Taxonomic revision of the Late Campanian-Maastrichtian (late Cretaceous) planktonic foraminiferal genus Rugotruncana Bronnimann and Brown, 1956, and a new paleontological species concept for planktonic foraminifera

摘要

The Late Cretaceous (late Campanian-Maastrichtian) planktonic foraminiferal genus Rugotruncana Bronnimann and Brown, 1956 is thoroughly revised. The genus is monospecific, with Rugotruncana circumnodifer (Finlay, 1940) being the only species included within it. Taxonomic revision of the genus was made by examination of type specimens of all species assigned to Rugotruncana in the past. The genus is characterized by the presence of an imperforate band and a weakly to strongly developed double keel along the test periphery. In addition, detailed scanning electron microscope observations reveal that the test ornamentation is asymmetrical, with variably developed rugae and costellae being parallel to the periphery on the spiral side and meridional on the umbilical side. These features serve to distinguish Rugotruncana from Rugoglobigerina and Globotruncana. Based on the morphological features revealed by the detailed test ultrastructure and ornamentation observations, Rugotruncana is included within Family Rugoglobigerinidae. A new paleontological species concept is proposed to accommodate Rugotruncana circumnodifer and other species of Cretaceous planktonic foraminifera.