The acuticosta-group (Ostracoda, Cytheroidea) in the Mid-European Eocene and Oligocene, with description of Lienenklausicythere n. gen.

摘要

The acuticosta-group of thaerocytherid Ostracoda, formerly placed in the genus Hermanites, is reviewed taxonomically and stratigraphically. Due to differences in carapace morphology, the species and subspecies of this group are now incorporated into the new genus Lienenklausicythere. In contrast to earlier assumptions, a phylogenetic lineage could only very tentatively be drawn to the Hungarian genus Asperrissimocythere Monostori 1998 from the Lutetian to Priabonian of the Hungarian Paleogene Basin. Lienenklausicythere n. gen. comprises the following species and subspecies: acuticosta acuticosta (Pietrzeniuk 1965), acuticosta multispinosa (Pietrzeniuk 1965) and acuticosta n. ssp. A, camela camela (Moos 1965), camela turbida (Moos 1968), and Lienenklausicythere n. sp. A aff. Lienenklausicythere camela (Moos 1965). In the Altmark-Brandenburg Basin first occurrences of L. acuticosta are dated as late Middle Eocene. This species occurred relatively widespread in the latest Eocene (presumably part of the TA4.3 cycle of the global sequence stratigraphy). The closely related L. camela known from Latdorf and the Bünde area, the Hessian Depression, the Upper Rhine Graben, and the Mainz Basin has its first appearance datum (FAD) in the latest Eocene and is widespread during the earliest Oligocene. Due to the accompanying fauna both species refer to shallow marine sublittoral and lagoonal palaeoenvironments. L. camela is indicative for the lower, i.e. the marine part of the lowermost Rupelian Rul-T/R-Cycle (presumably equivalent to the TA4.4 cycle of the global sequence stratigraphy) in the Hessian Depression, the Upper Rhine Graben and the Mainz Basin. In accordance with a westward directed warm water current, a westward and then southward migration of the acuticosta-group through the Hessian Depression is assumed. Homologisation of reticulate ornamental patterns in trachyleberidid as well as thaerocytherid Ostracoda (method of Liebau 1969, 1977, 1991 and Benson 1972) reveals similarities and differences between Cretaceous and Paleogene genera like Agrenocythere Benson 1972, Horrificiella Liebau 1975, Asperrissimocythere Monostori 1998 and the new genus Lienenklausicythere. The morphological relationship between Asperrissimocythere gantensis (Monostori 1977), the type species of Asperrissimocythere, and the German representatives of Lienenklausicythere n. gen. is discussed in detail. Noteworthy is the proof of a "carinocythereid" sexual dimorphism in Lienenklausicythere, i.e. similar to that in the Recent Carinocythereis Ruggieri 1956. Also similar to this latter genus is a differentiation of the anterior margin which was observed in Lienenklausicythere n. sp. A aff. Lienenklausicythere camela.