A NEW BALEEN WHALE FROM THE LATE MIOCENE OF DENMARK AND EARLY MYSTICETE HEARING

The extinct mysticete fauna of the North East Atlantic is primarily known from the abundant but fragmented Belgian specimens. Compared to the well-preserved contemporary mysticete fauna from deposits in North America, there are only few near complete European Miocene mysticete fossils. Presented here is a new, almost complete fossil baleen whale Uranocetus gramensis gen. et sp. nov. from the Upper Miocene Gram Formation in South West Denmark. It is the first stem-balaenopterid that has an initial stage of reduction in the mandibular cavity and a rostral configuration that is intermediate between that of other stem-balaenopterids and true balaenopterids. It is likely that Uranocetus used a gulp feeding technique that approaches that of balaenopterids. Details of the periotic and mandibular morphology place Uranocetus in the family Diorocetidae Steeman 2007. The large mandibular cavity in Uranocetus and most other extinct mysticetes, when compared to the reduced condition in recent mysticetes, is not an indication that early mysticetes used odontocete-like echolocation. In Uranocetus and a distantly related mysticete, high frequency sounds in the range odontocetes use for echolocation would suffer a significant volume loss across the lateral mandibular wall on the passage towards the inner ear. A reduction in the mandibular cavity in separate evolutionary lineages of mysticetes may be the result of a shift towards the use of low frequency sounds.