Evolution and biogeography of Paleogene microperforate planktonic foraminifera
Abstract Microperforations with a maximum diameter less than 1 μm characterize some Paleogene planktonic foraminifera and 5 microperforate groups are distinguished. Differences occur in pore density and wall textures as well as in the coiling mode. These groups are unrelated phylogenetically and the microperforate wall represents a morphological character of convergence. Parvularugoglobigerina , the earliest group, with smooth surface and scattered microperforations, evolved immediately after the K/T boundary in many localities. The Globoconusa group is characterized by a heavily pustulate wall and relatively coarser pores of lower density. Derived from Guembelitria , members of this group occur in almost every marine sequence of the lower Paleocene with no latitudinal preference, but they tend to dominate shallow water assemblages in epicontinental seas and possibly are related to coastal upwelling. Together with its immediate ancestor Woodringina and the evolutionary offshoots Zeauvigerina and Tubitextularia , the biserial Chiloguembelina contains the largest number of species, falling into 4 subgroups as here recognized. The chiloguembelinids dominated the early Paleocene, the high latitude middle Eocene, and the late Eocene-early Oligocene. The middle Eocene Guembelitria triseriata-Cassigerinelloita amekiensis lineage is defined by triserial to triserial-pseudoplanispiral coiling and occurs mainly in marginal seas and over oceanic rises in southern oceans. The tenuitellids, the latest group, first occur in the late Eocene, become common in the Oligocene-Miocene, and extend into the Quaternary and modern oceans. With a high frequency in high latitudes of the Oligocene, tenuitellids are considered to be cold water indicators.