Cetotherium riabinini is a species of Miocene Whale that was first described by ID Hofstein from a fossil discovered at Nikolaev in southern Ukraine in 1930, though unfortunately Hofstein's original manuscript has since been lost. The precise location where the specimen was found is also unclear, as Nikolaev was a sprawling city even in 1930; it is recorded that the specimen originates from limestone of 'late Sarmatian age', which is no longer a term widely used, but which probably implies the specimen is not much younger than 9.3 million years old. The accuracy of this is hard to assess without knowing the precise origin of the fossil, but rocks of this age are common in the area, and Cetotherium riabinini is comparable to other Whales of similar age.
In a preliminary paper published in the journal Acta Palaeontologica Polonica on 13 March 2013, Pavel Gol’din and Dmitry Startsev of the Taurida National University and Tatiana Krakhmalnaya of the V. Topachevsky Paleontological Museum of the National Academy of Sciences of Ukraine, present a redescription of Cetotherium riabinini.
Cetotherium riabinini as mounted on display at the V. Topachevsky Paleontological Museum. Gol'din et al. (2013).
The specimen comprises an almost complete skull plus 39 vertebrae, 8-9 right and 3 left ribs (Hofstein's notes imply that there were once more) and a partial forelimb. Cetotherium riabinini is a Baleen (Toothless) Whale, but less advanced along this evolutionary path than modern Rorquals; Gol'din et al. suggest that it (and other Miocene Toothless Whales) would not have been able to feed in a similar way to their modern relatives, but gulping large amounts of water into a throat pouch then straining it through their baleen, but rather dabbled in a similar manner to a Duck. It is also one of the earliest Whales to show pachyosteosclerotization of the skeleton, producing a form of exceptionally dense bon-tissue only seen in Whales, which serves as ballast enabling them to dive deeper.
Neurocranium of Cetotherium riabinini in dorsal view. Scale bar is 10 cm. Gol'din et al. (2013).
See also Choking on Fish is a significant cause of death for Dolphins in Indian River Lagoon, Florida, Genetic diversity in Grey Whales, Bowhead Whales in the Northwest Passage, Fossil beaked whales from the seafloor of the Southern Indian Ocean and A Sei Whale stranded in the Humber Estuary.
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