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. 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. An isolated tooth (
RBINS 2892) was named
Trichechodon koninckii in 1871. The fossils from Suffolk were named
Trichechodon huxleyi in 1865. For decades, however,
Ontocetus was tossed aside as a
physeterid, as the type specimen was believed to have been missing. For example,
Ontocetus was at one time considered a synonym of the physeterid
Hoplocetus. 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. 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. 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.
Misassigned species 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. == References ==