TAXONOMIC NOTES

The taxonomic concepts are those adopted by Rio, Raffi, et al. (1990), Raffi et al. (1993), and Raffi and Flores (1995). A summary of the most important taxa concepts is reported below.
Gephyrocapsids
The taxonomic concepts used for this group are those adopted by Rio, Raffi, et al. (1990) and modified by Raffi et al. (1993). Within gephyrocapsids, three taxa have been considered on the basis of biometric taxonomic entities:
  1. gephyrocapsids with sizes 4 µm labeled "small" Gephyrocapsa spp.;
  2. gephyrocapsids with sizes between 4 and 5.5 µm with an open central area labeled Gephyrocapsa oceanica s.l.; and
  3. gephyrocapsids with sizes 5.5 µm labeled "large" Gephyrocapsa spp.
Moreover, two morphospecies have been distinguished: Gephyrocapsa sp. 3 following Rio (1982) and Rio, Raffi, et al. (1990) and G. caribbeanica, a morphotype with a closed central area.
Reticulofenestrids
Within the reticulofenestrids two groups have been considered: the Reticulofenestra spp., which includes small-sized (<7 µm) reticulofenestrids such as Reticulofenestra minuta, R. haqii, R. minutula, and R. pseudoumbilicus, which, following the taxonomic concepts proposed by Raffi and Rio (1979) and Backman and Shackleton (1983), includes morphotypes >7 µm.
Calcidiscus
Within the genus Calcidiscus three species have been distinguished following the taxonomic concepts expressed in Rio, Fornaciari, et al. (1990) and Fornaciari et al. (1990):
  1. rounded Calcidiscus specimens with sizes 11 µm labeled Calcidiscus macintyrei;
  2. rounded Calcidiscus specimens with sizes 11 µm labeled Calcidiscus leptoporus; and
  3. elliptical Calcidiscus specimens labeled Calcidiscus premacintyrei.
Discoasterids
Discoasterids show a variable distribution and preservation pattern at different sites and stratigraphic intervals.
Pliocene species of Discoaster have been identified following Backman and Shackleton (1983).
The following late to middle Miocene five-rayed species of Discoaster have been recognized: D. bellus group, D.quinqueramus/berggrenii, D. hamatus, and Discoaster sp. 1 sensu Rio, Fornaciari, et al. (1990).
The Discoaster bellus group is characterized by five-rayed discoasterids with a small size (6-8 µm), a poorly developed central area, and by morphotypes with intergraded features between D. bellus and D. hamatus and between D. bellus and D. berggrenii. Five long rays with a spine extending and bending sharply near the tip characterize D. hamatus. In the California margin this species is present with specimens relatively smaller than average.
Discoaster berggrenii and D. quinqueramus are two distinct species with a distinct stratigraphic distribution. D. berggrenii appears and becomes extinct before D. quinqueramus, but because intergraded forms between the end members of these two species make their distinction difficult, they have been lumped together.
Discoaster sp. 1 is a small (6-8 µm) five-rayed Discoaster with a poorly developed central area and a very small knob evidenced by Rio, Fornaciari, et al. (1990) in the equatorial Indian Ocean that appears discontinuously within *CN9a.
The main six-rayed species of Discoaster observed during Leg 167 in the late-middle Miocene interval are: Discoaster variabilis, D. exilis, D. surculus, D. brouweri, D. intercalaris, D. neohamatus, D. micros, D. calcaris, and D. kugleri sensu Rio, Fornaciari, et al. (1990).
Discoaster brouweri, D. intercalaris, D. neohamatus, D. micros, D. calcaris, and D. kugleri have been determined adhering strictly to the original descriptions. D. variabilis and D. exilis have been intended in latu sensu. A large taxonomic concept has been used for D. exilis that includes transitional forms between D. variabilis and D. exilis. Discoasterids possessing "trifurcated" tips are assigned to D. surculus.
Ceratolithids
This horseshoe-shaped group of calcareous nannofossils is a minor component of the assemblage during the late Miocene-early Pliocene. Among nonbirefringent ceratolithids (Amaurolithus), only A. primus and A. delicatus have been recognized.
A. primus has two morphotypes: a primitive form with a thick arc comparable to the holotype (Bukry and Percival, 1971) and a more delicate crescent-shaped form that occurs together with A. delicatus. During Leg 167, only the more evolved form of A. primus has been observed. Also intergraded morphotypes between A. primus and A. delicatus are present, which make it difficult to distinguish between the two species and consequently to detect the LO of A. primus. Ceratolithus acutus, C. armatus, C. rugosus, and C. telesmus have been found in low frequencies and with discontinuous distribution. Therefore it has not been possible to recognize the biohorizons marked by these ceratolithids. A rare and discontinuous transitional morphotype between genus Amaurolithus and genus Ceratolithus has been observed and labeled Ceratolithus sp. 1. This form appears as partially birefringent; namely, one arm is birefringent like Ceratolithus and the other arm is not birefringent like Amaurolithus. Probably this form could be the result of hybridization between species of the two genera.

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