Globoquadrina dehiscens

Classification: pf_cenozoic -> Globigerinidae -> Globoquadrina -> Globoquadrina dehiscens
Sister taxa: G. conglomerata, G. dehiscens, G. sp.,


Citation: Globoquadrina dehiscens (Chapman, Parr & Collins, 1934)
Rank: Species
Basionym: Globorotalia dehiscens Chapman, Parr & Collins, 1934

(Note: This is a common, distinctive and biostratigraphically important species in the Miocene. Here we present an abbreviated synonymy list)

Taxonomic discussion:

We were not able to obtain new images of the holotype so we use the type illustration as our guide (Pl. 11.17, Figs. 1-3). This is a common, distinctive and biostratigraphically important form. When the diagnostic characteristics are well developed it is virtually unmistakable but populations can be variable and some individuals can show morphological overlap with species such as D. tripartita, D. larmeui, D. binaiensis, and D. baroemoenensis. The latter species, in particular, can show sharply angular chambers with pustulose umbilical shoulders, including the holotype itself (see discussion under D. baroemoenensis). Many authors since Grimsdale (1951) and Blow (1959) have considered Globorotalia quadraria Cushman and Ellisor to be a junior synonym of Globoquadrina dehiscens, which we have confirmed with new SEM images of the holotype of Globorotalia quadraria. According to Jenkins (1960), who examined topotype specimens, Globorotalia subdehiscens Finlay is a probable synonym of dehiscens. We have not investigated all possible synonymies in the Miocene, which we defer to future work. Globoquadrina dehiscens has long been considered nonspinose since Steineck and Fleisher (1978), although Cifelli (1982) argued that it was spinose. We have not observed spines or spine holes in this species but include it in the spinose group because of its apparently close evolutionary relationship with spinose Dentoglobigerina. [Wade et al. 2018]

Catalog entries: Globorotalia dehiscens, Globoquadrina subdehiscens, Globorotalia quadraria

Type images:

Distinguishing features: Low trochospiral, spiral side almost flat, umbilical side strongly convex; subquadrate;  3½-4 chambers in final whorl; umbilicus large, deep; aperture low, umbilical, covered by umbilical tooth

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:

Globoquadrina dehiscens is distinguished from closely related species of Dentoglobigerina (D. larmeui and D. baroemoenensis) by its quadrate outline, steeply and diagonally flattened, imperforate umbilical face, and elongate pointed triangular apertural tooth. This species is distinguished from D. tripartita by having 4 chambers in the final whorl, the flattened umbilical face and by the typically more prominent umbilical tooth/teeth. [Wade et al. 2018]

Wall type: Normal perforate, weakly cancellate. [Wade et al. 2018]

Test morphology: Low trochospiral, peripheral margin quadrate; in spiral view 4 chambers rapidly increasing in size (although the final chamber can be kummerform), elongate oval in shape, sutures flush, slightly curved; in umbilical view 4 chambers rapidly increasing in size, triangular in outline, becoming progressively flattened and angular; umbilicus open, surrounded by steep walls of chambers, diagonally flattened umbilical face of final chamber, umbilical shoulder sometimes pustulose, umbilical face wholly or partially non-perforate with an elongate pointed triangular apertural tooth; in edge view chambers triangular and projecting over the umbilicus, spiral side flat. [Wade et al. 2018]

Size: Maximum diameter 0.30 mm, minimum diameter 0.25 mm. [Wade et al. 2018]

Character matrix

test outline:Subquadratechamber arrangement:Trochospiraledge view:Planoconvexaperture:Umbilical
sp chamber shape:Subrectangularcoiling axis:Low-moderateperiphery:N/Aaperture border:Teeth
umb chbr shape:Globularumbilicus:Wideperiph margin shape:Moderately roundedaccessory apertures:None
spiral sutures:Weakly depressedumb depth:Deepwall texture:Cancellateshell porosity:Finely Perforate: 1-2.5µm
umbilical or test sutures:Moderately depressedfinal-whorl chambers:3.5-4.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Widespread, cosmopolitan. [Wade et al. 2018]

Isotope paleobiology: Classified as an intermediate-dweller by Keller (1985). Recorded as erratic and variable by Pearson and Shackleton (1995). [Wade et al. 2018]

Phylogenetic relations: Globigerina dehiscens praedehiscens Blow and Banner has long been cited as the ancestor of G. dehiscens. However, G. praedehiscens is now considered a junior synonym of D. tripartita. We concluded that this taxon evolved from Dentoglobigerina larmeui as originally suggested by Jenkins (1960). [Wade et al. 2018]

Most likely ancestor: Dentoglobigerina larmeui - at confidence level 3 (out of 5). Data source: Wade et al. 2018.

Biostratigraphic distribution

Geological Range:
Notes: The lowest occurrence of G. dehiscens is used to mark the base of Subzone M1b (Kennett and Srinivasan, 1983; Berggren and others, 1995; Wade and others, 2011). This appears to be reliable in the subtropics (e.g. Keller, 1980; Kennett and Srinivasan, 1983; Poore, 1984, Chaisson and Leckie, 1993; Leckie and others, 1993; Pearson, 1995) but a lower occurrence has been recorded in the southern latitudes of the Atlantic and Pacific Oceans (Premoli Silva and Spezzaferri, 1990; Spezzaferri, 1994). The highest occurrence in the uppermost Miocene has not been investigated in this study. [Wade et al. 2018] Since the first appearance of Gq. dehiscens is close to the Oligocene-Miocene boundary, it is useful in approximating this boundary in oceanic sequences (Srinivasan and Kennett, 1981a, 1981b, 1983). Although Gq. dehiscens has been found in some Pliocene sediments (Bizon and Bizon, 1972; Jenkins and Orr, 1972; Kennett and Srinivasan, 1975), its last appearance is widely accepted as marking the Miocene-Pliocene boundary in most areas (Berggren, 1973). [Kennett & Srinivasan 1983]
Last occurrence (top): in mid part of M14 [Atl.] zone (54% up, 5.9Ma, in Messinian stage). Data source: Wade et al. (2011), additional event; position within zone determined by linear interpolation from data in table 1 of Wade et al. (2011).
First occurrence (base): at base of M1b subzone (0% up, 22.4Ma, in Aquitanian stage). Data source: Wade et al. (2011), zonal marker

Plot of occurrence data:

Primary source for this page: Wade et al. 2018 - Olig Atlas chap.11 p.377; Kennett & Srinivasan 1983, p.184


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Globoquadrina dehiscens compiled by the pforams@mikrotax project team viewed: 8-7-2020

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