other shearwater genera are named: ''Calonectris'', which comprises three or four large shearwaters, and ''Ardenna'' ...

''), Cetaceans (''

Prosqualodon ''Prosqualodon'' is an extinct genus of Early to Middle Miocene cetacean from Argentina, Australia, New Zealand and Venezuela. Description ''Prosqualodon'' was related to and looked like modern toothed whales. It was about long and resembl ...

'', ''

Aulophyseter ''Aulophyseter'' is an extinct genus of sperm whales from the Miocene formations of the west and east coasts of North America. ''Aulophyseter'' reached a length of approximately with an estimated body weight of .R. Nieuwenhuys (1998) ''The ce ...

'', ''

Parietobalaena ''Parietobalaena'' is an extinct genus of baleen whale, belonging to the family Pelocetidae. Fossils are found in Miocene-aged marine strata in North America, Europe, Australia and Japan Japan ( ja, 日本, or , and formally , ''Nihonk ...

'') 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 . '' ...

'', '' 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 inhabit ...

'' 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 n ...

''. 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