Miocene baleen whales were highly diverse and included tens of genera.However, their taxonomy and phylogeny, as well as relationships with living whales, are still a subject of controversy.Here, "Mesocetus" argillarius, a poorly known specimen from Denmark, is redescribed with a focus on the cranial anatomy.It was found to represent not only a new genus, Tranatocetus gen.
nov., but also a new family; Tranatocetidae.The whales of this family have the rostral bones either overriding or dividing the frontals; the rostral bones are contacting the parietals and nasals dividing the maxillae on the vertex; the occipital shield is Nutritionals - Oral Supplements dorsoventrally bent.The tympanic bulla is particularly characteristic of this family featuring a short, narrow anterior portion with a rounded or squared anterior end and a wider and higher posterior portion that is swollen in the posteroventral area.
A phylogenetic analysis including 51 taxa supports a monophyletic group comprising most Neogene and modern whales, with Tranatocetidae being possibly closer related to Balaenopteridae (rorquals) than to Cetotheriidae.Tranatocetidae exhibit a charahteristic bulla shape.In fact, all Neogene and modern mysticete families examined have a unique shape of the tympanic bulla PROMOCODE that is diagnostic at family-level.Inclusion of problematic taxa like Tranatocetus argillarius in phylogenies brings new understanding of the distribution and diagnostic value of character traits.
This underlines the need for re-examination of earlier described specimens in the light of the wealth of new information published in later years.