SYSTEMATIC PALEONTOLOGY

The taxonomy used here follows McCartney and Harwood (1992) and McCartney et al. (1995), particularly in the use of genus designations.

Remarks: For discussion on our use of Bachmannocena see McCartney and Wise (1990).

Mesocena oamaruensis apiculata Schulz, 1928, p. 240, fig. 11.

Bachmannocena apiculata (Schulz); Bukry, 1987, pp. 403-404; McCartney and Wise, 1990, pl. 2, figs. 6-10; McCartney and Harwood, 1992, pl. 1, fig. 9.

Remarks: This taxon is not subdivided into multiple subspecies (see Bukry, 1987) in this study because of the low number of specimens that were observed and the lack of biostratigraphic significance.

Mesocena circulus (Ehrenberg), Ehrenberg, 1844, p. 65.

Bachmannocena circulus (Ehrenberg); Bukry, 1987, p. 404; McCartney and Harwood, 1992, pl. 2, figs. 1, 2; McCartney et al., 1995, pl. 4, figs. 1, 7; pl. 8, fig. 8.

Remarks: B. circulus has a large polygonal ring with small pointed spines. It was the dominant taxon in Sample 183-1138A-15R-CC, occurring two cores below the base of the Distephanus speculum speculum forma pseudofibula plexus. Similar occurrences of dominant B. circulus in a narrow horizon beneath the "pseudofibula plexus" have been found in ODP Hole 689B of Leg 113 (McCartney and Wise, 1990) and Holes 747A and 751A of Leg 120 (McCartney and Harwood, 1992), although the distance beneath the plexus varies considerably, suggesting that these acmes are not biostratigraphically relevant. In lower latitudes, B. circulus can be abundant in the Pliocene but is less common in the Miocene (McCartney et al., 1995).

Three specimens on this taxon were also found in Sample 183-1140A-15R-CC.

Mesocena diodon Ehrenberg, 1844, pp. 71, 84.

Bachmannocena diodon (Ehrenberg); Bukry, 1987, p. 404.

Bachmannocena diodon diodon (Ehrenberg); McCartney et al., 1995, pl. 4, figs. 2, 8.

Remarks: This taxon was abundant in Sample 183-1138A-21R-CC and co-occurs with the dominant B. circulus.

Dictyocha (Mesocena) elliptica Ehrenberg, 1840, p. 208; Ehrenberg, 1854, pl. 20(1), fig. 44a, b.

Mesocena elliptica (Ehrenberg); Bukry, 1978a, p. 819, pl. 6, figs. 6-13.

Bachmannocena elliptica (Ehrenberg); McCartney et al., 1995, p. 145.

Remarks: Only three specimens of this taxon were found in Sample 183-1138A-21R-CC. These specimens were fairly small, 30-50 µm, in comparison with other silicoflagellates viewed in this study, which placed them in B. elliptica rather than the somewhat larger and typically younger Bachmannocena quadrangula (see McCartney et al., 1995, for further discussion).

Dictyocha triacantha Ehrenberg, 1844, p. 80.

Corbisema triacantha (Ehrenberg); Busen and Wise, 1977, p. 713.

Dictyocha fibula var. aculeata Lemmermann, 1901, p. 261, pl. 11, figs. 1, 2.

Dictyocha aculeata (Lemmermann); Dumitrica, 1973, p. 907, pl. 9, figs. 5-10; McCartney et al., 1995, pl. 9, fig. 2.

Dictyocha calida Poelchau, 1976, p. 169, pl. 1, figs. c, d; pl. 3, figs. a-f.

Dictyocha calida calida Poelchau; Bukry, 1979a, p. 560, pl. 1, fig. 7; McCartney et al., 1995, p. 146.

Dictyocha varia f. extensa Locker, 1975, pp. 99-101, figs. 1/2, 3/3.

Dictyocha extensa (Locker); Locker and Martini, 1986, pp. 903, 904, pl. 2, figs. 10-12; pl. 11, fig. 3; McCartney et al., 1995, pl. 3, figs. 2-5; pl. 5, figs. 3, 7; pl. 8, fig. 8.

Remarks: This is an important taxon in the late Miocene and Pliocene of low latitudes, where it and D. varia form an evolutionary transition (see McCartney et al., 1995, and sources cited therein). It was found in the upper Miocene and lower Pliocene, with a single specimen in the lower Miocene. This taxon is typically more abundant at lower latitudes (see McCartney et al., 1995).

Dictyocha fibula Ehrenberg; Locker, 1974, p. 636, pl. 1, fig. 6 (= lectotype).

Dictyocha fibula fibula Ehrenberg; Locker and Martini, 1986, p. 904, pl. 5, figs. 1, 2; pl. 11, figs. 8, 9; McCartney et al., 1995, pl. 2, fig. 1; pl. 5, fig. 5.

Remarks: This group of dictyochid silicoflagellates, having the bridge parallel to the minor axis, are abundant in Miocene sediments of low and middle latitudes; they are less abundant in higher latitudes. The basal ring tends to be rather equant, making determination of the major axis difficult for tilted specimens. Specimens of D. extensa were smaller in size and had a higher basal ring aspect ratio than those of D. fibula. In this study, we accept Locker's (1974) designation of a large skeleton with a short-axis bridge as the lectotype for D. fibula; note that there is an error in the remarks for this taxon in McCartney et al. (1995), which states that the lectotype has a long-axis bridge.

Dictyocha fibula var. b Ehrenberg, 1843, p. 312, pl. 2, fig. IV 11.

Dictyocha fibula var. messanensis (Haeckel); Ling, 1970, pl. 18, fig. 14.

Dictyocha messanensis (Haeckel); McCartney et al., 1995, pl. 3, figs. 12, 13.

Remarks: D. messanensis is applied to a variety of skeletal morphologies that have a bridge inclined sinistrally when seen from apical view (note that flat-lying silicoflagellates are commonly viewed abapically, since they lay on a coverslip that has been turned over.) Locker and Martini (1986) and other workers divided this taxon into several subspecies and forms, but the number of specimens did not warrant subdivision in this study.

Dictyocha perlaevis Frenguelli, 1951, p. 279, fig. 4b, c.

Dictyocha fibula perlaevis (Frenguelli); Bukry, 1975b, p. 855, pl. 3, fig. 5.

Dictyocha perlaevis perlaevis Frenguelli; Bukry, 1979b, p. 984, pl. 3, figs. 6-11.

Remarks: This taxon was only found in Sample 183-1138A-18R-CC.

Dictyocha fibula var. pumila Ciesielski, 1975, p. 656, pl. 5, figs. 5-10; pl. 6, figs 1, 2.

Dictyocha aspera var. pygmaea Ciesielski, 1975, p. 655, pl. 4, figs. 1, 3, 4, 6.

Dictyocha pumila (Ciesielski); Bukry, 1978c, p. 642; McCartney and Harwood, 1992, p. 824, pl. 2, fig. 4.

Dictyocha pygmaea (Ciesielski), McCartney and Harwood, 1992, p. 824.

Remarks: Ciesielski (1975) described a group of interesting silicoflagellates with nearly square basal rings and basal spines often longer than the diameter of the basal ring from the lower Pliocene of Site 266. Ciesielski described the group as variations of two separate species, depending on whether the bridge was aligned with the long or short axis. McCartney and Harwood (1992) continued the practice of separating the long-axis and short-axis forms into two taxa, but noted that the biostratigraphic range and variation suggested that they were conspecific.

In this study, 50 specimens of D. pumila were found in Sample 183-1138A-12R-1, 100-101 cm, and 14 specimens were found in Sample 12R-2, 100-101 cm. They were rarely found elsewhere. The skeletons are consistently of small size, with spines that are often longer than the diameter of the basal ring. The basal ring is nearly square, making determination of the major axis and discrimination between the pumila and pygmaea forms difficult and probably influenced by the tilting of the specimen. D. pumila includes both forms. The D. pumila taxon is here given priority, instead of pygmaea, because it has been more frequently used and is the more abundant of the two forms. Where there was a determinable major axis, the bridge is parallel to the major axis in about two-thirds of the specimens.

Dictyocha varia Locker, 1975, pp. 99-101, figs. 3-7.

Dictyocha pulchella Bukry, 1975a, p. 687, pl. 4, figs. 1-3.

Remarks: See McCartney et al., 1995 for discussion of D. varia.

Cannopilus antarcticus Ciesielski, 1975, p. 654, pl. 1, figs. 1-9.

Distephanus antarcticus (Ciesielski); Ciesielski, 1991, pp. 80, 81.

Remarks: We follow the practice used by Bukry and Monechi (1985) and Ciesielski (1991) of not recognizing the genus Cannopilus and applying multiwindowed skeletal morphologies to Distephanus. Twelve specimens of this species were found in the lower Miocene of Hole 1040A.

Dictyocha boliviensis Frenguelli, 1940 (in part), p. 44, fig. 4a.

Distephanus boliviensis boliviensis (Frenguelli); Bukry, 1979b, p. 985, pl. 4, fig. 12; pl. 5, fig. 1; McCartney and Harwood, 1992, p. 824, pl. 3, figs. 1 (top), 2, 3.

Remarks: D. boliviensis is distinguished from D. speculum speculum by the larger basal ring, more equant basal spines, and an apical window that proportionally smaller in comparison to the basal ring. In some samples the two taxa are distinctly different, making their identification rather easy, but in other samples the range of variation overlaps, and identification becomes difficult and, perhaps, arbitrary. D. boliviensis specimens with five, seven, eight, and nine sides were counted separately to show the range of variation. Multiwindowed forms with six and more sides were also counted separately.

Dictyocha crux Ehrenberg, 1840, p. 207; Ehrenberg, 1854, pl. 18, figs. 5, 6; pl. 33(XV), fig. 9.

Distephanus crux crux (Ehrenberg); McCartney and Harwood, 1992, p. 824.

Remarks: Specimens of D. crux crux occur sporadically and in low abundance in the upper Oligocene and lower Miocene.

Halicalyptra depressa Ehrenberg, 1854, pl. 18, fig. 110.

Cannopilus depressus (Ehrenberg); Perch-Nielsen, 1975, p. 685, pl. 1, figs. 1-5.

Remarks: In this study, we counted specimens that had an almost spherical skeleton with many windows and more than six basal sides as D. depressus. The apical structure has a diameter larger than the basal ring, which sometimes prevented the precise determination of the number of basal sides.

Distephanus crux f. longispinus Schulz, 1928, p. 256, fig. 44.

Distephanus longispinus (Schulz); Bukry and Foster, 1973, p. 828, pl. 4, figs. 7, 8.

Octactis pulchra Schiller, 1925, pp. 67, 68, fig. c.

Distephanus pulchra (Schiller); Ling and Takahashi, 1985, p. 80, pls. 1, 2.

Remarks: Specimens of D. pulchra were typically eight-sided but there were some nine- and ten-sided forms, although these were not counted separately. The presence of this taxon is associated with high productivity (Murray and Schrader, 1983; Pisias et al., 1986).

Distephanus raupii Bukry, 1978b, p. 785, pl. 2, fig. 15; McCartney and Harwood, 1992, p. 825.

Remarks: Two specimens of this species were found in Sample 183-1138A-29R-CC and were sometimes abundant in samples from Hole 1040A. The specimens were differentiated from Distephanus speculum pentagonus by their smaller basal ring and the location where the struts intersect the basal ring, known as the strut attachment (see McCartney and Loper, 1989). The location of the strut attachment for D. raupii is at about the midpoint between the sides, whereas the attachments for D. speculum pentagonus are closer to the basal corners.

Dictyocha hemisphaerica Ehrenberg, 1844, pl. 17, fig. 5.

Distephanus speculum hemisphaericus (Ehrenberg); Bukry, 1975b, p. 854; McCartney et al., 1995, pl. 6, figs. 2, 5, 8; pl. 7, fig. 6.

Distephanus speculum var. pentagona Lemmermann, 1901, p. 264, pl. 11, fig. 19.

Distephanus speculum pentagonus Lemmermann; Bukry, 1976a, pp. 895, 896; McCartney and Wise, 1990, pl. 3, figs. 3-6; McCartney et al., 1995, pl. 7, fig. 4.

Remarks: D. speculum pentagonus is applied to five-sided silicoflagellates with apical rings of the same general size as co-occurring D. speculum. No special effort was made to distinguish this taxon from Distephanus quinquangellus, and the counts listed in this study may include examples of D. quinquangellus.

Dictyocha speculum Ehrenberg, 1840; Ehrenberg, 1854, pl. 18, fig. 57; pl. 19, fig. 41; pl. 21, fig. 44; pl. 22, fig. 47.

Distephanus speculum (Ehrenberg); Haeckel, 1887, p. 1565.

Distephanus speculum speculum (Ehrenberg); Bukry and Foster, 1973, p. 828, pl. 5, fig. 8.

Remarks: In the present study, seven- and eight-sided specimens and multiwindowed skeletons of D. speculum speculum were counted separately to illustrate the range of variation. The D. speculum speculum counts for Sample 183-1138A-1R-CC include 32 specimens with long spines (typically longer than the diameter of the basal ring.)

As noted above for D. boliviensis, there are some samples where there is overlapping taxonomic variation between the two common six-sided distephanid species. This subject deserves a detailed morphometric study. For this study, intermediate forms that had more pronounced long-axis spines were counted as D. speculum speculum, sometimes even though they were fairly large. There are two lines of evidence that suggest to us that these are two separate species. The first line of evidence is that they form distinctly separate size ranges in the Pliocene and Pleistocene. The second is that the unusual plexus morphologies occur exclusively among the small D. speculum speculum group; similar skeletons among the D. boliviensis are rare.

What might constitute a true species among the silicoflagellates is controversial, and opinions differ considerably among and between biologists and paleontologists. Recent biological study (Moestrup and Thomsen, 1990; Henriksen at al., 1993) shows that silicoflagellates have a life cycle that includes several skeleton-bearing stages. It remains to be determined if the skeletal morphologies might vary in size or shape during the course of the life cycle.

Distephanus speculum f. varians Gran and Braarud, 1935, p. 390, fig. 68a.

Distephanus speculum varians Gran and Braarud; Bukry, 1976a, p. 896, pl. 8, fig. 10.

Distephanus speculum notabilis f. notabilis Locker and Martini, 1987, p. 46, pl. 5, figs. 40, 41.

Distephanus speculum speculum f. notabilis Locker and Martini; McCartney and Wise, 1990, pl. 5, figs. 10-13; pl. 6, figs. 5, 7.

Remarks: This and the following two taxa represent variation within the D. speculum speculum forma pseudofibula plexus (McCartney and Wise, 1990; McCartney and Harwood, 1992). McCartney and Wise (1993) have shown that the amount of time interval during which the plexus occurs diminishes northward and defined three classes of plexid abundance. The plexid abundance in this study was Class II as defined by McCartney and Wise, and the geographical location is within the area shown as Class II on their figure 5.

Diagnosis: Six-sided basal ring with an apical ring nearly as large as the basal ring.

Description: Apical ring of diameter similar to or slightly smaller than the basal ring diameter. Skeletal elements of the apical ring are of smaller thickness than the basal elements and can have apical spines at the juncture where the strut meets the apical ring. Basal ring typically has six sides, but specimens with five, seven, and eight basal sides were observed. Basal ring may have major- and minor-axis spines. The corners of the apical ring are often positioned above the midpoint of the basal sides. The strut that connects the apical and basal rings are typically short, being less than the length of the basal radius.

Occurrence: Found in the middle Miocene of ODP Hole 1140A. Also found in the middle Miocene, Sample 120-747A-7H-6, 98-100 cm.

Size: Holotype, length of basal ring, 20 mm.

Repository: The microscope slide containing the holotype is located at the California Academy of Sciences Diatom Collection, slide #221057.

Holotype: Plate P1, fig. 1.

Type locality: ODP Sample 183-1140A-1R-CC.

Remarks: Although there is typically considerable variability in the size of the apical ring in comparison to the basal ring for D. speculum speculum, the apical ring of this taxon is unusual. Also unusual is the location of the apical spines, when present, which occur where the struts meet the corners of the apical ring. McCartney (1988) and McCartney and Loper (1989, 1992) have observed as a general rule for silicoflagellate skeletal morphology that intersections of skeletal elements are almost always triple junctions, either of three skeletal rods or of two rods and a spine. The apical spines on this taxon, however, appear to occur as part of a quadruple junction or a strut, two apical ring elements, and an apical spine. This unusual occurrence needs to be further examined using a scanning electron microscope.

We can find only one other similar specimen illustrated in the literature, that being by Perch-Nielsen, 1975 (pl. 6, fig. 13), which is from the lower Miocene. The common occurrence of this from Sample 183-1140A-1R-2, 108-109 cm, through 2R-1, 25-26 cm, suggests possible biostratigraphic use. This taxon was not found by McCartney and Harwood (1992), though subsequent work by Bohaty found specimens in Sample 120-747A-7H-6, 98-100 cm.

Distephanus speculum f. pseudofibula Schulz, 1928, p. 262, fig. 51a, b.

Distephanus speculum speculum f. pseudofibula Schulz; Locker and Martini, 1986, p. 907, pl. 7, fig. 5; McCartney and Wise, 1992, pl. 5, figs. 1-4; pl. 6, figs. 2, 3.

Distephanus speculum speculum f. pseudopentagonus McCartney and Wise, 1990, p. 750, pl. 5, fig. 6.

Remarks: This is an unusual five-sided variant of the "pseudofibula plexus." One specimen in Sample 183-1138A-12R-2, 100-101 cm, was identified as being a member of the plexid group because its size was consistent with other D. speculum speculum and smaller than dictyochid specimens in the same sample. Bohaty and Harwood (2000) have found some similar Eocene skeletal morphologies, but these are most likely derived from a different lineage than the Miocene forms.

Distephanus speculum f. varians Gran and Braarud, 1935, p. 390, fig. 68b.

Distephanus speculum speculum f. varians Gran and Braarud; McCartney and Wise, 1992, pl. 5, figs. 8, 9, 13a; pl. 6, figs. 4, 6.

Distephanus xenus Bukry, 1984, p. 557, pl. 1, figs. 11, 12; pl. 2, figs. 1-8; McCartney et al., 1995, pl. 10, figs. 4, 7.

Remarks: This species has a large hexagonal-shaped basal ring with a large apical ring that either lacks spines or has only rudimentary spines. A single specimen was found in Sample 183-1138A-12R-2,100-101 cm, during diatom study.

Dictyocha navicula biapiculata Lemmermann, 1901, p. 258, pl. 10, figs. 14, 15.

Naviculopsis biapiculata (Lemmermann); Bukry, 1978b, p. 787, pl. 3, figs. 9, 10.

Naviculopsis eobiapiculata Bukry, 1978b, p. 787, pl. 4, figs. 9-16; McCartney and Wise, 1987, p. 807, pl. 5, figs. 5-8.

Dictyocha biapiculata var. lata Deflandre, 1932, p. 500, figs. 30, 31.

Naviculopsis lata (Deflandre); Frenguelli, 1940, p. 61, fig. 11h; Bukry, 1982, p. 431, pl. 7, figs. 11-14.