pforams@mikrotax - Subbotina minima

Citation: Subbotina minima (Jenkins, 1966)

Basionym: Globigerina angiporoides minima Jenkins, 1966

Synonyms:

Globigerina angiporoides minima Jenkins, 1965:1096, fig. 7, nos. 52-57 [middle Eocene, Hampden Beach, South Island, New Zealand].
Globigerina (Subbotina) angiporoides minima Jenkins.—Jenkins, 1971:162, pl.17, figs. 510-515 [middle Eocene, Hampden Beach, South Island, New Zealand].
Subbotina angiporoides minima (Jenkins).—Blow, 1979:1255, pl. 12, fig. 7 [upper Eocene Zone P16, Lindi, Tanzania].
Subbotina angiporoides minima (Jenkins).—Spezzaferri and Premoli Silva, 1991:257, pl. XV, fig. 1 [lower Oligocene Zone P19 = Zone O1, DSDP Hole 538A, Gulf of Mexico], fig. 2 [lower Oligocene Zone P20 = Zone O1, DSDP Hole 538A, Gulf of Mexico].
Subbotina minima (Jenkins).—Li and others, 2003, pl. 1, fig. 30 [upper Eocene, Zone P15/P16, ODP Hole 1134A, Great Australian Bight].
Subbotina angiporoides (Hornibrook).—Olsson and others, 2006:126-129, pl. 6.6 (partim), fig. 5, SEM of paratype of Globigerina angiporoides [upper Eocene/lower Oligocene, Campbells Beach, South Island, New Zealand], figs. 9-11, SEMs of holotype of Globigerina angiporoides minima Jenkins [middle Eocene Globigerinatheka (Globigerapsis) index index Zone (not upper Eocene as stated by Olsson and others, 2006), Hampden Beach, South Island, New Zealand]. [Not Hornibrook, 1965.]
Not Subbotina angiporoides minima (Jenkins).—Nocchi and others, 1991:270, pl. 6, figs. 13-15 [lower Oligocene Zone P18-P20 = Zone O1-O2, ODP Hole 703A, Subantarctic South Atlantic Ocean] [=Subbotina angiporoides (Hornibrook)].

Taxonomic discussion:

Subbotina minima (Jenkins) was considered a junior synonym of Subbotina angiporoides (Hornibrook) by Olsson and others (2006). However, in our investigations of new material from the equatorial Pacific Ocean IODP Site U1334, we frequently find forms with a more open umbilicus and less compact test, which are much more typical of S. minima than with S. angiporoides. We therefore recognize S. minima as a distinct morphospecies. [Wade et al. 2018]

Jenkins (1965) suggested that S. minima is smaller than S. angiporoides and that this is a helpful characteristic for distinguishing between the two species. However, given the variability of illustrated specimens, we have not found this to be a particularly useful diagnostic feature and any size difference between the two species is subtle. [Wade et al. 2018]

In our opinion, one of the paratype specimens (Olsson and others, 2006, pl. 6.6, fig. 5) of S. angiporoides has a more lobate periphery and open umbilicus consistent with S. minima. Also, two of the paratype specimens illustrated by Jenkins as Globigerina angiporoides minima (1965, pl. 7, figs. 55, 56) share morphological characteristics, specifically a much tighter coiling mode and embracing final chamber, more similar to S. angiporoides. [Wade et al. 2018]

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: Like S. linaperta but chambers do not increase rapidly in size, hence outline triangular

Description

Test small to moderate size, umbilicus small, open, low trochospiral, “reuleaux” triangular in shape, axial periphery rounded; chambers globular, embracing, increasing slowly in size, 10-12 chambers coiled in 2 whorls, 3½-4 chambers in the final whorl; sutures weakly depressed, radial to slightly curved; aperture a low arch, umbilical to extraumbilical, bordered by a lip. [Wade et al. 2018]

Spinose, normal perforate, moderately cancellate, often thickened by addition of gametogenetic calcite, ruber/sacculifer-type wall.

Maximum diameter of holotype 0.37 mm. [Wade et al. 2018]

Biogeography and Palaeobiology

Common in high southern latitudes; probably cosmopolitan, although, so far no records in high northern latitudes. [Wade et al. 2018]

Multispecies stable isotope investigations from Site U1334 indicate that Subbotina minima calcifies in the thermocline. This species records more negative δ18O values in comparison to co-occurring S. utilisindex (Moore and others, 2014). [Wade et al. 2018]

Subbotina minima descended from S. linaperta in the middle Eocene and subsequently gave rise to S. angiporoides (Jenkins, 1965). [Wade et al. 2018]

Biostratigraphic distribution

Geological Range:
Notes: The range of S. minima is poorly constrained. It is described from the upper part of the middle Eocene. In the Gulf of Mexico, Spezzaferri and Premoli Silva (1991) found its extinction lower within Zone O3 than its descendant S. angiporoides. [Wade et al. 2018]
Last occurrence (top): within O3 zone (29.18-30.28Ma, top in Rupelian stage). Data source:
First occurrence (base): within Bartonian Stage (37.75-41.15Ma, base in Bartonian stage). Data source: Wade et al. 2018 (very poorly constrained

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

Hornibrook, N. d. B. (1965). Globigerina angiporoides n. sp. from the Upper Eocene and Lower Oligocene of New Zealand and the status of Globigerina angipora Stache, 1865. New Zealand Journal of Geology and Geophysics. 8(5): 834-838. gs

Jenkins, D. G. (1966b). Planktonic foraminiferal zones and new taxa from the Danian to lower Miocene of New Zealand. New Zealand Journal of Geology and Geophysics. 8 [1965](6): 1088-1126. gs

Jenkins, D. G. (1971). New Zealand Cenozoic Planktonic Foraminifera. New Zealand Geological Survey, Paleontological Bulletin. 42: 1-278. gs

Li, Q., McGowran, B. & James, N. P. (2003b). Eocene–Oligocene planktonic forminiferal biostratigraphy of Sites 1126, 1130, 1132, and 1134, ODP Leg 182, Great Australian Bight. Proceedings of the Ocean Drilling Program, Scientific Results. 182: 1-28. gs

Moore, T. C. et al. (2014). Equatorial Pacific Productivity Changes near the Eocene-Oligocene Boundary. Paleoceanography. 29: 825-844. gs

Nocchi, M., Amici, E. & Premoli Silva, I. (1991). Planktonic foraminiferal biostratigraphy and paleoenvironmental interpretation of Paleogene faunas from the subantarctic transect, Leg 114. Proceedings of the Ocean Drilling Program, Scientific Results. 114: 233-273. 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

Spezzaferri, S. & Premoli Silva, I. (1991). Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico. Palaeogeography Palaeoclimatology Palaeoecology. 83: 217-263. gs

Wade, B. S., Olsson, R. K., Pearson, P. N., Edgar, K. M. & Premoli Silva, I. (2018b). Taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 10): 307-330. gs

test outline:	Triangular	chamber arrangement:	Trochospiral	edge view:	Equally biconvex	aperture:	Umbilical
sp chamber shape:	Globular	coiling axis:	Low	periphery:	N/A	aperture border:	Thin lip
umb chbr shape:	Globular	umbilicus:	Narrow	periph margin shape:	Broadly rounded	accessory apertures:	None
spiral sutures:	Weakly depressed	umb depth:	Shallow	wall texture:	Spinose	shell porosity:	Finely Perforate: 1-2.5µm
umbilical or test sutures:	Weakly depressed	final-whorl chambers:	3.5-4	N.B. These characters are used for advanced search. N/A - not applicable