Jenkinsina


Classification: pf_cenozoic -> microperforate -> Guembelitriidae -> Jenkinsina
Sister taxa: Cassigerinelloita, Globoconusa, Guembelitria, Jenkinsina, Parvularugoglobigerina, Woodringina,
Daughter taxa (blue => in age window 0-300Ma)
Jenkinsina triseriata differs from Jenkinsina columbiana (Howe) by (1) its larger size; (2) having five rather than three or four chamber whorls; and (3) its lower apical angle. It is similar to Jenkinsina samwelli except for having (1) a larger, more highly arched aperture; (2) a thicker apertural lip; and (3) a greater twist to the coiling axis.
Jenkinsina columbiana differs from J. triseriata by (1) its smaller size; (2) having three rather than five chamber whorls; and (3) its higher apical angle.
Specimens which cannot be assigned to established species

Taxonomy

Citation: Jenkinsina Haynes, 1981
Rank: Genus
Type species: Guembelitria stavensis Bandy,1949
Taxonomic 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 (1998) 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.
[Huber et al. 2006]

Catalog entries: Jenkinsina;

Type images:

NB The short diagnoses are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus. They have initially been copied from the diagnostic characters/distinguishing features sections of the Eocene and Paleocene Atlases, they will be edited as the site is developed.

Description


Wall type: Microperforate, monolamellar, smooth to pustulose, and lacking pore mounds; [Huber et al. 2006]

Test morphology: test high trochospiral, triserial throughout, chambers globular and inflated; aperture a small arch at the base of final chamber, rimmed by a distinct lip.
[Huber et al. 2006]

Biogeography and Palaeobiology


Phylogenetic relations: 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 Guembelitria (Zone P1) 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 (R. Olsson, pers. observ.). Examination of the fine 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 HO of J. columbiana in upper Zone E12 from the LO of J. samwelli in upper Zone E16 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 and several species of Tenuitella (see below).
[Huber et al. 2006]

Biostratigraphic distribution

Geological Range:
Notes: Lower Eocene-lower Oligocene Zones E2 to lower Zone O5.
[Huber et al. 2006]
Last occurrence (top): in lower part of Bartonian Stage (35% up, 40Ma, in Bartonian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Ypresian Stage (2% up, 55.8Ma, in Ypresian stage). Data source: Total of range of species in this database

Plot of occurrence data:

Primary source for this page: Huber et al. 2006 - Atlas of Eocene Planktonic Foraminifera, chapter 16, p. 465

References:

Haynes, J.R., (1981). Foraminifera. John Wiley and Sons, New York.

Hofker, J., (1978). Analysis of a large succession of samples through the Upper Maastrichtian and Lower Tertiary of Drill Hole 47.2, Shatsky Rise, Pacific, Deep Sea Drilling Project. Journal of Foraminiferal Research, 8: 46-75.

Huber, B.T.; Olsson, R.K. & Pearson, P.N., (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene microperforate planktonic foraminifera (Jenkinsina, Cassigerinelloita, Chiloguembelina, Streptochilus, Zeauvigerina, Tenuitella, and Cassigerinella) and Problematica (Dipsidripella). In: Pearson, P.N. et al. (Editors), Atlas of Eocene Planktonic Foraminifera, Cushman Foundation Special Publication 41. Cushman Foundation Special Publication. Allen Press, Lawrence, Kansas, pp. 461-508.

Loeblich, A.R., Jr. & Tappan, H., (1988). Foraminiferal Genera and Their Classification (Volume I-II). Van Nostrand Reinhold Co., New York, 1059 pp.


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Jenkinsina compiled by the pforams@mikrotax project team viewed: 22-1-2018

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