[2] The family Cetotheriidae and the genus Cetotherium (sensu lato) have been used as wastebaskets for all kinds of baleen whales, most notably by Brandt 1873, Spassky (1954) and Mčedlidze 1970.

Based on more recent phylogenetic studies and revisions of many 19th century genera, much smaller monophyletic Cetotheriidae and Cetotherium sensu stricto is limited to a single or only a few species.

For example, Gol'din, Startsev & Krakhmalnaya 2013 included only C. rathkii and C. 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 the pygmy right whale was the sole surviving species of this family.

[13] Fossil records have revealed a predator-prey relationship between large sharks (e.g. O. megalodon) and Cetotheriids.