asanoi (Maiya, Saito, and Sato) = Globoquadrina
asanoi Maiya, Saito, and Sato, 1976
(Plate 1, figs. 19-22; Plate 2, figs. 1-3)
This is a large, distinct form, marked by four globular chambers in the final whorl, rounded outline, and high conical arrangement of early whorls. The distinct aperture is interiomarginal; a distinctly open moderately high arch with rim but lacking a lip. Aperture is umbilical to extraumbilical; in some forms, the aperture is distinctly umbilical in position. A detailed description of this form is provided by Saito et al. (1981; but the captions for the plates are reversed between N. asanoi and N. kagaensis). Lagoe and Thompson (1988) provided a synonymy list for N. asanoi resulting from earlier work in the California region. Keller (1978a, 1978b, 1978c) and Keller and Ingle (1981) included specimens assignable to N. asanoi within a taxon referred to as Neogloboquadrina pachyderma form 3. Keller (1979a, 1980) later assigned this form to N. asanoi. N. asanoi is a useful zonal marker for California margin sequences where it forms a distinct range zone (CM6). Our initial biostratigraphic studies (Lyle, Koizumi, Richter, et al., 1997) referred this form to Neogloboquadrina sp. (rounded). Poore (1981), during studies of California margin-drilled Neogene sequences (DSDP Leg 63), included forms we assign as N. asanoi in Neogloboquadrina atlantica.
N. asanoi is phylogenetically closely related to N. kagaensis. Maiya et al. (1976) considered that N. asanoi evolved into N. kagaensis. However, in the California margin sequences described here, N. kagaensis appears first and evolves in an apparently gradational bioseries into N. asanoi. Early populations of N. asanoi exhibit morphological gradation with the ancestral form—N. kagaensis. It seems that Maiya et al. (1976) suggested an opposite phylogenetic relationship between the two taxa because the sections in Japan in which these forms were first described were not of sufficient age to reveal their biostratigraphic and phylogenetic relations. For California, Lagoe and Thompson (1988) clearly demonstrated that N. asanoi is preceded by an illustrated form they referred to as Neogloboquadrina sp., which we assign to N. kagaensis. This supports our hypothesis of the evolution of N. asanoi from N. kagaensis.
Near the top of its range, N. asanoi became an even more rounded, highly trochospiral form with a high-arched aperture restricted to the umbilical region (Plate 2, figs. 1-3).
kagaensis (Maiya, Saito, and Sato) = Globoquadrina
asanoi Maiya, Saito, and Sato, 1976
(Plate 1, figs. 15-18)
This is a large, distinct form with 4.0-4.5 chambers in the final whorl and moderately quadrate equatorial periphery. The aperture is umbilical to extraumbilical, with a low arch and no distinct lip. This species is distinguished from N. asanoi by its more extraumbilical aperture, more quadrate equatorial periphery, and by 4.0-4.5 chambers in the final whorl instead of four (as in N. asanoi). A detailed description of this form is provided by Saito et al. (1981; plate captions are reversed between N. asanoi and N. kagaensis). Our early studies of Leg 167 materials (Lyle, Koizumi, Richter et al., 1997) referred this species to N. asanoi.
This species appears before and is considered to be the ancestor of N. asanoi (see discussion on N. asanoi). It seems likely that Keller (1979a, 1980) included both N. kagaensis and N. asanoi within a form assigned to N. asanoi. Lagoe and Thompson (1988) assigned forms that we consider to be N. kagaensis to Neogloboquadrina sp. They thus recognized the distinction between these two forms in the California Pliocene, demonstrated that N. kagaensis appeared first, and suggested that N. kagaensis may be ancestral to N. asanoi. Poore (1981) appears to have included this form in Neogloboquadrina atlantica in Pliocene sequences drilled on the California margin during DSDP Leg 63.
N. kagaensis is useful in biostratigraphically subdividing the Pliocene of the California margin. This form has a longer stratigraphic range than N. asanoi, having evolved earlier and survived longer—thus forming additional useful datum levels.
dutertrei (d'Orbigny) = Globigerina
dutertrei d'Orbigny, 1839
(Plate 2, figs. 4, 5)
This is a familiar species with five to six chambers in the final whorl and deep umbilical region. In the California margin sequences studied here, the taxa has an umbilical aperture and lacks umbilical plates.
humerosa praehumerosa Natori, 1976
(Plate 2, figs. 6, 7)
Populations of this form in the late Neogene sequences documented here are relatively large, have an open umbilical region and five chambers in the final whorl, and exhibit a narrow, distinct lip. These forms differ from N. humerosa humerosa in having five rather than six chambers in the final whorl and by the presence of a distinct lip (Natori, 1976).
pachyderma pachyderma (Ehrenberg) = Aristerospira
pachyderma Ehrenberg, 1861 (dextral, compressed form)
(Plate 1, figs. 1-3)
In this study we include forms in N. pachyderma pachyderma that are relatively small, dextrally coiled, with quadrate test, and have a gently compressed axial periphery. Typically, there are 4.0 to 4.5 chambers in the final whorl, and the final chamber is often reduced in size or kummerform. An apertural lip varies in strength. This species exhibits a wide range of variation and may represent more than one taxon, as has been suggested by Matoba and Oda (1982). Relationships remain unclear between this species and various forms of N. pachyderma identified by Keller (1978c). However, this form is similar to the dextral variety of N. pachyderma form 1, which is marked by a quadrate compact test. This species appears to include forms included by Matoba and Oda (1982) in both N. pachyderma pachyderma and N. pachyderma forma B. N. pachyderma pachyderma ranges discontinuously throughout the sequences (late early Pliocene to present day). Its spasmodic stratigraphic occurrence probably resulted from its strong affinity with warm rather than cool episodes.
pachyderma (Ehrenberg) A. (dextral, inflated form)
(Plate 1, figs. 4, 5, 9, 10)
This is a distinct species marked by a dextral-coiled, relatively large, highly rounded, lobulate test in both axial and equatorial peripheries; four globular chambers and relatively thin lip. This form has a short range during the early Quaternary. N. pachyderma A appears to be equivalent to N. pachyderma Form 2 of Keller (1978c) and N. pachyderma forma A of Matoba and Oda (1982). This species primarily differs from N. pachyderma pachyderma by its larger, more rounded test.
pachyderma (Ehrenberg) B. (sinistral, inflated form)
(Plate 1, figs. 11-14)
This is a sinistral-coiled form, exhibiting rounded equatorial and axial peripheries, generally with 4.0-4.5 globular chambers in the final whorl and a distinct, strong rimlike lip. This species occurs in high abundances during the late Quaternary. N. pachyderma B differs from N. pachyderma C by exhibiting inflated chambers, rounded outline, and consistently strong lip.
pachyderma (Ehrenberg) C. (sinistral, compressed form)
(Plate 1, figs. 6-8)
This is a relatively small, sinistral-coiled form, with quadrate test and relatively compressed axial periphery. Typically, there are 4.0-4.5 chambers in the final whorl. An apertural lip is relatively weak. Relationships are unclear between this taxon and forms of N. pachyderma described by Keller (1978c). This species differs from N. pachyderma B by its more compressed outline, greater number of chambers in the final whorl, and weaker apertural lip. This is a short-ranged latest Pliocene form.
(Globoconella) ikebei Maiya, Saito, and Sato = Globorotalia
ikebei Maiya, Saito, and Sato, 1976
(Plate 2, figs. 20-23)
A distinctive Pliocene representative of Globoconella with five chambers in the final whorl, axial periphery broadly rounded with no keel; equatorial periphery broadly circular to elongate; relatively high-arched aperture, interiomarginal and umbilical-extraumbilical in position. This species was identified and illustrated by Keller (1980) in the early Pliocene of the central North Pacific (DSDP Leg 32, Site 310), thus showing that its geographic range extended to the North Pacific beyond Japan, where it was first described (Maiya et al., 1976).
inflata (d'Orbigny) = Globigerina
inflata d'Orbigny, 1839
(Plate 2, figs. 10-15)
In the sequences examined, G. inflata is represented by early ("transitional"; Plate 2, figs. 10-12) forms and later (modern; Plate 2, figs. 13-15) forms as previously recognized by Keller (1978a, 1979a, 1979b, 1980) for North Pacific sequences. The range of G. inflata is often discontinuous in Leg 167 sequences and is usually represented by few specimens. As a result, we found it difficult to consistently differentiate the early and later forms, and thus have included both under G. inflata.
puncticulata (Deshayes) = Globigerina
puncticulata Deshayes, 1832
(Plate 2, figs. 8, 9)
This is a familiar Globoconella with four chambers in the final whorl, equatorial periphery gently quadrilobate; axial periphery bluntly rounded, with no keel; and aperture a distinct high arch bordered by a rim. The range of G. puncticulata overlaps that of Globorotalia (Globoconella) inflata in the late Pliocene, but no morphological gradation was observed between these two forms in the assemblages. It seems likely, therefore, that in the California region, G. puncticulata did not gradually evolve into G. inflata as has been observed in South Pacific Pliocene sequences (Kennett and Vella, 1975; Malmgren and Kennett, 1981).
decoraperta Takayanagi and Saito = Globigerina
druryi decoraperta Takayanagi and Saito, 1962
(Plate 2, figs. 16-19)
Distinguished by a compact test with four chambers in the final whorl, increasing uniformly in size as added; large, semicircular, high-arched aperture, bordered by distinct rim; and a coarsely cancellate surface. This is probably the same form referred to as Globigerina woodi decoraperta in California sequences by Bandy and Ingle (1970) and recognized as G. decoraperta by Poore (1981).