Globorotaloides eovariabilis

Classification: pf_cenozoic -> Globigerinidae -> Globorotaloides -> Globorotaloides eovariabilis
Sister taxa: G. atlanticus, G. stainforthi, G. eovariabilis, G. hexagonus, G. quadrocameratus, G. suteri, G. testarugosus, G. variabilis, G. sp.,


Citation: Globorotaloides eovariabilis Huber & Pearson, in Olsson et al. 2006
Rank: Species
Basionym: Globorotaloides eovariabilis
Taxonomic discussion:

Globorotaloides eovariabilis is a small but distinctive species that occurs frequently in the < 150 μm size fraction (although the holotype is slightly larger). It is long-ranging and most abundant in high latitude Eocene to early Oligocene or equatorial assemblages. It is possible that it is a junior synonym of G. hexagonus and the possibility that the Paleogene species had a spinose wall, whereas modern G. hexagonus does not (see discussion above). Eocene Globorotaloides eovariabilis usually does not have a bulla, however, we have observed in Oligocene populations from different localities (e.g., ODP Site 647, North Atlantic Ocean, and Site 1137, southern Indian Ocean) times when bullate and non-bullate forms co-occur (Plate 4.5, Figs. 11, 12). Removal or natural breakage of the bulla reveals the typical G. eovariabilis morphology beneath (Plate 4.5, Figs. 13). [Coxall & Spezzaferri 2018]

Catalog entries: Globorotaloides eovariabilis, Globorotalia (Turborotalia) pseudoimitata

Type images:

Distinguishing features: Test with 4½ to 6, final whorl chambers, increasing gradually in size.

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.


Diagnostic characters:

Globorotaloides eovariabilis differs from Globorotaloides quadrocameratus in having greater than 4 (typically 5 but up to 6½) final whorl chambers that are less inflated and increase more gradually in size; from Globorotaloides variabilis by its smaller size and more regular low trochospiral coiling and tendency for axial lateral compression and pinching of the periphery. It differs from Globorotaloides testarugosus in the more inflated chambers, lobate periphery, and curving of umbilical sutures and from Globorotaloides hexagonus, with which it intergrades, in the smaller size, slightly less inflated chambers and lower stratigraphic range (see discussion above). Where a central umbilical bulla occurs there is a single opening. [Coxall & Spezzaferri 2018]

Wall type: Normal perforate, coarsely cancellate, sacculifer-type wall texture, often with corroded interpore ridges resulting in a remnant wall texture consisting of distinct ‘rosettes’ around pores. Possibly spinose (modified from Olsson and others, 2006a). [Coxall & Spezzaferri 2018]

Test morphology: Test outline lobate, subcircular in axial view, axial periphery rounded to slightly compressed and pinched, biconvex, oval to egg-shaped in edge view; 3- 3½ whorls of slightly inflated chambers arranged in a flattened to slightly elevated trochospire; 14-15 chambers in adult tests, 4½-6½ in the final whorl increasing moderately in size; umbilicus shallow to moderately deep and narrow; umbilical sutures moderately depressed, curved, radial; spiral sutures initially indistinct, later weakly depressed, radial; aperture a low umbilical-extraumbilical arch extending one-third towards the peripheral margin, surrounded by a broad lip that extends into the umbilical area; tendency to develop an imperforate peripheral band in some Oligocene forms (modified from Olsson and others, 2006a). [Coxall & Spezzaferri 2018]

Size: Holotype (USNM 523429) maximum diameter 0.18 mm, breadth 0.10 mm; paratype a (USNM 523430) maximum diameter 0.13 mm, breadth 0.80 mm; paratype b (USNM 523430) maximum diameter 0.15 mm, breadth 0.93 mm. [Coxall & Spezzaferri 2018]

Character matrix

test outline:Lobatechamber arrangement:Trochospiraledge view:Equally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thick lip
umb chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:None
spiral sutures:Weakly depressedumb depth:Shallowwall texture:Cancellateshell porosity:Macroperforate: >2.5µm
umbilical or test sutures:Moderately depressedfinal-whorl chambers:4.5-6.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Global, including low and mid-latitudes. Can be common in southern and northern high latitudes. There may be an affinity with high productivity conditions. [Coxall & Spezzaferri 2018]

Isotope paleobiology: Globorotaloides eovariabilis exhibits relatively positive δ18O and negative δ13C compared to other species suggesting that it occupied a sub-thermocline planktonic habitat similar to Catapsydrax (Coxall, unpublished). [Coxall & Spezzaferri 2018]

Phylogenetic relations: Globorotaloides eovariabilis evolved from Globorotaloides quadrocameratus (Olsson and others, 2006a). [Coxall & Spezzaferri 2018]

Similar species:

Most likely ancestor: Globorotaloides quadrocameratus - at confidence level 4 (out of 5). Data source: Olsson et al. 2006, f5.1.
Likely descendants: Globorotaloides testarugosus; Globorotaloides variabilis;

Biostratigraphic distribution

Geological Range:
Notes: Lower Eocene (Olsson and others, 2006a) to upper Oligocene Zone O7 (Pearson and Wade, 2009), possibly extending into the lower Miocene (recorded as Globorotaloides permicrus at DSDP Sites 360, 26, 563 and 516, Spezzaferri, 1994), although difficult to determine because of the close similarities with G. hexagonus. The holotype and paratype are from the middle Eocene of ODP Hole 647A, southern Labrador Sea, which was assigned to calcareous nannofossil Zone NP16 by Firth (1989) and dated as 40.2 Ma on the revised Site 647 biomagnetochronology of Firth and others (2013). [Coxall & Spezzaferri 2018]
Last occurrence (top): within M1 zone (21.12-22.96Ma, top in Aquitanian stage). Data source: Coxall & Spezzaferri 2018
First occurrence (base): within E7 zone (45.72-50.20Ma, base in Ypresian stage). Data source: Olsson et al. 2006

Plot of occurrence data:

Primary source for this page: Coxall & Spezzaferri 2018 - Olig Atlas chap.4 p.97; Olsson et al. 2006 - Eocene Atlas, chap. 5, p. 79


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Globorotaloides eovariabilis compiled by the pforams@mikrotax project team viewed: 19-9-2020

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