Paragloborotalia semivera

Classification: pf_cenozoic -> Globigerinidae -> Paragloborotalia -> Paragloborotalia semivera
Sister taxa: P. acrostoma, P. incognita, P. pseudocontinuosa, P. semivera, P. kugleri, P. pseudokugleri, P. mayeri, P. siakensis, P. birnageae, P. continuosa, P. opima, P. nana, P. griffinoides, P. sp.,


Citation: Paragloborotalia semivera (Hornibrook, 1961)
Rank: species
Basionym: Globigerina semivera Hornibrook, 1961
Taxonomic discussion:

Hornibrook (1961) originally placed semivera in Globigerina on account of the umbilical tendency of the aperture. Jenkins (1967:1070) had stated that “G. siakensis is very close in morphology to G. nana semivera and may prove to be synonymous with it.”, but we recognize a clear distinction between siakensis and semivera. Chaisson and Leckie (1993) and Leckie and others (1993) had lumped P. semivera into a broader concept of P. mayeri s.l.; the ‘semivera’ form is restricted to the upper Oligocene of ODP Hole 803D and basal Miocene of Hole 806B. Jenkins (1977) suggested that acrostoma is a junior synonym of semivera, but we consider the two taxa to be unique and not directly related. [Leckie et al. 2018]

Catalog entries: Globigerina semivera

Type images:

Distinguishing features:

Like P. pseudocontinuosa but somewhat larger and with more chambers (4½-5) 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.


Diagnostic characters:

Hornibrook (1961) described semivera as having a relatively flat spiral side, three whorls with 4-4½ chambers in the final whorl, radial sutures and a wide umbilical to extraumbilical aperture bordered by a lip. However, Jenkins (1971) and Spezzaferri (1994) used a taxonomic concept based on 4½-5  chambers in the final whorl, with radial to slightly curved sutures on both the spiral and umbilical side. Specimens with 4-4½ chambers in the final whorl closely resemble pseudocontinuosa. Jenkins (1971) stated that most of the paratypes in the original type sample have 4 chambers in the final whorl, which he classified as G. (T.) nana pseudocontinuosa Jenkins. Jenkins (1971) also noted a complete range of variation between the two (sub)species in the type sample, an observation also made by examining semivera topotypes at the Natural History Museum in London (this study). Paragloborotalia semivera is differentiated from P. pseudocontinuosa by its somewhat larger size and in possessing more chambers within the final whorl. Both taxa are gradational throughout their ranges. Paragloborotalia semivera differs from opima in having a high loop-shaped aperture and moderate spire.

Paragloborotalia semivera is distinguished from acrostoma by its more compact, embracing chambers, higher spiral-side convexity, and by its lower arched aperture. It is differentiated from both siakensis and mayeri by having a higher, more convex spiral side, subcircular, less ovate equatorial outline, and a more compact test with more embracing chambers and a narrow, closed umbilicus. It is further differentiated from siakensis by having more embracing chambers and a less lobulate test and a higher arched aperture, and from mayeri in having less recurved sutures on the spiral side and fewer (typically 5 compared with 5½-6) chambers in the final whorl. In some cases P. semivera had been included within the taxonomic concept of mayeri and/or siakensis (Leckie and others, 1993; Chaisson and Leckie, 1993; Pearson and Wade, 2009) and pseudocontinuosa (Jenkins and Srinivasan, 1986). [Leckie et al. 2018]

Wall type: Normal perforate, coarsely cancellate, probably sparsely spinose in life, heavy gametogenetic calcification is often present.

Test morphology: Test large in size; low trochospiral, moderately lobulate in equatorial outline, chambers globular, inflated, embracing; 4½-5 chambers in ultimate whorl, increasing rapidly in size in initial whorl and slowly in the final whorl; in spiral view chambers subspherical, arranged in 2½-3 whorls, sutures depressed, radial to slightly curved; in umbilical view chambers spherical to subspherical, sutures depressed, radial, umbilicus very narrow to nearly closed, moderately deep; aperture umbilical-extraumbilical, moderately high arch bordered by a thickened, continuous rim or lip; in edge view chambers spherical, spiral side slightly convex, umbilical side equally convex, periphery broadly rounded. [Leckie et al. 2018]

Size: Maximum diameter of holotype 0.41 mm (original measurement); 0.39 mm (remeasured this study); thickness of holotype 0.28 mm (this study). [Leckie et al. 2018]

Character matrix

test outline:Subcircularchamber arrangement:Trochospiraledge view:Equally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thin 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:4.5-5.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Cosmopolitan; reported from the southwest Pacific Ocean (DSDP Leg 29; Jenkins, 1975), the southeast Atlantic Ocean (DSDP Leg 40; Jenkins, 1978), the English Channel, type Aquitanian-Burdigalian (Jenkins, 1966, 1977), and the Caribbean (Chaisson and D’Hondt, 2000). Berggren (ODP Leg 120; 1992) recorded semivera on the Kerguelen Plateau in the southern Indian Ocean. Kennett and Srinivasan (1983) reported a warm subtropical to temperate distribution. [Leckie et al. 2018]

Isotope paleobiology: No data available. [Leckie et al. 2018]

Phylogenetic relations: Derived from pseudocontinuosa by an additional chamber in the final whorl and larger size. [Leckie et al. 2018]

Most likely ancestor: Paragloborotalia pseudocontinuosa - at confidence level 4 (out of 5). Data source: Leckie et al. 2018.

Biostratigraphic distribution

Geological Range:
Notes: Lower Oligocene Zone O4 to lower Miocene Zone M5. In New Zealand, Hornibrook (1961) records a range from the upper Oligocene (lower Miocene?) Waitakian Stage to the lower middle Miocene Lillburnian Stage. Jenkins (1971) recorded the range from the upper Oligocene upper Whaingaroan Stage, Globigerina (G.) euapertura Zone, to the upper lower Miocene Clifdenian Stage, Praeorbulina glomerosa Zone (Zone N8/M5; Wade and others, 2011). In the southeast Atlantic Ocean, Jenkins (1978) reported a range of uppermost Oligocene G. euapertura Zone through the middle part of the lower Miocene G. triloba triloba Zone at DSDP Sites 360 and 362. In her detailed study of many DSDP sites from around the world ocean, Spezzaferri (1994) reported a lowest occurrence within lower Oligocene Subzone P21a (= O3/O4). [Leckie et al. 2018]
Last occurrence (top): within M5 zone (15.10-16.38Ma, top in Langhian stage). Data source: Leckie et al. 2018
First occurrence (base): within O4 zone (28.09-29.18Ma, base in Rupelian stage). Data source: Leckie et al. 2018

Plot of occurrence data:

Primary source for this page: Leckie et al. 2018 - Olig Atlas chap.5 p.163


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Paragloborotalia semivera compiled by the pforams@mikrotax project team viewed: 5-6-2020

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