Paragloborotalia acrostoma

Classification: pf_cenozoic -> Globigerinidae -> Paragloborotalia -> Paragloborotalia acrostoma
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 acrostoma (Wezel 1966)
Rank: species
Basionym: Globorotalia acrostoma Wezel 1966
Taxonomic discussion:

Wezel (1966) tentatively attributed acrostoma to the genus “Globorotalia” in quotation marks because of its cancellate rather than smooth wall of typical Globorotalia or Turborotalia; he further suggested that a new subgenus should be erected to accommodate “G.” acrostoma as well as other species like “G.” mayeri and “G.” continuosa.

Jenkins (1977) suggested that acrostoma is a junior synonym of semivera, while Poore (1979) suggested that acrostoma could be considered as a subspecies of mayeri. Despite the close morphologically similar characteristics with both semivera and mayeri, we recognize acrostoma as a unique taxon in large part because of its distinctive aperture and relatively limited biogeographic range in and around the Mediterranean and tropical Atlantic Ocean (e.g., Iaccarino, 1985). [Leckie et al. 2018]

Catalog entries: Globorotalia acrostoma

Type images:

Distinguishing features:

Like P. pseudocontinuosa, but 4½ - 5 chambers and with a higher arched aperture; not very lobulate, often pentagonal in outline.

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:

Typical 5 chambered forms are pentagonal in outline, but not very lobulate. Paragloborotalia acrostoma is similar to semivera in having 5 chambers in the final whorl and a compact test with a narrow umbilicus, but it differs from semivera by its distinctly higher arched, semi-circular aperture bordered by an imperforate rim or thin lip. It is distinguished from siakensis by its higher arched aperture and tendency for curved spiral-side sutures. Specimens of acrostoma with 4½ chambers in the final whorl (e.g., Spezzaferri, 1994) closely resemble pseudocontinuosa, but are differentiated from the latter by having a higher arched aperture. Paragloborotalia acrostoma differs from continuosa in the same ways that it does with pseudocontinuosa, but acrostoma is also distinguished by its more umbilical-extraumbilical aperture, compared with a more extraumbilical aperture in continuosa.

Paragloborotalia acrostoma is distinguished from mayeri by its slightly greater spiral-side convexity, narrower umbilicus, fewer chambers (typically 5 compared with 6), and more umbilical-extraumbilical aperture. Paragloborotalia acrostoma is transitional in morphologic character between semivera and mayeri, however, the similar first occurrences of acrostoma and mayeri during the latest Oligocene suggest that acrostoma either falls within the range of variability for early forms of mayeri, or that the two taxa are more distantly related homeomorphs. Because of the more compact nature of acrostoma, including its narrow umbilicus, and its distinctive semi-circular apertural characteristics and one fewer chamber than typical mayeri, we have retained acrostoma as a valid taxon. [Leckie et al. 2018]

Gr. (J.) acrostoma closely resembles Gr. (J.) mayeri but is easily distinguished by its four to four and one-half chambers in the final whorl and larger and higher-arched aperture. [Kennett & Srinivasan 1983]

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

Test morphology: Test small to large in size; very low trochospiral, moderately lobulate in equatorial outline, chambers globular, inflated, embracing; typically 5, sometimes with 4 or 4½ chambers in ultimate whorl, increasing rapidly in size; in spiral view chambers initially reniform becoming subspherical, arranged in 2½-3 whorls, sutures slightly depressed, slightly curved becoming radial between ultimate and penultimate chamber; in umbilical view chambers subspherical, sutures depressed, radial, umbilicus very narrow to nearly closed, moderately deep; aperture umbilical-extraumbilical, high arch bordered by a continuous imperforate rim or thin lip; in edge view chambers globular to subglobular, spiral side nearly flat to slightly convex, umbilical side more convex, periphery broadly but asymmetrically rounded. [Leckie et al. 2018]

Size: Maximum diameter of holotype and paratypes 0.23-0.36 mm, minimum diameter 0.19-0.32 mm, maximum thickness 0.16-0.26 mm (original measurements); holotype maximum diameter 0.33 mm, maximum thickness 0.23 mm (remeasured 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:4.5-5.0 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology

Geographic distribution: Warm to cool subtropical (Kennett and Srinivasan, 1983). Paragloborotalia acrostoma is a common component of Mediterranean and North Atlantic samples (Iaccarino and Salvatorini, 1979; Salvatorini and Cita, 1979; Iaccarino, 1985; Gennari and others, 2013; Foresi and others, 2014), but has also been reported in the equatorial and northwest Pacific Ocean (Keller, 1981), and in northern high latitude Atlantic Ocean sites (Poore, 1979; Spezzaferri, 1998). No occurrences have been recorded in the Southern Hemisphere. [Leckie et al. 2018]

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

Phylogenetic relations: Spezzaferri (1994) has proposed that P. acrostoma evolved from P. semivera during the early Miocene, however other authors have suggested the species evolved from P. mayeri/siakensis (Keller, 1981; Kennett and Srinivasan, 1983; Aze and others, 2011). Based on the similarity of 4 chambered pseudocontinuosa and the 4½ chambered forms of acrostoma, we propose that pseudocontinuosa is the likely ancestor of acrostoma. [Leckie et al. 2018]

Gr. (J.) acrostoma evolved during the earliest Miocene from Gr. (J.) mayeri by a reduction in number of chambers in the final whorl and by developing a larger and higher arched aperture (Srinivasan and Kennett, 1981a; Keller, 1981a). [Kennett & Srinivasan 1983]

Most likely ancestor: Paragloborotalia pseudocontinuosa - at confidence level 3 (out of 5). Data source: Leckie et al. 2018.

Biostratigraphic distribution

Geological Range:
Notes: Lower Miocene Subzone M1a to Zone M5. Wezel (1966) recorded a range from the Catapsydrax dissimilis Zone to Globigerinatella insueta Zone with questionable occurrences in or near the Globigerina ciperoensis ciperoensis-Globorotalia kugleri zonal boundary (Oligocene/Miocene boundary). Spezzaferri (1994) recorded a lowest occurrence of acrostoma near the Oligocene/Miocene boundary Subzone N4a. Multiple authors record acrostoma in Zone N8 (M5). [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 M1a subzone (22.44-22.96Ma, 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.130; Kennett & Srinivasan 1983, p.176


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Gennari, G., Spezzaferri, S., Comas, M. C., Rüggeberg, A., Lopez-Rodriguez, C. & Pinheiro, L. M. (2013). Sedimentary sources of the mud-breccia and mud volcanic activity in the Western Alboran Basin. Marine Geology. 339: 83-95. gs :: ::

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Jenkins, D. G. (1977). Lower Miocene planktonic forminfera from the a borehole in the English Channel. Micropaleontology. 23(3): 297-318. gs :: ::

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

Leckie, R. M. et al. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Paragloborotalia and Parasubbotina. 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(Chap 5): 125-178. gs :: ::

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Paragloborotalia acrostoma compiled by the pforams@mikrotax project team viewed: 5-7-2020

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