CATALOG OF ORIGINAL DESCRIPTIONS: Asymetria asymetrica Georgescu 2012

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Higher levels: pf_cat -> A -> Asymetria -> Asymetria asymetrica
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Asymetria asymetrica

Citation: Asymetria asymetrica Georgescu 2012
Rank: Species
Type locality: Type locality. Western North Atlantic Ocean (Blake Plateau), ODP Hole 1050C;geographical coordinates: 30° 05’ N, 76° 14’ W.
Type age: Upper Albian-lowermost Cenomanian (from the P. ticinensis Biozone to the lowermost part of the T. globotruncanoides Biozone).
Holotype Repository: Willi Karl Braun Micropaleontological Collection at the University of Calgary (Calgary, Alberta, Canada)
Type & figured specimens: Holotype. Specimen WKB 010116. Paratypes. Five specimens, WKB 010117-010121.

Current identification/main database link:


Original Description

Description. Test is low trochospiral and consists of 8-10 chambers arranged in 2-2.5 whorls; there are 4-5 (commonly 4-4.5) chambers in the final whorl. Earlier chambers are globular, then reniform in shape, gradually increasing in size. Chambers of the last whorl are radially elongate, with the elongation axis perpendicular or at a high angle to the previous whorl; up to three of the last formed ones bear one distal bulbous projection, which is rarely preserved. Sutures are distinct, depressed, straight to slightly curved, and radial on both test sides.  Test  shape  is  convex-concave,  slightly  asymmetrical  in  edge  view.  Aperture  is  a medium high arch extraumbilical-peripheral in position, and bordered by a wide tunnel- shaped lip; relict periapertural structures occur in the umbilical region. Umbilici are shallow and medium-sized, with a diameter of circa one third to one half of the maximum test diameter at the level of the first radially elongate chamber. Chamber ornamentation is asymmetrical: spiral side smooth and umbilical side ornamented with small pustules (0.6-1.1µm diameter), which are concentrated around the umbilicus; pustules occur also on the distal bulbous projections. Test wall is calcitic, hyaline, simple, and perforate; pores are simple, circular, and with a diameter of 0.4-1.0 µm.


Size: Holotype dimensions. Dmax=0.164 mm; Dmin=0.146 mm; Dmin/Dmax=0.890; t=0.074 mm; Average Dimensions. Dmax=0.135-0.164 mm; Dmin=0.096-0.146 mm; Dmin/Dmax=0.671-0.890; t=0.043-0.074 mm; t/Dmax=0.294-0.451; UD=0.040-0.051 mm; UD/Dmax=0.280-0.328. The ranges are based on the average measurements of ten specimens (holotype, paratypes and topotypes). t/Dmax=0.451; UD=0.046 mm; UD/Dmax=0.280.

Extra details from original publication

Remarks. Asymetria asymetrica differs from any other Cretaceous planktic foraminiferal species by the asymmetrically developed ornamentation, which is completely absent on the spiral side and pustulose on the umbilical one. Pustule occurrence on the distal bulbous projections is unique among the leupoldinid and schackoinid foraminifera, which further ads to this species uniqueness. The origins of A. asymetrica are unknown. Its early stage exhibits similarities with the late Aptian-early Albian Microhedbergella miniglobularis Huber and Leckie, 2011 and M. renilaevis Huber and Leckie, 2011; however, these two species are smooth and there is a time gap spanning the latest early Albian-early late Albian between their last occurrence and the first occurrence of A. asymetrica. Therefore, a direct ancestor- descendant relationship cannot be demonstrated at this time, but specimens resembling the M. miniglobularis-M. renilaevis group, and with petaloid last-formed chambers are known in the lower Albian (M. rischi Biozone) sediments of the Blake Plateau (Figure 7.14-16); these rare specimens herein assigned to A.? sp. document the beginnings of the chamber elongation in this group, and may indicate the Asymetria lineage initiation, which would eventually lead to the evolution of A. asymetrica in the late Albian. Additional material is necessary to confirm or reject this presumed phylogenetic relationship.

References:

Georgescu, M. D. (2012a). Morphology, taxonomy, stratigraphic distribution and evolutionary classification of the schackoinid planktic foraminifera (late Albian- Maastrichtian, Cretaceous). In, Bailey, D. R. , Howard, S. E. , (ed.) Deep-sea marine biology, geology, and human impact. Nova Publishers, New York 1-62. gs


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Asymetria asymetrica compiled by the pforams@mikrotax project team viewed: 7-12-2019

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