pforams@mikrotax - Subbotina crociapertura

Citation: Subbotina crociapertura Blow 1979

Basionym: Subbotina crociapertura

Synonyms:

Subbotina crociapertura Blow, 1979: 1257, pl. 176: figs. 1-9 [middle Eocene Zone E9, Sample RS 24, Kilwa area, Tanzania], pl. 177: figs. 1,2 [middle Eocene Zone E9, Sample RS 24, Kilwa area, Tanzania], pl. 190: figs. 6-9 [middle Eocene Zone E12, Sample RS 311. Kilwa area, Tanzania], pl.191: figs. 1-5 (figs. 2 and 3 = holotype) [middle Eocene Zone E12, Sample RS 311. Kilwa area, Tanzania]. [Not pl.160: fig. 2, Zone P10, KANE 9-core 42, Endeavour Seamount, equatorial Atlantic Ocean.]._Pearson and others, 2004:36, pl. 1: fig. 12 [middle Eocene Zone P11, Tanzania].

Taxonomic discussion: Blow emphasized the hook-shape of the aperture of Subbotina crociapertura, which he likened to the hooked end of an episcopal crozier. He regarded the apertural apparatus as a porticus, that is, a separate structure added after the formation of the chamber, not an extension of the chamber wall. Little was known about the growth of planktonic foraminifera at the time Blow described his new species, but subsequent studies have shown that the apertural apparatus is part of the chamber wall and that prior to gametogenesis additional calcite may be added. Although Blow was in error on the origin of the apertural apparatus in S. crociapertura, he believed that the derivation of the aperture was through Parasubbotina inaequispira (Subbotina) because of the tendency in P. inaequispira “to produce apertural systems with a slightly expanded to very slightly hooked distal part” (1979, p. 1259) (but see discussion under Parasubbotina inaequispira, Chapter 5).
All of the specimens of S. crociapertura except one (his pl. 176, fig. 5; here illustrated on Pl. 6.8, Fig. 8) from Tanzania illustrated by Blow, which includes the holotype, have a bulloides-type wall texture. However, the figure of S. crociapertura from the North Atlantic (his Pl. 160, fig. 2) as well as the one exception from Tanzania show a ruber/sacculifer-type wall texture. These specimens are similar to specimens from Tanzania on Plate 6.8, Figs. 9-14, which we have labeled S. cf. S. crociapertura because of the different wall texture. The holotype is from Zone E12 and the others are from Zones E8 and E9. It may be that the earlier morphotypes represent an early stage in the development of crociapertura, but we do not have sufficient stratigraphic control to show this.
Subbotina crociapertura is apparently little used by workers despite its distinctiveness. This may be in part due to a restricted biogeographic range. Blow’s record of the species is from low latitude localities in the southern hemisphere. We have recorded it from Tanzania and the Aragon Formation in Mexico, a
northern low latitude locality. Blow noted that the species was particularly common in the Indo-Pacific region. The origin of this species is most likely from S. roesnaesensis n. sp., which, although it has a ruber-type wall texture, has a more open umbilicus and an apertural lip which tapers in the posterior direction. The ruber-type wall texture appears closest to the bulloides-type and is regarded here as the most likely ancestor wall texture to the genus Globigerina which appears in the middle Eocene. Blow indicated that the range of S. crociapertura “virtually defines the Middle Eocene as a whole” (1979, p. 1259). Its origin appears to be in Zone E7. [Olsson et al. 2006]

Distinguishing features:
Parent taxon (Subbotina): Low trochospiral, tripartite test, with 3-4 rapidly inflating, globular chambers in final whorl. Umbilicus nearly closed by tight coiling. Wall cancellate with spines at nodes of the ridges, +/- spine collars.
This taxon: Chambers globular, slightly embracing. Aperture characteristically crooked, high-arched, and with prominent regular lip.

Description

This species is characterized by its globular, slightly embracing, chambers with a characteristically crooked, high-arched aperture bordered by a prominent regular lip. [Olsson et al. 2006]

Low trochospiral, test globular, oval in outline, chambers globular; in spiral view 4 globular, slightly embracing chambers in ultimate whorl, increasing rapidly in size, sutures moderately depressed, straight; in umbilical view 4 globular, slightly embracing chambers, increasing rapidly in size, sutures moderately depressed, straight, umbilicus small, open, enclosed by surrounding chambers, aperture umbilical to extraumbilical, elevated above the umbilicus, bordered by a prominent lip that tapers towards the posterior side of the ultimate chamber; in edge view chambers globular in shape, slightly embracing, aperture visible as a moderately high, circular arch, bordered by a prominent, regular lip. [Olsson et al. 2006]

Cancellate, normal perforate, spinose, bulloides-type wall structure. [Olsson et al. 2006]

Maximum diameter of holotype 0.43 mm, thickness 0.26 mm. [Olsson et al. 2006]

Biogeography and Palaeobiology

Distributed in low latitudes. [Olsson et al. 2006]
Aze et al. 2011 summary: Low latitudes; based on Olsson et al. (2006a)

Recorded with oxygen and carbon isotopic values indicative of a deep water habitat by Pearson and others (2001). [Olsson et al. 2006]
Aze et al. 2011 ecogroup 4 - Open ocean sub-thermocline. Based on very light _¹³C and very heavy _¹⁸O. Sources cited by Aze et al. 2011 (appendix S3): Coxall et al. (2000); Pearson et al. (2001a)

Subbotina crociapertura belongs to a lineage of subbotinids that developed a bulloides-type wall texture. It is probably related to S. roesnaesensis n. sp. [Olsson et al. 2006]

Most likely ancestor:
Subbotina yeguaensis - at confidence level 4 (out of 5). Data source: Olsson et al. 2006 f6.2.

Biostratigraphic distribution

Geological Range:
Notes: Zone E7 to Zone E12. [Olsson et al. 2006]
Last occurrence (top): within E12 zone (39.97-40.40Ma, top in Bartonian stage). Data source: Eocene Atlas
First occurrence (base): within E7 zone (45.72-50.20Ma, base in Ypresian stage). Data source: Eocene Atlas

Primary source for this page: Olsson et al. 2006 - Eocene Atlas, chap. 6, p. 133

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., Huber, B. T. & Berggren, W. A. (2006a). Taxonomy, biostratigraphy, and phylogeny of Eocene Globigerina, Globoturborotalita, Subbotina, and Turborotalita. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 6): 111-168. gs O

Olsson, R. K., Pearson, P. N. & Huber, B. T. (2006c). Taxonomy, biostratigraphy, and phylogeny of Eocene Catapsydrax, Globorotaloides, Guembelitrioides, Paragloborotalia, Parasubbotina, and Pseudoglobigerinella n. gen. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 5): 67-110. gs O

Pearson, P. N., et al. (2004). Paleogene and Cretaceous sediment cores from the Kilwa and Lindi areas of coastal Tanzania: Tanzania Drilling Project Sites 1–5. Journal of African Earth Sciences. 39: 25-62. gs

test outline:	Ovate	chamber arrangement:	Trochospiral	edge view:	Equally biconvex	aperture:	Umbilical
sp chamber shape:	Globular	coiling axis:	Low	periphery:	N/A	aperture border:	Thick lip
umb chbr shape:	Globular	umbilicus:	Narrow	periph margin shape:	Broadly rounded	accessory apertures:	None
spiral sutures:	Moderately depressed	umb depth:	Deep	wall texture:	Spinose	shell porosity:	Finely Perforate: 1-2.5µm
umbilical or test sutures:	Moderately depressed	final-whorl chambers:	4-4	N.B. These characters are used for advanced search. N/A - not applicable

Subbotina crociapertura

Taxonomy

Description

Biogeography and Palaeobiology

Biostratigraphic distribution

References:

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