Acarininapseudotopilensis (Subbotina, 1953).—Pearson and others, 1993:124, pl. 1: figs. 13-15 [Zones P11-12, DSDP Site 523, South Atlantic Ocean]. [Not Subbotina, 1953.]
Acarininapraetopilensis (Blow, 1979).—Wade and others, 2001:277: figs. 3f-3h [Zone P14, ODP Site 1051, western North Atlantic Ocean].—Wade, 2004:28, pl. 1: figs. g-h [Zone P14, ODP Site 1052, western North Atlantic Ocean]. [Not Blow, 1979.]
Taxonomic discussion: Despite being abundant throughout almost the whole of the middle Eocene, Acarininamcgowrani 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]
Distinguishing features: Parent taxon (Acarinina): Moderate to low trochospire; chambers ovoid, usually 4-6 in final whorl. Wall muricate with pustules on umbilical shoulders; This taxon: Like A. pseudotopilensisbut with more compact test, which is densely muricate, and with more incised sutures.
NB These concise distinguishing features statements are used in the tables of daughter-taxa to act as quick summaries of the differences between e.g. species of one genus. They are being edited as the site is developed and comments on them are especially welcome.
Description
Diagnostic characters: Acarininamcgowrani 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 Acarininabullbrooki group. Small bullae are frequently present (see holotype), and are more common than in most other acarininids. [Berggren et al. 2006] 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. Wall type: Densely muricate, nonspinose, normal perforate. Size: Maximum diameter of holotype 0.25-0.30mm.
Character matrix
test outline:
Subquadrate
chamber arrangement:
Trochospiral
edge view:
Planoconvex
aperture:
Umbilical-extraumbilical
sp chamber shape:
Inflated
coiling axis:
Low
periphery:
N/A
aperture border:
N/A
umb chbr shape:
Inflated
umbilicus:
Narrow
periph margin shape:
Subangular
accessory apertures:
Sutural
spiral sutures:
Strongly depressed
umb depth:
Deep
wall texture:
Coarsely muricate
shell porosity:
Finely Perforate: 1-2.5µm
umbilical or test sutures:
Strongly depressed
final-whorl chambers:
3-4.5
N.B. These characters are used for advanced search. N/A - not applicable
Biogeography and Palaeobiology
Geographic distributionWidely 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 paleobiologyRelatively negative δ18O and positive δ13C values indicate a mixed layer habitat. Size fraction data shows a large change in δ13C 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 _13C and relatively light _18O. Sources cited by Aze et al. 2011 (appendix S3): Pearson et al. (1993); Wade & Kroon (2002) Wade (2004) Phylogenetic relationsAcarininamcgowrani evolved from A. pseudotopilensis near the base of the middle Eocene and gave rise to A. praetopilensis. [Berggren et al. 2006]
Geological Range: Notes: Acarininamcgowrani 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): in lower part of E7a subzone (30% up, 49.6Ma, in Ypresian stage). Data source: Eocene Atlas
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested.
Grey shading between taxa indicates intergrading species within an anagenetic lineage (data from
Lamyman et al. 2026).
Histogram - Neptune occurrence data from DSDP and ODP proceedings. Pale shading <50 samples in time bin. Interpret with caution & read these notes
Taxon plotted: Acarinina mcgowrani, synonyms included - Acarinina mcgowrani;
Primary source for this page: Berggren et al. 2006 - Eocene Atlas, chap. 9, p. 291
References:
Berggren, W. A., Pearson, P. N., Huber, B. T. & Wade, B. S. (2006b). Taxonomy, biostratigraphy, and phylogeny of Eocene Acarinina. 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 9): 257-326. gsO
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
Bolli, H. M. (1957a). Planktonic foraminifera from the Eocene Navet and San Fernando formations of Trinidad. In, Loeblich, A. R. , Jr., Tappan, H., Beckmann, J. P., Bolli, H. M., Montanaro Gallitelli, E. & Troelsen, J. C. (eds) Studies in Foraminifera. U.S. National Museum Bulletin . 215: 155-172. gs
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. gs
Wade, B. S. & Kroon, D. (2002). Middle Eocene regional climate instability: Evidence from the western North Atlantic. Geology. 30: 1011-1014. gs
Wade, B. S. (2004). Planktonic Foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the Late Middle Eocene. Marine Micropaleontology. 51: 23-38. gs
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. gs
Acarinina mcgowrani compiled by the pforams@mikrotax project teamviewed: 17-7-2026
Eocene_Atlas_pl09-13_fig12.jpg
Eocene_Atlas_pl09-13_fig13.jpg
Eocene_Atlas_pl09-13f_8-15-16.jpg
Eocene_Atlas_pl09-13_fig12.jpg
Eocene_Atlas_pl09-13_fig13.jpg
Eocene_Atlas_pl09-13f_8-15-16.jpg
holotype: A. mcgowrani
paratype: A. mcgowrani
paratype: A. mcgowrani
