Subbotina crociapertura Blow 1979 from: Pearson, P.N.Olsson, R.K.Hemleben, C.Huber, B.T.Berggren, W.A. (2006): Atlas of Eocene Planktonic Foraminifera. p. 1-513 | . |
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Species Subbotina crociapertura Blow 1979 |
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| Diagnosis / Definition: |
Pearson et al. (2006):
DESCRIPTION.
Type of wall: Cancellate, normal perforate,
spinose, bulloides-type wall structure.
Test morphology: 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 ulnbilical
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.
Size: Maximum diameter of holotype 0.43 mm,
thickness 0.26 mm. |
| Discussion / Comments: |
Pearson et al. (2006):
DISTINGUISHING FEATURES.-
This species is
characterized by its globular, slightly embracing, chambers with a characteristically crooked, high-arched aperture bordered by a prominent regular lip.
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
inaeguispira (Subbotina) because of the tendency in P
inaeguispira "to produce apertural systems with a
slightly expanded to very slightly hooked distal part"
(1979, p. 1259) (but see discussion under Pa~asubbotirza
inaeguispira, Chapter 5).
All of the specimens of S. crociapertura except
one (his pl. 176, fig. 5; here illdztrated on PI. 6.8, Fig. 8)
from Tanzania illustrated by Blow, which includes the
holotype, have a bu1loide.s-type wall texture. However,
the figure of S. crociapertura from the North Atlantic
(his PI. 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.
Subhotina 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 rubertype
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.
PHYLOGENETIC RELATIONSHIPS.-
Subbotina
crociapertura belongs to a lineage of subbotinids that
developed a bu1loide.s-type wall texture. It is probably
related to S. roesnaesensis n. sp.
GEOGRAPHIC DISTRIBUTION .-
Distributed in low latitudes.
STABLE ISOTOPE PALEOBIOLOGY.-
Recorded
with oxygen and carbon isotopic values indicative of a
deep water habitat by Pearson and others (2001). |
| Systematics: |
35
Ordo Foraminiferida
Superfamilia Globigerinaceae
Familia Globigerinidae
Genus Subbotina
Species Subbotina crociapertura
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| Synonym list: |
Pearson et al. (2006):
1979 Subbotina crociapertura Blow. - Blow : p.1257 pl. 176, fig. 1-9 [middle Eocene Zone E9, Sample RS 24, Kilwa area, Tanzania];
pl. 177, fig. 1, 2 [middle Eocene Zone E9, Sample RS 24, Kilwa area, Tanzania];
pl. 190, fig. 6-9 [middle Eocene Zone E1 2, Sample RS 3 1 1. Kilwa area, Tanzania];
pl. 191, fig. 1-5 (figs. 2 and 3 = holotype) [middle Eocene Zone E12, Sample RS 31 1, Kilwa area, Tanzania] [Not pl. 160; fig. 2, Zone P 10, KANE 9, core 42, Endeavour Seamount, equatorial Atlantic Ocean]
2006 Subbotina crociapertura Blow. - Pearson et al. : p.132 pl. 6.8; fig. 1-14 (Pl. 6.8, Figs. 1,2: reillustration of holotype of Subbotina crociapertura Blow)
(PI. 6.8, Figs. 3-8 reillustration of paratypes of Subbotina crociapertura Blow)
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| References: |
Blow,W.H. (1979):
The Cainozoic Globigerinida. 3 Vols p. 1413 pp
Pearson,P.N.; Nicholas,C.J..; Singano,J.M..; Bown,P.R..; Coxali,H.K..; van Dongen,B.E..; Huber,B.T.; Karega,A..; Lees,J.A..; Misaky,E..; Pancost,R.D..; Pearson,M.. and Roberts,A.P.. (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 Vol. 39 p. 25-62
Pearson,P.N.; Olsson,R.K.; Hemleben,C.; Huber,B.T. and Berggren,W.A. (2006):
Atlas of Eocene Planktonic Foraminifera. p. 1-513
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