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Genus Jenkinsina Haynes 1981 | ||||||
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| Diagnosis / Definition: | ||||||
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Pearson et al. (2006): DESCRIPTION. Wall microperforate, monolamellar, smooth to finely pustulose, and lacking pore mounds; test high trochospiral, triserial throughout, chambers globular and inflated; aperture a small arch at the base of final chamber, rimmed by a distinct lip. |
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| Discussion / Comments: | ||||||
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Pearson et al. (2006): TYPE SPECIES.- Guembelitria stavensis Bandy, 1949. DISCUSSION.- Haynes (1981) distinguished Jenkinsina from Guembelitria based on the absence of pore mounds. In a study of Paleogene triserial planktonic foraminifera, Jenkins and others (1 998) supported this distinction with SEM images of well-preserved specimens of both genera. Although Loeblich and Tappan (1988) considered Jenkinsina to be a junior Synonym of Chiloguembelitria Hofker(1978) based on SEM observation of topotypes of the type species of both genera (the primary type specimens have been lost), further SEM study of topotype material led Jenkins and others (1998) to conclude that the type species of Chiloguembelitria, C. danica Hofker (1978), does have pore mounds and therefore is not synonymous. SEM observation of the shell microstructure of a well preserved specimen of Jenkinsina columbiana (Pl. 16.1, Figs. 10- 11) reveals that it has a monolamellar wall. This seems to be a consistent feature of the microperforates, as it has been observed in Guembelitria cretacea and several species of Tenuitella. PHYLOGENETIC RELATIONSHIPS.- Jenkins and others (1998) noted that there is no direct phylogenetic connection between Danian species of Guembelitria and early Eocene species of Jenkinsina, and postulated instead that Jenkinsina may have evolved from the biserial genus Chiloguembelina during the early Eocene. This assertion needs to be verified, as forms bearing an intermediate morphology between Chiloguembelina and Jenkinsina have not been observed. While there is still a considerable stratigraphic gap between the highest occurrence of Guemhelitria (Zone PI) and the first occurrence of Jenkinsina (Zone E2), this gap was thought to be considerably larger in Jenkins's study, which predates discovery of J. columbiana in lowermost Eocene sediments in Egypt and New Jersey (K. Olsson, pers. observ.). Examination of the line fraction from Paleocene sediments may lead to further narrowing of this stratigraphic gap and would suggest a direct phylogenetic linkage between Jenkinsina and Guembelitria. Absence of Jenkinsina from strata separating the H0 of J. columbiana in upper Zonc E12 from the L0 of J. samwelli in upper Zone E 16 suggests that samwelli may have evolved independently from a different ancestor. Further investigation of middle-upper Eocene sediments is required to determine the phylogeny of this group. SEM observation of the shell microstructure of a well preserved specimen of Jenkinsina columbiana reveals that it has a monolamellar wall (Pl. 16.1, Figs. 10- 11). This may be a consistent feature of the microperforates, as it has now been observed in Guembelitria cretacea an several species of Tenuitella (see helow). STRATIGRAPHIC RANGE.- Lower Eocene-lower Oligocene Zones F2 to lower Zone O5 GEOGRAPHIC DISTRIBUTION.- Cosmopolitan. |
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| Systematics: | ||||||
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35 Ordo Foraminiferida Superfamilia Globigerinaceae Familia Guembelitriidae Genus Jenkinsina |
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| Synonym list: | ||||||
| Pearson et al. (2006): 1949 Guembelitria stavensis Bandy. - Bandy : p.124 pl. 24; fig. 5 Type species
1981 Jenkinsina Haynes. - Haynes : p.313
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| Was used in synonym list of: | ||||||
| References: | ||||||
Bandy,O.L. (1949): Haynes,J.R. (1981): 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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