pforams@mikrotax - Igorina pusilla

Citation: Igorina pusilla (Bolli 1957)

Basionym: Globorotalia pusilla pusilla Bolli 1957

Synonyms:

Globorotalia pusilla pusilla Bolli, 1957a:78, pl. 20: figs. 8-10 [Globorotalia pusilla pusilla Zone, Guayaguayare Well 159, Trinidad Leasholds, Ltd., Lizard Springs Fm., Trinidad].—Bolli and Cita, 1960:388, 389, pl. 34: fig. 4a-c [Globorotalia pusilla pusilla Zone, Pademo d'Adda, northern Italy],
Planorotalites tauricus Morozova, 1961:16, pl. 2: fig. 3 [Acarinina indolensis Subzone (Dn2 III1), Michurino Substage, Urukh River, northern Caucasus]. Globorotalia (Globorotalia ?) pusilla pusilla Bolli.—Hillebrandt, 1962:128, pl. 11: fig. 18a,b [Globorotalia pusilla pusilla Zone, Reichenhall-Salzburg Basin, Austro-German border].
Globorotalia pusilla pusilla (?) Bolli. —Shutskaya, 1970b:218, pl. 22: fig. 3a-c [lower subzone of Acarinina tadjikistanensis djanensis Zone, lower Danatin Formation, Malyi Balkhan Ridge, western Turkmenia].
Globorotalia pusilla Bolli.—Pujol, 1983:652, pl. 2: figs. 12, 13 [Globorotalia pusilla Zone, DSDP Hole 516F/86/4: 6-9 cm; Rio Grande Rise, South Atlantic Ocean].
Morozovella pusilla pusilla (Bolli).—Snyder and Waters, 1985:446, 449, 460, pl. 8: figs. 15-17 [Morovozella pusilla pusilla Zone, DSDP Site 549/20/5: 18-20 cm; northeastern Atlantic Ocean],
Planorotalites pusilla pusilla (Bolli).—Toumarkine and Luterbacher, 1985:108, fig. 12:13a-c [holoype reillustrated], fig. 12:14a-c [Zone P3, DSDP Hole 144A/3/4: 120-122 cm; South Atlantic Ocean]. [Olsson et al. 1999]

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]

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.

Description

Biogeography and Palaeobiology

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)

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.

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]

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:

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

test outline:	Subcircular	chamber arrangement:	Trochospiral	edge view:	Inequally biconvex	aperture:	Umbilical-extraumbilical
sp chamber shape:	Inflated	coiling axis:	Low	periphery:	N/A	aperture border:	Thin lip
umb chbr shape:	Inflated	umbilicus:	Narrow	periph margin shape:	Subangular	accessory apertures:	None
spiral sutures:	Weakly depressed	umb depth:	Shallow	wall texture:	Smooth	shell porosity:	Finely Perforate: 1-2.5µm
umbilical or test sutures:	Weakly depressed	final-whorl chambers:	5-6	N.B. These characters are used for advanced search. N/A - not applicable

Igorina pusilla

Taxonomy

Description

Biogeography and Palaeobiology

Biostratigraphic distribution

References:

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