Catalog - Igorina praecarinata

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Other pages this level: I. isabellae, I. paraspiralis, I. praecarinata

Igorina praecarinata

Citation: Igorina praecarinata Soldan et al. 2011

Type specimens: Holotype (Micro-Unimi no. 1977); paratypes 1 and 2 (Micro-Unimi no. 1978 and 1979, respectively)

Type sample (& lithostrat): 198-1209B-24H-7, 41–42 cm.

Type age (chronostrat): Palaeocene, P3-4

Type locality: Shatsky Rise, Pacific, ODP Site 1208B (32.65N; 158.51E;)

Type repository: Milan; Micropaleontological Collection, Universita` degli Studi di Milano, Dipartimento di Scienze della Terra ÔÔA. DesioÕÕ, Italy.

Test moderately to strongly biconvex, periphery essentially circular, peripheral margin subacute, surface texture pustulose; umbilical side very flat with 5–6 triangular chambers, intercameral sutures straight, weakly incised, umbilicus small, round and narrow; spiral side with 6–7 crescentic chambers in last whorl, intercameral sutures strongly recurved; aperture an interiomarginal, umbilical- extraumbilical, low arch extending nearly to the periphery.

Diameter 0.22 mm; thickness 0.13 mm

Globorotalia (Acarinina) sp. in Blow, 1979, pl. 87, fig. 9.
Globorotalia (Acarinina) convexa convexa Subbotina in Blow, 1979, pl. 88, fig. 3.
Igorina albeari (Cushman and Bermudez) in Olsson and others, 1999, p. 69, pl. 56, figs. 13–16.
Igorina pusilla (Bolli) in Sprong and others, 2009, p. 70, fig. 4, 4a–c, 5a–c.
Igorina albeari (Cushman and Bermudez) in Sprong and others, 2009, p. 70, fig. 4, 7a–c.

Derivation of name. Refers to the absence of a keel on the peripheral margin.

Occurrence. Zones P3b–P4a (basal part).

Geographic distribution. This species has been recorded at low and mid latitudes and it is present in (sub)tropical fossil assemblages from the Atlantic and Pacific oceans.

Remarks. Igorina praecarinata is considered here as an intermediate form between I. pusilla and the keeled taxa (I. laevigata with well-developed keel and I. albeari sometimes with a slight keel on the last chamber). This form has never been described by previous authors because it has often been reported as I. pusilla or I. albeari (Sprong and others, 2009) or it was interpreted as a primitive (early) form of Igorina albeari (Olsson and others, 1999; Sprong and others, 2009). Nevertheless, I. praecarinata can be distinguished from other igorinids, particularly I. pusilla and I. albeari, by its very flat umbilical side and in the marked compression of the chambers. Blow (1979) illustrated in edge view a specimen from Zone P3 that he assigned to Globorotalia (Acarinina) convexa convexa. The peripheral margin of this form is very similar to that of I. praecarinata and probably should be included in this taxon. Generally, I. praecarinata lacks the carina, but in some specimens show a slight keel on the last chamber. In Hole 1209B (Subzone P3b), we have found several specimens characterized by a high spire (Fig. 16.8). In these morphotaxa, the umbilical side is very flat and never displays a keel on the last chamber. Igorina praecarinata descended from I. pusilla, and according to our analysis it evolved into I. laevigata and I. albeari in Subzone P3b.

Distinguishing features. Igorina praecarinata is distinguished from I. pusilla in having a more acute peripheral margin. It differs from I. laevigata in the absence of a well- developed keel and from I. albeari in possessing a much flatter umbilical side and fewer chambers in the last whorl.

References:

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. 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. & Cau, A. (2011). Phylogenetic relationships and evolutionary history of the Paleogene genus through parsimony analysis. Journal of Foraminiferal Research. 41: 260-284. gs

Sprong, J., Speijer, R. P. & Steurbaut, E. (2009). Biostratigraphy of the Danian/Selandian transition in the southern Tethys. Special reference to the lowest occurrence of planktic foraminifera Igorina albeari. Geologica Acta. 7: 63-77. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Igorina praecarinata Soldan et al. 2011

Igorina praecarinata

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