Cushman Foundation Special Publication No. 46 p. 415-428, 2018 Chapter 15 WALL TEXTURES AND HIGHER TAXONOMY OF OLIGOCENE MICRO- AND MEDIOPERFORATE PLANKTONIC FORAMINIFERA Paul N. Pearson School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, U.K. Email: [email protected] ABSTRACT New microstructural observations on the tests of between the two major groups (trochospiral versus microperforate and medioperforate planktonic biserial or enrolled-biserial), these wall textures foraminifera from the Oligocene are presented likely indicate separate evolutionary radiations and comparisons are made with some Holocene from different groups of benthic foraminifera specimens. Two types and two subtypes of wall and so help define the higher taxonomy of the texture are distinguished: the glutinata-type (in planktonic foraminifera. Accordingly, the following Globigerinita and Tenuitella; with the danvillensis- superfamilies are recognized in the chapters of this subtype in Dipsidripella), and the ototara-type (in work: Globigerinitoidea and Guembelitriodea. most Chiloguembelina), with the chipolensis-subtype Their placement relative to other superfamilies of (in Cassigerinella and some Chiloguembelina). foraminifera is not yet known. Given also the gross morphological differences INTRODUCTION in the Cassigerinellidae which usually exhibit pores that are a little larger than 1 µm in diameter. Although Previous taxonomic atlases of the Paleogene Planktonic such divisions are always to some extent arbitrary, the Foraminifera Working Group (Olsson and others, 1999; term medioperforate is here revised to indicate walls Pearson and others, 2006) followed Fleisher (1974) with pores in the range 1-2 µm because the range 2-4 by recognizing a fundamental distinction between µm includes large numbers of species that naturally the ‘macroperforate’ wall texture (with pores >1 group with the other macroperforates. The purpose of µm in diameter) which is typical of the Superfamily this work is to propose a more formal classification Globigerinoidea and the ‘microperforate’ wall texture of Oligocene microperforate and medioperforate wall (with pores <1 µm in diameter) found in other groups, textures and to help delimit two groups of taxa that including Families Guembelitriidae, Chiloguembelinidae, probably had independent origins in the benthos. This Heterohelicidae and Cassigerinellidae. Variant textures wall texture classification is intended to complement the within the microperforate category were noted, including macroperforate classification developed, among others, the supposedly monolamellar wall of some taxa and the by Fleisher (1974, 1975), Steineck and Fleisher (1978), presence or absence of pore mounds or costellae in others Hemleben and others (1999), Hemleben and Olsson (e.g., Huber and others, 2006). Li and Radford (1991) (2006), and Chapter 3 (this volume). introduced the term ‘medioperforate’ for wall textures Originally, planktonic foraminifera were divided with pores in the range 1-4 µm. This is a useful term into genera and higher taxa mainly on the basis of general because 1 µm is not always a meaningful cut-off point test morphology, chamber shape, and apertural position for distinguishing wall textures, including for example (e.g. Galloway, 1933; Cushman, 1940, Bermúdez, 1952: Pearson see reviews by Bolli and others, 1957:19, and Lipps, Superfamily Heterohelicacea: these serial taxa are now 1966). Because such features are now thought to have acknowledged as being microperforate. (Note that the evolved independently many times, this resulted in what correct suffix for superfamilies of protists is –oidea are now recognized as only distantly related groups not –acea “when workers treat them as animals for the being lumped together, creating polyphyletic higher purposes of nomenclature” which is the case in this work; taxa. In the 1960s, some authors attempted to establish see International Code of Zoological Nomenclature, a more natural classification by differentiating higher 1999, Article 1.1.1, see also Article 29.2.) Blow (1969, taxa based on wall textures as observed using the light 1979) also argued for an evolutionary link between microscope (e.g., Parker, 1962; Wade, 1964; Lipps Globigerinita and the modern species Candeina nitida 1966). This approach was accelerated with the SEM and recognized an intermediate species as C. praenitida. which revealed test surfaces in unprecedented detail Although this has been supported by genetic evidence (e.g., Fleisher, 1974, 1975; Steineck and Fleisher, 1978; it is doubtful on wall texture grounds (see discussion Blow, 1979). below). Fleisher (1974:1011-1012) proposed the Kennett and Srinivasan (1983) described and ‘microperforate’ wall texture as a distinct category, illustrated with high quality SEMs the microperforate exemplified by the genus Globigerinita. He described wall texture of Globigerinita, Tenuitella, Globigerinatella it as characterized by ‘extremely small perforations’ and Candeina, and suggested that together they form (i.e., pores) on an otherwise smooth surface, with a natural group. However their illustrations of the small pustules common in some forms. Fleisher’s Candeina wall, while it is clearly microperforate (pores newly described genus Tenuitella was assigned to the <1 μm), does not compare closely with the other genera, microperforate category and, following Jenkins (1965), even in their own images (see Kennett and Srinivasan, he regarded Globigerinita and Tenuitella as closely 1983, pl. 57, fig. 8). related in an evolutionary sense, underlining the point Loeblich and Tappan (1984, 1988) made the first that the wall texture could be used to identify natural attempt to use the microperforate wall to establish a higher groups. This was a significant development because taxonomy. They assigned all non-serial microperforate species that are now included in these taxa had previously planktonic foraminifera to Family Candeinidae, which been assigned to various macroperforate genera such as was then subdivided into Subfamilies Tenuitellinae, Globigerina, Turborotalia and Globorotalia. Globigerinitinae, and Candeininae. This arrangement Steineck and Fleisher (1978) developed and implies that all non-serial microperforate foraminifera formalized the wall texture classification of Fleisher are part of a single clade which is a sister group to the (1974, 1975) and made a compelling case for the use macroperforates. of wall textures in identifying phylogenetically related In their influential work on modern planktonic groups. The ‘microperforate’ wall was one of five foraminifera, Hemleben and others (1989) avoided a textures identified by them among Neogene planktonic formal higher taxonomy but divided modern species into foraminifera, the others being ‘spinose’ (exemplified spinose and nonspinose groups, with the microperforate by Globigerina bulloides), ‘cancellate spinose’ forms (including Tenuitella, Globigerinita, Candeina (exemplified byTrilobatus trilobus), ‘cancellate’ and, by and serial forms) forming a division of the nonspinose inference, nonspinose (as exemplified byGloboquadrina category (see also Spezzaferri, 1994). dehiscens) and finely perforate-smooth (as exemplified Li and Radford (1991) summarized the by Globorotalia cultrata). stratigraphic and biogeographic distribution of Paleogene Blow (1969, 1979; the latter a posthumous micro- and medioperforate species and argued that they work developed several years before the publication belong to “several phylogenetically unrelated groups”, of date) also pioneered SEM investigations but he did which they identified five. Two of Li and Radford’s five not recognize the microperforate wall as delineating groups (Parvularugoglobigerina and Globoconusa) are a major subdivision in his classification of planktonic restricted to the Paleocene and one (Cassigerinelloita) foraminifera and some of his genera contain both macro- to the Eocene and so are not considered further here. and microperforate forms. He did nevertheless separate The remaining three (Chiloguembelina, Cassigerinella, serial taxa such as Chiloguembelina and Guembelitria and Tenuitella) persist into the Oligocene. In essence from the Globigerinitoidea and included them in the they recognized three of the wall types or subtypes of 416 Chapter 15 - Wall Textures Oligocene planktonic foraminifera that are formalized Pearson and Wade (2009) presented new in this paper. images of the micro- and medioperforate ultrastructure In the Atlas of Paleocene Planktonic of exceptionally well-preserved uppermost Oligocene Foraminifera, Olsson and others (1999; following taxa from Trinidad and Puerto Rico. They showed that Liu and Olsson, 1992, and Olsson and others, 1992), Cassigerinella has a different wall texture from the presented a wall texture classification that included group that comprises Tenuitella and Globigerinita (and a single major category of microperforate wall with which is also seen in Miocene Globigerinatella and various informal subcategories distinguished mainly by Mutabella). They separated the Family Cassigerinellidae the shape and distribution of pustules, pores and pore from Family Globigerinitidae and suggested these two mounds (see Hemleben and others, 1999:16, fig. 6). groups had separate origins in the benthos. A distinctive Except for Zeauvigerina, the Paleocene microperforates feature of the Cassigerinella wall (discussed further were regarded as a natural group descended from the