Revision of the genus Halitherium (Mammalia: Sirenia) from the Oligocene of Europe
Final Report Abstract
The systematic relationships of the Sirenia are obscure and controverse. Halitherium schinzii from the early Oligocene of Europe and Halitherium christolii from the late Oligocene of Austria yielded numerous specimens once recognised as separated species, but which are synonymised today on the grounds of intraspecific variability or ontogeny. Recent studies revealed a disagreement of the intraspecific determination of Halitherium schinzii besides the fact that existing synonymy lists of Sirenia are reflecting a more or less subjective point of view. The presence of two different species at least in the German Oligocene is hypothesised. Halitherium schinzii which represents the best sampled sirenian from the early Oligocene sandy and clayey marine sediments of Germany, especially the Mainz Basin and the Leipzig Bay, is supposed to be the only taxon in these localities. Halitherium schinzii forms together with H. taulannense (late Eocene of France) and H. christolii (late Oligocene of Upper Austria) a species-complex currently regarded as valid within the European Palaeogene, but which, however, is a paraphyletic assemblage. A closer examination of the genus Halitherium was the aim of this project focusing on the morphological redescription of all known valid species of Halitherium and of as many referred specimens as possible. In this context, the Central and North American species of Halitherium, H. alleni and H. antillense, are included for the first time. It was one of the main objectives to prove if the genus Halitherium can be claimed to be monophyletic finding appropriate characters. A new compehensive phylogenetic analysis is the final aim, also in order to clarify the intrageneric relationships of Halitherium and its systematic position within the Dugongidae. The study of various sirenian fossils from the Rupelian (lower Oligocene) of Germany and Belgium usually determined as H. schinzii reveal significant morphological differences especially in the area of the supraoccipital. This cranial bone has never before considered to be diagnostic, but clearly contributes to a wider knowledge on intra- and/or interspecific differences in sea cows. Two morphological types can be distinguished in general. Type one shows a very prominent crown-like external occipital protuberance. Type two lacks an external occipital protuberance. The nuchal crest of the latter is concave in the median plane reflecting a completely opposite structure as is described for type one. "Halitherium bronni", which, however, was not considered to be valid until today, displays such kind of rostrad extending nuchal crest. A considerably number of skeletons of the extant Dugong dugon and the three living species of Trichechus were investigated to test the intraspecific variation that is indicated for H. schinzii andi H. christolii since the beginning of the 20th century. The observations show that the role of ontogenetic stages and sexual dimorphism is of minor importance. Intraspecific variation affects the morphology of the temporal crests, for example, but the basic skeletal structures do not change in ontogeny and between males and females. That means, a presence of two distinguished morphospecies of the German Oligocene is indicated supporting the validity of "Halitherium bronni".
Publications
- (2006): Funde von Halitherium (Sirenia) aus dem Unteroligozän des Rhein-Ruhr-Gebietes. - Berichte des Instituts für Geowissenschaften Christian-Albrechts-Universität Kiel, 22: 146; Kiel
Voss, M.
- (2007): Considerations on the ecology of fossil sperm whales. - [In;] Warren, A, (ed.); Conference on Australasian Vertebrate Evolution, Palaeontology and Systematics. - Geological Society of Australia Abstracts, 85: 45; Melbourne
Hampe, O.
- (2007): Discoveries of Sirenian remains from the early Oligocene of the Rhine-Ruhr area (Germany) and a new look on the genus Halitherium. - [In:] Warren, A. (ed.): Conference on Australasian Vertebrate Evolution, Palaeontology and Systematics. - Geological Society of Australia Abstracts 85: 45; Melbourne
Voss, M.
- (2007): The systematics of xenacanthid sharks - A critical review. - Ichthyolith Issues Special Publication, 10; 44-45; Uppsala
Hampe, O.
- (2008): Landmark analyses of mysticete crania: A contribution to the phylogenetic relationships of baleen whales.— [In:] Kohno, N. (ed.); Fifth Conference on Secondary Adaptation of Tetrapods to life in Water - Abstracts, 20-21; Tokyo (Nat Nus. Nat. Sci.)
Hampe, O. & Baszio, S.
- (2008): New finds of Halitherium (Sirenia, Mammalia) from the lower Oligocene of the Rhine area, Germany. - Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, 249(3): 257-269, 10 Abb., 2 Tab.; Stuttgart
Voss, M.
- (2008): Vertebrae anomaly in fossil sea cows (Mammalia, Sirenia). - Erlanger Geologische Abhandlungen, Sonderband 6: 117; Erlangen
Voss, M.
- (2009): New aspects on innerspecific variation in the genus Halitherium (Mammalia: Sirenia). - Journal of Vertebrate Paleontology Supplement, 29(3): 196; Bristol
Voss, M.
- (2009); Taxonomic and systematic problems within the genus Halitherium (Mammalia: Sirenia). - Terra Nostra, 3: 118; Bonn
Voss, M.
