Acarinina interposita

Classification: pf_cenozoic -> muricate non-spinose -> Truncorotaloididae -> Acarinina -> Acarinina interposita
Sister taxa: A. medizzai, A. collactea, A. pentacamerata, A. aspensis, A. echinata, A. pseudosubsphaerica, A. alticonica, A. soldadoensis, A. interposita, A. cuneicamerata, A. angulosa, A. africana, A. sibaiyaensis, A. esnehensis, A. mckannai, A. subsphaerica, A. bullbrooki, A. punctocarinata, A. boudreauxi, A. rohri, A. topilensis, A. praetopilensis, A. mcgowrani, > >>


Citation: Acarinina interposita Subbotina 1953
Rank: Species
Basionym: Acarinina interposita
Taxonomic discussion: This distinctly inflated (globular) form is characteristic of lower Eocene assemblages; it is predominantly dextrally coiled throughout its range. We have observed it to appear in Zone E4 in Egypt and to grade into A. pentacamerata at stratigraphically higher/ younger levels.
We question the high latitude records of forms cited under this name (see synonymy listing above); they do not appear to display the robust, inflated morphology characteristic of low latitude representatives, and indeed some of the forms are recorded from distinctly lower stratigraphic levels (Zone AP5 [which approximately correlates with Zone E2]) and contain only 3 chambers in the final whorl (Lu and Keller, 1993). [Berggren et al. 2006]

Catalog entries: Acarinina interposita;

Type images:

Distinguishing features: This taxon is distinguished by its 4-4½ chambers (in the final whorl), planoconvex, distinctly muricate, test with umbilically inflated (globular) chambers; umbilical side of test distinctly inflated, accompanied by loose arrangement of chambers resulting in scalloped, lobulate peripheral margin.

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.


Diagnostic characters: This taxon is distinguished by its 4-4½ chambers (in the final whorl), planoconvex, distinctly muricate, test with umbilically inflated (globular) chambers; umbilical side of test distinctly inflated, accompanied by loose arrangement of chambers resulting in scalloped, lobulate peripheral margin. [Berggren et al. 2006]

Wall type: Densely muricate on both sides, non-spinose; normal perforate. [Berggren et al. 2006]

Test morphology: Low-trochospiral; relatively large, robust, test with embracing, appressed chambers; plano-convex, weakly lobate, circular outline, rounded periphery in edge view; 4-4½ chambers in final whorl, increasing slowly in size, generally globular; sutures depressed, radial, weakly curved; muricae more strongly developed on umbilical than on spiral side, short, thick muricae concentrated around umbilicus, which is narrow, deep; about 10-12 chambers in 2-3 whorls on spiral side; early chambers obscured by muricate texture, chambers of final whorl increasing slowly in size, essentially equidimensional; sutures radial, straight, only slightly depressed; muricae tend to concentrate along peripheral margin; in edge view planoconvex; profile of early chambers rounded, with flattening of ante- and/or penultimate chamber resulting in subacute margin; peripheral margin; aperture an umbilical-extraumbilical arch, bordered by thin lip, extending almost to peripheral margin. [Berggren et al. 2006]

Size: Diameter 0.35-0.55 mm, thickness 0.20-0.25 mm. [Berggren et al. 2006]

Character matrix

test outline:Subcircularchamber arrangement:Trochospiraledge view:Planoconvexaperture:
umb chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thin lip
sp chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:None
umbilical or test sutures:Weakly depressedumb depth:Deepwall texture:Coarsely muricateshell porosity:Finely Perforate: 1-2.5µm
spiral sutures:Weakly depresseddiameter mm:0.35-0.55width mm:breadth mm:0.20-.025
final-whorl chambers:4.0-4.5

Biogeography and Palaeobiology

Geographic distribution: Occurs commonly in the Tethys (Egypt) and in the northern Caucasus. [Berggren et al. 2006]
Aze et al. 2011 summary: Tethys (Egypt) and in the northern Caucasus; based on Berggren et al. (2006b)

Isotope paleobiology: No data available. [Berggren et al. 2006]
Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts. Based on very heavy δ13C and relatively light δ18O. Sources cited by Aze et al. 2011 (appendix S3): this study

Phylogenetic relations: This taxon seems to have been derived from A. soldadoensis and evolved into A. pentacamerata by an increase in the number of chambers in the whorl and a change in the spire height. [Berggren et al. 2006]

Most likely ancestor: Acarinina soldadoensis - at confidence level 4 (out of 5). Data source: Berggren et al. (2006) fig9.2.

Biostratigraphic distribution

Geological Range:
Notes: Zone E4 to Zone E6. [Berggren et al. 2006]
Last occurrence (top): within E6 zone (50.20-50.67Ma, top in Ypresian stage). Data source: Eocene Atlas
First occurrence (base): within E4 zone (52.54-54.61Ma, base in Ypresian stage). Data source: Eocene Atlas

Plot of occurrence data:

Primary source for this page: Berggren et al. 2006 - Atlas of Eocene Planktonic Foraminifera, chapter 9, p. 290


Berggren, W.A.; Pearson, P.N.; Huber, B.T. & Wade, B.S., (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Acarinina. In: Pearson, P.N. et al. (Editors), Atlas of Eocene Planktonic Foraminifera, Cushman Foundation Special Publication 41. Allen Press, Lawrence, Kansas, pp. 257-326.

Blow, W.H., (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea), 2. E. J. Brill, Leiden, 1413 pp.

Huber, B.T., (1991). Paleogene and Early Neogene Planktonic Foraminifer Biostratigraphy of Sites 738 and 744, Kerguelen Plateau (Southern Indian Ocean). Proceedings of the Ocean Drilling Program, Scientific Results, 119: 427-449.

Krasheninnikov, V.A.; Serova, M.Y. & Basov, I.A., (1988). Stratigrafiya I planktonnyie foraminiferyi paleogena: vyisokikh shirot Tikhogo okeana. Akademiya Nauk SSSR, Trudy, 429: 1-120.

Lu, G. & Keller, G., (1993). The Paleocene-Eocene transition in the Antarctic Indian Ocean: Inference from planktic foraminifera. Marine Micropaleontology, 21: 101-142.

Stott, L.D. & Kennett, J.P., (1990). The Paleoceanographic and Paleoclimatic signature of the Cretaceous/Paleogene boundary in the Antarctic: Stable isotopic results from ODP Leg 113. Proceedings of the Ocean Drilling Program, Scientific Results, 113: 829-848.

Subbotina, N., (1953). Foraminiferes fossiles d'URSS Globigerinidae, Globorotaliidae, Hantkeninidae. Bureau de Recherches Geologiques et Minieres, 2239: 1-144.


Acarinina interposita compiled by the pforams@mikrotax project team viewed: 22-3-2018

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