Odd partnerships among middle Eocene (Bartonian) Nummulites: Examples from the Transylvanian (Romania) and Dorog (Hungary) Basins

Nummulites assemblages recovered from the middle Eocene of the Transylvanian Basin (Romania) and Dorog Basin (Hungary) were studied in order to infer the paleoecological structuring of the assemblages. The studied material consists mostly of A and B-generation tests of Nummulites perforatus in both basins. However, specimens of Nummulites beaumonti, and of Nummulites striatus were sporadically recorded in the Transylvanian and Dorog Basin respectively. The co-occurrence of two different Nummulites taxa, which show a striking size difference in protoconch and adult test, suggests that the small-sized Nummulites beaumonti and Nummulites striatus were the odd partners of the large-sized Nummulites perforatus during the Bartonian (middle Eocene). The co-occurrence of these closely related species might reflect their different life strategies, growth rate and/or the use of different reproduction seasons. The association of the same large partner with two distinct small-sized partners in two different, but connected basins is due to the wider paleogeographic distribution, and more abundant occurrence of the larger partner (N. perforatus), as compared to N. beaumonti and N. striatus, the smaller-sized partners. (C) 2016 Elsevier B.V. All rights reserved.