Morphometric And Stratophenetic Basis For Phytogeny And Taxonomy In Late Cretaceous Gublerinid Planktonic Foraminifera

摘要

Taxonomic revision of the gublerinid serial planktonic foraminifera of the Late Cretaceous (late Campanian-Maastrichtian) reveals that the group consists of two genera, Gublerina Kikoiene 1948 and Praegublerina gen. nov., which evolved from the finely costate, biserial species Heterohelixplanata (Cushman 1938). Three species are included within Praegublerina: P. pseudotessera (Cushman 1938), P. acuta (de Klasz 1953) and P. robusta (de Klasz 1953), the first being the oldest of the genus and a descendant of Heterohelix planata (Cushman 1938). Gublerina cuvillieri Kikoine 1948 and G. rajagopalani Govindan 1972 are retained within Gublerina. The two lineages are recognized based on gross test architecture, test ornamentation, pore size and internal test morphology. Our study reveals the existence of an evolutionary continuum between lineages in which the gublerinid-type chamber proliferation is independently developed in Gublerina and Praegublerina. The new taxonomic framework reflects the iterative pattern of planktonic foraminiferal evolution and it results in a better understanding of the stratigraphic and geographic distribution of the gublerinid taxa. Stable isotopic comparison of G. rajagopalani and G. cuvillieri with co-occurring late Maastrichtian benthic and planktonic species indicates that the two Gublerina species shared the same depth habitat near the thermocline.