Pelagiarctos
Encyclopedia
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.
s. 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 root
s (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.
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
).
or Paleoparadoxia
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
that lived during the Mid Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
, approx. 13-15 mya. Its remains have been found in the Sharktooth Hill Bonebed, in Kern
Kern
Kern may refer to:* Kern , the process of adjusting the spacing between characters in a proportional font* Kern , a light infantry unit in Medieval Irish armies...
county, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. It was originally described as an Otariidae, though it is now usually considered to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
Odobenidae.
Anatomy
To date, the only material of Pelagiarctos that has been found includes a handful of partial mandibleMandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s. The mandibles themselves are approximately the same size as those of the contemporaneous pinniped Allodesmus kernensis
Allodesmus
Allodesmus is an extinct genus of pinniped from the Miocene and related to the genus Desmatophoca. It measured about long and weighed .- References :* After the Dinosaurs: The Age of Mammals by Donald R. Prothero...
, but differ in that the cheek teeth have two root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s (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
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
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.
Paleoenvironment
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
Isurus
Isurus is a genus of mackerel sharks in the family Lamnidae, commonly known as the mako sharks. There are two living species, the common shortfin mako shark and the rare longfin mako shark , and several extinct species known from fossils. They range in length from 9 to 15 feet, and have an...
, Sphyrna
Sphyrna
Sphyrna is a genus of hammerhead sharks in the family Sphyrnidae. It currently consists of the following species:*Sphyrna corona S. Springer, 1940 *Sphyrna couardi Cadenat, 1951...
, Carcharocles), turtles (Psephophorus
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 seven species, P. polygonus, P. calvertensis, P. eocaenus, P....
), seabirds (Osteodontornis
Osteodontornis
Osteodontornis is an extinct seabird genus. It contains a single named species, Osteodontornis orri , which was described quite exactly one century after the first species of the Pelagornithidae was. O...
, Diomedea, Puffinus
Puffinus
Puffinus is a genus of seabirds in the order Procellariiformes. It comprises about 20 small to medium-sized shearwaters. There are two other shearwater genera: Calonectris, which comprises three large shearwaters, and Procellaria with another four large species...
), Cetaceans (Prosqualodon
Prosqualodon
Prosqualodon is an extinct genus of cetacean.Prosqualodon was related to and looked like modern toothed whales. It was about long and resembled a dolphin...
, Aulophyseter
Aulophyseter
Aulophyseter is an extinct genus of sperm whale from the Miocene formations of the West and East coasts of North America as well as the Patagonian region of South America...
, [[Parietobalaena]]) and other pinnipeds (Allodesmus
Allodesmus
Allodesmus is an extinct genus of pinniped from the Miocene and related to the genus Desmatophoca. It measured about long and weighed .- References :* After the Dinosaurs: The Age of Mammals by Donald R. Prothero...
, Neotherium
Neotherium
Neotherium mirum is an extinct species of walrus. It was smaller than living forms and it did not have long tusks. Males were larger than females....
).
Paleobiology
Because of its large size, adaptions geared toward crunching bones, and rarity in the fossil record, Pelagiarctos is 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 MetaxytheriumMetaxytherium
Metaxytherium is an extinct genus of dugong that lived from the Miocene to the Pleistocene. Its remains have been found in Africa, Asia, Europe, North America, and South America.- Sources :*Manatees and Dugongs of the World by Jeff Ripple...
or Paleoparadoxia
Paleoparadoxia
Paleoparadoxia is a genus of large, herbivorous marine mammals that inhabited the northern Pacific coastal region during the Miocene epoch . It ranged from the waters of Japan , to Alaska to the north, and down to Baja California, Mexico...
.