Iaccarino (1985):
Blow & Banner considered this taxon as the immediate ancestor of Globoquadrina dehiscens dehiscens. The major distinguishing features according to them are the number of chambers in the last whorl (only three are visible in the umbilical side of adult specimens), the globosely subconical axial profile, the smoothly and broadly rounded axial periphery, and the small but deep and open umbilicus. Steeply sloping umbilical margins characterize the chambers of the last whorl. The aperture is a very low arch bordered by a flap like triangular lip which projects into the umbilicus as a tooth.
The change in the position of the aperture from umbilicalextraumbilical in G. dehiscens praedehiscens to umbilical in G. dehiscens dehiscens has been considered by Blow & Banner as the evolutionary character which distinguishes the two species. Such an evolutionary lineage is not accepted by all stratigraphers and has given rise to controversial opinions. According to Stainforth er al. (1975) G. dehiscens praedehiscens is a 'transitional variant' of Globigerina tripartita. This species does show great variability but G. dehiscens praedehiscens can be included in it only if interpreted in a broad sense (three chambers in the last whorl, elongated aperture, globose and appressed chambers in the last whorl).
Quilty (1976):
Remarks: There is no dorsal supplementary aperture, and this
feature seems to be the main differentiation between Globoquadrina dehiscens praedehiscens and Globigerinoides pseudosellii Brönnimann and Resig. The aperture has been retouched in the figured specimen to emphasize the presence of the tooth. |
Blow,W.H. and Banner,F.T. (1962):
The Mid-Tertiary (Upper Eocene to Aquitanian) Globigerinaceae.
In: Fundamentals of Mid‑Tertiary Stratigraphical Correlation Eds: Eames, F.E.Banner, F.T.Blow, W.H.Clarke, W.J. p. 61‑151
Quilty,P.G.. (1976):
Planctonic foraminifera DSDP Leg 34- Nazca Plata . DSDP initial reports Vol. 34
Iaccarino,S. (1985):
Mediterranean Miocene and Pliocene planktic foraminifera.
In: Plankton stratigraphy Eds: Bolli, H.M.Saunders, J.B.Perch-Nielsen, K. p. 283-314
Spezzaferri,S. and Silva,I.S.. (1990):
Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico . Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 83 p. 217-263
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