Paragloborotalia continuosa

Classification: pf_cenozoic -> Globigerinidae -> Paragloborotalia -> Paragloborotalia continuosa
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 continuosa (Blow, 1959)
Rank: species
Basionym: Globorotalia opima subsp. continuosa Blow, 1959
Taxonomic discussion:

Jenkins (1971) considered Globorotalia continuosa to be a subspecies of G. mayeri. Bolli and Saunders (1982a) considered continuosa to be a 4 chambered variant of mayeri, and therefore placed continuosa in synonymy with mayeri. We disagree with this assessment and consider the 4 chambered P. continuosa as distinct. Bolli and Saunders (1982a) further state that G. continuosa has the same range as G. mayeri, both of which have a first occurrence in the upper Oligocene Globigerina ciperoensis ciperoensis Zone (= Zone O6, G. ciperoensis Partial Range Zone; Wade and others, 2011). This conclusion has possible implications about the relationship, if any, between Paragloborotalia continuosa and P. pseudocontinuosa. Jenkins (1971), on the other hand, reported similar, middle Miocene first occurrences for both mayeri and closely related continuosa. These varying ranges and phylogenetic relationships are not supported by this study.

Paragloborotalia continuosa may have been derived directly from nana rather than pseudocontinuosa based on the small size and extraumbilical position of the aperture, flat spiral side, radial spiral-side sutures, and quadrilobate test like nana, albeit not as compact and distinctly more lobulate than nana. Both nana and continuosa have a smaller, less inflated final chamber than pseudocontinuosa and incognita. P. continuosa is a continuation of the nana-like quadrilobate form well into the Miocene.

Paragloborotalia continuosa has a widely varying stratigraphic range owing to its very close similarity, if not direct phyletic relationship with P. pseudocontinuosa (see additional discussion under that species). Jenkins (1960, 1967, 1971, 1975, 1978) reports distinct ranges for the two taxa: upper Oligocene to lower Miocene for P. pseudocontinuosa and middle to upper Miocene for P. continuosa. Jenkins maintained that P. pseudocontinuosa was derived from P. nana and the ancestor of Globorotalia (Globoconella) zealandica Hornibrook in the lower Miocene G. trilobus trilobus Zone, and that P. continuosa was derived from P. mayeri in the lower middle Miocene G. mayeri mayeri Zone. However, a number of researchers report a lower Miocene first occurrence for continuosa (e.g., Kennett and Srinivasan, 1983; Chaisson and Leckie, 1993). [Leckie et al. 2018]

Catalog entries: Globorotalia opima continuosa

Type images:

Distinguishing features: Like P. nana but less compact and periphery lobulate; aperture higher arched aperture with a more distinctive lip.

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:

Paragloborotalia continuosa was originally recognized as having four chambers in the final whorl and a high-arched aperture with a distinctive comma shape (Blow, 1959). It is differentiated from P. nana by having a higher arched aperture with a more distinctive lip, and a less compact, more lobulate equatorial outline. Paragloborotalia continuosa is small, like P. nana, which is the primary way both taxa are distinguished from P. opima. Additionally, P. continuosa is distinguished from P. opima by its higher-arched, extraumbilical aperture. It is differentiated from P. siakensis and P. mayeri by being more subquadrangular in profile with fewer (only 4) chambers in the final whorl (Fox and Wade, 2013). Bolli and Saunders (1982a, 1985) stated that the morphology of P. continuosa and P. mayeri is identical with the main difference being fewer chambers in the final whorl of continuosa, and the overall smaller test size.

Paragloborotalia continuosa differs from pseudocontinuosa by its more extraumbilical aperture, less spherical chambers (ovate to subspherical), and flatter spiral side. Rate of chamber inflation in continuosa is less than observed in pseudocontinuosa and incognita; this is particularly evident in edge view by the smaller, less inflated final chamber. It differs from acrostoma in having only 4 chambers in the final whorl, a lower apertural arch, and radial spiral sutures. [Leckie et al. 2018]

Wall type: Normal perforate, coarsely cancellate, possibly sparsely spinose in life, heavy gametogenetic calcification is often present. [Leckie et al. 2018]

Test morphology: Test small to medium in size; very low trochospiral, quadrate and lobulate in equatorial outline, chambers globular, inflated, embracing; 4 chambers in ultimate whorl, increasing rapidly in size; in spiral view chambers moderately inflated, ovate to subspherical, arranged in 2½ whorls, sutures slightly depressed, radial; in umbilical view chambers strongly inflated, sutures slightly depressed, radial, umbilicus narrow, moderately deep; aperture a moderately high comma-shaped arch extending midway onto the peripheral edge, more extraumbilical than umbilical-extraumbilical, bordered by a narrow, thickened, continuous lip; in edge view chambers ovate to subspherical, spiral side flat, periphery broadly rounded. [Leckie et al. 2018]

Size: Maximum diameter of holotype 0.26 mm (original measurement); 0.19 mm (remeasured this study); thickness 0.11 mm (this study). [Leckie et al. 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:4.0-4.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Cosmopolitan. [Leckie et al. 2018]

Isotope paleobiology: Majewski (2003) reported a shallow depth habitat for late middle Miocene continuosa based on stable isotope analyses from ODP Site 744 in the southern Indian Ocean. [Leckie et al. 2018]

Phylogenetic relations: Jenkins (1971) described very little morphologic difference between homeomorphs continuosa and pseudocontinuosa; Jenkins recognized the two taxa based on phylogenetic and stratigraphic evidence with pseudocontinuosa being derived from nana in the Oligocene and continuosa derived from mayeri in the middle Miocene. We agree that the two taxa are sufficiently distinct based primarily on their stratigraphic ranges, as well as subtle differences in their morphology, but we suggest that continuosa was also derived from nana. [Leckie et al. 2018]

Most likely ancestor: Paragloborotalia nana - at confidence level 2 (out of 5). Data source: Leckie et al. 2018.
Likely descendants: Neogloboquadrina acostaensis; Neogloboquadrina pachyderma;

Biostratigraphic distribution

Geological Range:
Notes: Paragloborotalia continuosa first appeared in the uppermost Oligocene or lowermost Miocene (Chaisson and Leckie, 1993; Spezzaferri, 1994). It ranges into the upper Miocene Zone M13 (Spiegler and Jansen, 1989; Berggren, 1992; Chaisson and Leckie, 1993; Chaisson and Pearson, 1997; Chaisson and D’Hondt, 2000). [Leckie et al. 2018]
Last occurrence (top): within M13 zone (6.14-9.83Ma, top in Messinian stage). Data source: Leckie et al. 2018
First occurrence (base): within M1 zone (21.12-22.96Ma, base in Aquitanian 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.137; Kennett & Srinivasan 1983, p.190


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Paragloborotalia continuosa compiled by the pforams@mikrotax project team viewed: 22-10-2019

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