Paragloborotalia pseudocontinuosa

Classification: pf_cenozoic -> Globigerinidae -> Paragloborotalia -> Paragloborotalia pseudocontinuosa
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 pseudocontinuosa (Jenkins, 1967)
Rank: species
Basionym: Globorotalia opima Bolli subsp. continuosa Blow.—Jenkins, 1960
Taxonomic discussion:

Jenkins (1960) described the occurrence of Globorotalia opima subsp. continuosa Blow in two distinct stratigraphic levels in the Lakes Entrance oil shaft of Victoria, in southeastern Australia. The lower occurrences are confined to the upper Oligocene-lower Miocene pre-Globoquadrina dehiscens dehiscens to Globigerinoides triloba triloba Zones, while the younger forms are limited to the upper Miocene Globorotalia menardii miotumida Zone. According to Jenkins (1960:366) these older forms “are a little larger” and the aperture is “a little larger” than the very similar younger forms. The two light microscope photomicrograph hypotypes illustrated by Jenkins and representing the two distinct levels, are indistinguishable. Jenkins (1967) went on to describe the older forms as a new subspecies: Globorotalia nana pseudocontinuosa. Jenkins (1967: 1076) concluded that the two taxa were homeomorphs; G. mayeri continuosa evolved from Globorotalia mayeri mayeri “well after the extinction of G. nana pseudocontinuosa”.

Blow (1959) reported a range for Globorotalia opima subsp. continuosa from the lower Miocene Catapsydrax stainforthi Zone to the lower Pliocene Sphaeroidinella seminulina Zone. According to Jenkins (1967:1076), pseudocontinuosa and continuosa are very similar and “morphologically indistinguishable”. Hoskins (1984, figs. 8:1-4) illustrated specimens identified as continuosa from the middle Miocene O. suturalis Zone (Lillburnian Stage, New Zealand) that closely resemble pseudocontinuosa based on the large spherical final chamber. Further study may warrant synonymizing pseudocontinuosa with continuosa. However, for now, we will continue to recognize two distinct taxa (e.g., Jenkins, 1971; Spezzaferri, 1994); P. pseudocontinuosa is here considered to be the Oligocene morphotype characterized by a slightly convex spiral side and more umbilical aspect of the high arched aperture, while P. continuosa is a longer ranging Miocene morphotype characterized by its flat spiral side and more extraumbilical aspect of the moderately high, comma-shaped aperture. [Leckie et al. 2018]

Catalog entries: Globorotalia nana pseudocontinuosa

Type images:

Distinguishing features:

Characterized by its spherical chambers that increase moderately rapidly as added. 4 chambers in 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:

Paragloborotalia pseudocontinuosa is characterized by its spherical chambers that increase moderately rapidly as added. It is differentiated from P. continuosa by its more umbilical-extraumbilical, high arched aperture with a thickened rim (although the paratype more closely resembles continuosa), and more spherical chambers. The aperture in the holotype of pseudocontinuosa is loop shaped and distinctly higher than in the holotype of continuosa; the aperture of continuosa is more extraumbilical in position. It is distinguished from nana in having a higher arched aperture, a faster rate of chamber expansion, a more ovate test, and lobulate equatorial profile, and from both nana and opima in having a high loop-shaped aperture and moderate spire. Paragloborotalia pseudocontinuosa is also smaller than P. opima.

It is differentiated from incognita by its greater spiral-side convexity, radial spiral sutures, and more spherical final chamber, The rate of chamber inflation in P. pseudocontinuosa is similar to P. incognita but greater than in P. continuosa; the final chamber of pseudocontinuosa and incognita is distinctly more inflated than in continuosa, which also has a more extraumbilical aperture than the latter two taxa. Basically, incognita is larger and has a flatter spiral side and slightly curved spiral sutures, while continuosa differs from pseudocontinuosa in having a more extraumbilical aperture; there are gradations between all of these end-members. However, P. pseudocontinuosa has also previously been synonymised with P. incognita (e.g., Berggren and others, 1983; Kennett and Srinivasan, 1983; Li and others, 1992), indicating that there are subtle differences in the test morphology between these two taxa. Here we consider both to be valid taxa despite their similar morphologies. In addition, pseudocontinuosa ranges back to the early Oligocene, while incognita has its first occurrence in the earliest Miocene. The flatter spiral side and slightly curved sutures of incognita display advanced, transitional features between P. pseudocontinuosa and Globoconella zealandica.

Paragloborotalia pseudocontinuosa closely resembles semivera. Jenkins (1971) stated that most of the paratypes in the type sample of semivera have 4 chambers in the final whorl, which he classified as G. (T.) nana pseudocontinuosa Jenkins (also Hoskins, 1984). Jenkins (1971) and Hoskins (1984) also noted a complete range of variation between the two (sub)species in this lower Miocene sample (Awamoan Stage, G. trilobus trilobus Zone). Paragloborotalia pseudocontinuosa is differentiated from semivera by its higher, almost circular aperture, and in possessing fewer chambers (4) in the final whorl. Some specimens of pseudocontinuosa may have a kummerform final chamber (Hoskins, 1984; figs. 7:10-12). Paragloborotalia pseudocontinuosa is distinguished from acrostoma by having only 4 chambers in the final whorl; we propose that pseudocontinuosa gave rise to acrostoma in the early Miocene. [Leckie et al. 2018]

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

Test morphology: Test small to medium in size; low trochospiral, quadrate and lobulate in equatorial outline, chambers globular, inflated, embracing; some specimens may develop a kummerform final chamber; 4 chambers in ultimate whorl, increasing moderately to rapidly in size; in spiral view chambers moderately inflated, spherical, arranged in 2½-3 whorls, sutures slightly depressed, radial; in umbilical view chambers strongly inflated, sutures slightly depressed, radial, forming a cross, umbilicus narrow, moderately deep; aperture umbilical-extraumbilical, moderate to high loop-shaped arch, bordered by a narrow, often thickened, continuous lip; in edge view chambers spherical, spiral side slightly convex, periphery broadly rounded. [Leckie et al. 2018]

Size: Maximum diameter of holotype 0.23 mm (original measurement); 0.27 mm (remeasured this study); thickness of holotype 0.19 mm. Maximum diameter of illustrated paratype 0.28 mm, thickness 0.20 mm (this study). [Leckie et al. 2018]

Character matrix

test outline:Ovatechamber 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:4.0-4.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Cosmopolitan with recorded occurrences in the southwest Pacific Ocean (DSDP Leg 29; Jenkins, 1975); southeast Atlantic Ocean (DSDP Leg 40, Jenkins, 1978; DSDP Leg 73, Poore, 1984); English Channel, and type Aquitanian-Burdigalian (Jenkins, 1966, 1977). [Leckie et al. 2018]

Isotope paleobiology: No data available. Specimens analyzed by Wade and others (2007) are now considered P. opima. [Leckie et al. 2018]

Phylogenetic relations: Paragloborotalia pseudocontinuosa was likely derived from nana in the mid-Oligocene (Zone O4). Jenkins and Srinivasan (1986) report the lowest occurrences of 5 chambered forms, attributed to semivera, at about the same stratigraphic level as the lowest occurrences of pseudocontinuosa. Based on the close similarity of the two taxa discussed above, we propose that 4 chambered pseudocontinuosa was the direct ancestor of the 5 chambered semivera. Paragloborotalia pseudocontinuosa also gave rise to incognita near the time of the Oligocene/Miocene boundary by becoming flatter on the spiral side, having slightly curved spiral sutures, and in having a subspherical final chamber that is slightly elongated in the direction of coiling. We propose that pseudocontinuosa gave rise to acrostoma in the early Miocene by increasing the number of chambers in the final whorl to 5. [Leckie et al. 2018]

Most likely ancestor: Paragloborotalia nana - at confidence level 3 (out of 5). Data source: Leckie et al. 2018.
Likely descendants: Paragloborotalia acrostoma; Paragloborotalia incognita; Paragloborotalia semivera;

Biostratigraphic distribution

Geological Range:
Notes: Zone O2 to Zone M5. The species spans the Oligocene and ranges into the middle Miocene (Spezzaferri, 1994), however there are very few studies in which P. pseudocontinuosa is a common component of Miocene material. Jenkins (1967) states that Globorotalia nana pseudocontinuosa (= P. pseudocontinuosa) ranges from the mid-Oligocene (Whaingaroan Stage, G. euapertura Zone) to lower middle Miocene (lower Lillburnian Stage, O. suturalis Zone) and does not overlap with middle Miocene G. mayeri continuosa (= P. continuosa). In the southeast Atlantic Ocean, the last occurrence of P. pseudocontinuosa is in the lower Miocene Globigerinoides trilobus trilobus Zone of DSDP Sites 360 and 362, whereas G. mayeri continuosa is reported to occur from the middle Miocene G. mayeri mayeri through the upper Miocene G. conomiozea Zone (Jenkins, 1978). A similar stratigraphic range for Globorotalia (Turborotalia) pseudocontinuosa is reported for DSDP Sites 279, 281, and 282 in the southwest Pacific (Jenkins, 1975). Poore (1984) recorded a lowest occurrence of pseudocontinuosa within lower Oligocene Zone OL2 (= ~O2) at DSDP Site 522 in the southeast Atlantic Ocean, and a highest occurrence in the lowermost Miocene Subzone M1a. Spezzaferri (1994) reported a range from lower Oligocene Subzone P21a (= O3/4) to within the middle Miocene based on her detailed study of numerous deep sea sites. Jenkins and Srinivasan (1986) also report a first occurrence of pseudocontinuosa in lower Oligocene Subzone P21a from the southwest Pacific Ocean. In a review paper of southern mid- and high latitude planktonic foraminiferal biostratigraphy and chronostratigraphy, Jenkins (1993) reported a lowest occurrence in lower Oligocene Zone P19. [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 O2 zone (30.28-32.10Ma, 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.157


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

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