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Archaeoglobigerina australis


Classification: pf_mesozoic -> Rugoglobigerinidae -> Archaeoglobigerina -> Archaeoglobigerina australis
Sister taxa: A. australis, A. blowi, A. bosquensis, A. cretacea, A. mateola, A. sp.,

Taxonomy

Citation: Archaeoglobigerina australis Huber 1990
Rank: Species
Basionym: Archaeoglobigerina australis
Taxonomic discussion: Although end member morphotypes included in this species show considerable differences in chamber development and apertural characteristics no distinct populations could be recognized as a separate species in the Maud Rise and Falkland Plateau assemblages. Serial dissection of large, adult specimens and X-ray micrographs (Huber, 1994) have revealed penultimate whorl morphologies identical to small forms, here considered as juvenile specimens of A. australis.
Gerontic forms of A. australis resemble specimens of A. bosquensis Pessagno that were described from Santonian sediments in the western Gulf Coastal Plain (Pessagno, 1967) and the Falkland Plateau (Sliter,1977; Krasheninnikov and Basov, 1983). The Gulf Coast holotype and
paratype of A. bosquensis differ from A. australis by having a smoother test surface and lacking kummerform chambers and apertural flaps. However, poor preservation of the type material and uncertainty of the morphologic variability among Gulf Coast populations of A. bosquensis preclude an adequate comparison of these taxa. Falkland Plateau specimens described as A. bosquensis, which are very well preserved and occur in high abundance, do not bear apertural flaps, are generally higher spired and have a narrower, deeper umbilicus than most forms of A. australis, although some forms of the latter species (e.g., PI. 3, Fig. 7) are very similar. The stratigraphic distribution of these two species and their morphologic similarity suggest that A. australis is a descendant of A. bosquensis.
No specimens with tegilla, imperforate peripheral margins, peripheral keels, or meridionally arranged costellae have been found. Therefore, this species is not placed in Rugoglobigerina or Rugotruncana. Inclusion in Archaeoglobigerina differs from the original description of that genus, which suggests that tegilla should be observed in "perfectly preserved specimens" (Pessagno, 1967, p. 315). Because this structure is absent from the Gulf Coast type species of Archaeoglobigerina (A. blowi Pessagno) and the holotype of Archaeoglobigerina bosquensis, it
is not considered as a primary generic character. Either the definition of this genus needs to be modified, or a new genus should be created to accommodate the non-keeled, non-tegillate forms. [copied from Chronos database]

Type images:

Original description: Archaeoglobigerina australis Huber 1990: Test coiled in a moderate to high spire, unequally biconvex, spiral side usually more convex than umbilical side, average diameter of adult specimens 0.28 mm, average breadth 0.15 mm. Chambers strongly inflated, globular, increasing moderately in size with four to five and one-half in the penultimate whorl, increasing gradually in size with three and three-quarters to five and three-quarters in the ultimate whorl, 12 to 15 comprising the tests of adult specimens, final chamber usually kummerform. Proloculus diameter of adult specimens averaging 16 m, initial whorl diameter averaging 71 m, with a mean of 4.4 chambers in the initial whorl. Sutures moderately to strongly depressed, radial and straight on both the spiral and umbilical sides. Apertures of juvenile specimens extra-umbilical in position, having greater width than height, bordered by a narrow, thickened lip. Apertures of adult specimens umbilical to slightly extra-umbilical in position, often bordered by a broad flap that may completely extend across the umbilicus, with relict apertural flaps sometimes coalescing to form a pseudo-tegillum. Umbilicus deep, narrow to broad, comprising an average of 28% of the maximum test diameter. Test surface covered with fine to coarse, randomly situated pustules, surface of final chamber usually with finer pustulose ornament than previous chambers. Outer wall radial hyaline and finely perforate.

Entries in the Catalog of original descriptions: Archaeoglobigerina australis;

Geological Range:
Last occurrence (top): within A. mayaroensis zone (67.30-69.18Ma, top in Maastrichtian stage). Data source: [copied from Chronos database]
First occurrence (base): within G. falsostuarti (-Ma, base in stage). Data source: [copied from Chronos database]

Plot of occurrence data:

NB Plotting of Neptune data has been disabled on the Mesozoic pages because the dataset is both small and badly affected by a few sites with erroneous age models (our obs Huber, Petrizzo, Young, Nov 2016). The data can still be viewed via the range plottertool - tools menu.

Character matrix

test outline:Circularchamber arrangement:Trochospiraledge view:aperture:Umb.-extraumbilical
umb chamber shape:Inflatedcoiling axis:Low-moderateperiphery:N/Aaperture border:Thick porticus
sp chbr shape:Inflatedumbilicus:Narrowperiph margin shape:Moderately roundedaccessory apertures:None
umbilical or test sutures:Moderately depressedumb depth:Deepwall texture:Moderately muricateshell porosity:Macroperforate: >2.5
spiral sutures:Moderately depresseddiameter mm:0.28width mm:breadth mm:0.15 mm
final-whorl chambers:4.5-5.5

References:

Huber, B.T., (1990). Maestrichtian planktonic foraminifer biostratigraphy of the Maud Rise (Weddell Sea, Antarctica): ODP Leg 113 Holes 689B and 690C. Proceedings of the Ocean Drilling Program, Scientific Results, 113: 489-513.


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Archaeoglobigerina australis compiled by the pforams@mikrotax project team viewed: 22-8-2017

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