Revision of the genus Halitherium (Mammalia: Sirenia) from the Oligocene of Europe

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Four disarticulated, incompletely preserved Sirenia skeletons were described morphologically, systematically and stratigraphically from the lower Oligocene of the Rhine-Ruhr area. After extensive comparative studies, one of the partial skeletons could clearly be assigned to Halitherium schinzi known from the Mainz Basin. Two extremely fragmentary remains could be assigned to the genus Halitherium; a species determination is uncertain. Another partial skeleton, determined as Halitherium based on common characters, was recognized as a new species (Voß 2005: provisionally as Halitherium sp. type K-H) because of the presence of some individual characteristics. At present, two species of Halitherium are regarded as valid within the European Oligocene, H. schinzi KAUP 1838 and H. christoti FITZINGER 1842. Both taxa show a great intraspecific variability (e.g. KAUP 1855, LEPSIUS 1882, ABEL 1904, SlCKENBERG 1934). In addition, the differences between H. schinzi and H. christoli are minimal (ABEL 1904). A specific allocation of the skeletal remains from the Rhine-Ruhr area was accordingly difficult. We propose a phylogentic analysis of the Sirenia based on morphological-systematic treatment of the sirenians from the Palaeogene of Germany, Belgium and Austria focusing on the systematic position of the genus Haffthenum within the Dugongidae.