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Species Globorotalia merotumida Blow & Banner 1965


Alternative name:
Globorotalia (Globorotalia) merotumida Blow & Banner 1965
Discussion / Comments:
Bolli & Saunders (1985):
Banner & Blow (1965a) proposed a lineage G. merotumida G. tumida plesiotumida G. tumida tumida, that developed according to Blow (1969) from G. paralenguaensis in the earliest part of Zone N 16 (= Globorotalia acostaensis Zone). Based on our observations this lineage is not related to the G. lenguaensis plexus. Instead, it developed only in the Late Miocene Globorotalia humerosa Zone (= N 17) from the G. menardii stock. In areas where the lineage is continuously developed as is the case in the low latitude Indo Pacific realm, all gradations from the G. menardii ancestor via G. merotumida G. plesiotumida to G. tumida tumida occur in the highest Miocene within a comparatively short time interval. It is for these reasons and the fact that the evolutionary lineage is usually only poorly or incompletely developed in the low latitude Atlantic realm, from where it is usually absent within the Early Pliocene Globorotalia margaritae margaritae Zone to near the top of the Pliocene (Bolli & Krasheninnikov, 1977), that their use in biostratigraphy is limited. This applies in particular to the use of G. merotumida, G. plesiotumida and G. tumida to define the zones N 16, and N 17 and N 18. Stainforth et al. (1975) arrive at the same conclusion in their discussions of the plexus. According to Banner & Blow (1965a) G. merotumida differs from G. plesiotumida 'in possessing (1) a test which is smaller in size at the same growth stage as measured by the number of chambers present, (2) a slower increase in whorl height as seen dorsally, (3) more uniformly enlarging chambers, (4) more consistently oblique dorsal intercameral sutures, (5) a thinner and more finely perforate test wall, (6) a thinner carina, (7) a relatively greater ventral convexity, and (8) a relatively broader apertural face'. According to the same authors 'G. merotumida has a much more convex and tumid test than any subspecies of G. (G.) cultrata (s.l.) (d'Orbigny)'.
Chaisson & Pearson (1997):
Specimens possibly assignable to Globorotalia merotumida are found in Sample 154-925B-18H-3, 66-68 cm.
Chaisson & Leckie (1993):
Remarks: This is a small species. In edge view its umbilical side is slightly more highly vaulted than its spiral side. Its test wall is finely perforate but smooth. Similar species: Globorotalia plesiotumida is derived from G. merotumida, and the two taxa are commonly gradational. G. plesiotumida tends to be slightly larger than G. merotumida. However, the most reliable character for differentiating between them is the proportions of the final chamber viewed from the spiral side. Specimens in which the width of the final chamber exceeds the radial length are G. merotumida. Individual specimens whose dimensions are nearly equal are assigned to G. plesiotumida.
Systematics:

1
 Superregnum Eukaryota
  Regnum Protoctista
   Phylum Ciliophora
    Subphylum Postciliodesmatophora
     Ordo Globigerinida
      Superfamilia Globorotaliaceae
       Superfamilia Nonionacea
        Familia Globorotaliidae
         Genus Globorotalia
          Species Globorotalia merotumida
Synonym list:
Bolli & Saunders (1985):
1965 Globorotalia (Globorotalia) merotumida Blow & Banner. - Banner & Blow : p.1352 figs. 1a-c
1985 Globorotalia merotumida Blow & Banner. - Bolli & Saunders : p.225 figs. 33.7; 6,10,12
Chaisson & Pearson (1997):
1965 Globorotalia (Globorotalia) merotumida Blow & Banner. - Banner & Blow : p.1352 text-fig. 1
1983 Globorotalia (Globorotalia) merotumida Blow & Banner. - Kennett & Srinivasan : p.154 pl. 37; fig. 4-6
1985 Globorotalia merotumida Blow & Banner. - Bolli & Saunders : p.227 fig. 33.7
Chaisson & Leckie (1993):
1965 Globorotalia (Globorotalia) merotumida Blow & Banner. - Banner & Blow : p.1352 text-fig. 1
1983 Globorotalia (Globorotalia) merotumida Blow & Banner. - Kennett & Srinivasan : p.154 pl. 37; fig. 4-6
1985 Globorotalia merotumida Blow & Banner. - Bolli & Saunders : p.227 fig. 33.7
1993 Globorotalia merotumida Blow & Banner. - Chaisson & Leckie : p.175 pl. 7; fig. 11-15
References:

Banner,F.T. and Blow,W.H. (1965):
Two new taxa of the Globorotaliinae (Globigerinacea, Foraminfera) assisting determination of the late Miocene/middle Miocene boundary . Nature Vol. 207

Kennett,J. and Srinivasan,M.S. (1983):
Neogene Planktonic Foraminifera - A Phylogenetic Atlas.

Bolli,H.M. and Saunders,J.B. (1985):
Oligocene to Holocene low latitude planktic foraminifers.
In: Plankton Stratigraphy Eds: Bolli, H.M.Saunders, J.B. p. 155-262

Chaisson,W.P. and Leckie,R.M. (1993):
High-Resolution Planktonic Foraminifer Biostratigraphy of Site 806, Ontong Java Plateau (Western Equatorial Pacific).
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 130 Eds: Berger, W.H.Kroenke, L.W..Mayer, L.A..et al. p. 137-178

Chaisson,W.P. and Pearson,P.N. (1997):
Planktonic foraminifer biostratigraphy at Site 925: middle Miocene–Pleistocene.
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 154 Eds: Shackleton, N.J.Curry, W.B.Richter, C.Bralower, T.J.
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