Pelagiarctos
Pelagiarctos was a genus of walrus that lived during the Mid Miocene, approx. 13-15 mya. Its remains have been found in the Sharktooth Hill Bonebed, in Kern County, California. 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 mandibles. The mandibles themselves are approximately the same size as those of the contemporaneous pinniped "Allodesmus kernensis", but differ in that the cheek teeth have two roots (instead of one, as in "Allodesmus") and  that the dentary 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, specifically borophagine dogs and hyaenids. 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 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" or "Paleoparadoxia". But in a 2014 study indicates that it was not an apex predator.