Pelagiarctos was a genus of walrus that lived during the Mid Miocene, approx. 13-15 myr. Its remains have been found in the Sharktooth Hill Bonebed, in Kern County, California. It was originally described as an , though it is now usually considered to be a basal .
Anatomy
To date, the only material of
Pelagiarctos that has been found includes a handful of partial
. The mandibles themselves are approximately the same size as those of the contemporaneous pinniped
Allodesmus, but differ in that the cheek
teeth have two
(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.
