Cetotherium

Cetotherium ("whale beast") is a genus of extinct cetaceans from the family Cetotheriidae. They lived in what is now Central Europe, North America, Japan, and even Peru during the Neogene Period. They had a length of 5-6 meters, while in rare cases, the largest specimens had a length of 7 meters.

Taxonomy[]

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.

Formerly assigned to Cetotherium[]

The following species were originally described as nominal species of etotherium but have been either re-assigned to other genera or removed from Cetotherium:

Cetotherium furlongi Kellogg, 1925, is known from a partial skull from the Burdigalian of the Vaqueros Formation in California, but the holotype is lost.
Cetotherium Riabinini Strobel, 1875, known from the early-Late Miocene of the Paratethys Megalake in Central Europe.
Cetotherium klinderi Brandt, 1871, is known from an isolated earbone from Miocene sediments in Chişinău, Moldova. Although fragmentary, it does not appear to be congeneric with either of the two valid species of Cetotherium.
Cetotherium maicopicum Spasski, 1951, based on a specimen from the late Miocene of the Russian Caucasus, has been re-assigned to the genus Kurdalagonus;; from the same region.
Cetotherium mayeri Brandt, 1871, known from a partial skeleton, is apparently not congeneric with Cetotherium.

Evolution[]

Cetotheres came into existence during the Oligocene epoch. However the Cetotheriidae family had been divided into two sub-groups: Cetotheriidae itself & even Tranatocetidae. Most species are relatively small (for a whale) at a size of 5-9 metres long, and the group are occasionally referred to as dwarf baleen whales. Around 12 million years ago, a giant sea was disconnected from the world's oceans. Spanning across Southeastern Europe and Northwestern Asia, the Paratethys Megalake was the largest lake to ever exist. This giant lake was home to a variety of marine mammals, including pinnipeds, Beaked whales & most notably, two of prehistory’s smallest baleen whales: Cetotherium. Most commonly, C. Riabinini & C. Rathkii. Despite how they both had a size of 5-7 meters, a study revealed that these whales had a more narrow oral cavity, indicating that they used a form of suction feeding, similar to modern gray whales, Cetotherium would have swam toward the bottom of the Megalake and would have sifted through lake bed for Crustaceans using Suction-Feeding. However, between 9.75-7.65 Million years ago, the Megalake experienced several drying episodes. Overtime, the lake lost one third of its water volume and 75 percent of its surface during the most extreme events. the water in the lake became too toxic and barren due to higher salt concentrations. Most of the organisms that lived in the megalake would have gone extinct and any that survived would have gotten sick and deformed during the water acidification process, dying in excruciating death in the now toxic watery death trap. However, other commonly known Cetotheriidae species were found in many different locations, including Piscobalaena, a 5-meter baleen whale from the Pisco formation of Peru, and the Mixocetus, a 9-11 meter long Tranatocetid-Cetotherine whale from the Modelo-Capistrano Formations of what is now California.

Paleobiology[]

Fossil records have revealed a predator-prey relationship between large sharks (e.g. O. megalodon) and Cetotheriids. The raptorial toothed whales, Livyatan melvillei and Aulophyseter, may too have posed a threat to these whales.