Das phylogenetische System der Tanaidacea und die Frage nach Alter and Herkunft der Crustaceenfauna des antarktischen Festlandsockels1,2

Abstract

The phylogenetic system of the Tanaidacea and the question of age and origin of the crustacean fauna on the Antarctic shelf The final breakup of Gondwanaland during the Tertiary not only played an important role in establishing modern climates and oceanic currents but also had a tremendous influence on the composition of the Recent crustacean fauna. Analysis of the fossil record of the Tanaidacea shows that all Recent families had evolved before the Eocene. They all, therefore, had the chance to colonize the Antarctic shelf area. However, the tanaidacean fauna of this region is represented exclusively by phylogenetically young taxa. The species composition is atypical and does not correspond to those of other zoogeographic regions. Surprisingly, in the West Antarctic there occur some phylogenetic older taxa which are not recorded from the East Antarctic. In general, the species composition of the East Antarctic tanaidacean fauna is more like that of the deep sea while that of the West Antarctic is characterized by additional “littoral elements”. For the interpretation of recognized distribution patterns are most important geological events and the resulting effects on the changes in the world climates, e. g. it is commonly excepted that there is a continuous decrease of the surface water temperature since the paleocene. Deduced from foraminiferan data, it can be assumed that almost the entire Antarctic tanaidacean fauna was extinguished during the first dramatic drop of temperature. Cold-stenothermic eurybathic species then have colonized the Antarctic shelf. After the phase of maximal glaciation in the Pliozene the fauna of the West Antarctic was finally modified by Magellanian elements, which in some cases have to be accepted as phylogenetic old forms. Other available information on Crustacea, especially for Cirripedia, Ostracoda, Decapoda, and Isopoda support this interpretation. Therefore, it may be assumed that the Recent Antarctic crustacean fauna was established mainly about 38 m. y. ago. Practically no primitiv forms exist in this region, i. e. there are no relict species. On the contrary, we have to suggest that an important part of the fauna is represented by apomorphic species which have reached the Antarctic shelf from the deep sea. Polar emergence is a more likely hypothesis at the moment than tropical submergence. However, the final elucidation of this question can be given only after detailed phylogenetic analysis of the fauna of the adjacent deep sea basins.