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Ontocetus
''Ontocetus'' is an extinct genus of walrus, an aquatic carnivoran of the family Odobenidae, endemic to coastal regions of the southern North Sea and the southeastern coastal regions of the U.S. during the Miocene-Pleistocene. It lived from 13.6 mya—300,000 years ago, existing for approximately .〔(PaleoBiology Database: ''Ontocetus'', basic info )〕
==Taxonomy==
The type species, ''Ontocetus emmonsi'', was named by Joseph Leidy in 1859 on the basis of a single tusk-like tooth (USNM 329064) collected by Ebenezer Emmons from the early Pliocene (Zanclean) Yorktown Formation of North Carolina.〔J. Leidy. 1859. (on Dromatherium sylvestre and Ontocetus emmonsi ). Proceedings of the Academy of Natural Sciences of Philadelphia 1859:162〕
In the meantime, marine mammals fossils were being unearthed in Neogene deposits in the vicinity of Antwerp, Belgium as well as Suffolk, England. One of these fossils was identified as an odobenid and named ''Alachtherium cretsii.'' in 1867.〔B. Du Bus. 1867. Sur quelques mammiferes du crag d'Anvers. Bulletins de L'Academie Royale des Sciences, des Lettres et des Beaux-Arts 24:562-577〕 An isolated tooth (RBINS 2892) was named ''Trichechodon koninckii'' in 1871.〔P. J. Van Beneden. 1871. Les Phoques de la mer scaldisienne. Bulletins de L'Academie Royale des Sciences, des Lettres det des Beaux-Arts de Belgique 32:5-18〕 The fossils from Suffolk were named ''Trichechodon huxleyi'' in 1865.〔E. R. Lankester. 1865. On the sources of the mammalian fossils of the Red Crag, and the discovery of a new mammal in that deposit, allied to the walrus. Quarterly Journal of the Geological Society of London 21:221-232〕 For decades, however, ''Ontocetus'' was tossed aside as a physeterid, as the type specimen was believed to have been missing.〔R. Kellogg. 1925. A fossil physeteroid cetacean from Santa Barbara County California. Proceedings of the United States National Museum 66(27):1-8〕 For example, ''Ontocetus'' was at one time considered a synonym of the physeterid ''Hoplocetus''.〔E. L. Trouessart. 1898. Catalogus mammalium tam viventium quam fossilum 5:665-1264〕 In the meantime, further Pliocene walrus fossils were collected from the North Atlantic, including the holotypes of ''Alachitherium antverpiensis'', ''Alachitherium antwerpiensis'', ''Prorosmarus alleni'', and ''Alachitherium africanum''.〔G. Hasse. 1909. Les Morses Pliocene poederlien a Anvers. Bulletin de la Societe Belge de Geologie de Paleontologie et D'Hydrologie (Bruxelles) 23:293-322〕〔L. Rutten. 1907. On fossil trichechids from Zeeland and Belgium. Proceedings of the Royal Netherlands Academy of Arts and Sciences 10(1):2-14〕〔E. W. Berry and W. K. Gregory. 1906. Prorosmarus alleni, a new genus and species of walrus from the upper Miocene of Yorktown, Virginia. American Journal of Science 21:444-450〕〔D. Geraads. 1997. Carnivores du Pliocene terminal de Ahl al Oughlam (Casablanca, Maroc). Géobios 30(1):127-164〕
In 2008, all specimens of Pliocene odobenids from the North Atlantic region were reviewed following the rediscovery of the ''Ontocetus emmonsi'' holotype in the 1990s. ''T. huxleyi'', ''A. cretsii'', ''A. antwerpiensis'', ''A. antverpiensis'', ''A. africanum'', and ''P. alleni'' were declared junior synonyms of ''O. emmonsi'' based on comparisons with USNM 329064. ''T. koninckii'', however, was found to be undiagnostic and designated a ''nomen dubium''.〔N. Kohno and C. E. Ray. 2008. Pliocene walruses from the Yorktown Formation of Virginia and North Carolina, and a systematic revision of the North Atlantic Pliocene walruses. Virginia Museum of Natural History Special Publication 14:39-80〕
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