Acarinina mcgowrani


Classification: pf_cenozoic -> muricate non-spinose -> Truncorotaloididae -> Acarinina -> Acarinina mcgowrani
Sister taxa: A. africana, A. alticonica, A. angulosa, A. aspensis, A. boudreauxi, A. bullbrooki, A. coalingensis, A. collactea, A. cuneicamerata, A. echinata, A. esnaensis, A. esnehensis, A. interposita, A. mcgowrani, A. mckannai, A. medizzai, A. nitida, A. pentacamerata, A. praetopilensis, A. primitiva, A. pseudosubsphaerica, A. pseudotopilensis, A. punctocarinata, A. quetra, A. rohri, A. sibaiyaensis, A. soldadoensis, A. strabocella, > >>

Taxonomy

Citation: Acarinina mcgowrani Wade & Pearson 2006
Rank: Species
Basionym: Acarinina mcgowrani
Synonyms:
Taxonomic 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. [Berggren et al. 2006]

Catalog entries: Acarinina mcgowrani;

Type images:

Short diagnosis: 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 pseudotopilensismcgowranipraetopilensis lineage from the co-occurring Acarinina bullbrooki group. Small bullae are frequently present (see holotype), and are more common than in most other acarininids.

NB The short diagnoses are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus. They have initially been copied from the diagnostic characters/distinguishing features sections of the Eocene and Paleocene Atlases, they will be edited as the site is developed.

Description


Diagnostic characters: 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 pseudotopilensismcgowranipraetopilensis lineage from the co-occurring Acarinina bullbrooki group. Small bullae are frequently present (see holotype), and are more common than in most other acarininids. [Berggren et al. 2006]

Wall type: Densely muricate, nonspinose, normal perforate.

Test morphology: Chambers arranged in a
moderate trochospiral, test compact with 2 whorls, typically 4 (but ranging from 3-4½) chambers in the final whorl, gradually increasing in size; peripheral outline weakly lobate; chambers on umbilical side, wedge-shaped 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 circum-cameral 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.

Biogeography and Palaeobiology


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 1051 and 1052, DSDP Site 523) and Tanzania. [Berggren et al. 2006]
Aze et al. 2011 summary: Low to middle latitudes; based on Berggren et al. (2006b)

Isotope paleobiology: Relatively negative ∂18O and positive ∂13C values indicate a mixed layer habitat. Size fraction data shows a large change in ∂13C 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). [Berggren et al. 2006]
Aze et al. 2011 ecogroup 1 - Open ocean mixed-layer tropical/subtropical, with symbionts. Based on very heavy δ13C and relatively light δ18O. Sources cited by Aze et al. 2011 (appendix S3): Pearson et al. (1993); Wade & Kroon (2002) Wade (2004)

Phylogenetic relations: Acarinina mcgowrani evolved from A. pseudotopilensis near the base of the middle Eocene and gave rise to A. praetopilensis. [Berggren et al. 2006]

Biostratigraphic distribution

Geological Range:
Notes: 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 E13 (Wade, 2004). [Berggren et al. 2006]
Last occurrence (top): within E13 zone (37.99-39.97Ma, 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

Plot of occurrence data:

Primary source for this page: Berggren et al. 2006 - Atlas of Eocene Planktonic Foraminifera, chapter 9, p. 291

References:

Berggren, W.A.; Pearson, P.N.; Huber, B.T. & Wade, B.S., (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Acarinina. In: Pearson, P.N. et al. (Editors), Atlas of Eocene Planktonic Foraminifera, Cushman Foundation Special Publication 41. Allen Press, Lawrence, Kansas, pp. 257-326.

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, 1413 pp.

Bolli, H.M., (1957). Planktonic foraminifera from the Eocene Navet and San Fernando formations of Trinidad. In: Loeblich, A.R., Jr. et al. (Editors), Studies in Foraminifera: U.S. National Museum Bulletin 215. U.S. Government Printing Office, Washington, D.C., pp. 155-172.

Pearson, P.N.; Shackleton, N.J. & Hall, M.A., (1993). Stable isotope paleoecology of middle Eocene planktonic foraminifera and multi-species isotope stratigraphy, DSDP Site 523, South Atlantic. Journal of Foraminiferal Research, 23: 123-140.

Wade, B.S. & Kroon, D., (2002). Middle Eocene regional climate instability: Evidence from the western North Atlantic. Geology, 30: 1011-1014.

Wade & Pearson 2006 [sorry, not in our bibliography yet]

Wade, B.S., (2004). Planktonic Foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the Late Middle Eocene. Marine Micropaleontology, 51: 23-38.

Wade, B.S.; Kroon, D. & Norris, R.D., (2001). Orbitally forced climate change in the Late Middle Eocene at Blake Nose (Leg 171B): Evidence From Stable Isotopes In Foraminifera. Geological Society of London, Special Publications, 183: 273-291.


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Acarinina mcgowrani compiled by the pforams@mikrotax project team viewed: 27-7-2017

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