Cetotherium ("whale beast") is an extinctgenus ofbaleen whales from the familyCetotheriidae.^[2]

Cetotherium Temporal range:Miocene–Pliocene PreꞒ Ꞓ O S D C P T J K Pg N
Mounted skeleton ofCetotherium riabinini
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Suborder:	Whippomorpha
Infraorder:	Cetacea
Family:	Cetotheriidae
Subfamily:	†Cetotheriinae Whitmore & Barnes, 2008
Genus:	†Cetotherium Brandt 1843
Species[1]
†C. crassangulumCope, 1895 †C. furlongiKellogg, 1925 †C. rathkiiBrandt, 1843 (type) †C. riabininiHofstein, 1948

The family Cetotheriidae and the genusCetotherium (sensu lato) have been used aswastebaskets for all kinds of baleen whales, most notably byBrandt 1873, Spassky (1954) andMčedlidze 1970. Based on more recent phylogenetic studies and revisions of many 19th century genera, much smaller monophyletic Cetotheriidae andCetotheriumsensu stricto is limited to a single or only a few species. For example,Gol'din, Startsev & Krakhmalnaya 2013 included onlyC. rathkii andC. riabinini in the genus and only ten genera in the family.^[3]

Cetotheriidae were thought to have gone extinct during the Pliocene until 2012, when it was hypothesized that thepygmy right whale was the sole surviving species of this family.^[4]

The following species were originally described as nominal species ofCetotherium but have been either reassigned to other genera or removed fromCetotherium:

• Cetotherium furlongi Kellogg, 1925,^[5] is known from a partial skull from theBurdigalian of the Vaqueros Formation inCalifornia, but the holotype is lost.^[6]
• Cetotherium gastaldii Strobel, 1875,^[7] known from the early Pliocene-age Sabbie d'Asti Formation of thePiedmont region in Italy, is now the type species of theeschrichtiid genusEschrichtioides.^[8]
• Cetotherium klinderi Brandt, 1871,^[9] is known from an isolated earbone from Miocene sediments inChişinău,Moldova. Although fragmentary, it is not congeneric with the two species ofCetotherium.^[3][10]
• Cetotherium maicopicum Spasski, 1951,^[11] based on a specimen from the lateMiocene of the RussianCaucasus, was reassigned to the genusKurdalagonus from the same region in 2012, although Gol'din and Startsev (2016) have questioned this referral.^[12][10]
• Cetotherium mayeri Brandt, 1871,^[9] known from a partial skeleton, has been reassigned toMithridatocetus.^[3][10]

Cetotherium incertum Brandt, 1873, known from a vertebra, and"Ziphius" priscus Eichwald, 1840 arenomina dubia, whileCetotherium pusillum Nordmann, 1860 requires re-assessment.^[10]

Cetotheres came into existence during theOligocene epoch. The cetotheres have been divided into two sub-groups. One group includesCetotherium. From an evolutionary perspective, these whales share some characteristics of theBalaenopteridae andEschrichtiidae.^[13]

Fossil records have revealed a predator-prey relationship between large sharks (e.g.O. megalodon) and Cetotheriids. The raptorialtoothed whale,Livyatan melvillei, may too have posed a threat to these whales.^{[citation needed]}

• Evolution of cetaceans