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| Anonymous: Unedited TaxonConcept data | ||||||
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Species Jenkinsina columbiana Howe 1939 | ||||||
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| Diagnosis / Definition: | ||||||
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Pearson et al. (2006): DESCRIPTION.- Type of wall: Microperforate, monolammellar, finely pustulose to smooth, lacking pore mounds. Test morphology: Test small, side view nearly pyramidal with a high apical angle (~60°), periphery lobulate; chambers triscrial, about nine chambers forming the adult test in above three whorls, increasing rapidly in size; inflated, spherical; sutures depressed, three chambers increasing moderately in size surround a moderately deep umbilicus; aperture a low, semi-circular arch at the base of the final chamber, bordered by a thin lip. Size: Holotype: Lenght 0.15 mm, breadth 0,12 mm. |
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| Discussion / Comments: | ||||||
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Pearson et al. (2006): DISTINGUISHING FEATURES.- Jenkinsina columbiana differs from J. triseriata by (1) its smaller size; (2) having three rather than five chamber whorls; and (3) its apical angle. DISCUSSION.- Several authors (e.g., Kroon and Nederbragt, 1990; Li and Radford, 1992) regard this species and the more elongate form J. triseriata (=Guembelitria stavensis Bandy) as synonymous. However, Jenkins and others (1998) considered J. colmbiana as a distinct form that evolved from J. triseriata, based primarily on observation of the type specimens and previously illustrated hypotypes. We follow the recommendation of Jenkins and others (1998) but note that a more thorough comparative biogeographie and biostratigraphie study of these taxa is warranted. The oldest specimens included in this study, from zone E2 (Pl. 16.1, Figs. 7, 8), have a smoother test than speciemens from Zone E4 and higher (e.g. Pl. 16.1, Fig. 10, 11), but none of the observed specimens has pore mounds, as is found in Guembelitria cretacea from the lowermost Paleocene. PHYLOGENETIC RELATIONSHIPS.- Uncertain. As noted above, there is a considerable stratigraphic gap between the last occurrence of microperforate triserial guembelitriids in the Danian and the first occurrence of J. columbiana in the early Eocene. Careful study of the fine fraction from the middle and upper Paleocene sediments may reveal the missing phylogenetic link between these triserial microperforate taxa. Alternatively, absence of pore mounds in J. columbiana may suggest derivation from a chiloguembelinid ancestor during the earliest Eocene. STRATIGRAPHIC RANGE.- Lower to middle Eocene; Zone E2 through E12. Jenkinsina columbiana has been identified within Zone E2 in the New Jersey Coastal Plain and in the Dababiya core drilled at the type section for the base of the Eocene 35 km south of Luxor, Egypt (R .K. Olsson and W. A. Berggren, pers. comm.). The stratigraphic range of J. columbiana needs further documentation as it has often been overlooked in biostratigraphic studies and it has been confused with other triserial taxa. GEOGRAPHIC DISTRIBUTION.- Cosmopolitan. STABLE ISOTOPE PALEOBIOL0GY.- No data are available. |
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| Systematics: | ||||||
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35 Ordo Foraminiferida Superfamilia Globigerinaceae Familia Guembelitriidae Genus Jenkinsina Species Jenkinsina columbiana |
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| Synonym list: | ||||||
| Pearson et al. (2006): 1939 Guembelitria columbiana Howe. - Howe : p.6 pl. 8; fig. 12, 13 [middle Eocene, Cook Mountain Fm., Louisiana]
1998 Jenkinsina columbiana Howe. - Jenkins et al. : p.67 pl. 3; fig. 1-5 [middle Eocene, Selsey, England; middle
Eocene, Peyreblanque, Biarritz, S.W. France]
2006 Jenkinsina columbiana Howe. - Pearson et al. : p.467 pl. 16.1; fig. 5-12
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| Specimen: | ||||||
| Louisiana State University Museum - Louisiana, Inventory number: slide 101 |
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| References: | ||||||
Howe,H.V. (1939): Jenkins,D.G.; Whittaker,J.E. and Curry,D. (1998): 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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