Acarinina wilcoxensis

Classification: pf_cenozoic -> Truncorotaloididae -> Acarinina -> Acarinina wilcoxensis
Sister taxa: << < 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, A. quetra, A. pseudotopilensis, A. wilcoxensis, A. esnaensis, A. primitiva, A. coalingensis, A. nitida, A. strabocella, A. sp.


Citation: Acarinina wilcoxensis (Cushman & Ponton 1932)
Rank: Species
Basionym: Globorotalia wilcoxensis
Taxonomic discussion: This taxon, described originally from the Bashi Formation (Zone P6a) of the U .S. Gulf Coast, is the stem form of the early Eocene radiation of the pseudotopilensis -quetra group. Berggren (1960a, 1968) considered that wilcoxensis evolved from the late Paleocene form Acarinina esnaensis (LeRoy), itself a senior synonym of Acarinina intermedia Subbotina, a view maintained here, while Blow (1979, p. 965) considered esnaensis a junior synonym of wilcoxensis. Acarinina esnaensis (and A. intermedia) were originally described from stratigraphic levels within/correlative to Zone P4, not the lower Eocene as implied by Blow (1979). Acarinina wilcoxensis may be differentiated from the morphologically similar esnaensis /intermedia by its larger size, more elongate/oval shaped test and more acute axial periphery.
Admittedly the holotype individuals of esnaensis and wilcoxensis (see Plates 9.11 and 9.23 of this paper) are markedly similar. However, the species concept of this taxon is based on a broader consideration of the variation exhibited by individuals from levels within Zone E3-4. The illustration of Bolli (1957a, pl. 7-9) of wilcoxensis may be taken as exemplary and demonstrates the (predominantly) subquadrate, somewhat more anguloconical character of wilcoxensis; esnaensis generally is more elongate and has a subrounded periphery in edge view.
Acarinina wilcoxensis berggreni (El Naggar) was described from Zone P5 in Egypt and said to differ from esnaensis in its “compressed test, smaller size, fewer chambers in the last whorl, subrounded to subacute periphery, much narrower umbilicus and peculiar aperture”. Blow (1979, p. 968-970) considered berggreni to be characterized by having distinctly flattened terminal chamber(s) on the spiral side, axially subangulate periphery in terminal chamber(s), and peripheral concentration (but not fusion) of muricae and to represent a transition to/morphologic link between wilcoxensis sensu stricto and quetra (with its disjunct, laterally angulate chambers). Blow (1979, p. 968) included Bolli’s (1957a) illustration of wilcoxensis (with subacute periphery) in berggreni, thus providing a clear illustration of his concept of the taxon. Blow (1979) indicated that wilcoxensis appeared only marginally earlier/lower (mid-Zone P6, = basal Zone E3) than berggreni (base Zone P7, = upper part of Zone E3), although El Naggar (1966, p. 201) indicated that the first appearance of berggreni overlapped with the terminal part of the range of Globorotalia velascoensis (i.e., within the Zone E1-E2 interval).
Stott and Kennett (1990, p. 560), on the other hand, distinguished wilcoxensis and berggreni in Maud Rise (Subantarctic) assemblages, but viewed wilcoxensis as the morphotype with greater axial angularity and flattened spiral surface (Blow, 1979). The morphologic differences between these two forms are viewed as those of degree not kind and berggreni is included in the synonymy of wilcoxensis here. [Berggren et al. 2006]

Catalog entries: Globorotalia wilcoxensis, Globorotalia berggreni

Type images:

Distinguishing features: Test (sub)quadrate, with 4-chambers in the final whorl, planoconvex, with subrounded to (later) subacute axial outline; distinctly muricate.

NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus.
They are being edited as the site is developed and comments on them are especially welcome.


Wall type: Densely muricate (both sides), normal perforate, nonspinose. [Berggren et al. 2006]

Morphology: Plano-convex, elongate-oval, equatorial outline moderately lobulate; chambers subangular to low conical, inflated on spiral side; 4 chambers in final whorl, increasing rapidly in size; sutures depressed, radial, weakly curved; umbilicus narrow, deep; aperture an umbilical-extraumbilical arch, bordered by thin lip, extending almost to peripheral margin; on spiral side about 10-12 chambers in 2½ -3 whorls; chambers, lens-shaped to semi-circular, increasing rapidly in size and overlapping previous chambers; intercameral sutures depressed, curved; sutural openings (apparently caused by secondary calcification over the projecting edges of previously calcified chamber margins) present on well-preserved individuals, often obscured by thickened, hollow muricae; muricae tend to concentrate along peripheral margin but test remains non-carinate; in edge view test is planoconvex; profile of early chambers rounded, with flattening of ante- and/or penultimate chamber resulting in subacute margin; peripheral margin distinctly muricate but not carinate. [Berggren et al. 2006]

Size: Maximum diameter of holotype 0.38 mm, thickness: 0.22 mm. [Berggren et al. 2006]

Character matrix

test outline:Lobatechamber arrangement:Trochospiraledge view:Planoconvexaperture:Umbilical-extraumbilical
sp chamber shape:Inflatedcoiling axis:Lowperiphery:N/Aaperture border:Thin lip
umb chbr shape:Inflatedumbilicus:Narrowperiph margin shape:Moderately roundedaccessory apertures:None
spiral sutures:Strongly depressedumb depth:Deepwall texture:Coarsely muricateshell porosity:Finely Perforate: 1-2.5µm
umbilical or test sutures:Strongly depressedfinal-whorl chambers:4.0-4.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Widely distributed in (sub)tropical areas (Caribbean, Atlantic, Indo-Pacific, Tethyan/Mediterranean province); present also in austral areas of the South Atlantic (Maud Rise) and Indian Ocean (Kerguelen Plateau). [Berggren et al. 2006]
Aze et al. 2011 summary: Low to high latitudes; 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: Evolved from Acarinina esnaensis and is the ancestor of the Acarinina pseudotopilensis -quetra group. [Berggren et al. 2006]

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

Biostratigraphic distribution

Geological Range:
Notes: Uppermost Zone P5 (just below the PETM event) to Zone E5. [Berggren et al. 2006]
Last occurrence (top): within E5 zone (50.67-52.54Ma, top in Ypresian stage). Data source: Eocene Atlas
First occurrence (base): within P5 zone (55.96-57.10Ma, base in Thanetian stage). Data source: Eocene Atlas

Plot of occurrence data:

Primary source for this page: Berggren et al. 2006 - Eocene Atlas, chap. 9, p. 320


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Berggren, W. A., Pearson, P. N., Huber, B. T. & Wade, B. S. (2006b). Taxonomy, biostratigraphy, and phylogeny of Eocene Acarinina. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 41(Chap 9): 257-326. gs V O

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Acarinina wilcoxensis compiled by the pforams@mikrotax project team viewed: 21-4-2021

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