Clavigerinella nazcaensis Quilty 1976 from: Quilty, P.G.. (1976): Planctonic foraminifera DSDP Leg 34- Nazca Plata . DSDP initial reports Vol. 34 | . |
Notice: This catalogue page may contain unedited data.
|
Species Clavigerinella nazcaensis Quilty 1976 |
|
|
|
| Diagnosis / Definition: |
Quilty (1976):
Diagnosis: Distinguished from other members of the genus by the extreme radial elongation of clavate chambers which are structurally weak so that the species is most easily identified by its individual broken chambers.
Description: Test delicate, almost planispiral, ventral side of test very weakly concave. Early part of test globigerine with four chambers per whorl with umbilical or umbilical-extraumbilical, moderately low arched rimless aperture. After slightly more than one whorl, chambers
start to be a little radially elongate and parallel sided, the aperture becomes entirely extraumbilical-peripheral and develops a weak to strong rim or lip. At this stage there are 4 to 5 chambers per whorl. After 2 to 3 such chambers, later chambers increase markedly in the degree of radial elongation developing a knob-like distal extremity which is of the same diameter as the proximal end. Intermediate parts
of the chamber have a smaller diameter, providing a structurally weak zone for later breakage. At this stage there are 5 to 6 chambers per whorl and the aperture has shifted distally from extraumbilicalperipheral to become entirely within the anteroventral proximal part of each chamber. It seems to lie always within the thicker, proximal
part of each chamber. There seems to be no lip or rim. This aperture forms the weakest part of the chamber and breakage usually occurs here. The ultimate mature chambers have a well differentiated, parallel-sided portion between the knob-like distal extremity and the expanded proximal end. This is only rarely seen on more complete specimens. Wall structure is of finely perforate, radial calcite. |
| Discussion / Comments: |
Quilty (1976):
Remarks: The new species is most readily identified in samples by the common presence of broken, discrete very elongate, clavate chambers as shown in Plate 18, Figure 12 which illustrates a random selection of such chambers. I have seen no complete specimens but about 50 fragmentary specimens were separated. The marked ontogenetic development described above is very striking. This species illustrates once again the degree of homeomorphy possible in Late Cretaceous and Tertiary planktonic foraminifera. The
similarities with Hastigerinoides (particularly H. alexanderi, H. watersi), Clavatorella, and species of more recent genera such as Hastigerinella and Hastigerina are obvious. Until now, it seemed that the lineage including previously described species of Clavigerinella died out at the end of the Eocene. This now seems not to be the case.Clavigerinalla nazcaensis is a direct descendant of the Eocene species. Srinivasan and Kennett (1974) have recently described Clavatorella nicobarensis from the Pliocene of Car Nicobar, taking it to be a direct descendant of C. bermudezi.il is much more probably that the species is a direct descendant of Clavigerinella
nazcaensis n. sp. and that there is no link with Clavatorella at all. More recently, Buckley (1974) has described Clavatorella oveyi from the Recent of the Indian Ocean. C. oveyi is a descendant of C. bermudezi. Two lineages are now reasonably well known although many intermediate links are missing. 1) The two species of Clavatorella (C. bermudezi and C. oveyi) are large, robust forms with coarsely perforate walls and radially clavate
chambers which are relatively short. An important consideration of this evolution is that the change over about 15 million years is not very great and the use of C. bermudezi as an index for N8-N11 may be suspect. In Hole 319, it occurs in the basal part of N12. 2) All species of Clavigerinella have radially elongate chambers with
finely perforate walls. At the end of the Eocene, planispiral coiling gave way to very low trochospiral coiling. In the Eocene and Oligocene, adult chambers were distinctly clavate, but by the Pliocene, the clavate distal extremities of chambers had given way to a tapering
extremity. The evolution from C. nicobarensis is not known. Several possibilities should be considered. If any member of the post Eocene Clavigerinella lineage can be shown to have tribrachiate spines, these members of Clavigerinella can probably be placed in Hastigerinella. Another possible descendant is Bolliella.The evolution of the species mentioned and some tentative suggestions are included in Figure 6. A lesson to be learned form the evolution of Clavigerinella and Clavatorella is that, despite the enormous amount of information available on Tertiary planktonic foraminifera, there are major lineages
of important species whose evolution is still virtually unknown. The new species was recorded by Jenkins and Orr (1972) from the C. cubensis Zone (approximately N2) from DSDP Hole 77B, to the westnorthwest of the Nazca plate.Measurements: Longest individual broken chamber 0.5 mm. Estimated maximum diameter of species 0.9 mm.
Derivation of name: The species is named for the Nazca plate, drilled by Leg 34 of the DSDP. |
| Synonym list: |
Quilty (1976):
|
| References: |
Jenkins,D.G. and Orr,W.N. (1972):
Planktonic foraminiferal biostratigraphy of the eastern equatorial Pacific—DSDP Leg 9.
In: Initial Reports of the Deep Sea Drilling Project Vol. 9 Eds: Hays, J.D.et al. p. 1059-1193
Quilty,P.G.. (1976):
Planctonic foraminifera DSDP Leg 34- Nazca Plata . DSDP initial reports Vol. 34
|
This work is licensed under a Creative Commons Attribution 2.5 License.
|
|
Taxon Concept provided by