pforams@mikrotax - Igorina pusilla pforams@mikrotax - Igorina pusilla

Igorina pusilla


Classification: pf_cenozoic -> Truncorotaloididae -> Igorina -> Igorina pusilla
Sister taxa: I. tadjikistanensis, I. albeari, I. pusilla, I. sp.

Taxonomy

Citation: Igorina pusilla (Bolli 1957)
Taxonomic rank: species
Basionym: Globorotalia pusilla pusilla Bolli 1957
Synonyms:
Taxonomic discussion: Igorina pusilla is the earliest representative of the biconvex, praemuricate igorinids. The small, biconvex test, deep funnel-shaped entrances to the pores, and distinctly praemuricate surface serves to differentiate this form (and its descendants) from the mainline morozovellids and suggests that /. pusilla represents the founding species of a separate lineage among early Paleogene planktonic foraminifera. There appears to be little confusion in the identification of this species. We note, however, that Planorotalites tauricus Morozova (1961) is a middle Paleocene igorinid species from the northern Caucacus that we regard as synonymous with /. pusilla. [Olsson et al. 1999]

Catalog entries: Globorotalia pusilla pusilla, Planorotalites tauricus

Type images:

Distinguishing features:
Parent taxon (Igorina): Test small, biconvex, evolute, margin narrowly rounded or angular, sometimes with a keel; 5-6 chambers in final whorl
Wall, coarsely cancellate, praemuricate, often pustulose.
This taxon: Test small, essentially circular, biconvex, cancellate, pustulose test with 5-6 chambers in last whorl; sutures on umbilical side radial, depressed, on spiral side moderately to strongly curved, depressed/weakly incised; axial periphery subacute and non-carinate; umbilicus narrow, shallow, aperture an interiomarginal, umbilical-extraumbilical arch extending towards, but not reaching, the periphery.

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.

Description


Diagnostic characters:
Relatively small (generally <0.25mm in diameter), essentially circular, biconvex, cancellate, pustulose test with 5-6 chambers in last whorl; intercameral sutures on umbilical side radial, depressed, on spiral side moderately to strongly curved, depressed/weakly incised; axial periphery subacute and non-carinate; umbilicus narrow, shallow, aperture an interiomarginal, umbilical-extraumbilical arch extending towards, but not reaching, the periphery. [Olsson et al. 1999]

Character matrix
test outline:Subcircularchamber arrangement:Trochospiraledge view:Inequally biconvexaperture:Umbilical-extraumbilical
sp chamber shape:Inflatedcoiling axis:Lowperiphery:N/Aaperture border:Thin lip
umb chbr shape:Inflatedumbilicus:Narrowperiph margin shape:Subangularaccessory apertures:None
spiral sutures:Weakly depressedumb depth:Shallowwall texture:Smoothshell porosity:Finely Perforate: 1-2.5µm
umbilical or test sutures:Weakly depressedfinal-whorl chambers:5-6 N.B. These characters are used for advanced search. N/A - not applicable

Biogeography and Palaeobiology


Geographic distribution
Igorina pusilla has been recorded from predominantly low latitude (sub)tropical locations (Figure 27). [Olsson et al. 1999]
Aze et al. 2011 summary: Low to middle latitudes; based on Olsson et al. (1999)

Isotope paleobiology
No data available. [Olsson et al. 1999]
Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts; based on comparison with other species of the genus.

Phylogenetic relations
We believe that the igorinids are derived from the nonkeeled, praemuricate forms of the inconstans -uncinata plexus as previously suggested by Pearson (1993). Although the exact pattern of ancestry has not been worked out, Igorina pusilla is probably derived from forms similar to P. inconstans or P. uncinata by development of more involute coiling. This transformation may have occurred through the suppression of the later stages of ontogeny by speeding up the rate of maturation. This change in the timing of maturation would account for the small size of mature igorinids. [Olsson et al. 1999]

Most likely ancestor:
Praemurica uncinata - at confidence level 4 (out of 5). Data source: Olsson et al. (1999), f5a.
Likely descendants: Igorina albeari; Igorina tadjikistanensis; plot with descendants

Biostratigraphic distribution

Geological Range:
Notes: Zone P3a to Zone P3b (lower part). [Olsson et al. 1999]
Last occurrence (top): in upper part of P3b subzone (80% up, 60.9Ma, in Selandian stage). Data source: Olsson et al. (1999), f5a
First occurrence (base): at base of P3a subzone (0% up, 62.3Ma, in Danian stage). Data source:

Plot of occurrence data:

Primary source for this page: Olsson et al. 1999 - Atlas of Paleocene Planktonic Foraminifera, p. 70

References:

Bolli, H. M. & Cita, M. B. (1960). Globigerine e Globorotalie del Paleocene di Paderno d'Adda (Italia). Rivista Italiana di Paleontologia e Stratigrafia. LXVI(3): 1-42. gs

Bolli, H. M. (1957d). The genera Globigerina and Globorotalia in the Paleocene-Lower Eocene Lizard Springs Formation of Trinidad. In, Loeblich, A. R. , Jr., Tappan, H., Beckmann, J. P., Bolli, H. M., Montanaro Gallitelli, E. & Troelsen, J. C. (eds) Studies in Foraminifera. U.S. National Museum Bulletin . 215: 61-82. gs

Hillebrandt, A. , von (1962). Das Paleozän und seine Foraminiferenfauna im Becken von Reichenhall und Salzburg. Abhandlungen Bayerischen Akademie der Wissenschaften. 108: 1-182. gs

Morozova, V. G. (1961). Datsko-Montskie planktonnye foraminifery yuga SSSR [Danian-Montian Planktonic Foraminifera of the Southern USSR]. Paleontologicheskiy Zhurnal. (2): 8-19. gs O

Olsson, R. K., Hemleben, C., Berggren, W. A. & Huber, B. T. (1999). Atlas of Paleocene Planktonic Foraminifera. Smithsonian Institution Press, Washington, DC. (85): 1-252. gs

Postuma, J. A. (1971). Manual of planktonic foraminifera. Elsevier for Shell Group, The Hague. 1-406. gs

Pujol, C. (1983). Cenozoic planktonic foraminiferal biostratigraphy of the South-Western Atlantic (Rio Grande Rise): Deep Sea Drilling Project Leg 72. Initial Reports of the Deep Sea Drilling Project. 72: 623-673. gs

Shutskaya, E. K. (1970b). Stratigrafiya, foraminifery i paleogeografiya nizhnego paleogena Kryma, predkavkaz'ya i zapadnoi chadsti srednei azii [Stratigraphy, Foraminifera and Paleogeography of the Lower Paleogene in the Crimea, Precaucasus and the Western Part of Central Asia]. Trudy Vsesoyuznego Neftyanogo Nauchno-Issledovatel'skogo Geologo-Razvedochnogo Instituta (VNIGRI). 70(1): 256-. gs

Snyder, S. W. & Waters, V. J. (1985). Cenozoic planktonic foraminiferal biostratigraphy of the Goban Spur Region, Deep Sea Drilling Project Leg 80. Initial Reports of the Deep Sea Drilling Project. 80: 439-472. gs

Soldan, D. M., Petrizzo, M. R., Silva, I. P. & Cau, A. (2011). Phylogenetic relationships and evolutionary history of the Paleogene genus through parsimony analysis. Journal of Foraminiferal Research. 41: 260-284. gs

Toumarkine, M. & Luterbacher, H. (1985). Paleocene and Eocene planktic foraminifera. In, Bolli, H. M., Saunders, J. B. & Perch-Neilsen, K. (eds) Plankton Stratigraphy. Cambridge Univ. Press, Cambridge 87-154. gs

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Igorina pusilla compiled by the pforams@mikrotax project team viewed: 16-12-2025

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