About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 925

Last Page: 926

Title: Surface Wall Texture and Evolutionary Classification of Cenozoic Planktonic Foraminifera: ABSTRACT

Author(s): Robert L. Fleisher, P. Lewis Steineck

Article Type: Meeting abstract


The classification most widely applied to Cenozoic planktonic Foraminifera employs relatively simple morphologic criteria, such as chamber shape and apertural position, to sort test forms into genera. Because the criteria are few and distinct, this traditional approach is easy to apply and has been generally accepted by stratigraphic paleontologists. Most morphologic features, however, evolved several times during the Cenozoic. Peripheral keels appeared independently at least eleven times. Form-genera based solely on such features are unavoidably polyphyletic.

Surface wall texture, in contrast, has been evolutionarily conservative during the Tertiary. Once developed, the few basic wall-textural types persisted within lineages. A classification based primarily on surface wall textures and secondarily on gross morphology most accurately reflects patterns of descent recognized from species-by-species evaluation of

End_Page 925------------------------------

ancestor-descendant relations and conveys important stratigraphic and paleoecologic information.

Most Cenozoic species, for example, are usually assigned to either Globorotalia or Globigerina. Used in this way, these taxa are over-inclusive and provide no information beyond a mnemonic clue to apertural position. As appropriately modified, Globorotalia is exclusively a Neogene genus, and Paleogene species are assigned to Acarinina, Morozovella, and Planorotalites. Globigerina is largely a middle Tertiary taxon, containing only a few cool-water modern species; most late Neogene globigeriniforms belong in Neogloboquadrina or Globoturborotalita. An emphasis on phyletic species-grups is requisite for the development of multiple-phyletic zonations.

End_of_Article - Last_Page 926------------

Copyright 1997 American Association of Petroleum Geologists