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Species Cassigerinelloita amekiensis Stolk 1965 | ||||||
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| Diagnosis / Definition: | ||||||
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Pearson et al. (2006): DESCRIPTION. Type of wall: Microperforate, with micropores ranging from 0.005 to 0.01 mm diameter, finely to moderately pustulose, pustules on final one to two chambers, wall thicker on earlier chambers than penultimate and ultimate chambers. Test morphology: Test small, polygonal, subspherical, lacking a true umbilicus; chambers arranged in a series of very low triserial whorls that are coiled so that the test has two distinct coiling axes, increasing rapidly in size, 6-8 chambers visible on the outside coils, 8-10 comprising adult tests; sutures moderately depressed; primary aperture visible in most but not all specimens, interiomarginal, semicircular or low-arched, with or without a thin lip, generally located across the suture between the penultimate and antepenultimate chambers; supplementary apertures may be present on the opposite side of the chamber with the primary aperture or on earlier chambers. Size: Holotype, maximum diameter 0.13 mm; general size range 0.07-0.14 mm. |
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| Discussion / Comments: | ||||||
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Pearson et al. (2006): DISTINGUISHING FEATURES- Characterized by small, subglobular test with a rotating triserial axis of coiling, indistinguishable umbilicus and often indistinguishable primary aperture. DISCUSSI0N.- This distinctive form has often been overlooked in biostratigraphic studies because of its small test size. Its relatively short stratigraphic range in the lower middle Eocene makes it a valuable biomarker, particularly for correlation of southern high latitude sites, where it occurs abundantly. PHYLOGENETIC RELATIONSHIPS.- On the basis of similarity in wall texture, coiling, and the interiomarginal aperture as well as stratigraphic overlap, Li and Radford (1992) suggested that C. amekiensis probably descended from Jenkinsina triseriata following a change from unidirectional triserial coiling to an offset, rotating triserial coiling. STRATIGRAPHIC RANGE.- Upper lower - lower Eocene; Zone E7 to Zone E9 at lower latitudes, nominate taxon for the Cassigerinelloita amekiensis Taxon Range Zone (AE4) at southern high latitudes. First recorded in the uppermost(?) lower Eocene to middle Eocene in the Bende Ameki Group in eastern Nigeria (Stolk, 1965), and found to range into upper Zone E9 in southeastern Tanzania, Tanzania Drilling Projet, Site 13, with its highest occurrence observed just below the highest occurrence of Morozovella aragonensis (P. N. Pearson, unpublished data). At most southern high latitude sites, the H0 of C. amekiensis is recorded at the same level as or just above the F0 of Guemhelitria triseriata (Nocchi and others, 1991; Li and Radford, 1992). Although Huber (1991) reported the reverse to apply at Site 738, reexamination of samples from that site revealed that the H0 of J. triseriata is at the same level as the L0 of C. amekiensis (Huber and Quillévéré, 2005). Its range is diachronous between low and high latitudes, its first occurrence is slightly earlier at southern high latitudes, whereas its last occurrence is later at low latitudes. GEOGRAPHIC DISTRIBUTION .- Li and Radford (1992) suggest C. amekiensis preferred inhabiting cool, unstable environments, such as zones of upwelling and southern high latitude surface waters. Its limited occurrence at low latitudes (e.g., Nigeria and Tanzania) may be a consequence of its preference for shelf environments or an artifact of having been overlooked because of its small test size. STABLE ISOTOPE PALEOBIOL0GY.- No data available. REPOSITORY.- Musée Géologique Africain, Dakar, Senegal. |
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| Synonym list: | ||||||
| Pearson et al. (2006): 1965 Cassigerinelloita amekiensis Stolk. - Stolk : p.264 pl. 1-3 [lower
middle Eocene, Bende Ameki Group, Nigeria]
1990 Globigerina sp. B . - Stott & Kennett : p.559 pl. 5; fig. 1-14 [lower-middle Eocene, ODP Site 689, Maud Rise,
Antarctica]
1991 Cassigerinelloita amekiensis Stolk. - Nocchi et al. : p.267 pl. 4; fig. 1-2 [lower middle Eocene
Zone PlO-ll, ODP Hole 703A, mid-Atlantic Ridge,
southern South Atlantic Ocean,]
1991 Cassigerinelloita amekiensis Stolk. - Huber : p.439 pl. 7; fig. 11 [lower middle Eocene, ODP Site 738, Kerguelen
Plateau, southern Indian Ocean]
1992 Cassigerinelloita amekiensis Stolk. - Li & Radford : p. 595-599 pl. 1, fig. 1-13;
pl. 2, fig. 1-9 [lower
middle Eocene, ODP Site 749, Kerguelen Plateau,
southern Indian Ocean]
2006 Cassigerinelloita amekiensis Stolk. - Pearson et al. : p.468 pl. 16.2; fig. 6-17
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| References: | ||||||
Stolk,J.. (1965): Stott,L.D. and Kennett,J.P. (1990): Nocchi,M.; Amici,E. and Premoli Silva,I. (1991): Huber,B.T. (1991): Li,Q. and Radford,S.S.. (1992): Pearson,P.N.; Olsson,R.K.; Hemleben,C.; Huber,B.T. and Berggren,W.A. (2006): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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