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 13.3 million years.[1]

Ontocetus
Temporal range: Miocene to Late Pleistocene,
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Odobenidae
Genus: †Ontocetus
Leidy, 1859
Species:
†O. emmonsi
Binomial name
†Ontocetus emmonsi
Leidy, 1859

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.[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]

Misassigned species

As a side note, Ontocetus 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.[13]

References
  1. PaleoBiology Database: Ontocetus, basic info
  2. Leidy J (1859). "[Remarks on Dromatherium sylvestre and Ontocetus emmonsi]". Proceedings of the Academy of Natural Sciences of Philadelphia. 1859: 162.
  3. 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
  4. 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
  5. Lankester E. R. (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 (1–2): 221–232. doi:10.1144/gsl.jgs.1865.021.01-02.28. S2CID 130245053.
  6. Kellogg R (1925). "A fossil physeteroid cetacean from Santa Barbara County California". Proceedings of the United States National Museum. 66 (27): 1–8. doi:10.5479/si.00963801.66-2564.1.
  7. E. L. Trouessart. 1898. Catalogus mammalium tam viventium quam fossilum 5:665-1264
  8. 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
  9. Rutten L (1907). "On fossil trichechids from Zeeland and Belgium". Proceedings of the Royal Netherlands Academy of Arts and Sciences. 10 (1): 2–14.
  10. Berry, E. W.; Gregory, W. K. (1906). "Prorosmarus alleni, a new genus and species of walrus from the upper Miocene of Yorktown, Virginia". American Journal of Science. 21 (126): 444–450. Bibcode:1906AmJS...21..444B. doi:10.2475/ajs.s4-21.126.444.
  11. Geraads D (1997). "Carnivores du Pliocene terminal de Ahl al Oughlam (Casablanca, Maroc)". Géobios. 30 (1): 127–164. doi:10.1016/s0016-6995(97)80263-x.
  12. Kohno N., Ray C. E. (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.
  13. Alexandra T. Boersma; Nicholas D. Pyenson (2015). "Albicetus oxymycterus, a New Generic Name and Redescription of a Basal Physeteroid (Mammalia, Cetacea) from the Miocene of California, and the Evolution of Body Size in Sperm Whales". PLOS ONE. 10 (12): e0135551. Bibcode:2015PLoSO..1035551B. doi:10.1371/journal.pone.0135551. PMC 4674121. PMID 26651027.
  • 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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