Redescription of the Late Oligocene heterodont odontocete <i>Eosqualodon langewieschei</i> from the historic Doberg of Bünde, Germany

The fossil record of the late Oligocene, spanning from 27 to 23 Ma, bears evidence of the first major burst of diversification of crown Cetacea. The discovery of new species is crucial to understanding the full picture of this diversification burst, but review of poorly studied taxa is necessary as well. One such neglected taxon is <i>Eosqualodon</i>, a member of the heterodont odontocete family Squalodontidae, whose taxonomy has been neglected for decades. Here we examine the Chattian age (∼27 Ma) type species of <i>Eosqualodon</i> from north-western Germany. Represented by a complete skull and mandible, <i>Eosqualodon langewieschei</i> has historically received neither sufficient diagnosis nor description. Our redescription demonstrates <i>E. langewieschei</i> clearly bears diagnostic traits of the Squalodontidae, which include the robust, procumbent incisors and posterior teeth with crenulated and nodular enamel; this interpretation is supported by our phylogenetic analysis. However, our comparisons with species of <i>Squalodon</i> demonstrate that <i>E. langewieschei</i> is distinct from <i>Squalodon</i> and thus that the genus <i>Eosqualodon</i> is valid. Contrary to the taxonomy of previous workers, our phylogenetic analysis failed to capture a sister relationship between <i>E. langewieschei</i> and <i>Eosqualodon latirostris</i>, leading us to consider this genus to be monotypic, pending the revision of <i>E. latirostris. Eosqualodon langewieschei</i> possesses an enlarged temporal fossa, a dorsoventrally tall coronoid process of the mandible and a fossa on the coronoid ramus for jaw adductor musculature; these observations point to a macrophagous feeding strategy much like another late Oligocene odontocete, <i>Ankylorhiza.</i>