Desmatophoca

''Desmatophoca'' is an extinct genus of early pinniped that lived during the Miocene, and is named from the Greek "phoca", meaning seal. A taxon of the family Desmatophocidae, it shares some morphological similarities with modern true seals.Ray, C. (1976). Fossil Marine Mammals of Oregon. ''Systematic Zoology, 25''(4), 420-436. Two species are recognized: ''Desmatophoca oregonensis'' and ''Desmatophoca brachycephala''Berta, A. (1994). A New Species of Phocoid Pinniped Pinnarctidion from the Early Miocene of Oregon. ''Journal of Vertebrate Paleontology, 14''(3), 405-413.''.'' Little information exists regarding ''Desmatophoca'', due to the small number of fossil samples obtained and identified.

Unlike modern pinnipeds, ''Desmatophoca'' did not survive into the Holocene. There is some scientific debate as to whether any ''Desmatophoca'' species may have been present in the Oligocene, but without fossil samples obtained from this era, this is based primarily on conjecture. All samples of fossil ''Desmatophoca'' were found in marine deposits in Washington and Oregon, in the USA, which could indicate a geographic range of what is now the Pacific Northwest.

Description

Despite sharing morphological similarities with extant true seals, ''Desmatophoca'' differ in unique and important ways. They had significantly shorter tails, and were likely much shorter overall than modern seals. Despite their small size compared with the seals of today, they had heavier, and likely more powerful jaws.Wortman, J. T. (1906). A new fossil seal from the marine Miocene of the Oregon coast region. ''Science, 24''(603), 89-92). Because of this, it is likely they had a stronger bite force than any seal alive today, making them formidable hunters of their time. Like modern seals, they were carnivorous, and their large orbits indicate a sight-based hunting strategy.

Skull and dentition

''Desmatophoca'' skulls are characterized with large orbits, indicating the carnivorous pinnipeds were likely hunters reliant on sight. Through comparisons with extant pinnipeds, ''Desmatophoca'' were determined to be either grip and tear feeders (biting prey and shaking it into smaller portions to consume) or pierce feeders (biting prey and using slight suction to draw it fully into the mouth).

''Desmatophoca'' mandibles are thick, and they possess wide coronoid processes; both of which provide jaw strength associated with grip and tear feeders.Kienle, S., & Berta, A. (2018). The evolution of feeding strategies in phocid seals (Pinnipedia, Phocidae). ''Journal of Vertebrate Paleontology, 38(''6), Journal of Vertebrate Paleontology, 02 November 2018, Vol.38(6). The thickness of the mandible is especially important, as it provides both high bite force and increased surface area for muscular attachment between the jaws, which allows for stronger mastication.Churchill, M., & M. Clementz. (2015). Functional Implications of Variation in Tooth Spacing and Crown Size in Pinnipedimorpha (Mammalia: Carnivora). ''The Anatomical Record, 298''(5), 878-902. The extremely thick mandibles also serve as a diagnostic characteristic of this genus. Despite this evidence that indicates they may have been grip and tear feeders, ''Desmatophoca'' possess long tooth rows, which is characteristic of pierce feeders. But, they likely lacked the diagnostic small mastication muscles that would be present on a true pierce feeder. Because they have traits that would lend themselves to either strategy, it is still heavily debated which feeding strategy ''Desmatophoca'' utilized. Many agree it is likely the seals used some combination of pierce and rip and tear feeding, or potentially a new strategy not yet observed that served as a middle ground between the two.

''Desmatophoca'' have morphologically similar skulls to other predators of fish and squid, indicating this was the prominent makeup of their diet. However, it has been proposed that ''D. oregonensis'' were actually filter feeders, though their lack of diagnostic features (such as complex tooth cuspation and simple dentition). Further comparisons between ''Desmatophoca'' teeth with extant seals indicates they were a generalist species.

A distinct diagnostic characteristic of ''Desmatophoca'' skulls is the unusually large and widely-spaced paraoccipital process, something not seen in modern carnivores. They also have a rudimentary postorbital process compared with extant seals and other ''Desmatophocidae''''.''

Classification

''Desmatophoca'' is the genus within the larger clade ''Desmatophocidae'', which also contains the genus '' Allodesmus''''.'' ''Allodesmus'' and ''Desmatophoca'' are both monophyletic, and are closely related sister groups.Boessenecker, R. & Churchill M. (2018). The last of the desmatophocid seals: A new species of Allodesmus form the upper Miocene of Washington, USA, and a revision of the taxonomy of Desmatophocidae. ''Zoological Journal of the Linnean Society, 184''(1), 211-235. The two genera both have large preoccipital processes, similar cranium shapes, and short rostrums. ''Desmatophoca'' is thought to be the more primitive of the two, lacking the two-rooted postcanine teeth and prenarial shelf of ''Allodesmus''''.''
''Desmatophocidae'' have a close sister taxon as well, '' Phocidae'', and both are found within the broad monophyly of ''Phocoidea''.Berta, A., & R. J. Emry. (2002). The Miocene pinniped Desmatophoca oregonensis Condon, 1906 (Mammalia, Carnivora), from the Astoria Formation, Oregon. ''Smithsonian Contributions to Paleobiology, 93'', 113-147. All members of ''Phocoidea'', including ''Desmatophoca,'' share large orbits, bulbous cheektooth crowns, and expanded contact between the squamosal and the jugal.Fulton, T. & C. Strobeck. (2010). Multiple fossil calibrations, nuclear loci and mitochondrial genomes provide new insight into biogeography and divergence timing for true seals (Phocidae, Pinnipedia). ''Journal of Biogeography, 37''(5), 814-829.

The genus ''Desmatophoca'' consists of two known species: ''D. oregonensis'' (named for Oregon, the state it was discovered in) and ''D. brachycephala''''.''

Discovery

The first ''Desmatophoca'' discovered was ''D. oregonensis,'' by Professor Thomas Condon in 1906, a year before his death.

It was found in the middle Miocene layer of the Astoria Formation in Newport, Oregon. It was described and classified based solely off of a skull and partial jaw, and at the time, it helped shed light on the relationship between modern pinnipeds and other terrestrial carnivores. The use of ''D. oregonensis'' helped solidify the theory that modern seals evolved from terrestrial carnivores, and not the other way around. By comparing morphologies of D. oregonensis with extant terrestrial carnivores, it was determined that Desmatophoca shares a most recent common ancestor with bears and mustelids. This fossil sample also helped throw out the theory that seals share their most recent common ancestor with dogs and other canines, which was a popular thought at the time.

The second species of ''Desmatophoca, D. brachycephala'' was discovered in 1987 by Barnes, in the late Miocene layer of the Astoria Formation that jetted into southwest Washington state.

Limitations

Because fossil ''Desmatophoca'' have only appeared from the same site, the Astoria Foundation in the Pacific Northwest, there is a bias in the data that has been collected. Additionally, few fossil ''Desmatophoca'' have been found and successfully categorized, meaning there is still much to be discovered about this species. In fact, of 388 instances of fossil pinniped species being identified successfully, only 5% of these samples belong to ''Desmatophocidae,'' comprising 11 species.

References

{{Taxonbar, from=Q1635102

Miocene pinnipeds
Prehistoric pinnipeds of North America
Miocene mammals of North America
Fossil taxa described in 1906
Pinnipeds of North America
Carnivorans of North America
Prehistoric carnivoran genera