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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



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
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]
2006 Acarinina n sp. mcgowrani Wade & Pearson. - Pearson et al. : p.293 pl. 9.13; fig. 1-16
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
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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