Kennett & Srinivasan (1983):
Sa. dehiscens evolved directly from Sphaeroidinellopsis paenedehiscens by developing a small, supplementary aperture at the chamber suture contact on the spiral side. By
definition, this marks the change from Sphaeroidinellopsis to Sphaeroidinella and defines the base of Zone N19.
Bolli & Saunders (1985):
The primary types and additional specimens illustrated on Fig. 39 display some of the great variability encountered in the genus Sphaeroidinella Test size and shape, and development of apertures and flanges associated with them are to a considerable degree the result of different growth stages and the influence of prevailing ecological conditions. Because the individual taxa proposed are all linked by intermediate forms, and are not of stratigraphic significance, we place them here all in synonymy with S. dehiscens. With the exception of S. immatura, where the distinctive features are not visible on the holotype drawing, the other holotypes placed here in synonymy are reproduced on Fig. 39 to allow for direct comparison. S. ionica ionica described from the Mediterranean Late Pliocene is a very small specimen, either a juvenile form or dwarfed for ecological reasons. In other areas, where conditions are more favourable, Sphaeroidinella grows considerably larger. The holotype of S. ionica evoluta from the Mediterranean Early Pleistocene compares in size with a normally developed adult form. In addition it possesses a small abortive last chamber, a feature seen not infrequently also in smaller specimens like that illustrated on Fig. 39.8. We consider that the two subspecies ionica and evoluta, though from different stratigraphic levels, do not necessarily reflect two evolutionary steps as intimated by their authors, but rather represent two growth stages or two adult forms that developed under different environmental conditions. S. dehiscens excavata was considered by its authors to differ from S. dehiscens in having less embracing chambers, resulting in the apertures being more highly arched and more widely open so that the earlier chambers are exposed within the test. Its range was given as Holocene, Zone N 23. It is difficult to use these criteria to draw a clear line between this subspecies and S. dehiscens. Under the right conditions forms of the excavata type can already occur in the Pleistocene, possibly even earlier. Particularly where calcium carbonate dissolution was taking place, openings in Sphaeroidinella may become still more accentuated, in addition to the dissolution of the interior portions of the test which are attacked first. Examples of this are illustrated on Figs. 39.3, 6.
Chaisson & Leckie (1993):
Remarks: The secondary aperture on the spiral side is diagnostic. The
overall shape of this species is subspherical. A thin, irregular flange often
borders the primary aperture. In later specimens the secondary aperture may
also be flanged. The cortex is thick and complete, obscuring the final whorl.
Similar species: See Sphaeroidinellopsis paenadehiscens. |
Parker,W.K. and Jones,T.R. (1865):
On some foraminifera from the North Atlantic and Arctic Oceans, including Davis Straits and Baffin's Bay . Philosophical Transactions of the Royal Society Vol. 155 p. 325–441
Cushman,J.A. (1919):
Fossil foraminifera from the West Indies . Carnegie Institute, Washington Publ. Vol. 291 p. 21-71
Banner,F.T. and Blow,W.H. (1960):
Some primary types of species belonging to the superfamily Globigerinaceae . Contributions from the Cushman Foundation for Foraminiferal Research Vol. 11(1) p. 1-41
Banner,F.T. and Blow,W.H. (1965):
Progress in the planktonic foraminiferal biostratigraphy of the Neogene . Nature Vol. 208 p. 1164-66
Cita,M.B. and Ciaranfi,N.. (1972):
new species of Sphaeroidinella from Late Neogene deep sea Mediterranean sediments (DSDP Leg XIII) . Riv. Ital. Paleontol. Vol. 78(4) p. 693-710
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
Vincent,E. and Toumarkine,M. (1990):
Neogene planktonic foraminifers from the Western Tropical Indian Ocean, Leg 115.
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 115 Eds: Duncan, R.A..Backman, J.Peterson, L.C. p. 795-836
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
Berggren,W.A.; Hilgen,F.J.; Langereis,C.G.; Kent,D.V.; Obradovich,J.D.; Raffi,I.; Raymo,M.E. and Shackleton,N.J. (1995):
Late Neogene chronology: New perspectives in high-resolution stratigraphy . Geological Society of America Bulletin Vol. 107(11)
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.
Chaisson,W.P. and d'Hondt,S.L. (2000):
Neogene planktonic foraminifer biostratigraphy at Site 999, Western Caribbean Sea.
In: Proceedings of the Ocean Drilling Program, Scientific Results Vol. 165 Eds: Leckie, R.M.Sigurdsson, H.Acton, G.D.Draper, G. p. 19-56
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