Editing Pinniped (section)

===Evolution===
{{Further|List of fossil pinnipedimorphs}}
[[File:Puijila BW.jpg|thumb|right|Restoration of ''Puijila'']]
One popular hypothesis suggested that pinnipeds are [[polyphyletic|diphyletic]] (descended from two ancestral lines), with walruses and otariids sharing a [[Most recent common ancestor|recent common ancestor]] with [[bear]]s; and phocids sharing one with [[Musteloidea]]. However, morphological and molecular evidence support a [[monophyletic]] origin.<ref name="Berta">Berta, A. "Pinniped evolution" in {{harvnb|Perrin|Würsig|Thewissen|2009|pp=861–866}}</ref> A 2021 genetic study found that pinnipeds are more closely related to musteloids.<ref>{{cite journal|author1=Hassanin, A.|author2=Veron, G.|author3=Ropiquet, A.|author4=van Vuuren, B. J.|author5=Lécu, A.|author6=Goodman, S. M.|author7=Haider, J.|author8=Nguyen, T. T.|year=2021|title=Evolutionary history of Carnivora (Mammalia, Laurasiatheria) inferred from mitochondrial genomes|journal=PLOS ONE|volume=16|issue=2|page=e0240770|doi=10.1371/journal.pone.0240770|pmid=33591975 |pmc=7886153 |bibcode=2021PLoSO..1640770H |doi-access=free }}</ref> Pinnipeds [[Cladogenesis|split]] from other caniforms 50&nbsp;million years ago ([[Mya (unit)|mya]]) during the [[Eocene]].<ref name=leptin>{{cite journal |vauthors=Hammond JA, Hauton C, Bennett KA, Hall AJ |year=2012 |title=Phocid seal leptin: Tertiary structure and hydrophobic receptor binding site preservation during distinct leptin gene evolution |journal=PLOS ONE |volume=7 |issue=4 |page=e35395 |doi=10.1371/journal.pone.0035395 |editor1-last=Nikolaidis |editor1-first=Nikolas |bibcode=2012PLoSO...735395H |pmid=22536379 |pmc=3334926|doi-access=free }}</ref> The earliest fossils of pinnipeds date back to the [[Chattian|Late Oligocene]].<ref>{{Cite journal |last=Valenzuela-Toro |first=Ana |last2=Pyenson |first2=Nicholas D. |date=27 November 2019 |title=What do we know about the fossil record of pinnipeds? A historiographical investigation |url=https://royalsocietypublishing.org/doi/10.1098/rsos.191394 |journal=[[Royal Society Open Science]] |language=en |volume=6 |issue=11 |pages=191394 |doi=10.1098/rsos.191394 |issn=2054-5703 |pmc=6894555 |pmid=31827869 |access-date=13 November 2024}}</ref> Fossil animals representing basal lineages include ''[[Puijila]]'', of the [[Early Miocene]] in Arctic Canada. It resembled a modern otter, but shows evidence of quadrupedal swimming—retaining a form of aquatic locomotion that led to those employed by modern pinnipeds. ''[[Potamotherium]]'', which lived in the same period in Europe, was similar to ''Puijila'' but more aquatic.<ref name="Dawson2009">{{Cite journal |author1=Rybczynski, N. |author2=Dawson, M. R. |author3=Tedford, R. H. |doi=10.1038/nature07985 |title=A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia |journal=Nature |volume=458 |issue=7241 |pages=1021–24 |year=2009 |pmid=19396145|bibcode=2009Natur.458.1021R |s2cid=4371413 }}</ref> The braincase of ''Potamotherium'' shows evidence that it used its [[whiskers]] to hunt, like modern seals.<ref>{{Cite journal |last1=Lyras |first1=G. A. |last2=Werdelin |first2=L |last3=van der Geer |first3=B. G. M. |last4=van der Geer |first4=A. A. E. |year=2023 |title=Fossil brains provide evidence of underwater feeding in early seals |journal=Communications Biology |language=en |volume=6 |issue=1 |page=747 |doi=10.1038/s42003-023-05135-z |pmid=37591929 |issn=2399-3642|pmc=10435510 }}</ref> Both ''Puijila'' and ''Potamotherium'' fossils have been found in lake deposits, suggesting that seal ancestors were originally adapted for fresh water.<ref name="Dawson2009"/>

[[File:Enaliarctos mealsi.JPG|left|thumb|Fossil of ''Enaliarctos'']]
''Enaliarctos'', a fossil species of late [[Oligocene]]/early Miocene (24–22&nbsp;mya) [[California]], closely resembled modern pinnipeds; it was adapted to an aquatic life with flippers and a flexible spine. Its teeth were more like land predators in that they were more adapted for [[Carnassial|shearing]]. Its hind-flippers may have allowed it to walk on land, and it probably did not leave coastal areas as much as its modern relatives. ''Enaliarctos'' was likely more of a fore-flipper swimmer, but could probably swim with either pair.<ref name="Berta"/> One species, ''Enaliarctos emlongi'', exhibited notable [[sexual dimorphism]], suggesting that this physical characteristic may have been an important driver of pinniped evolution.<ref name=Cullenetal2014>{{cite journal|last1=Cullen|first1=T. M.|last2=Fraser|first2=D.|last3=Rybczynski|first3=N.|last4=Shroder-Adams|first4=C.|title=Early evolution of sexual dimorphism and polygyny in Pinnipeda|journal=Evolution|date=2014|volume=68|issue=5|pages=1469–1484|doi=10.1111/evo.12360|pmid=24548136|s2cid=10389875|doi-access=free}}</ref> A closer relative of extant pinnipeds was ''[[Pteronarctos]]'', which lived in [[Oregon]] 19–15 mya. As in modern seals, the [[maxilla]] or upper jaw bone of ''Pteroarctos'' intersects with the [[Orbit (anatomy)|orbital wall]]. The extinct family [[Desmatophocidae]] lived 23–10&nbsp;mya in the North Pacific. They had long skulls that with large orbits, interlocked [[zygomatic bone]]s and rounded [[molar (tooth)|molar]]s and [[premolars]]. They also were sexually dimorphic and may have been capable of swimming with both or either pair of flippers.<ref name="Berta"/> They are grouped with modern pinnipeds, but there is debate as to whether they are more closely related to phocids or to otariids and walruses.<ref>{{cite journal|last1=Boessenecker|first1=R. W.|last2=Churchill|first2=M.|year=2018|title=The last of the desmatophocid seals: a new species of ''Allodesmus'' from the upper Miocene of Washington, USA, and a revision of the taxonomy of Desmatophocidae|journal=Zoological Journal of the Linnean Society|volume=184|issue=1|pages=211–235|doi=10.1093/zoolinnean/zlx098}}</ref><ref name="Berta Churchill Boessenecker 2018"/> A 2024 study places them within Phocidae, specifically Phocinae.<ref name=Park2024/>

[[Image:Archaeodobenus restoration.PNG|thumb|Reconstruction of ''[[Archaeodobenus]] akamatsui'' family Odobenidae]]
The ancestors of the Otarioidea and Phocoidea diverged around 25&nbsp;mya.<ref name=Nyakatura>{{cite journal|last1=Nyakatura|first1=K|last2=Bininda-Emonds|first2=O. R. P.|year=2012|title=Updating the evolutionary history of Carnivora (Mammalia): a new species-level supertree complete with divergence time estimates|journal=BMC Biology|volume=10|page=12|doi=10.1186/1741-7007-10-12|doi-access=free|pmid=22369503|pmc=3307490}}</ref> Phocids are known to have existed for at least 15&nbsp;million years,<ref name="Berta"/> and molecular evidence supports a divergence of the Monachinae and Phocinae lineages around this time.<ref name="Berta Churchill Boessenecker 2018"/> The fossil genera ''[[Monotherium]]'' and ''[[Leptophoca]]'' of southeastern North America represent the earliest members of Monachinae and Phocinae respectively.<ref name="Berta"/> Both lineages may have originated in the North Atlantic, and likely reached the Pacific via the [[Central American Seaway]]. Phocines mainly stayed in the Northern Hemisphere, while the monachines diversified southward.<ref name="Berta Churchill Boessenecker 2018"/> The [[Lineage (evolution)|lineages]] of Otariidae and Odobenidae split around 20&nbsp;mya.<ref name=Nyakatura/> The earliest fossil records of otariids are in North Pacific and dated to around 11&nbsp;mya. Early fossil genera include ''[[Pithanotaria]]'' and ''[[Thalassoleon]]''.<ref name="Berta"/> The ''Callorhinus'' lineage split the earliest, followed by the ''[[Eumetopias]]''/''[[Zalophus]]'' lineage and then the rest, which colonized the Southern Hemisphere.<ref name="Berta"/><ref name="Berta Churchill Boessenecker 2018"/> The earliest fossils of Odobenidae—''[[Prototaria]]'' of Japan and ''[[Proneotherium]]'' of Oregon—date to 18–16&nbsp;mya. These primitive walruses had normal sized canines and fed on fish instead of mollusks. Later taxa like ''[[Gomphotaria]]'', ''[[Pontolis]]'' and ''[[Dusignathus]]'' had longer canines on both the upper and lower jaw. The familiar long upper tusks developed in the genera ''[[Valenictus]]'' and ''Odobenus''. The lineage of the modern walrus may have spread from the North Pacific to the North Atlantic through the Caribbean and Central American Seaway 8–5&nbsp;mya, and then back to the North Pacific via the Arctic 1&nbsp;mya, or to the Arctic and subsequently the North Atlantic during the [[Pleistocene]].<ref name="Berta"/>