Lineage Genera Classification of Lower Paleogene Planktonic Foraminifera: ABSTRACT

Abstract

Current classifications of planktonic Foraminifera rely on rigid structural hierarchies, defining genera as narrow morphologic entities, commonly with long and discontinuous ranges. Such classifications do not satisfy the criteria of either monophyly or practicality. More properly, genera are based on phyletic successions of species through time, thus creating natural (Linnaean), monophyletic, and stratigraphically restricted taxa. Lower Paleocene species are here reclassified into five lineage-genera. These genera partly overlap in gross morphology and in certain iteratively developed analogous structures, but possess adequate diagnostic features (especially wall texture) for recognition. All presently recognized Paleocene lineages except the chilogumbelinids (including Globoconusa) are derived from the early Danian species Globorotalia pseudobulloides, and become sufficiently divergent for generic distinction by late Danian time. This species is derived from, and congeneric with, Hedbergella monmouthensis. Globanomalina includes smooth-walled, compressed, globorotaloid forms with slit-like extraumbilical apertures; finely perforate peripheral rims (keels) occur in two species. Morphotypes transitional with the Eocene planispiral genus Pseudohastigerina occur in the uppermost Paleocene and are best interpreted to be part of the reaction range of Globanomalina chapmani. Subbotina includes globigerinid forms with pitted, coarsely perforate (reticulate) walls; late middle Eocene populations gave rise to the predominantly Neogene genera Globorotaloides and Catapsydrax. An innovation critical for phylogeny was the development of coarsely hispid wall surfaces, which first appeared in neanic chambers of the early Danian form, Globorotalia pseudobulloides praecursoria. Intensification and persistence into adult chambers of hispid ornamentation accompanied the transition of G. pseudobulloides praecursoria to Globorotalia inconstans in middle Danian time. G. inconstans is the phyletic base for two isochronous radiations characterized by densely hispid wall surfaces. Acarinina includes globigerinid forms with rounded chambers and umbilical to extraumbilical primary apertures. Dorsal sutural apertures appear in two middle Eocene species (Truncorotaloides of authors); these forms, however, are phyletic dead-ends and are not here afforded generic recognition. Morozovella includes globorotaloid forms with conicotruncate chambers and peripheral concentrations of somewhat elongate rugosities (keels). Both radiations diverge into several disparate lineages. Poorly understood problems of intense parallelism and isomorphism preclude for the present more refined delineation of phylogenies. End_of_Article - Last_Page 465------------