Globorotaloides variabilis


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

Taxonomy

Citation: Globorotaloides variabilis Bolli, 1957
Rank: species
Basionym: Globorotaloides variabilis Bolli, 1957
Synonyms:
Taxonomic discussion:

Globorotaloides variabilis is not a well known species and the original concept has been only weakly applied. Blow (1969, 1979) treated Globorotaloides variabilis as a subspecies of Globorotaloides hexagonus (Natland). Kennett and Srinivasan (1983) recognized G. variabilis from the late Miocene of the southwestern Pacific Ocean. Their figured specimen (Kennett and Srinivasan, 1983; pl. 53, figs. 6-8, reproduced here on Pl. 4.12, Figs. 15 and 16), which is nonbullate and somewhat pinched around the periphery, has propagated a rather narrow concept of the taxon as being non-bullate and close to G. hexagonus. Our assessment of the type material, however, demonstrates greater variability within the taxon, including bullate forms rather similar to Bolli’s types and our topotypes (Pl. 4.12, Figs. 5, 9-12), as well as forms closely comparable to Kennett and Srinivasan’s examples. [Coxall & Spezzaferri 2018]

Catalog entries: Globorotaloides variabilis;

Type images:

Distinguishing features: Like G. suteri but with more compressed early chambers, more curved sutures, and more (5-6 vs 4-5) chambers in the final whorl.

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.

Description


Diagnostic characters:

Globorotaloides variabilis as the name suggests shows some irregularity in its late-stage coiling and other features. The final bulla-like chamber may cover part of or the entire umbilicus. The primary aperture is also umbilical in adult forms, whereas in most other Globorotaloides species it is umbilical-extraumbilical, although in forms transitional to G. hexagonus the aperture is more extraumbilical. It is distinguished from species of Catapsydrax by the flattened spiral side. Forms without the terminal bulla-like chamber can be distinguished from Globorotaloides hexagonus and Globorotaloides eovariabilis by the more embracing chambers and more umbilical position of the primary aperture. Some specimens lack a bulla, revealing the umbilical position of the primary aperture and a lip (Pl. 4.12, Figs. 13, 14 and 15, 16). [Coxall & Spezzaferri 2018]


Wall type: Normal perforate, coarsely cancellate, spinose (?), ruber/sacculifer-type wall structure. [Coxall & Spezzaferri 2018]

Test morphology: Low trochospiral, equatorial periphery lobate, axial periphery rounded; chambers subangular to ovate in early stage, later becoming ovate to globular; 2-2½ whorls; 4½-6 slightly embracing chambers in final whorl, chambers of final whorl increase fairly gradually in size, final chamber typically a bulla or bulla-like, may cover part of or the entire umbilicus; spiral view, sutures distinctly curved to retroflexed in early stage, becoming more radial in the adult stages in some specimens, depressed, inner whorl distinctly flattened; umbilical view, chambers increase rapidly in size, sutures moderately depressed, straight; umbilicus small, primary aperture a slit or low arch, bordered by narrow thickened lip, umbilical-extraumbilical in early stage, later becoming umbilical, in the mature stage this becomes covered by the bulla-like final chamber with one infralaminal aperture. Coiling variable. [Coxall & Spezzaferri 2018]

Size: Maximum diameter of holotype 0.45 mm. [Coxall & Spezzaferri 2018]

Character matrix

test outline:Ovatechamber arrangement:Trochospiraledge view:Equally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Crescenticcoiling axis:Lowperiphery:N/Aaperture border:Bulla
umb chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:Infralaminal
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 at mid- to low latitudes. [Coxall & Spezzaferri 2018]

Isotope paleobiology: No data available. [Coxall & Spezzaferri 2018]

Phylogenetic relations: Globorotaloides variabilis probably evolved from Globorotaloides eovariabilis in Zone O3/O4 and was ancestral to G. stainforthi and G. hexagonus. [Coxall & Spezzaferri 2018]

Most likely ancestor: Globorotaloides eovariabilis - at confidence level 3 (out of 5). Data source: Kennett & Srinivasan 1983; Coxall & Spezzaferri 2018 .
Likely descendants: Globorotaloides hexagonus; Globorotaloides stainforthi;

Biostratigraphic distribution

Geological Range:
Notes: Uncertain due to the variability and scarcity of the morphotype and therefore uncertainty in consistency of positive identifications. Bolli and Saunders (1985) show G. variabilis to be restricted to Miocene Zones N8-N17, disappearing prior to the base of the Pliocene. Subsequent constraints extend the first appearance back to lower Oligocene Subzone P21a (Zone O3/O4) (Atlantic Ocean DSDP Sites 17A, 363 and 516, and Indian Ocean ODP Site 707; Spezzaferri, 1994), or possibly Zone P20 (Zone O2) (DSDP Site 94 Gulf of Mexico). Spezzaferri’s (1994) best constraint for the highest occurrence of G. variabilis is N8-N9 (M5/M6), as seen at DSDP Sites 17A, 363 and 588. Reports of this species in the Pliocene (Poore, 1981: Zone N19) are likely to be a bullate form of G. hexagonus. [Coxall & Spezzaferri 2018]
Last occurrence (top): within N18 zone (5.20-5.72Ma, top in Zanclean stage). Data source: Chaisson & Pearson (1997)
First occurrence (base): within O3 zone (29.18-30.28Ma, base in Rupelian stage). Data source: Coxall & Spezzaferri 2018

Plot of occurrence data:

Primary source for this page: Coxall & Spezzaferri 2018 - Olig Atlas chap.4 p.113; Kennett & Srinivasan 1983, p.214

References:

Aze, T. et al. (2011). A phylogeny of Cenozoic macroperforate planktonic foraminifera from fossil data. Biological Reviews. 86: 900-927. gs

Blow, W. H. (1969). Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In, Bronnimann, P. & Renz, H. H. (eds) Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967. E J Brill, Leiden 380-381. gs

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs

Bolli, H. M. & Saunders, J. B. (1985). Oligocene to Holocene low latitude planktic foraminifera. In, Bolli, H. M. , Saunders, J. B. & Perch-Neilsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge, UK 155-262. gs

Bolli, H. M. (1957b). Planktonic foraminifera from the Oligocene-Miocene Cipero and Lengua formations of Trinidad, B.W.I. In, Loeblich, A. R. , Jr. , Tappan, H. , Beckmann, J. P. , Bolli, H. M. , Montanaro Gallitelli & E. Troelsen, J. C. (eds) Studies in Foraminifera. U.S. National Museum Bulletin. 215: 97-123. gs

Brönnimann, P. & Resig, J. (1971). A Neogene globigerinacean biochronologic time-scale of the southwestern Pacific. Initial Reports of the Deep Sea Drilling Project. 7(2): 1235-1469. gs

Chaisson, W. P. & Leckie, R. M. (1993). High-resolution Neogene planktonic foraminifer biostratigraphy of Site 806, Ontong Java Plateau (Western Equatorial Pacific). Proceedings of the Ocean Drilling Program, Scientific Results. 130: 137-178. gs

Chaisson, W. P. & Pearson, P. N. P. (1997). Planktonic foraminifer biostratigraphy at Site 925: Middle Miocene–Pleistocene. Proceedings of the Ocean Drilling Program, Scientific Results,. 154: 3-31. gs

Coxall, H. K. & Spezzaferri, S. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene Catapsydrax, Globorotaloides, and Protentelloides. In, Wade, B. S. , Olsson, R. K. , Pearson, P. N. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46: 79-125. gs

Hooyberghs, H. J. F. & de Meuter, F. (1972). Biostratigraphy and inter-regional correlation of the Miocene deposits of Northern Belgium based on planktonic foraminifera; the Oligocene-Miocene boundary on the southern edge of the North Sea basin, Brussels. Koninklijke Vlaamse Academie voor Wetenschappen, Letteren en Schone Kunsten van België.. -. gs

Keller, G. (1985). Depth stratification of planktonic foraminifers in the Miocene Ocean. In, Kennett, J. P. (ed.) The Miocene Ocean: Paleoceanography and Biogeography. GSA Memoir. 163: 1-337. gs

Kennett, J. P. & Srinivasan, M. S. (1983). Neogene Planktonic Foraminifera. Hutchinson Ross Publishing Co., Stroudsburg, Pennsylvania. 1-265. gs

Natland, M. L. (1938). New Species of Foraminifera from off the West Coast of North America and from the Later Tertiary of the Los Angeles Basin. Bulletin of the Scripps Institute of Oceanography, Tech. Ser.. 4(5): 137-164. gs

Poore, R. Z. (1981). Miocene through Quaternary planktonic foraminifers from offshore southern California and Baja California. Initial Reports of the Deep Sea Drilling Project. 63: 415-436. gs

Premoli Silva, I. & Spezzaferri, S. (1990). Paleogene planktonic foraminifer biostratigraphy and paleoenvironmental remarks on paleogene sediments from Indian Ocean sites, Leg 115. Proceedings of the Ocean Drilling Program, Scientific Results. 115: 277-314. gs

Quilty, P. G. (1976). Planktonic foraminifera DSDP Leg 34, Nazca Plate. Initial Reports of the Deep Sea Drilling Project. 34: 629-703. gs

Spezzaferri, S. (1994). Planktonic foraminiferal biostratigraphy and taxonomy of the Oligocene and lower Miocene in the oceanic record. An overview. Palaeontographia Italica. 81: 1-187. gs


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Globorotaloides variabilis compiled by the pforams@mikrotax project team viewed: 26-6-2019

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