Daughter taxa (time control age-window is: 0-800Ma)
Igorina tadjikistanensis Test small, biconvex, moderately lobulate, densely and finely praemuricate test; axial periphery subrounded to subacute, noncarinate; spiral sutures depressed, strongly recurved, tangential to inner whorl, often obscured by dense murical network; umbilicus small, shallow as a result of tight coiling mode.
Igorina albeari Test moderately to strongly biconvex; sutures on spiral side strongly recurved yielding trapezoidal-shaped chambers; peripheral margin distinctly carinate, particularly on last chambers.
Igorina pusilla 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.
Igorina sp. Specimens which cannot be assigned to established species
Taxonomy
Citation: Igorina Davidzon, 1976Taxonomic rank: genusType species: Acarininatadjikistanensis Bykova, 1953Taxonomic discussion: As Pearson (1993:212) observed, the group of "biconvex, muricate morozovellids" (see Boersma and Premoli Silva, 1983; Premoli Silva and Boersma, 1989)— including the pusilla -laevigata, convexa, and broedermanni plexus of forms—is probably distinct from Acarinina and mainstream morozovellids. He considered these forms inappropriately placed in Igorina Davidzon (Loeblich and Tappan, 1988), inasmuch as the type species of the latter, Globorotaliatadjikistanensis Bykova, was considered an enigmatic, biconvex morozovellid from the upper part of Zone P3a, and probably is related to conicotruncata. Recent examination and SEM reillustration of the holotypes of Globorotaliatadjikistanensis Bykova (pl. 11: figs. 4-6) and Globorotaliaconvexa Subbotina (pl. 11: figs. 1-3), however, have shown these forms to be synonymous, with tadjikistanensis having priority. Igorinids are characterized by their small, coarsely cancellate tests, evolute coiling, and distinctive blunt, praemuricate surface texture. [Olsson et al. 1999]
Soldan et al. (2014) argued that the broedermanni lineage (speies broedermanni, lodoensis and anapetes) evolved separately from Acarinina rather than from the earlier Igorina species and so they propose removing these species from Igorina into a new genus, Pearsonites. This proposal has been followed here. [editor's comment - JRY 2019]
Distinguishing features: Parent taxon (Truncorotaloididae): Muricate This taxon: 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.
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
Biogeography and Palaeobiology
Phylogenetic relationsWe believe that the Igorinids evolved from Praemurica about the time of appearance of the first morozovellids (M. praeangulata, M. angulata). Like many globigerininid groups, the igorinids show a trend toward chamber compression and development of a peripheral keel, but this trend is reversed in the Eocene with the evolution of the I. broedermanni group. [Olsson et al. 1999]
Most likely ancestor:Praemurica - at confidence level 0 (out of 5). Data source: Olsson et al. 1999.
Biostratigraphic distribution
Geological Range: Last occurrence (top): at top of P5 zone (100% up, 56Ma, in Thanetian stage). Data source: Total of ranges of the species in this database First occurrence (base): within P3a subzone (61.33-62.29Ma, base in Danian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Primary source for this page: Olsson et al. 1999 - Atlas of Paleocene Planktonic Foraminifera, p. 68
References:
Davidzon, R. M. (1976). Novyy paleogenovyy rod planktonnykh foraminifer. [A new Paleogene genus of planktonic foraminifera.]. Trudy Vsesoyuznogo Nauchno-issledovatel'skogo Geologorazvedochnogo Neftyanogo Instituta (VNIGNI), Tadzhikskoe Otdelenie,. 183: 197-199. gs
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
Soldan, D. M., Petrizzo, M. R. & Silva, I. P. (2014). Pearsonites, a new Paleogene planktonic foraminiferal genus for the broedermanni lineage. Journal of Foraminiferal Research. 44: 17-27. gs
Igorina compiled by the pforams@mikrotax project teamviewed: 20-1-2025
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