Taxonomic revision and evolutionary classification of the biserial Cretaceous planktic foraminiferal genus Laeviheterohelix Nederbragt, 1991

Abstract

Taxonomic re-evaluation of the Upper Cretaceous serial planktic foraminiferal genus Laeviheterohelix Nederbragt, 1991 revealed that the genus is polyphyletic. Three genera are recognized, two new, Steineckia n. gen. and Fleisherites n. gen., and one emended, namely Laeviheterohelix. Steineckia n. gen. is the oldest serial planktic foraminifer with pore mounds and it appears restricted to the upper Turonian sediments of the South Atlantic (Falkland Plateau). It includes only the type species, Steineckia steinecki n. sp. The genus Laeviheterohelix is revised and according to the emendation proposed here consists only of species from the Upper Coniacian-Campanian stratigraphic interval: L. pulchra (Brotzen, 1936) – emended and L. reniformis (Marie, 1941) – emended. The species with smooth tests and occasionally with incipient costae of the Maastrichtian are included within Fleisherites n. gen. Its type species is Fleisherites glabrans (Cushman, 1938). This newly proposed taxonomic framework is based on detailed, scanning electron microscope-based observations on the test ornamentation and ultrastructure. The taxonomic significance of the presence/absence of the pore mounds, periapertural pustulose area and pore mound size is of paramount importance in documenting the iterative evolution pattern in the serial planktic foraminifera with smooth test wall or ornamented with pore mounds.