The anatomy of a late Miocene baleen whale from Ukraine

Abstract

We re-describe Cetotherium riabinini, a little known baleen whale from the Late Miocene of the Eastern Paratethys. C. riabinini is represented by an exceptionally well-preserved skull and partial skeleton, and is shown to be closely related to C. rathkii, the only other member of the genus. Cetotheriids from the Eastern Paratethys are remarkable for their pachyosteosclerotic postcranial skeleton, and are among the youngest known cetaceans displaying such an anatomy. C. riabinini is hypothesised to have followed a generalised feeding strategy combining herpetocetine-like continuous suction feeding, as seen in the mallard Anas platyrhynchos, and eschrichtiid-like intermittent suction feeding. This hypothesis may explain the mechanism and function of cranial kinesis in baleen whales. Many characteristics of the mysticete skull likely evolved as a result of cranial kinesis, thus leading to multiple instances of morphological convergence across several different phylogenetic lineages.