Ontocetus
| Ontocetus Temporal range: Miocene to Late Pleistocene,
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|---|---|
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| Specimen of O. emmonsi that was once the holotype of Alachtherium cretsii | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Parvorder: | Pinnipedia |
| Family: | Odobenidae |
| Subfamily: | Odobeninae Leidy, 1859 |
| Genus: | †Ontocetus Leidy, 1859 |
| Type species | |
| O. emmonsi | |
| Species | |
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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 13.3 million years.[1]
Taxonomy
[edit | edit source]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.[2]
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.[3] An isolated tooth (RBINS 2892) was named Trichechodon koninckii in 1871.[4] The fossils from Suffolk were named Trichechodon huxleyi in 1865.[5] For decades, however, Ontocetus was tossed aside as a physeterid, as the type specimen was believed to have been missing.[6] For example, Ontocetus was at one time considered a synonym of the physeterid Hoplocetus.[7] 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.[8][9][10][11]
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.[12]
In 2024, reassessment of a pair of mandibles from the UK and a mandible from Belgium that had been assigned to O. emmonsi resulted in the establishment of a second species in the genus, O. posti.[13]
Misassigned species
[edit | edit source]O. oxymycterus was named by Remington Kellogg in 1925 on the basis of USNM 10923, collected from the middle Miocene (Serravallian) Monterey Formation in Santa Barbara, California.[6] It was recombined as Scaldicetus oxymycterus by Kohno and Ray (2008), since O. emmonsi was odobenid and O. oxymycterus was physeteroid.[12] Boersma and Pyenson (2015) made it the type species of the genus Albicetus.[14]
References
[edit | edit source]- ^ PaleoBiology Database: Ontocetus, basic info
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- ^ 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
- ^ 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
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- ^ E. L. Trouessart. 1898. Catalogus mammalium tam viventium quam fossilum 5:665-1264
- ^ G. Hasse. 1909. Les Morses Pliocène poederlien à Anvers. Bulletin de la Société Belge de Géologie de Paléontologie et d'Hydrologie (Bruxelles) 23:293-322
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- Evolution: What the Fossils Say and Why It Matters by Donald R. Prothero and Carl Buell
- Marine Mammals: Evolutionary Biology by Annalisa Berta, James L. Sumich, and Kit M. Kovacs
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