| Ontocetus | |
|---|---|
 | |
| Specimen ofO. emmonsi that was once theholotype ofAlachtherium cretsii | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Clade: | Pinnipedia |
| Family: | Odobenidae |
| Subfamily: | Odobeninae Leidy, 1859 |
| Genus: | †Ontocetus Leidy, 1859 |
| Type species | |
| O. emmonsi | |
| Species | |
| |
Ontocetus is an extinct genus ofwalrus, anaquaticcarnivoran of thefamilyOdobenidae, endemic to coastal regions of the southernNorth Sea and the southeastern coastal regions of the U.S. during theMiocene-Pleistocene. It lived from 13.6mya—300,000 years ago, existing for approximately13.3 million years.[1]
The type species,Ontocetus emmonsi, was named byJoseph Leidy in 1859 on the basis of a single tusk-like tooth (USNM 329064) collected byEbenezer Emmons from the earlyPliocene (Zanclean)Yorktown Formation ofNorth Carolina.[2]
In the meantime, marine mammals fossils were being unearthed inNeogene deposits in the vicinity ofAntwerp,Belgium as well asSuffolk,England. One of these fossils was identified as an odobenid and namedAlachtherium cretsii. in 1867.[3] An isolated tooth (RBINS 2892) was namedTrichechodon koninckii in 1871.[4] The fossils from Suffolk were namedTrichechodon huxleyi in 1865.[5] For decades, however,Ontocetus was tossed aside as aphyseterid, as the type specimen was believed to have been missing.[6] For example,Ontocetus was at one time considered a synonym of the physeteridHoplocetus.[7] In the meantime, further Pliocene walrus fossils were collected from the North Atlantic, including the holotypes ofAlachitherium antverpiensis,Alachitherium antwerpiensis,Prorosmarus alleni, andAlachitherium africanum.[8][9][10][11]
In 2008, all specimens of Pliocene odobenids from the North Atlantic region were reviewed following the rediscovery of theOntocetus emmonsi holotype in the 1990s.T. huxleyi,A. cretsii,A. antwerpiensis,A. antverpiensis,A. africanum, andP. alleni were declared junior synonyms ofO. emmonsi based on comparisons with USNM 329064.T. koninckii, however, was found to be undiagnostic and designated anomen dubium.[12]
In 2024, reassessment of a pair of mandibles from the UK and a mandible from Belgium that had been assigned toO. emmonsi resulted in the establishment of a second species in the genus,O. posti.[13]
O. oxymycterus was named byRemington Kellogg in 1925 on the basis ofUSNM 10923, collected from the middleMiocene (Serravallian) Monterey Formation inSanta Barbara,California.[6] It was recombined asScaldicetus oxymycterus by Kohno and Ray (2008), sinceO. emmonsi was odobenid andO. oxymycterus was physeteroid.[12] Boersma and Pyenson (2015) made it the type species of the genusAlbicetus.[14]
