Calcareous Nannofossil Genus Scyphosphaera: Structure, Taxonomy, Biostratigraphy, and Phylogeny

Scyphosphaerids are frequently encountered in low-latitude Miocene-Pliocene sediments. The genus first evolved in the early Eocene (calclcareous nannofossil Zone NP12), but abund diversityance and diversity remained low until middle Miocene Zones NN5-NN6, when global radiation began. More new species (24) evolved during the Miocene NN5-NN6 and NN9 zonal intervals than at any other time. The abundance acme for the genus is the late Miocene (NN9)-late Miocene NN9-late Pliocene (NN15) interval. Diversity peaked in early Pliocene Zones NN12 and NN13, with 31 extant species. Abundance and diversity began to decline markedly in the late Pliocene, with a first wave of extinctions occurring in late Pliocene Zone NN16B. A second wave of extinctions began in late Pleistocene Zone NN20. Only two scyphosphaerid species live in the oceans today (S. apsteinii and S. cohenii). Scyphosphaera is a highly polymorphic genus. Some species have been named based on relatively minor differences in shape: S. antilleana and S. apsteinii var. dilata are here considered to be synonyms of S. cohenii; S. australiensis a synonym of S. kamptneri; S. biarritzensis a synonym of S. apsteinii; S. darraghi a synonym of S. campanula; S. expansa a synonym of S. porosa; S. galeana a synonym of S. cylindrica; S. globulata a synonym of S. globulosa; S. queenslandensis a synonym of S. deflandrei; and S. turnris a synonym of S. lagena. One new species, S. excelsa, and one variety, S. recurvata var. projectura are named in this study. First and last stratigraphic occurrences of some 45 scyphosphaerid species and one variety are documented. Some of these species may be useful as secondary biostratigraphic zonal markers. INTRODUCTION The genus Scyphosphaera was erected by Lohmann (1902) for living cells bearing large, cup-shaped coccoliths. Fifty-three species and one variety have been assigned to this genus since 1902, yet the genus remains one for which many nannofossil workers make only a cursory attempt to list the species present in an assemblage. Also, despite the many species available, almost no use is currently made of any species as a biostratigraphic marker. These situations are caused in part by taxonomic uncertainty at the species level, and by the lack of well documented first and last stratigraphic occurrences. The main purposes of this paper are to attempt to clarify aspects of the taxonomy and phylogeny of the genus and to make an assessment of the biostratigraphic ranges of the species. Comments are also made on the structure, morphology, and function of the coccoliths, and the paleoecology of the genus. PREVIOUS STUDIES The first illustration of what would later be called "Scyphosphaera" appears in the HMS Challenger reports. Murray and Renard (1891) illustrated forms from South Atlantic sediments that look like S. apsteinii, although the authors refer to them as "...fragments of other calcareous organisms." Lohmann (1902) proposed the name "Scyphosphaera " for cells he found in living plankton samples collected from the Mediterranean. Lohmann (1902) noted that tall, "cup-shaped" forms occupied the equatorial region of the phytoplankton cell, whereas flat, "bowl-shaped" coccoliths covered the rest of the cell. Lohmann (1902) named only the type species, Scyphosphaera apsteinii. Only minor comments on scyphosphaerids appeared in the literature between the time of Lohmann's (1902; 1913) early papers on living forms and Deflandre's (1942) report on the first fossil forms. Working on Neogene sediments from Algeria, Deflandre (1942) named five new species and one variety; Deflandre (in Deflandre and Fert 1954) added one more species based on further examination of the Algerian samples. Kamptner (1955) examined chalk samples collected from the Indonesian island of Rotti. He found all seven of the scyphosphaerid taxa previously recorded by Lohmann and Deflandre, and named 12 new species of his own. Kamptner (1963; 1967) followed this by adding eight more new species he found in Quaternary sediments from the Pacific and Atlantic Oceans. Martini (1968) named one new species; Lezaud (1968), Stradner (1969), Boudreaux and Hay (1969), and Bukry and Percival (1971) each named two species, and Mtiller (1974) named three species, bringing the total number of named species of scyphosphaerids to 39 by the early 1970s. Important studies in the mid1970s were those of Rade (1975), who named six new species and proposed a phylogenetic lineage for the genus, and Jafar (1975a) who proposed two new species and made needed revisions to Kamptner's (1955) study. Jafar (1975a) restudied the same Rotti sample examined by Kamptner, confirming the presence of the 19 scyphosphaerid species reported by Kamptner (1955) in the sample, as well as four of the species reported by Kamptner (1963; 1967) from elsewhere. Because Kamptner (1955) did not designate type specimens for his twelve new species, Jafar (1975b) designated neotypes for them. More recently, Varol (1984; 1989) named five new species from Malta, Turkey, and the Solomon Islands. Previous overviews of the genus have been given by Perch-Nielsen (1985) and Aubry (1990). Aubry (1990) gave a particularly detailed account of the genus, and, inter alia, was the first to elucidate the structure of lopadoliths. micropaleontology, vol. 44, no. 4, pp. 351-384, text-figures 1-29, plates 1-6, table 1, 1998 351 This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 04:13:01 UTC All use subject to http://about.jstor.org/terms William G. Siesser: Calcareous nannofossil Genus Scyphosphaera: structure, taxonomy, biostratigraphy, and phylogeny