Acarinina mcgowrani Wade & Pearson 2006 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 Acarinina mcgowrani Wade & Pearson 2006 |
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Diagnosis / Definition: |
Pearson et al. (2006):
DESCRIPTION.
Type of wall: Densely muricate, nonspinose,
normal perforate.
Test morphology: Chambers arranged in a
moderate trochospiral, test compact with 2 whorls,
typically 4 (but ranging from 3-4 1/2) chambers in the final
whorl, gradually increasing in size; peripheral outline
weakly lobate; chambers on umbilical side, wedgeshaped
or triangular, with final chamber oval in umbilical
view, typically twice as long as high, and subrounded to
angular in edge view; chambers densely muricate, with
large, conical muricae concentrated in the circumcameral
region of the final chamber, but not fused into
muricocarina; sutures distinct, deeply incised and radial;
umbilical-extraumbilical aperture set in a deep umbilicus;
bullae common; on spiral side chambers subrectangular
or ovoid; supplementary apertures frequently occur,
fringed by thin muricae; sutures incised, radial to weakly
curved; sutures of both sides are commonly intruded by
slender muricae; strong tendency for a preferred coiling
direction, either dextral or sinistral, depending on the
location and stratigraphic level.
Size: Maximum diameter of holotype 0.25-
0.30mm. |
Discussion / Comments: |
Pearson et al. (2006):
ETYMOLOGY.-
Named in honor of Professor Brian
McGowran of University of Adelaide for his
contributions to the taxonomy of Paleogene
foraminifera.
DISTINGUISHING FEATURES .-
Acarinina mcgowrani n.sp. is closely related to the middle Eocene species A. praetopilensis and the early Eocene species A. pseudotopilensis. It is distinguished from both species by its more compact test, which is densely muricate,
and by having more incised sutures. Unlike A. praetopilensis it does not show circum-cameral fusion
of muricae into an incipient circum-cameral
muricocarina, and the chamber periphery is usually more
rounded. The muricae are typically more conical than
in other acarininids and long, slender muricae intrude
into the sutures and fringe the primary and
supplementary apertures. Sutures are distinct and deeply
incised on both the umbilical and spiral sides, a feature
that distinguishes the pseudotopilensis - mcgowrani -
praetopilensis lineage from the CO-occurring Acarinina
bullbrooki group. Small bullae are frequently present
(see holotype), and are more common than in most other
acarininids.
DISCUSSION.-
Despite being abundant throughout
almost the whole of the middle Eocene, Acarinina
mcgowrani n. sp. has not been formally recognized as a
distinct species. Previous studies (e.g., Wade and others,
2001; Wade and Kroon, 2002; Wade, 2004; Pearson and
others, 1993,2001,2004) have used a broad concept of
either A. praetopilensis or A. pseudotopilensis to
accommodate these highly muricate, compact forms.
However, following study of type material from Russia,
we now recognize A. pseudotopilensis to be a
stratigraphically restricted component of early Eocene
assemblages. The distinctive features of A.
praetopilensis, as described by Blow (1979), include a
circum-cameral muricocarina and angular final chamber
similar to A. topilensis. These features also necessitate a
restricted concept, hence the need for a new species.
PHYLOGENETIC RELATIONSHIPS.-
Acarinina mcgowrani evolved from A. pseudotopilensis near the base of the middle Eocene and gave rise to A. praetopilensis.
STRATIGRAPHIC RANGE.-
Acarinina mcgowrani characterizes almost the whole of the middle Eocene. It
evolved in Zone E7 and was one of the final large
acarininids to become extinct, which just preceded the
extinction of Morozovelloides in upper Zone E 13 (Wade,
2004).
GEOGRAPHIC DISTRIBUTION.-
Widely
distributed, but most abundant in low and mid latitudes,
common in central equatorial Pacific Ocean (ODP Site
865), North and South Atlantic Ocean (ODP Sites 105 1
and 1052, DSDP Site 523) and Tanzania.
STABLE ISOTOPE PALEOBIOL0GY.-
Relatively
negative ò18O and positive ò13C values indicate a mixed
layer habitat. Size fraction data shows a large change in
ò13C through ontogeny suggestive of a symbiotic
relationship like other muricate forms; Pearson and
others, 1993 (recorded as pseudotopilensis); Wade and
Kroon, 2002; Wade 2004 (recorded as praetopilensis). |
Systematics: |
35 Ordo Foraminiferida
Superfamilia Globigerinaceae
Familia Truncorotaloididae
Genus Acarinina
Species Acarinina mcgowrani
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Synonym list: |
Pearson et al. (2006):
p 1979 Globorotalia (Acarinina) bullbrooki Bolli. - Blow : p.1043 pl. 155; fig. 3-5 [Zone P9-P10,
KANE 9, piston core 42, Endcavour Seamount, equatorial
Atlantic Ocean]; [Not Bolli, 1957]
1993 Acarinina pseudotopilensis Subbotina. - Pearson et al. : p.124 pl. 1; fig. 13-15 [Zones P1 1-12, DSDP
Site 523, South Atlantic Ocean];
[Not Subbotina, 1953]
2001 Acarinina praetopilensis Blow. - Wade & Norris : p.277 fig. 3f-3h [Zone P 14, ODP Site 105 1, western
North Atlantic Ocean]
2004 Acarinina praetopilensis Blow. - Wade : p.28 pl. 1; fig. g-h [Zone P 14, ODP Site 1052, western North Atlantic Ocean].
[Not Blow, 1979]
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Specimen: |
Smithsonian Museum of Natural History, Washington, D.C., Inventory number: USNM 528417
Smithsonian Museum of Natural History, Washington, D.C., Inventory number: USNM 528418
Smithsonian Museum of Natural History, Washington, D.C., Inventory number: USNM 528419
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References: |
Blow,W.H. (1979): The Cainozoic Globigerinida. 3 Vols p. 1413 pp
Pearson,P.N.; Shackleton,N.J. and Hall,M.A. (1993): The Stable Isotope Paleoecology of Middle Eocene Planktonic Foraminifera and Multi-species integrated Isotope Stratigraphy . Journal of Foraminiferal Research Vol. 23 p. 123-140
Wade,B.S.. and Norris,R.D. (2001): Orbitally forced climate change in the late Middle Eocene at Blake Nose (Leg 171B): Evidence from stable isotopes in foraminifera. In: Western North Atlantic Palaeogene and Cretaceous Palaeoceanography Vol. 183 Eds: Kroon, D.Norris, R.D.Klaus, A.. p. 273-291
Wade,B.S.. (2004): Planktonic foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the late Middle Eocene . Marine Micropaleontology Vol. 51 p. 23-38
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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